The+introduction+of+NS2
(超详细答案)综合学术英语教程2 答案 上海交通大学出版 蔡基刚
综合学术英语教程2 答案之青柳念文创作Unit 1 Multidisciplinary EducationKeys to the ExercisesApproaching the Topic1. 1) The aim of college education is to produce individuals who are well on their way to becomeexperts in their field of interest.2) The growing importance of producing professionals who have the skills to work with peoplefrom a diverse set of disciplines.3) First, through an interdisciplinary approach; Second, through a multidisciplinary approach.4) College education should produce individuals who may later become expert who areinterdisciplinary problem solvers.2. 1) f 2) d 3) a 4) e 5) g 6) m 7) j 8) k 9) l 10) i 11) b 12) h 13) c4. (1) offered (2) stresses (3) ability (4) different (5) approach(6) increasingly (7) graduates (8) enter (9) positions (10) Employment6. 1) Multidisciplinary studies.2) They both believe that current college education should lay emphasis on multidisciplinary studies, which is a prerequisite to producing future expert who are interdisciplinary problem solvers.3) Open.4) Open.5) Open.Reading about the Topic3. 1) The students have brought to MIT their individual gifts, such as their own intellect, energy,ideas, aspirations, distinctive life experience and point of view, etc.2) They represent the geographic and symbolic center of MIT.3) Names of intellectual giants.4) Leonardo da Vinci was a painter, scientist, engineer, sculptor, inventor, city planner andarchitect.4.Set 1: 1) c 2) e 3) d 4) h 5) a 6) g 7) f 8)bSet 2: 1) e 2) a 3) h 4) b 5) c 6) f 7) d 8) g5.(b) Para. A (b) Para. B (a) Para. C (c) Para. D(f) Para. E (e) Para. F (d) Para. G (g) Para. A6. 1) Because for him, the simplicity he appreciated in nature became his ultimate standard indesign.2) First was da Vinci’s complete disregard for the accepted boundaries between different f ields of knowledge. The second facet of da Vinci’s character was his respect for and fascination with nature. The third quality of da Vinci’s character was an enthusiastic demand forhands-on making, designing, practicing and testing, and for solving problems in the real world.3)“There is a good chance that you will never again live and work in a community with as manydifferent cultures and backgrounds as MIT.”(Para. F)4) Because by doing so, the students can engagethemselves in new intellectual adventures so as to use their time at MIT to its fullest potential. 5) It means that “They took the initiative to search for the deepest answers, instead of sitting backand letting things happen to them.”7. Set 1: 1) h 2) d 3) a 4) g 5) f 6) e 7) b8) cSet 2: 1) c 2) g 3) d 4) a 5) h 6) f 7) e 8) b8. 1) She wanted to describe for the new students three of his characteristics that particularly f it with the value of MIT.2) Because by doing so, the students can encounter the most stimulating minds and inspiring role models, experience a life in a community with diversif ied cultures and backgrounds and participate in various new intellectual adventures, so that they can get the most out of theirMIT education.3) The three of Da Vinci’s characteristics willbe the heritage of MIT to be inherited by the students. She hoped that the new students would follow Da Vinci as well as a great manyextraordinary MIT teachers as their role models to use their time to its fullest potential.4) Multidisciplinary thinking is a mode of thinking that goes beyond disciplinary boundaries inorder to gain new ideas and fresh perspectives.9. 1) Human ingenuity will never devise any inventions more beautiful, nor more simple, nor moreto the purpose than Nature does. (Para. A)2) For Da Vinci, the simplicity he appreciated in Nature became his ultimate standard in design.(Para. B)3) Be as determined in your curiosity as Leonardo da Vinci — and you will use your time atMIT to its fullest potential. (Para. F)4) MIT is a place of practical optimism and of passionate engagement with the most importantproblems of the world. (Para. G)5) I had long since observed that people of accomplishment rarely sat back and let thingshappen to them. (Para. H)10. Many scientists and engineers at MIT pursue simplicity in their design and development oftechnologies.Exploring the Topic4. 1) It is believed that a multidisciplinary approach to scientific education is of vital importance.2) Second, a multidisciplinary emphasis is believed to be a prerequisite to training individuals.3) It cannot be denied that these f irms are participating in turning out the future thinkers.4) How about examining our problems about science and technology from a liberal artsperspective.5) Surprisingly, however, our universities and colleges fail to switch from the conventionaldivisions and departmental sections to daily extracurricular multidisciplinary work.5. Reading 1 begins with a contrast —“College education has always had the responsibility to ...However, ... we also see the growing importance of producing ...”. The introduction of Reading2 is informative as well as interesting, which arouses the readers’ interest to go on reading. Integrated Exercises2. (1) ultimate (2) spirit (3) feed (4) approach (5) property (6) represent(7) discipline (8) aspiration (9) inspire (10) perspective (11) inherit (12) generate3.(1) inspiring (2) generation (3) collaborative (4) aspiring (5) Intelligent(6) inherit (7) celebrity (8) speculated (9) representative (10) anatomical4. (1) D (2) A (3) C (4) B (5) D (6) A (7) B (8) C (9) A (10) C5. (1) Many celebrated researchers around the world are collaborating to develop a new vaccine.(2) The scientists’ experiment generated an unexpected outcome.(3) If the systems are restructured, their effectiveness will be ultimately integrated into theglobal economy.(4) The doctors speculate that he died of a stroke caused by a blow on the head.(5) The murder trial attracted considerable public attention.(6) The aspiration for college education inspires people in remote areas to work hard.(7) He inherited his parents’ fortune after their death.(8) He disregarded his father’s advice and left college.(9) In this address, he asked the youngsters, who embody the spirits of the nation, to join thecampaign.(10) The special diet incorporates many different fruits and vegetables.7. (1) Whoever run the red light shows a complete disregard for public safety.(2) Success, as he explained, was nothing more than a consistent pursuit of art and good luck.(3) The new product has benef ited from research work at the crossroads between biological andmedical studies.(4)It was amazing that his idea echoed well the great philosopher’s belief, which he claimed notto have heard about before.(5) The one-month intense training program prepared the team members well for possibleemergencies.(6) The audience was deeply impressed with the vigor and power of the speech delivered by theenvironmentalist.(7) This traveling experience will provide you witha rare opportunity to sample a different way oflife.(8) Using the limited time to its fullest potential is one of the must-have/required skills in adapting to the fast-paced modern life.(9) More and more countries are bringing robots to bear on their various problems.(10) These students are encouraged from a very early age to follow their own boundless interestswell beyond the boundaries of conventional belief in obedient learning.8.A. (1) B (2) C (3) B (4) B (5) DB. As multidisciplinary design has become a trend in the industry, there is a need for moreemphasis on multidisciplinary perspectives. Educational institutions should take their role in training individuals who can function in a collaborative environment and be prepared to facemultifaceted projects that they may not have been exposed to. However, our universities andcolleges fail to shift from traditional divisions and departmental sections to multidisciplinarywork being practiced on a daily basis outside theclassroom.C. 1) F 2) T 3) F 4) T 5) TD. (1) what learning is about (2) be inquisitive (3) learn a new subject(4) analyze a new problem (5) teacher-taught (6) master-inspired(7) self-learner (8) the trap of dogma (9) no single simple answer(10) black and white (11) critical thinking (12) tolerant and supportive(13) a new thesis topic (14) flexibility (15) style of leadershipUnit 2 The Scientific MethodKeys to the ExercisesApproaching the Topic1. 1) The Scientific Method is a body of techniques for investigating phenomena and acquiringknowledge, as well as correcting/integrating previous knowledge. It involves gatheringobservable, empirical and measurable evidence, the collection of data through observationand experimentation, and the formulation andtesting of hypotheses.2)Scientists put forward hypotheses to explain what is observed. They then conduct experimentsto test these hypotheses. The steps taken in the experiment must be capable of replication andthe results emerge as the same. What is discovered may lead to a new hypothesis.3) Scientists are human and can be unintentionally biased; total objectivity is impossible.4) Scientists are human and can be unintentionally biased. Science uses our senses and our sensescan be mistaken. We can never understand something as it really is because our very presence affects what is being studied.5) ① Science is both a body of knowledge and a process.② Science is exciting.③ Science is useful.④ Science is ongoing.⑤ Science is reliable.⑥ Science is a community endeavor.2. 1) c 2) g 3) e 4) f 5) a 6) d 7) h 8) k9) b 10) i 11) j4. (1) aspects (2) process (3) satisfy (4) technologies (5) puzzle(6) collection (7) evidence (8) ensure (9) diversity (10) professional6. 1) Science.2) It brings to mind many different pictures: white lab coats and microscopes, a scientist peeringthrough a telescope, the launch of the space shuttle, and so on.3) Science can discover the laws to understand the order of nature.4) Because it relies on a systems of checks and balances, which helps ensure that science moves towards greater accuracy and understanding, and this system is facilitated by diversity within the scientific community, which offers a range of perspectives on scientific ideas.5) Open.Reading about the Topic3. 1) The modern scientific method is characterizedby confirmations and observations which“verified”the theori es in question, but some genuinely testable theories, when found to befalse, are still upheld by their admirers, which rescues the theory from refutation only at theprice of destroying, or at least lowering, its scientific status.2) A theory which is not refutable by any conceivable event is non-scientific.3) Their theories were constantly verified by their clinical observations. They always fitted andwere always confirmed.4) Light must be attracted by heavy bodies (such as the sun).5) There is the risk involved in a prediction: the theory is incompatible with certain possibleresults of observation —in fact with results which everybody before Einstein would haveexpected.4. Set 1: 1) c 2) a 3) d 4) b 5) f 6) e 7) h 8) gSet 2: 1) b 2) e 3) a 4) f 5) d 6) c 7) h8) g5. Para. A (b) Para. B (c) Para. C (e)Para. D (e) Para. E (a) Para. F (d)6. 1) Observations, hypotheses, and deductions, then conclusions.2) You will need to research everything that you can f ind about the problem.3) You shouldn’t change the hypothesis. Instead, try to explain what might have been wrongwith your original hypothesis.4) An important thing to remember during this stage of the scientific method is that once youdevelop a hypothesis and a prediction, you shouldn’t change it, even if the results of yourexperiment show that you were wrong.5) Because there is a chance that you made a miscue somewhere along the way.7. Set 1: 1) c 2) a 3) d 4) b 5) f 6) e 7) h8) gSet 2: 1) e 2) g 3) a 4) f 5) c 6) b 7) d 8) h8. 1) Observation, as the f irst stage of thescientific method, is a way of collecting informationfrom any possible sources, which can serve as a foundation in verifying a theory. In thisprocess, one should expect an event which could refute the theory. Only through beingrefuted by new observations which are incompatible with the theory could it be falsified, which ref lects its truescientific virtue.2) A hypothesis is a possible solution to a problem, based on knowledge and research, while atheory is a hypothesis confirmed by the research findings. Every theory cannot be applied toevery situation; otherwise, it is not a good theory.3) It is always possible to verify nearly every theory, but that would rescue the theory fromrefutation at the price of destroying, or at least lowering its scientific status.4) To falsify a theory is more valuable, because a theory which is not refutable by any conceivableevent is non-scientific.9. 1) Because of this personal experience and an interest in the problem, you decide to learn moreabout what makes plants grow. (Para. B)2) The experiment that you will design is done to test the hypothesis. (Para. D)3) Through informal, exploratory observations of plants in a garden, those with more sunlightappear to grow bigger. (Para. H)4) The judges at your science fair will not take points off simply because your results don’tmatch up with your hypothesis. (Para. K)5) You cannot prove the hypothesis with a single experiment, because there is a chance that youmade a miscue somewhere along the way. (Para. Q) 10. Observation, the initial stage of the research, requires a thorough understanding of a researchproject you have chosen by collecting adequate information from various sources, and isfollowed by the next stage known as hypothesis, an uncomplicated statement that defineswhat you think the outcome of your experimentwill be.Exploring the Topic4. 1) Science does not include explanations based on no empirical evidence.2) The human nature of science, however, renders it unlikely to be free of personal prejudices, misapprehensions, and bias.3) The scope of science encompasses the whole universe and natural world.4) Science is a process of deciding whether the acquired evidence may prove what is mostlikely to be correct currently.5) It is not possible to prove a hypothesis witha single experiment, as chances are that amistake was made somewhere in the process. Integrated Exercises2. (1) additional (2) illustrate (3) interpret (4) conduct (5) previous (6) involve(7) design (8) verify (9) reflect (10) collect (11) research (12) support3.(1) methodical (2) commitment (3) achievable (4) assume (5) illogical(6) exposure (7) constitutive (8) emphatic (9) confirmation (10) identity4. (1) A (2) B (3) A (4) D (5) A (6) B (7) C (8) A (9) D (10) B5. (1) This observation motivated Newton to developa theory of gravity.(2) Other scholars attempt to approach the subject from an economical perspective.(3) Participating in the activity will provide one with an initial taste of the objectives ofsociology.(4) Scientists insisted there was a rationalexplanation for the strange phenomenon.(5) To most young people, higher education is nothing but a process of acquiring knowledge.(6) The study demonstrates the necessity of taking a much broader view in the matter.(7) The new car’s design successfully integrates art and technology.(8) China actually encountered the identical stages of its development in the early 1990s to the West.(9) The virus can spread to a document or application between computers and render thecomputer useless.(10) If the sustainable development of small economies is facilitated, their effectiveness will beultimately integrated into the global economy.7. 1) We could not attend a conference without hearing some talks about change and challenge.2) Things seem highly optimistic in the light of numerous reports, especially from countrydistricts.3) I am in favor of the argument that urbanization should be controlled properly.4) Something slowly began to dawn on me — I still loved what I did.5) My computer does not work because it was rendered paralyzed by some viruses.6) Experts are working on the plan in question. And they’ll come to an answer.7) A national curriculum framework is logically incompatible with pupil-centered learning.8) For many women success is often achieved at the price of their married life.9) Many attempts had been made before I successfully entered a key university.10) There is a good chance that it will turn fine tomorrow.8. A. (1) B (2) A (3) C (4) A (5) BB. Understanding scientific method is critical to your scientific endeavor. The scientific method is a series of steps that serve as guidelines for scientific efforts, and a tool that helps scientists solve problems and determineanswers to questions in a logical format.There are two forms of scientific method: the experimental method and the descriptivemethod. The former employs numerical data and graphs, used in physical sciences, whilethe latter gathers Information through visual observation and interviewing, employed inzoology and anthropology. The scientific method involves five steps, namely, identifying a problem, researching the problem, formulating a hypothesis, conducting an experiment andreaching a conclusion.C. (1) The process of science, in contrast to the linear steps of the simplified scientific method, is iterative.(2) Science circles back on itself so that useful ideas are built upon and used to learn even more about the natural world.(3) Gregor Mendel showed that inheritance is particulate that information is passed along indiscrete packets that cannot be diluted.(4) Any point in the process leads to manypossible next steps, and where that next stepleads could be a surprise.(5) Science may involve many different people engaged in all sorts of different activities indifferent orders and at different points in time.D. (1) natural world (2) investigations (3) basic question(4) information (5) Experiments (6) detailed understanding(7) built upon (8) deepen and extend (9) in the process(10) testing (11) observation (12) new direction(13) in different orders (14) represent (15) less importantUnit 3 A ncient China’s Contribution to ScienceKeys to the ExercisesApproaching the Topic1. 1) Needham is the world’s famous Sinologist and author of Science and Civilization inChina.2) The European people just take these inventions for granted. All originated in China buthave long since been adopted by the West.3) They helped to inspire the European agricultural and industrial revolutions.4) It has won five literary awards in America and been translated into 43 languages.5) His book, The Spirit of Chinese Invention, was approved by the Chinese Ministry ofEducation for use in connection with the national secondary curriculum in China.2. 1) f 2) k 3) c 4) a 5) o 6) n 7) g8) e9) d 10) m 11) i 12) h 13) j 14) l 15) b 4. (1) credit (2) considerable (3) befriended (4) breakthroughs (5) thoroughly(6) flown (7) academic (8) embark (9) suggested (10) staff6. 1) The overlooked great breakthroughs in ancient China.2)Dr. Needham argued that a proper book on thehistory of Chinese science and technologywould have a wide bearing on the general history of thought and ideas.3) He helped to bring due credit to China’s overlooked contribution to scientific innovation. 4) Yes, he does. Because he believed that a proper popular book would have a wide bearing onthe general history of thoughts and ideas, which could not be possible if the book was tooacademic.Reading about the Topic3. 1) Both Westerners and Chinese people are ignorant of the fact that the West imported a lot ofinventions from ancient China.2) Because more than half of the basic inventions and discoveries upon which the“modern world”rests come from China.3) Because they take many great achievements for granted, and even the Chinese themselveslost sight of the truth, so their western inheritors wouldn’t trouble themselves to know thetruth.4) Because it is always more satisfying to the ego to think that they have reached theirpresent position alone and unaided, and that they are the proud masters of all abilities and all crafts.4. Set 1: 1) d 2) e 3) a 4) b 5) c 6) g 7) f 8) hSet 2: 1) d 2) g 3) e 4) h 5) b 6) a 7) c 8) f5. Para. A (e) Para. B (b) Para. C (f) Para. D(a) Para. E (a)Para. F (a) Para. G (c) Para. H (g) Para.I (h) Para. J (d)6. 1) The three inventions transform-ed completely the modern world and mark-ed it off fromthe ancient and the Middle Ages.2) The European agricultural revolution, which laid the basis for the Industrial Revolution,came about only because of the importation of Chinese ideas and inventions.3) The truth that half of the basic inventionsand discoveries originated from China needs to be imparted to schoolchildren. The purpose is to let them know the truth and then tobridge the chasm between the East and the West.4) The bureaucratic organization of China in its earlier stages strongly helped science togrow; only in its later ones did it inhibit further growth, and in particular prevented a breakthrough which has occurred in Europe.5) The author points out the reasons why China was developed in the past but backward atpresent and why the West was underdeveloped in the past but advanced at present.7. Set 1: 1) c 2) g 3) h 4) b 5) f 6) d 7) a8) eSet 2: 1) c 2) d 3) g 4) e 5) a 6) b 7) f 8) h8. 1) The two readings both list a series of great inventions and discoveries that originated in ancient China. Reading 1 tends to be factual, while Reading 2 is more critical of the fact that the Chinese are ignorant of their ancientachievements and the Westerners simply take them for granted.2) The argument in Reading 2 is more reasonable and acceptable since the author uses a lot of examples and examines the question from both the Chinese and Western perspectives toillustrate his point.3) Reading 2 holds more obvious negative attitudes towards Westerners.4) It would be better if the nations and the peoples of the world had a clearer understandingof each other, allowing the mental gap between East and West to be bridged. (Reading 2)The discoveries and inventions made in Europe in the seventeenth century and thereafterdepended so much in so many cases on centuries of previous Chinese progress in science,technology and medicine. (Reading 3)9. 1) He regarded the origins of these inventions as “obscure”and he died without everknowing that all of them were Chinese. (Para.B)2) Chauvinistic Westerners, of course, always try to minimize the indebtedness of Europe toChina in the ancient and the Middle Ages, but often the circumstantial evidence iscompelling. (Para. C)3) In many cases we simply cannot identify the channels through which knowledge wasconveyed from East to West. (Para. C)4) Modern science which developed in the seventeenth century was a mathematization ofhypotheses about nature, combined with experimentation. (Para. D)5) One factor which must have great relevance here is the circumstance that the feudalism ofEurope and China were fundamentally different. (Para. E)10.The feudalism of China differed greatly from that of Europe in that its bureaucraticorganization promoted the growth of science in ancient China but inhibited its furtherdevelopment later on.Exploring the Topic4. 1) Increasingly being bewitched by the advanced European technology, the Chinese haveforgotten their own achievements.2) A book like that would be absolutely non-academic; it would nevertheless have afar-reaching influence on the general history of thought and ideas.3) The lesson to be drawn from the history of agriculture can best illustrate the ignorance ofthe egoistic westerners.4) The Chinese and Westerners are equally surprised when they realize that modernagriculture, modern shipping and even the essential design of the steam engine alloriginated from China.5) A clear understanding among the nations and the peoples of the world would be welcomedto bridge the gap between East and West.5. 2) The deafening noise, and the glare of the engine fire, would have a bad effect on nerves.Further, being moved through the air at a high speed would do great injury to delicatelungs. The sudden plunging of a train into the darkness of a tunnel, and the equally sudden rush into full daylight, would cause great damage to the eyesight.3) What was it that enabled them to become great or successful? Were they born withsomething special? Or did their greatness have more to do with timing, devotion and,perhaps, an uncompromising personality? The answer is a never surrender attitude. If greatachievers share anything, it is an unrelenting drive to succeed. There is a tendency to thinkthat they are endowed with something super-normal.Integrated Exercises2. (1) insight (2) expertise (3) obscure (4) backward(5) undertake (6) ignorant (7) acknowledge (8) essential(9) minimize (10) shatter (11) fading (12) illustration3.(1) insightful (2) transformation (3) respectively (4) dazzling (5) resurgent(6) indebted (7) backwards (8) irrelevant (9) unparalleled (10) illusionary4. (1) C (2) D (3) A (4) B (5) A (6) A (7) C (8) D (9) B (10) D5. (1) Examples will be drawn from literature and popular media to illustrate the range ofleadership and non-leadership behaviors and competencies.(2) You’ll never be able to eliminateinterruptions altogether but you can do a lot to minimizethem.(3) There is evidence that the movie reinforces negative stereotypes about women.(4) The violence to property will do nothing to facilitate that investigation.(5) Determination and effort enable-d the young man to acquire success.(6) The project was held back by budget restraints.(7) We will continue to press governments in the region to undertake political reforms.(8) This level of economic growth is unprecedented and unique.(9) This policy could isolate the country from the other permanent members of the UnitedNations Security Council.(10) The profound economic effect would accumulate day by day, and much of it might bereversible.7. (1) It must be realized that China experienceda great transformation in the last century.(2) However, it is rather questionable whether the majority of Americans know the truthabout China and Chinese people.(3) All of the information can be conveyed by simple graphs.(4) It is essential that our children absorb this lesson into their outlook on the world.(5) It is a lesson that all of us should take to heart.(6) We must never lose sight of the fact that many inventions originated in China.(7) Many of us take it for granted that technology is the top priority in economicdevelopment.(8) How was it that you had the right information at the right place and at the right time?(9) I can think of no better illustration of the importance of higher education than the fact that many university graduates have become the leaders in various f ields.(10) The demand for a raise ref lects as much a desire for the recognition of their success asfor more money.8. A. (1) C (2) B (3) D (4) D (5) CB. China’s ancient great inventions and discoveries, as the forerunners of some of the modern technologies, both enhance the quality of human life and change Chinese historyof science. The most signif icant ones are papermaking, gunpowder, compass and printing.Paper, one of the most widely used and indispensable materials, led to subsequent innovations like paper currency, woodblock printing and ceramic movable type printing.The most important invention of gunpowder。
新时代研究生学术英语综合教程2教师手册
新时代研究生学术英语综合教程2教师手册全文共10篇示例，供读者参考篇1Hello everyone, I'm here to talk about the Teacher's Manual for the New Era Research Student Academic English Comprehensive Course 2. This book is super cool because it helps teachers like us teach students all about academic English in a fun and interactive way.The Teacher's Manual is full of awesome tips and tricks to help us make our lessons interesting and engaging. It has detailed lesson plans, fun activities, and lots of ideas to keep our students interested and excited about learning. We can use the manual to create a dynamic and interactive classroom environment where our students can improve their English skills while having fun.One of the best things about the Teacher's Manual is that it covers all aspects of academic English, including reading, writing, speaking, and listening. This means that we can help our students become well-rounded English speakers and writers. 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It also has sample lesson plans and assessments to make teaching easier.One thing I really like about this book is that it covers a lot of different topics. It talks about reading, writing, speaking, and listening. It also has sections on grammar and vocabulary. Sobasically, it's a one-stop shop for all your academic English needs.Another cool thing about this book is that it's really easy to use. The instructions are simple and the exercises are fun. Plus, it has lots of examples and explanations to help you understand the concepts better.Overall, I think this book is a great resource for teachers who want to help their students improve their academic English skills. It's easy to use, covers a lot of topics, and has lots of helpful tips. So if you're a teacher looking for a way to help your students succeed in English, I definitely recommend checking out "New Era Research Graduate Academic English Integrated Course 2 Teacher's Manual".篇3Hello everyone! Today I want to talk to you about the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual". It may sound like a mouthful, but don't worry, I'll break it down for you!First of all, this manual is like a guide for teachers who are helping graduate students improve their academic English skills. In this book, you will find lots of tips and tricks to help studentswrite better essays, give great presentations, and do awesome research.One of the things the manual talks about is how to write a good thesis statement. This is like the main idea of your essay, and it's super important to get it right. The manual gives examples and exercises to help students practice writing strong thesis statements.Another thing the manual covers is how to use sources in your research. It's important to give credit to the people whose ideas you're using in your work. The manual shows students how to properly cite sources and avoid plagiarism.There are also sections on grammar and vocabulary, which are essential for writing clear and professional academic papers. The manual breaks down complex grammar rules and gives tips on how to expand your academic vocabulary.In conclusion, the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual" is a great resource for teachers who want to help their students succeed in their studies. With its practical tips and exercises, students can improve their academic English skills and become better researchers and writers.篇4Hey guys! Today I wanna talk to you about this super cool book called "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Guide". It's all about helping teachers teach us graduate students how to rock our academic English skills!First off, this book has tons of awesome tips and tricks for reading, writing, speaking, and listening. It helps us understand tricky academic vocabulary and grammar, and gives us practice exercises to improve our skills.The book also has real-life examples of academic essays and presentations, so we can see what good academic English looks and sounds like. It even has activities to help us practice researching and citing sources properly.One of my favorite parts of the book is the "Activities" section. It has fun games and group activities that make learning academic English super fun and interactive. Plus, it helps us work on our teamwork and communication skills!Overall, this book is like having a super smart English teacher right in your hands. It's packed with everything we need tosucceed in our graduate studies and beyond. So grab a copy and let's start improving our academic English skills together!篇5Hi teacher! Today I want to tell you about the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual". It's a really cool book that helps us learn English in a fun and interesting way.First of all, this book has so many useful tips and strategies for improving our English skills. It helps us with reading, writing, listening, and speaking English. The activities in the book are really fun and they help us practice what we've learned.The grammar section in the book is great too. It explains grammar rules in a simple and easy-to-understand way. There are also lots of exercises to practice what we've learned. It really helps us improve our English grammar.The vocabulary section is awesome too. It teaches us lots of new words and how to use them in sentences. There are also exercises to help us remember the words and use them correctly.I also love the listening and speaking activities in the book. They help us practice our listening skills and speaking skills in afun way. It's really helped me become more confident in speaking English.Overall, the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual" is a fantastic book for helping us improve our English skills. I've learned so much from it and I know you will too. Thanks for teaching us with this awesome book!篇6Hey guys, today I'm going to talk about the "New Era Research-oriented Academic English Comprehensive Course 2 Teacher's Manual". It's a super important book for our teachers to help us learn academic English better.This book is full of useful information and tips on how to improve our English skills. It covers everything from reading, writing, listening, speaking, grammar, vocabulary, and more. The activities and exercises in the book are really fun and interesting, which makes learning English a lot more enjoyable.One of the coolest things about this book is that it includes real-life examples of academic English in action. This helps us understand how to use English in a more professional and academic way. It also gives us a better idea of what to expectwhen we go on to higher education or start working in a professional setting.The book also has lots of useful strategies for improving our English skills, like how to take notes, how to write essays, how to give presentations, and so much more. These skills are super important for us to succeed in our academic and professional lives.Overall, the "New Era Research-oriented Academic English Comprehensive Course 2 Teacher's Manual" is a must-have for all teachers who want to help us become better English speakers and writers. It's packed with tons of useful information and tips that will really help us improve our English skills. Make sure to check it out and ask your teacher to use it in class!篇7Hello everyone, I’m going to tell you about the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual"! This book is super important for teachers who want to help students improve their English skills. Let’s dive into the details!First off, this book covers a wide range of topics, from academic writing to public speaking. It’s designed to helpstudents become better communicators and researchers. The book is divided into different units, each focusing on a specific aspect of academic English. It’s filled with useful tips, exercises, and examples to help students master the skills they need.One of the key features of this book is the emphasis on critical thinking. The authors encourage students to think critically about the information they read and hear, and to develop their own arguments based on evidence. This is a valuable skill for any student, whether they are studying science, literature, or history.Another great thing about this book is that it includesreal-life examples of academic writing. Students can see how to structure a paper, cite sources, and write clearly and persuasively. This hands-on approach helps students understand what is expected of them in the academic world.Overall, the "New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual" is a valuable resource for any teacher who wants to help students succeed in their studies. It’s engaging, practical, and full of useful information. I highly recommend it to all teachers who want to bring out the best in their students!So, if you want to help your students improve their English skills and succeed in their academic careers, make sure to check out this book. Happy teaching!篇8The New Era Research Graduate Academic English Integrated Course 2 Teacher's Manual is a super important book that helps teachers teach students how to use academic English. It's like a treasure map for learning! The book is full of tips and tricks to help students improve their English skills and do well in their studies.First off, the book talks about all the different types of academic English, like writing essays, giving presentations, and doing research. It even has exercises and activities to practice these skills. It's like a fun English adventure!The book also has lots of vocabulary and grammar tips to help students sound more professional. There are also sections on how to read and write academic articles, which are super useful for doing research projects.One of the best parts of the book is that it has real-life examples of academic English in action. So students can see howto use the language in a practical way. It's like having a secret weapon for learning English!Overall, this book is a must-have for any teacher who wants to help their students succeed in their studies. It's full of valuable information and will definitely help improve students' English skills. So let's all grab our copy of the New Era Research Graduate Academic English Integrated Course 2 Teacher's Manual and start our English adventure today!篇9Hey guys, have you heard about the New Era Research Graduates Academic English Comprehensive Tutorial 2 Teacher's Manual? It's like a super cool book that helps teachers like your teachers to teach us better in school. Let me tell you more about it!Firstly, this book is all about learning academic English, which is like a more advanced kind of English that we use in school for writing essays and reports. It helps us to sound more professional and smart when we talk and write in English.In the manual, there are lots of fun activities and exercises for us to do in class. These activities help us practice reading,writing, speaking, and listening in English. There are also tips and tricks for studying better and getting good grades in school.The book covers topics like research skills, critical thinking, and academic writing. It teaches us how to do research, analyze information, and present our ideas in a clear and organized way. It's like a guide to becoming a super smart and successful student!Our teachers use this manual to plan their lessons and help us improve our English skills. They also use it to assess our progress and give us feedback on our work. It's like having a super teacher's helper in the classroom!So, next time you see your teacher using the New Era Research Graduates Academic English Comprehensive Tutorial 2 Teacher's Manual, remember that it's there to help us become awesome English speakers and writers. Let's study hard and have fun learning together!篇10Hi guys! Today let's talk about the New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual. It's super important for teachers to know how to help us become better at English!First off, this manual is all about helping us improve our English skills in a fun and effective way. It covers lots of different topics like reading, writing, listening, and speaking. There are also tips for teachers on how to make our learning experience more engaging and interesting.One cool thing about this manual is that it includes plenty of activities and exercises for us to practice what we've learned. There are also quizzes and tests to help us track our progress and see how much we've improved.The manual also provides guidance on how to teach specific English skills like grammar, vocabulary, and pronunciation. This is super helpful for teachers who want to make sure they're covering all the important aspects of English language learning.Overall, the New Era Research Graduate Academic English Comprehensive Course 2 Teacher's Manual is a great resource for teachers who want to help us get better at English. So next time you're in class, make sure to thank your teacher for all their hard work in following this awesome manual!。
NS2_introduction_guide
NS2入门指导---SeaSon & crabhit From DB lab of HIT序很多人都问我新手应该看些什么资料，或者怎么熟悉NS2这个工具。
这是让很多入门者非常头痛的问题，包括我自己，当初也是困难重重，不过现在让我说我也没什么印象了，因为我当时比较盲目看了很多兑现在一点儿用都没有的资料。
为了能让写的东西真的对新手有所帮助，刚才跟我师弟crabhit谈了谈，所以总结了一下，希望能起到抛砖引玉的作用。
当然，只是我们的粗略见解，如有不足，欢迎指正。
SeaSon’email: yuhui.wu@Crabhit’email: crabhit@一． 安装(Cygwin+ns2.2*)这应该是让很多人头大的问题，因为NS2安装比较另类，所以很多人已如果安装的时候稍有闪失，便会出现很多莫名其妙的问题，这时候一般人会选择重装，但是如果你的问题如果是cygwin（一般NS2如果是从官方网站上下载的就不会有问题），无论重装多少次都是没用的。
所以一定要确保你安装的Cygwin是正确的，如果你在哈尔滨可以联系我我有一个完整版本的Cygwin，已经经过无数人测试没有任何问题，不过大于2G，所以不能放到网上，只能找我来拷了。
至于NS2你如果不是特别喜欢刺激的人就安装ns-1llinone-2.2*，至于单个安装的我也装过，装好了也会出现一些莫名其妙的问题。
版本如果没有特殊需求就安装最新的ns-allinone-2.29。
具体安装方法，柯老师已经写的很完整了，已经包括Cygwin的下载，我就不罗嗦了，网址如下:http://140.116.72.80/~smallko/ns2/setup_en.htm安装成功之后，按照网页中的提示，测试脚本，如果没什么问题，应该就是成功了。
二、初学者要看什么资料1．语言基础C/C++是使用ns2的基础。
调试的过程中出现的错误大多数都是C/C++常见的错误，比如空指针等等。
对北欧两项的认识英语作文
对北欧两项的认识英语作文Dive into the thrilling world of Nordic combined, a sport that's as unique as it is demanding, blending the grace of cross-country skiing with the adrenaline rush of ski jumping. It's not just a competition; it's a symphony of speed, precision, and endurance, a true test of a winter athlete's mettle. Imagine soaring through the crisp Nordic air, then swiftly transitioning to a cross-country sprint—this is the essence of the Nordic combined.This sport, a true gem of the winter Olympics, hails from the snowy landscapes of Scandinavia, where it's more thanjust a pastime; it's a cultural phenomenon. The term "Nordic" is a nod to the region's heritage, and the "combined" part refers to the two distinct disciplines that athletes must master. It's like trying to excel at a high-speed ballet followed by a marathon—no easy feat!Local lingo often refers to the ski jumpers as "birds of prey" due to the way they glide through the air, a testament to their skill and the sport's poetic nature. The cross-country segment is where the real endurance comes into play, with athletes pushing through the snow-packed trails, their breaths visible in the frosty air.Each competition is a narrative of strategy and physical prowess. The ski jump sets the stage, with distances determining start intervals for the cross-country race. It'sa high-stakes game where every meter counts, and theathletes' grit is as冰冻 (freezing) as the Nordic winds they face.The Nordic combined is more than a sport; it's a celebration of the human spirit's ability to conquer the elements. It's a dance with nature, a display of strength, and a narrative that unfolds against a backdrop of snow-capped mountains and icy tracks. It's a sport that captures the heart of the North, and once you witness the drama and determination unfold, you'll be hooked, just like the locals who cheer on with fervor and pride. So, buckle up and get ready to be swept away by the dynamic duo of ski jumping and cross-country skiing in the Nordic combined.。
新核心综合学术英语教程第二册_Unit_2
Claudius Ptolemy
Claudius Ptolemy was a Greco-Egyptian writer of Alexandria, known as a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. Ptolemy was the author of several scientific treatises, three of which were of continuing importance to later Islamic and European science. The first is the astronomical treatise now known as the Almagest. The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known in Greek as the Tetrabiblos (―Four books‖), in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day.
In this unit, you will
• learn about the concept ―scientific method‖ and its application in science; • research ―verification of theories‖ and falsification of theories‖ on the Internet and find reliable information; • learn words, expressions, and sentence patterns related to the theme and use them in writing and speech; • learn strategies such as listening for introduction (listening), skimming (reading), agreeing and disagreeing (discussing), writing thesis statements (writing), etc; • learn the deductive and inductive method of reasoning; • give an oral presentation on an assigned topic to the class.
Springer Handbook of Robotics 第二版说明书
Second edition of Springer Handbook of Robotics | Robohubexpansion of robotics across the boundaries with related disciplines. Again, the authors have been asked to step outside of their comfort zone, as the Editorial Board have teamed up authors who never worked together before.No doubt one of the most innovative elements is the inclusion of multimedia content to leverage the valuable written content inside the book. Under the editorial leadership of Torsten Kröger, a web portal has been created to host the Multimedia Extension of the book, which serves as a quick one-stop shop for more than 700 videos associated with the specific chapters. In addition, video tutorials have been created for each of the seven parts of the book, which benefit everyone from PhD students to seasoned robotics experts who have been in the field for years. A special video related to the contents of the first chapter shows the journey of robotics with the latest and coolest developments in the last 15 years. As publishing explores new interactive technologies, an App has been made available in the Google/IOS stores to introduce an additional multimedia layer to the reader’s experience. With the app, readers can use the camera on their smartphone or tablet, hold it to a page containing one or more special icons, and produce an augmented reality on the screen, watching videos as they read along the book.。
全新版大学英第二版语综合教程2听力原文Unit
Unit 5 Unsolved MysteriesListening and SpeakingAudio Track 2-5-1In the picture on the left, a criminal is breaking a law; he is committing a crime.In the picture on the right, the detective is catching and arresting the criminal.In the picture in the center, the detective is questioning the criminal but he is not making a confession.Audio Track 2-5-2/Audio Track 2-5-3The greatest detectiveSherlock Holmes is probably the greatest detective ever known — well, at least he’s one of the most famous. Bu t he never actually existed … he’s an imaginary detective who appears in sixty stories created by the Scottish author Sir Arthur Conan Doyle.Doyle was not always a writer. He started his career as a doctor. Fortunately for us, he did not have many patients. He needed money and so he started to write stories.The first Sherlock Holmes story was published in 1887, and was called AStudy in Scarlet. Later, a magazine published The Adventures of Sherlock Holmes and readers loved it!What makes Sherlock Holmes so special Well, he was very intelligent and successful. He always arrested the criminal — every single time — with the help of his partner, Dr. Watson.In the stories, Holmes lived at 221B Baker Street in London, England. Thousands of people visit that address every year. There’s also a Sherlock Holmes Museum in London.Audio Track 2-5-4/Audio Track 2-5-5/Audio Track 2-5-6Mike: … So, we can look forward to warmer temperatures. It’ll be a good weekend for the beach. Over to you, Alexa.Alexa: Thank you for that weather report, Mike. And finally, this story just in. … We have a report that a local man, Nick Brown, saw some strange lights. He was driving home at about 10 . He said the lights were bright and they moved across the sky. He stopped at a gas station and talked to a police officer about the lights. The police officer had seen the lights, too. Mike: Hmm … that’s a strange story. What happened nextAlexa: Well, Mr. Brown took some pictures, but there was no film in his camera. Finally, he called his wife on his cell phone. But by that time, the lights were gone.Mike: Well, I know that there is a legend around here about mysteriouslights … a lot of local people have seen the lights. It’s starting to seem like those lights really exist. What do you think, AlexaAlexa: I don’t believe it. I think it’s some kind of hoax!Audio Track 2-5-7/Audio Track 2-5-8It was raining heavily. I couldn’t see clearly. I drove slowly. Suddenly, I saw a young girl. She was dressed neatly and standing in the middle of the road. I was surprised! Somehow, I stopped the car quickly.“What are you doing” I asked. She looked at me strangely but didn’t answer. “Are you OK” I asked. “I’m fine,” she answered. Then she smiled happily and walked away quietly. Nervously, I drove to my hotel and checked in. I told the clerk about the little girl. “Do you know her” I asked. “Oh yes,” he said calmly.“That’s Mary Anne. She died five years ago on that road. It was a car accident during a rainstorm.”Audio Track 2-5-9The Tunguska MysteryIt was early morning. June 30, 1908, in eastern Russia. Suddenly, a terrible explosion rocked the forest in Tunguska. People fell to the ground, and all the trees for 2000 square kilometers were knocked down. People heard the explosion 800 kilometers away, and the fire burned for many weeks.Audio Track 2-5-10/Audio Track 2-5-11What caused this terrible explosion A century later, scientists are still trying to find the answer. Here are some possible explanations.1. An asteroid: Asteroids are very large pieces of rock that go around in space and sometimes hit the planet. They can cause lots of damage. Some of them weigh as much as 100,000 tons. If an asteroid hit the earth, it would cause a huge explosion.2. A comet: Comets are giant balls of gas, ice, and rock with long tails. They travel through space in a regular pattern. Encke’s Comet was near Earth in 1908, and it’s possible that a part of it broke off and hit the earth.3. A UFO accident: Some people believe that a spaceship crashed into the ground in Siberia and its engine exploded.4. An extraterrestrial attack: Another idea is that extraterrestrials, that is, people from other planets, attacked the earth. Extraterrestrials might have wanted to destroy the earth, so they aimed their weapons at Earth and set fire to the forest.5. A scientific experiment: Another idea is that scientists made a mistake during an experiment with electricity. A man named Nikola Tesla tried to build a “supergun” that used electricity. Maybe it was a test of his gun and it didn’t work correctly.Audio Track 2-5-12/Audio Track 2-5-13Q: Where is Marfa and what exactly is it famous forA: Marfa is a small town in west Texas in the United States. It’s famous for the “Marfa mystery lights.”Q: What are the mystery lights exactlyA: No one knows for sure. There are many different ideas about that.Q: Can you describe themA: That’s a difficult question. Different people see different lights. They are not always the same. I can say that they appear after sunset in the sky. They dance mysteriously in air and vanish. Then they suddenly reappear. Q: Some people say they are car headlights. Do you think soA: No, I don’t. A man first saw the mystery lights over 100 years ago. The man was Robert Ellison and the year was 1883. Of cour se we didn’t have cars in 1883.Q: What do you think causes the lightsA: There are many theories. The Native Americans thought the lights were stars falling to Earth. Some people think uranium gas causes the lights. Other people suggest that ball lightning does it. Ball lightning is lightning in the shape of circle. It often appears just after a rainstorm.Q: What are some of the weirdest ideas about the lightsA: Well, some people call them “ghost lights.” They think ghosts do it. That’s the strangest ide a. Some say they are UFOs. I don’t think so.Q: What do the experts sayA: They can’t figure it out. Some engineers even came from Japan one time. They studied the lights, but couldn’t solve the mystery.Q: Are the local people scaredA: No, actually, they aren’t. They like the lights. And every year in early September there’s a big town festival to celebrate the mystery lights.Audio Track 2-5-14Q: What do you think causes the lightsA: There are many theories. The Native Americans thought the lights were stars falling to Earth. Some people think uranium gas causes the lights. Other people suggest that ball lightning does it. Ball lightning is lightning in the shape of circle. It often appears just after a rainstorm.Q: What are some of the weirdest ideas about the lightsA: Well, some people call them “ghost lights.” They think ghosts do it. That’s the strangest idea. Some say they are UFOs. I don’t think so. Q: What do the experts sayA: They can’t figure it out. Some engineers even came from Japan one time. They studied the lights, but couldn’t solve the mystery.Q: Are the local people scaredA: No, actually, they aren’t. They like the lights. And every year in early September there’s a big town festival to celebrate the mystery lights.Audio Track 2-5-151. That man seems angry.2. She speaks French.3. Your sister looks tired.4. He practices the piano every day.5. My aunt always watches the news.6. My friend knows the answer.Audio Track 2-5-16/Audio Track 2-5-17Stye: Do you know the Dodd DiamondFrye: Of course! The museum owns it.Stye: Not anymore! Someone stole it last night!Frye: Really How did it happenStye: Well, it’s unlikely the criminal walked into the room. There’s an alarm on the floor.Frye: But there’s no alarm for the skylight.St ye: You’re right! I bet the criminal climbed down a rope. Then he took the diamond without touching the floor!Audio Track 2-5-18A: I love chocolate.B: There's a good chance that's true. I know you like sweets. You probably like chocolate, too.A: My family has moved house six times.B: It doesn't seem possible.A: Why do you say thatB: I've known you since we were kids.Audio Track 2-5-19A: Do you believe that Bruno Hauptmann was the real kidnapperB: I doubt that he was. Nobody's likely to be so silly to leave all the evidence there for people to find. Besides, he never made a confession, did heA: If it wasn’t him … it could have been Betty Gow. What do you think B: Well, it’s unlikely that she did it. She loved the baby. She even fainted at the trial.A: That’s true. Then it could have been Ernie Brinkert.B: Why do you think it could be himA: Well, he’s Violet Sharpe’s boyfriend. He knew about the Lindberghs. It’s quite possible that he made a secret plan with his girlfriend to kidnap the baby for money.B: That’s nonsense. His girlfriend had an alibi. She wasn’t in the house on the day the baby was kidnapped.A: Maybe that was part of the secret plan. Perhaps she was purposefully outof the house.B: Well, possibly. But Ernie’s handwriting didn’t match the kidnapper’s note. How can you explain thatA: I dare say that was also part of the plan. He could have deliberately written the note in a handwriting that is different to normal.B: It doesn’t seem possible. He couldn’t possibly have fooled the c ourt.Video CourseVideo Track 2-5-1Agnes: When I was visiting my grandfather in his village I witnessed a very strange event. It wasn’t raining and the women of the village went to a special place to make the rain fall. And that night it rained.Dave: T here’s a strange tale in Mexico about La Llorona who is a woman who wanders the streets weeping for her dead sons. When there is a strong wind they say you can hear La Llorona .Catherine: In New Jersey there’s a thing or a monster called the “Jersey Devil.” They say it’s very big and hairy but also very sneaky and that it moves from tree to tree.Lourdes: My favorite mysteries are about UFOs, which means Unidentified Flying Objects. I’m not sure if the UFOs are real or if they are a hoax, but I would like to think that they are real.Alejandra: One of the mysteries that I find interesting and has not beensolved yet is the one of the Pyramids. How they made them. How they brought in those very heavy pieces of stone to build the Pyramids. Calum: My advisor and my teacher told us that the dorm that we lived in was haunted, and one time late at night all the lights turned off suddenly and it was very strange and quite scary.Video Track 2-5-2Agnes: When I was visiting my grandfather in his village I witnessed a very strange event. It wasn’t raining and the women of the village went to a special place to make the rain fall. And that night it rained.Calum: My advisor and my teacher told us that the dorm that we lived in was haunted, and one time late at night all the lights turned off suddenly and it was very strange and quite scary.Video Track 2-5-3Roberto: Does anybody know why Tara asked us to come here today Takeshi: She said something about solving a crime and arresting a criminal. Claudia: Arresting a criminalTara: Yes, a criminal.Takeshi: Hey, Tara. Nice hat!Tara: Someone in this room has committed a crime.All: What Come on. What are you talking aboutTara: A theft. Someone ate Sun-hee’s yogurt!Sun-hee: Well, my yogurt is missing. But it’s OK. It’s only yogurt. Tara: It starts with yogurt. Next time it’s your cookies, your ice cream … who knows where it will endSun-hee: OK ... OK. Go on.Tara: It’s very likely one of you did it because you all have a key to this apartment.Takeshi: I only use my key for emergencies. And besides, you live here, you have a key … maybe you took it …Tara: I’m the detective, I didn’t do it. Now. The thief worked calmly, quietly, and very neatly. Note the weapon. (holds up spoon) Clean and dry. Roberto: I didn’t do it. I have an alibi. I was out of town last week … just got home last night.Tara: I know you didn’t do it, Roberto. I asked you to come here today because you are a friend of the thief — Claudia!Claudia: WhatTara: Confess! You’re always too busy to go shopping! You didn’t have any yogurt. You were hungry. It was late! You waited until everyone went to bed and then you slowly entered the kitchen, you made sure no one was there, then you carefully took this spoon and — very quietly — opened the refrigerator door and ate Sun-hee’s yogurt!Claudia: (jokingly) No! No! It’s not true!Mike: (enters apartment using key) Hey, everyone! (to Tara while taking spoon and walking towards fridge) Thanks. Nice hat! (to all while eating yogurt) What’s upVideo Track 2-5-4Roberto: Does anybody know why Tara asked us to come here today Takeshi: She said something about solving a crime and arresting a criminal. Claudia: Arresting a criminalTara: Yes, a criminal.Takeshi: Hey, Tara. Nice hat!Tara: Someone in this room has committed a crime.All: What Come on. What are you talking aboutTara: A theft. Someone ate Sun-hee’s yogurt!Sun-hee: Well, my yogurt is missing. But it’s OK. It’s only yogurt. Tara: It starts with yogurt. Next time it’s your cookies, your ice cream … who knows where it will endSun-hee: OK … OK. Go on.Video Track 2-5-5Tara: It’s very likely one of you did it because you all have a key to this apartment.Takeshi: I only use my key for emergencies. And besides, you live here, youhave a key … maybe you took i t …Tara: I’m the detective, I didn’t do it. Now. The thief worked calmly, quietly, and very neatly. Note the weapon. (holds up spoon) Clean and dry. Roberto: I didn’t do it. I have an alibi. I was out of town last week … just got home last night.Tara: I know you didn’t do it, Roberto. I asked you to come here today because you are a friend of the thief — Claudia!Video Track 2-5-6Claudia: WhatTara: Confess! You’re always too busy to go shopping! You didn’t have any yogurt. You were hungry. It was late! You waited until everyone went to bed and then you slowly entered the kitchen, you made sure no one was there, then you carefully took this spoon and — very quietly — opened the refrigerator door and ate Sun-hee’s yogurt!Claudia: (jokingly) No! No! It’s not true!Mike: (enters apartment using key) Hey, everyone! (to Tara while taking spoon and walking towards fridge) Thanks. Nice hat! (to all while eating yogurt) What’s upAudio Track 2-5-20One day, Tara found that someone had eaten Sun-hee’s yogurt withoutnotice. So, she asked everyone to help her solve this “crime.” She thought that it was very likely that one of her friends stole Sun-hee’s yogurt because they all had a key to the apartment. While Sun-hee the owner was quite calm and generous about the missing yogurt, Tara got serious about the matter. She warned everyone that a misdemeanor might gradually become a real crime if it were not checked at the start. She seemed to be determined to solve the crime, though in a humorous way. She accused Takeshi first, but he denied it. While Tara was showing everyone the “weapon” — a clean, dry spoon — Roberto said that he had an alibi and hadn’t done it. Tara said she knew he hadn’t done it and that Claudia had done it! Just as Claudia was protesting that it wasn’t true, Mike suddenly walked in. He calmly went to the refrigerator, took out some yogurt, and ate it! Finally everyone came to know who the “thief” really was.。
柳木川电子有限公司EJA系列电子压力传感器用户手册说明书
Y okogawa Electric Corporation IM 01C22A00-12E 2nd EditionIM 01C22A00-12E1.INTRODUCTIONThank you for purchasing the DPharp electronic pressure transmitter.This manual contains important note and handling cautions for the DPharp EJA Series DifferentialPressure/Pressure Transmitters with NEPSI certifica-tion, option code /NS2 and /NF2.Refer to each of the following user’s manuals for standard specifications, functions, handling cautions,and operations, etc.Table 1 List of Individual User’s ManualsEJA110A, EJA120A, and EJA130A IM 01C21B01-01E EJA210A and EJA220A IM 01C21C01-01E EJA310A, EJA430A, and EJA440A IM 01C21D01-01E EJA510A and EJA530A IM 01C21F01-01E EJA110 and EJA120 IM 01C22B01-01E EJA210 and EJA220 IM 01C22C01-01E EJA310 and EJA430 IM 01C22D01-01E EJA118W, EJA118N, and EJA118Y IM 01C22H01-01E EJA438W and EJA438N IM 01C22J01-01E EJA115 IM 01C22K01-01ET01.EPSDocument No.Model2. NEPSI Certificationa.NEPSI Intrinsically Safe TypeCaution for NEPSI Intrinsically safe type.Note 1.Model EJA Series differential, gauge, andabsolute pressure transmitters withoptional code /NS2 are applicable for use in hazardous locations• Applicable Standard: GB3836.1:2000,GB3836.4:2000• Type of Protection and Marking Code: Ex ia IIC T4• Ambient Temperature :–40 to 60°C • Max. Process Temp.: 120°C • Enclosure: IP67Note 2.Entity Parameters• Intrinsically safe ratings are as follows:Maximum Input Voltage (Ui) = 30 V Maximum Input Current (Ii) = 165 mA Maximum Input Power (Pi) = 0.9 WMaximum Internal Capacitance (Ci) = 22.5 nF Maximum Internal Inductance (Li) = 730 µH Maximum Internal Inductance (Li) = 730 µH • Installation RequirementsUo ≤ Ui, Io ≤ Ii, Po ≤ Pi,Co ≥ Ci + Ccable, Lo ≥ Li + Lcable Uo, Io, Po, Co, and Lo are parameters of barrier.Note 3.Installation• In any safety barreir used output current must be limited by a resistor 'R' such that Io=Uo/R.• The safety barrier must be NEPSI certified.• Input voltage of the safety barrier must be less than 250 Vrms/Vdc.• The instrument modification or parts replacement by other than authorized representative of Yokogawa Electric Corporation and will void NEPSI Intrinsically safe certification.• The cable entry devices and blanking elements for type n shall be of a certified type providing a level of ingress protection of at least IP54, suitable for the conditions of use and correctly installed.• Electrical Connection:The type of electrical connection is stamped near the electrical connection port according to the following marking.Note 4. Operation • WARNING:WHEN AMBIENT TEMPERATURE ≥ 55°C,USE THE HEAT-RESISTING CABLES ≥ 90°C.Note 5. Special Conditions for Safe Use • WARNING:IN THE CASE WHERE THE ENCLOSURE OF THE PRESSURE TRANSMITTER IS MADE OF ALUMINUM, IF IT IS MOUNTED IN AN AREA WHERE THE USE OF ZONE 0 IS REQUIRED,IT MUST BE INSTALLED SUCH, THAT, EVEN IN THE EVENT OF RARE INCIDENTS, IGNI-TION SOURCES DUE TO IMPACT AND FRICTION SPARKS ARE EXCLUDED.[Intrinsically Safe]FD No. IM 01C22A00-12E 2nd Edition: June 2011(YK)All Rights Reserved, Copyright © 2007, Yokogawa Electric Corporationb.NEPSI Flameproof TypeCaution for NEPSI flameproof type.Note 1.Model EJA Series differential, gauge, andabsolute pressure transmitters withoptional code /NF2 are applicable for usein hazardous locations:• Applicable Standard: GB3836.1:2000,GB3836.2:2000• Type of Protection and Marking Code:Ex d IIC T6...T4• Enclosure: IP67• Maximum Process Temperature: 120°C (T4),100°C (T5), 85°C (T6)• Ambient Temperature: –40 to 75°C (T4), –40 to80°C (T5), –40 to 75°C (T6)• Supply Voltage: 42 V dc max.• Output Signal: 4 to 20 mA dcNote 2.Wiring• In hazardous locations, the cable entry devices shallbe of a certified flameproof type, suitable for theconditions of use and correctly installed.• Unused apertures shall be closed with suitableflameproof certified blanking elements. (The plugattached is certificated as the flame proof IP67 as apart of this apparatus.)• In case of ANSI 1/2 NPT plug, ANSI hexagonalwrench should be applied to screw in.Note 3. Operation• WARNING:AFTER DE-ENERGIZING, DELAY 10 MINUTESBEFORE OPENING.• WARNING:WHEN AMBIENT TEMPERATURE ≥ 70°C,USE THE HEAT-RESISTING CABLES ≥ 90°C.• Take care not to generate mechanical sparkingwhen accessing to the instrument and peripheraldevices in a hazardous location.Note 4. Maintenance and Repair• The instrument modification or parts replacementby other than authorized representative ofYokogawa Electric Corporation is prohibited andwill void NEPSI Certification.Revision RecordJanuary 20071st edition New PublicationJune 20112nd edition Delete certificaion No.IM 01C22A00-12E。
新视野大学英语读写教程(第二版)第二册课文及翻译 2解析
1 Unit 1Time-Conscious AmericansAmericans believe no one stands still. If you are not moving ahead, you are falling behind. This attitude results in a nation of people committed to researching, experimenting and exploring. Time is one of the two elements that Americans save carefully, the other being labor."We are slaves to nothing but the clock," it has been said. Time is treated as if it were something almost real. We budget it, save it, waste it, steal it, kill it, cut it, account for it; we also charge for it. It is a precious resource. Many people have a rather acute sense of the shortness of each lifetime. Once the sands have run out of a person's hourglass, they cannot be replaced. We want every minute to count.A foreigner's first impression of the US is likely to be that everyone is in a rush—often under pressure. City people always appear to be hurrying to get where they are going, restlessly seeking attention in a store, or elbowing others as they try to complete their shopping. Racing through daytime meals is part of the pace of life in this country. Working time is considered precious. Others in public eating-places are waiting for you to finish so they, too, can be served and get back to work within the time allowed. You also find drivers will be abrupt and people will push past you. You will miss smiles, brief conversations, and small exchanges with strangers. Don't take it personally. This is because people value time highly, and they resent someone else "wasting" it beyond a certain appropriate point.Many new arrivals in the States will miss the opening exchanges of a business call, for example. They will miss the ritual interaction that goes with a welcoming cup of tea or coffee that may be a convention in their own country. They may miss leisurely business chats in a restaurant or coffee house. Normally, Americans do not assess their visitors in such relaxed surroundings over extended small talk; much less do they take them out for dinner, or around on the golf course while they develop a sense of trust. Since we generally assess and probe professionally rather than socially, we start talking business very quickly. Time is, therefore, always ticking in our inner ear.Consequently, we work hard at the task of saving time. We produce a steady flow of labor-saving devices; we communicate rapidly through faxes, phone calls or emails rather than through personal contacts, which though pleasant, take longer—especially given our traffic-filled streets. We, therefore, save most personal visiting for after-work hours or for social weekend gatherings.To us the impersonality of electronic communication has little or no relation to the significance of the matter at hand. In some countries no major business is conducted without eye contact, requiring face-to-face conversation. In America, too, a final agreement will normally be signed in person. However, people are meeting increasingly on television screens, conducting "teleconferences" to settle problems not only in this country but also—by satellite—internationally.The US is definitely a telephone country. Almost everyone uses the telephone to conduct business, to chat with friends, to make or break social appointments, to say "Thank you", to shop and to obtain all kinds of information. Telephones save the feet and endless amounts of time. This is due partly to the fact that the telephone service is superb here, whereas the postal service is less efficient.Some new arrivals will come from cultures where it is considered impolite to work too quickly. Unless a certain amount of time is allowed to elapse, it seems in their eyes as if the task being considered were insignificant, not worthy of proper respect. Assignments are, consequently, given added weight by the passage of time. In the US, however, it is taken as a sign of skillfulness or being competent to solve a problem, or fulfill a job successfully, with speed. Usually, the more important a task is, the more capital, energy, and attention will be poured into it in order to "get it moving".美国人认为没有人能停止不前。
第二十章 过渡元素
f区元素
d 区元素显示出许多区别于主族元素的性质：
● 熔、沸点高，硬度、密度大的金属大都集中在这一区 ● 不少元素形成有颜色的化合物 ● 许多元素形成多种氧化态从而导致丰富的氧化还原行为 ● 形成配合物的能力比较强，包括形成经典的维尔纳配合物
和金属有机配合物 ● 参与工业催化过程和酶催化过程的能力强
20.2.2 氧化态
同周期元素族氧化态稳定性变化趋势
● 红色为常见的氧化 态
● 同同期自左至右形成族 氧化态的能力下降
● 由图清楚说明了由 Sc 至 Cu 族氧化态的热力 学稳定性趋势
● 有人声称已制备出FeO4
同周期元素低氧化态稳定性变化趋势
d 区金属自左至右族氧化态稳定性下降和低氧化态稳定上升的趋
第二十章 过渡元素(Ⅰ)
本章内容：
20.1 引言 20.2 第一过渡系元素的基本性质 20.3 钪 20.4 钛 20.5 钒 20.6 铬 20.7 锰
本章重点: 钛、钒、铬的重要化合物的主要性质
d 区元素的电子分别填充在 3d 亚层、4d 亚层和 5d 亚层上 .
1996年2月德国科学家宣布发现112号元素， 使第四过渡系的空格 终于被填满.
420 593 752 659 661 650 558 373 285 112
431 789 782 851 778 790 669 565 368 61
金属元素的原子化焓是金属内部原子结合力强弱的一种标志，较高的 原子化焓可能是由于较多的价电子（特别是较多的未成对电子）参与形成
金属键.这种结合力似乎也应该反映在过渡元素的上述物理性质上。
Question 3 随周期性的增加，为什么主族元素低氧化
态趋于稳定，而过渡元素高● 过渡元素因 “惰性电子对效应” ● 过渡元素是 I1 和 I2 往往是第 二、三 过渡系列比第 一 过渡系大
教材知识解读 选择性必修第二册 Unit 1 Science and Scientists
Ⅰ.认阅读单词1．cholera n．霍乱2．diarrhoea n．腹泻3．dehydration n．脱水4．contradictory adj.相互冲突的；对立的；不全都的5．germ n．微生物；细菌；病菌6．pump n．泵；抽水机；打气筒7．water pump水泵8．household n．一家人；家庭；同住一所(套)房子的人9．raw adj.未煮的；生的；未经处理的；原始的10．statistic n．[pl.]统计数字；统计资料；统计学11．epidemiology n．流行病学12．microscope n．显微镜13．protein n．蛋白质14．cell n．细胞；小房间；单间牢房15．virus n．病毒16．vaccine n．疫苗17．framework n．框架；结构18．theoretical framework理论框架19．rainbow n．彩虹20．concrete n．混凝土adj.混凝土制的；的确的；具体的21．plasma n．血浆22．aerospace n．航空航天工业23．patriotic adj.爱国的24．mechanical adj.机械的；发动机的；机器的25．mechanic n．机械师；机械修理工26．aviation n．航空制造业；航空；飞行27．jet n．喷气式飞机28．missile n．导弹29．astronomer n．天文学家30．astronomy n．天文学31．telescope n．望远镜Ⅱ.记重点单词1．severe adj.极为恶劣的；格外严峻的；严峻的2．subscribe v i.认购(股份)；定期订购；定期交纳(会费)3．suspect v t.& v i.怀疑；疑有；不信任n．犯罪嫌疑人；可疑对象4．blame v t.把……归咎于；责怪；指责n．责怪；指责5．handle n．把手；拉手；柄v t.处理；搬动；操纵(车辆、动物、工具等)；(用手)触碰6．link n．联系；纽带v t.把……连接起来；相关联7．substantial adj.大量的；价值巨大的；重大的8．decrease n．削减；降低；削减量v t.& v i.(使大小、数量等)削减；减小；降低9．transform v t.使改观；使转变形态v i.转变；转变10．thinking n．思想；思维；见解11．finding n．发觉；调查结果；(法律)判决12．initial adj.最初的；开头的；第一的13．solid adj.牢靠的；固体的；坚实的n．固体14．cast v t.(cast，cast)投射；向……投以(视线、笑容等)；投掷15．shadow n．阴影；影子；背光处16．pour v t.倒出；倾泻；斟(饮料)17．leadership n．领导；领导地位；领导才能18．trace v t.追溯；追踪；查出n．痕迹；遗迹；踪迹19．outstanding adj.优秀的；杰出的；明显的20．abstract adj.抽象的；理论上的n．(文献等的)摘要21．concept n．概念；观念22．besides prep.除……之外(还) ad v.而且；此外23．brilliant adj.聪颖的；绝妙的；光明的24．furthermore ad v.此外；再者25．fault n．弱点；过错26．shift n．转变；转换；轮班v i.& v t.转移；挪动；转向Ⅲ.知拓展单词1．frustrated adj.懊恼的；懊丧的；失意的→frustrate v t.使懊恼；使懊丧→frustration n．懊丧；懊恼；挫败2．infection n．感染；传染→infect v t.使感染；传染→infectious adj.感染的；传染的3．proof n．证据；证明；检验→prove v t.证明link v．证明是4．multiple adj.数量多的；多种多样的→multiply v i.& v t.乘；繁殖5．intervention n．介入；出面；干涉→intervene v i.干扰；介入6．pure adj.洁净的；纯的；纯粹的→purely ad v.完全地；纯粹地→purify v t.净化；使……洁净7．defend v t.保卫；防守；辩解→defense/defence n．防备；保卫；爱护8．assistant n．助理；助手→assist v t.& v i.挂念；帮忙→assistance n．挂念；帮忙；救济9．gifted adj.有天赋的；有天才的；天资聪慧的→gift n．礼物；天赋10．steady adj.稳定的；平稳的；稳步的→steadily ad v.稳定地；持续地11．vivid adj.生动的；鲜亮的；丰富的→vividly ad v.生动地；逼真地；鲜亮地1．idiom n．习语；成语2．ignore v t.忽视3．illegal adj.非法的；不合法的4．immediately ad v.马上5．immigration n．移民6．import v t.& n．进口；输入7．impression n．印象；感觉8．incorrect adj.不正确的；错误的Ⅳ.背核心短语1．once and for all最终地；彻底地2．subscribe to同意；赞同3．thanks to幸亏；由于4．break out(战斗、打斗等不开心的事情)突然开头；爆发5．in charge of主管；掌管6．come down患(病)；染上(小病)7．above all最重要的是；尤其是8．die from/of死于9．in time准时；迟早10．be likely to do sth 很可能做某事Ⅴ.悟经典句式1．Cholera used to be one of the most feared diseases in the world，until a British doctor，John Snow，showed how it could be overcome.(until引导的时间状语从句)在英国医生约翰·斯诺向人们呈现如何战胜霍乱之前，霍乱曾是世界上最令人恐惊的疾病之一。
基于Ka波段信道编码的建模与仿真
基于Ｋａ波段信道编码的建模与仿真作者：顾海龙陈树新王兴亮来源：《现代电子技术》2008年第17期摘要：阐述了仿真技术的内涵，介绍了通信仿真的一般步骤。
结合Ka波段信道编码的建模与仿真实例，基于蒙特卡洛仿真技术，使用Simulink搭建其仿真模型并进行仿真，在此基础上给出一个完整的通信系统的仿真模型，通过系统的仿真与分析可以看出Simulink在系统建模和仿真中的巨大优势。
最后根据仿真结果分析系统性能，验证了模型的正确性。
关键词：系统仿真；通信仿真；蒙特卡洛仿真；Simulink中图分类号：TN911.22 文献标识码：B 文章编号：1004373X(2008)1705104Modeling and Simulation of Channel Coding Based on Ka-BandGU Hailong，CHEN Shuxin，WANG Xingliang(Telecommunication Engineering Institute,Air Force Engineering University,Xi′an,710077,China)Abstract：This paper expatiates the connotation of simulation technique and gives an introduction to the ecumenical steps of communication simulation.The example of modeling and simulation of channel coding based on Ka-band in Simulink is given,which utilizes the Monte Carlo simulation technique.Through that,an integrated simulation model of communication system is given and the large advantage of Simulink in system modeling and simulation has been brought forth.In the final of the paper,the correctness of the model is validated by analyzing the simulation results.Keywords：system simulation；communication simulation；Monte Carlo simulation；Simulink1 引言近年来，在系统科学、控制理论、信息处理技术以及计算机技术的发展推动下，仿真科学在理论研究、工程应用、仿真工程和工具开发环境等许多方面取得了令人瞩目的成就，并已经逐渐发展为一门综合性学科。
ns2原理
Basics of a discrete event simulator on networking<illidan.modeler@>Northern Capital, Republic of PandariaThis is an introductory survey on network simulators, intended for people who're going to take a network simulator for their thesis or work.1. Discrete Event Simulation at a glanceDiscrete event simulation(DES) is a way to model and simulate a real-life system. Widely used instances of packet-level discrete event simulator on networking include:OPNET Modeler,Qualnet,ns2,OMNeT++,etc.Below I will talk about DES in a few sentences by a TCP connection example in which a client tries to set up a TCP connection to a server on the same Ethernet LAN. A possible DES implementation for this system may be (EV is "event"):EV1: client: TCP sends out a SYN packet, sets a timerEV2: client: the packet arrives at the IP module, IP module encapsulates it and passes it down to Ethernet MAC layerEV3: client: Ethernet MAC encapsulates the IP packet and passes it down to a link, timer Trans_Delay is set to model transmission delayEV4: client: Timer Trans_Delay expires and the Ethernet packet arrives at the server's Ethernet MAC moduleEV5: server: the MAC decapsulates it and delivers it up to IP moduleEV6: server: the IP module decapsulates the packet, delivers it up to TCP moduleEV7: server: TCP module generates a SYN/ACK packet accordingly and passes it down to its IP module...EVn1: client: TCP receives the SYN/ACK, replies with an ACK...EVn2: server: TCP receives the ACK, the connection is establishedThe process of TCP connection setup is modeled as this sequence of events.When we discuss performance of a networking system, we use terms like "bit rate", "delay", "jitter", "throughput", many of which are related to time. So we cannot ignore "time" in simulating a networking system.In DES, time is an attribute of an event, eg. EV1 has time value of t1(EV1 occurs at t1), EV2 has t2. Events happen at discrete time spots(hence the "D" in DES). Events may happen at the same time spot, but are still executed sequentially.In the example, EV1, 2, 3 have the same time value(t1=t2=t3) but will be executed in the order shown above.Time in the DES world is logical time. It doesn't have direct relation to wall-clock time. To understand it easier,you may just take it as an attribute for the sequential events. The time value of the current event is called current "simulation time".In the example, the only places that the simulation time advances are events like EV4, atwhich point the timer expires. We already know T1=T2=T3, so the simulation time is the same in the first 3 events. Usually, for the simulation time to advance, we use a timer. In the example, when it goes to EV4, the expired timer pushes the simulation time ahead.After a simulation run with this event list, we get the TCP setup delay:T(delay) = Tn2-T1. Other results, like traffic throughput(bits/sec),can be calculated via the time values.2. ComponentsA packet-level discrete event simulator can be divided into three main components:core platformprotocol librarydocumentation.The main platform include several functionalities:User Interface (UI)Simulation EngineRandom Number Generator (RNG)Result Analysis ToolBefore we continue, let's recall the way we do a network simulation:1. Set up topology2. Configure protocol parameters (WLAN ESSID, IP address, TCP window, Routing protocol timers, etc)3. Set traffic pattern (size of packet, inter arrival time of packets, source and destination)4. Run simulation5. Analyze the resultsIn this process, we make use of the core platform's functionalities.2.1 User InterfaceThe user interface may be graphical user interface (GUI), textual and command line, or hybrid.In case of GUI, we drag the models from a pallet e, dropping them on the working place, connecting them to each other. By now we're finished with Step 1 and 2. Then we configure traffic or application pattern right on the model icons in the working place. After that we run simulation and analyze the results in the GUI. Working with GUI is friendly and efficient. But GUI has its own shortcoming. It might be more difficult to do various form of batch operation (eg. changing the WLAN CTS/RTS threshold with different values on tens of nodes) in GUI than in textual UI. Examples of GUI simulators are OPNET Modeler and Qualnet (they're commercial and proprietary software).In a textual UI, we compose formatted texts or scripts for Step 1, 2 and 3. After that we issue a command in the OS's shell to run simulation. Finally we run some utility to analyze the results. An example of this is GloMoSim, a dead academic project. The topology and protocol parameters are defined in formatted plain text (somewhat like a configuration file for a ftp server). Then we run the simulation from shell, after which we have to analyze the results, also a formatted plain text, by tools like gawk.With a hybrid UI, we do some tasks by GUI while others in textual and command line. Take OMNet++ for example. The topology is defined by a formatted text in NEtwork Description (NED) language (developed by the same project) while the protocol parameters given in .inifiles. We execute the simulation (a simulation is a separate executable) in the shell and run it by a prompted TKEnv GUI.2.2 Simulation EngineSimulation engine is the unit that executes the discrete event simulation. It stores the event list, like the one given at the beginning of this document, in a data structure (usually an improved list) and manipulates it. When an event occurs, it runs related protocol or algorithm code. When the event's code ends, it deletes the event from the event list and moves on to the next one, and so forth.Speed of simulators is not easy to compare, since they use their own network protocol implementation which might be quite different from others in terms of features and fidelity. But speed of simulation engine might be compared. Let the engine run simulation of very simple events. The one with higher events/sec is the faster one.Note that parallel engine may be faster generally, but simulation in parallel engine may not be as fast as one in a sequential engine. If the protocol implementation doesn't make good use of the engine, the multi-thread overhead will overpass the parallel benefits.2.3 Result Analysis ToolSimulator with GUI usually have a graphical result analysis tool integrated. We can get curves and histogram in a panel by a few clicks.But with the textual ones, the best and possible way is to write gawk script by ours els, to analyze the result.2.4 Random Number GeneratorTo simulate the stochastic behavior of our live world, we need the RNG to generate random numbers. The generated sequence of numbers is, however, deterministic. You run the same simulation multiple times, the RNG just produces the same number sequence. So the dynamic behavior and result of a simulation is repeatable, making it possible to debug a simulation. You may change value of "seed", an attribute of the RNG, to yield a different number sequence. A simulator may implement its own RNG or use an exiting open-source RNG.2.5 External InterfaceSome simulators have external interfaces like HLA, Hardware-in-the-Loop, 3D Visualizer. With these extensions a simulator may join a HLA federation or visualize its simulation scenarios in 3D.3. Protocol LibraryFSF (guys that develop GNU) always say "a kernel is far from an OS". True. The core platform is far from a simulator. You need a somewhat sophisticated model library. Usually a protocol library consists of wide used protocols and a few cutting-edge protocols, for each layer in the TCP/IP-like protocol stack. Examples of mature protocols include HTTP, TCP, IP, Ethernet. Examples of new protocols are 802.16, LTE, etc.For commercial simulators, you will usually get a suite of mature (or you might say "old") protocols in a default software package. New or special protocol(MPLS, etc) suites are sold separately as value-added product.For OMNeT++, strictly speaking, the name only refers to the core platform. The model libraries are developed by third parties and licensed separately, but have downloadhyper-links on OMNeT++'s website.The primary source to get protocol library is the vendor, for commercial ones, or developer's website, for open-source-like ones. But there are supplements. You can find "contributed" protocol model on the web. NIST, INRIA and some universities usually put their models on line for sharing.Mobility support is a big concern for a protocol library.It isn't difficult to support physically moving nodes. But it costs considerable effort to implement mobility-enabled protocols, such as Mobile IP, UMTS. So when you're choosing a simulator, spend a bit time reading its documents about mobility support.The biggest headache with the protocol library is compatibility among release versions.For example, you developed a model suite, based on the simulator's current protocol library, referencing its data structures and functions. However, in the next release, the data structures and functions are changed, for some reasons. You'll have to spend time modifying the source code of your own models, otherwise it might not work.It might happen that you download from a academic website a protocol suite that you've been searching for for quite a while, but it doesn't work with your version of simulator, complaining with compilation errors or invalid memory access. But it costs quite a while to modify the model code to comply with new model library. This happens, since using distributed protocols is a "Renpin(RP)" practice. Get prepared for the worst.4. Pros and Cons of Simulator InstancesIn this section we discuss about the pros and cons of simulators.4.1 OPNET ModelerPros:Friendly and efficient GUI;Rich model library covering many networking fields;Friendly and sophisticated debugging support (even with GUI debugger in late releases); Visual finite state machine;Many existing (US and Chinese) papers based on this simulatorCons:Model files encrypted, difficult to share;Encrypted model files best to be edited via built-in text editor, which is too simple and inconvenientDepending too much on GUI, sometimes inconvenient for batch operation;GUI developed with legacy graphic library for win32, seemingly difficult to make further GUI improvement (I think its Linux version doesn't have this problem);High license fee4.2 QualnetPros:Rich model library covering many networking fields;Rich wireless mesh protocols;Cons:Model files encrypted, difficult to share;High license fee4.3 ns2Pros:GPL licensedMany participants worldwideCons:Otcl for ns2 not descriptiveNo good debug supportNo automatic result analysis toolConsistency among version (like trace format, etc)Documentation not well organized and not synchronized with model library4.4 OMNet++Pros:Intuitive work flowDescriptive topology setup and parameter assignment (NED and ini)Cons:Limited model library5. Miscellaneous5.1 Source availableI read vague description that "OPNET Modeler is closed source while ns2 is open-source" on several sites on the web.Well, right here I'd like to restrict the term "open-source" to the definition given by Open Source Initiative (). For non-open-source software, I use "source available" to mean the user being able to read and modify the source code.For commercial simulators(OPNET Modeler, Qualnet, etc), the core platform isclosed-source. But the model library is source-available to the user. You may modify it to meet your need or take it as a basis for your new protocol models.For true open-source software, like ns2, licensed under GPL, source code of core platform and model library is all available to the user.For OMNeT++, though it isn't licensed under an open-source license, its license is quite similar to BSD license. So, it might be acceptable to call it "open source software".5.2 Layering flexibilityOPNET Modeler and OMNeT++ don't have restriction on layering. Those there are existing nodes with a certain protocol stack, you can build your protocol stacks with built-in or your own protocol modules. So a node might not have a host-to-host layer (TCP etc) and its application layer directly works upon a internetwork layer (IP etc).But ns2 and Qualnet are TCP/IP-binding. A node has all the layers of a TCP/IP-like stack. You cannot add one more or delete one.5.3 Personal OpinionI like ns2's being open-source licensed and being under active development, but itspoor-managed documentation is a headache. OMNeT++ is cool. And I appreciate its business model, compared with the legacy one of OPNET and Qualnet. OMNeT++ has acommercial variant called OMNEST. The two are developed in synchronization, just like RHELvs. Fedora, SuSE Enterprise vs. OpenSuSE.If there's a network simulator as powerful and friendly as Ubuntu Linux for an OS, it'll be much happier doing simulation based network research. Will it be the underway ns-3?~~That's all I have to say about that. Comments are appreciated.AppendixAcronymsDES = Discrete Event SimulationGUI = Graphical User InterfaceHLA = High Level ArchitectureIP = Internet ProtocolMPLS = Multi Protocol Label SwitchingOS = Operating SystemRHEL = Red Hat Enterprise LinuxTCP = Transmission Control Protocol。
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ReviewClay in cement-based materials:Critical overview ofstate-of-the-artM.L.Nehdi ⇑Department of Civil and Environmental Engineering,University of Western Ontario,London,Ontario,Canadah i g h l i g h t sCritical overview of effects of clay in cement-based materials is provided. Dimensional stability of aggregates bearing clay minerals is examined. Treatment of clays to mitigate their detrimental effects in concrete is outlined. Research on nano-clays in cement-based materials is highlighted.How to resolve ambiguity related to clays in cement-based materials is discussed.a r t i c l e i n f o Article history:Received 23May 2013Received in revised form 10October 2013Accepted 31October 2013Available online 28November 2013Keywords:Clay SandAggregate Concrete Workability Admixture Swelling Durability Nanoa b s t r a c tLimitations in guidelines and standards on the amount of clay in sand and coarse aggregate micro-fines and the influence of such micro-fines on fresh and hardened concrete properties is often ambiguous for practitioners and quality control professionals.This is compounded by conflicting related data in the open literature and the inadequacy of some standard test procedures for capturing the real problems associated with the presence of clays in cement-based materials.This paper examines the various types of clay,limitations on clays in aggregates in various standards,and the test methods used to assess the presence of clays in aggregates.A critical overview of literature on the possible effects of clay in cement-based materials is provided,including effects on water demand,workability,mechanical strength,dimensional stability and chemical admixtures dosage.The problem of dimensional stability of aggre-gates bearing clay minerals is examined.Possible chemical treatment of clays to mitigate their detrimen-tal effects in concrete is also outlined.Finally,emerging research on using nano-clays in cement-based materials is highlighted and recommendations to resolve ambiguity related to the presence of clays in cement-based materials are proposed.Ó2013Elsevier Ltd.All rights reserved.Contents 1.Introduction (373)2.Different clay minerals and their behaviour................................................................................3733.Mechanisms of clay swelling............................................................................................3744.Effects of clay on properties of concrete...................................................................................3745.Effects of clay on chemical admixtures....................................................................................3766.Expansion of aggregates with clay bearing minerals.........................................................................3767.Test methods for clay in cement-based materials ...........................................................................3767.1.Aggregate durability index ........................................................................................3777.2.Sand equivalent test .............................................................................................3777.3.Methylene blue test .............................................................................................3777.4.Grace colorimetric modified methylene blue method ..................................................................3788.Standard limitations on clay content in aggregates..........................................................................3789.Chemical treatment of aggregates to mitigate effects of clay ..................................................................37810.Nano-clay in cement-based materials....................................................................................3790950-0618/$-see front matter Ó2013Elsevier Ltd.All rights reserved./10.1016/j.conbuildmat.2013.10.059⇑Tel.:+1(519)6612111x88308.E-mail address:mnehdi@uwo.ca11.Concluding remarks (381)References (381)1.IntroductionThe Spanish proverb puts it best:‘‘clay and lime conceal much evil’’.This author sensed such perception of clay through personal involvement in high-profile international projects(e.g.two of the tallest buildings in the world,world’s deepest and second largest water pumping and treatment plant,one of the world’s largest air-ports,a world landmark bridge,etc.).Ambiguity arises when stan-dards,technical provisions and subsequently project specifications may be unnecessarily restrictive on the amount of micro-fines al-lowed in aggregates used in concrete,while locally available sands and/or coarse aggregates cannot meet such limitations at compet-itive cost.Often futile debate emerges on what exactly is the nat-ure of aggregate micro-fines at hand,is it responsible for any performance issues of the concrete produced,how such an influ-ence can be accurately quantified for various microfine contents, and can the limits on micro-fines be relaxed without short-or long-term performance problems of the concrete.The discussion can be fuelled with conflicting pieces of information sourced from the open literature or through personal communications.Therefore,this article is an attempt to demystify clay in con-crete,critically overview the state-of-the-art on this issue,and pro-vide a self-contained document that can scrutinise existing related data and the various pieces of evidence,examine the available test methods for evaluating the existence and effects of clays in ce-ment-based materials,and essentially savefort of navigating through this often2.Different clay minerals and theirDetailed information on clay mineralsin Fowden et al.[24].Clay minerals areand layered crystalline substances thatweathering of certain rock formingicates of aluminium and other metallictially two fundamental crystal layers,alumina(octahedral).It is basically theare stacked together with differentthe crystal lattice that differentiates clayite,illite and montmorillonite from onegeological conditions and prevailingmine which type of clay is formed.Clay minerals are commonly found in75l m material)of natural aggregates.ically less than2l m in size,but can be10sized clay materials and their unit cellsative charges on their surfaces.Whenbetween clay particles gets occupied byThe simultaneous presence of negativelyand the dipoles of water create electro-tract and hold the dipoles of water.Claymulti-layer formations.The chargedcharge around the particles are togetherlayer[39].The space between layers and the freeinterlayer space are the chief reasons formineral has a swelling behaviour.Theabsorption of water dipoles to theto be achieved.With decreased interlayeramong the layers become powerful and of water,so swelling does not occur.Conversely,as the interlayer space becomes more significant,interlayer forces are so that water absorption in the interlayer space can progress until interlayer bonds fail.Hence,the clay particles get separated and rearranged and swelling occurs.The extent and kinetics of the mechanisms de-scribed above depend on several other parameters acting individ-ually or in combination.These include the density of the surface charge,the type and valence of the cations,the concentration of the electrolytes and the dielectric constant.Therefore,swelling depends on the type of clay mineral.Gener-ally,smectite minerals,with montmorillonite being a chief repre-sentative of this group,are considered swelling.Such smectites encompass repeat units of silica,gibbsite(aluminium hydroxyl groups)and adjacent silica layers joined by Van der Waals bonds (Fig.1).The substitution of aluminium for magnesium in the gibb-site layer and for silicon in the silica layer results in a net negative charge in smectites,thus imparting a high cation exchange capac-ity.In addition to their high cation exchange capacity,the inter-layer spacing between silica layers can increase in smectites through water absorption,causing substantial swelling.Con-versely,clay minerals such as pyrophyllite,margarite and illite are considered non-swelling.For instance,kaolinites comprise re-peat units of silica and gibbsite and lack the inter-layer spacing found between adjacent silica layers in smectites.Hence,their cat-ion exchange capacity is less than that of smectites and is predom-1.Schematic illustration of the layered structure present in montmorillonite (courtesy of J.Plank,2013).M.L.Nehdi/Construction and Building Materials51(2014)372–382373d-spacing when exchangeable cations are hydrated by an aqueous solution[7].The presence of clay minerals in coarse andfine aggregates can have remarkable effects on the workability of fresh concrete,effec-tiveness of chemical admixtures,and on the mechanical strength, dimensional stability and durability of hardened concrete.There-fore,it is paramount to determine the type and content of clay minerals in aggregates,develop rapid and reliablefield test meth-ods to quantify deleterious clay minerals in aggregate stockpiles and recommend remedial techniques,if any,to make the clay-con-taminated aggregates adequate for use in concrete.In this article,a critical overview of the effects of clay minerals in cement-based materials is provided.The test methods used to assess the presence of clay in aggregates are examined,and inter-national standards on clay minerals in concrete are highlighted. The problem of dimensional stability of aggregates bearing clay minerals is discussed.Possible chemical treatment of clays to mit-igate their detrimental effects in concrete is also outlined.Finally, emerging research on using nano-clays in cement-based materials is highlighted.It is hoped that this critical analysis of international literature could mitigate existing ambiguity on the topic of clay in concrete among engineers and practitioners.3.Mechanisms of clay swellingThe mechanisms of clay swelling have been extensively dis-cussed in the literature.Only aspects relevant to clays in cement-based materials are considered herein.Much of this discussion is based on a review by Anderson et al.[8].In contact with water, exchangeable cations in the clay interlayer space tend to hydrate, forcing clay layers apart.Swelling can occur via two different re-gimes;crystalline and osmotic swelling.Crystalline swelling can occur in all types of clay minerals.This was shown to be a short-range swelling occurring in a discrete fashion,through the stepwise formation of mixtures of interlayer hydrates.Several layers of water molecules line up to form a qua-si-crystalline structure between unit layers resulting in an in-creased interlayer spacing.For instance,smectite clays absorb water and form one-,two-,three-and four-layer hydrates.The equilibrium layer spacing for a certain clay mineral is the state whereby the thermodynamic potential(free energy)is a global minimum given thermodynamic constraints of temperature,pres-sure,and water chemical potential(Anderson et al.[8]).Typical interlayer spacing recorded in the crystalline swelling regime ranges from9to20Å.Osmotic swelling occurs in particular clay minerals known to contain exchangeable cations in the interlayer region.When the concentration of cations in the interlayer space is higher than that in the surrounding solution,water molecules migrate into the interlayer space to restore cation equilibrium.This type of swelling can cause appreciably larger volume increases(interlayer spacing of20–130Å)than that resulting from crystalline swelling.For in-stance,smectites can swell in this osmotic fashion.Conversely, K+saturated smectite clay do not swell in this manner and form crystalline hydrates even in aqueous suspension[52].Thus,the K+ion can be used to prevent the swelling of sodium saturated clay minerals(Anderson,2010).The type,size and charge of exchangeable cations present in the clay interlayer space have a predominant effect on the magnitude of clay swelling.Water desorption isotherm measurements of montmorillonite intercalated with different monovalent exchange-able cations(Li+,Na+,K+,Rb+and Cs+)indicated that for larger cations,less water is adsorbed[40].Clay minerals incorporating monovalent cations having larger hydration energies tend to swell more than those containing cations with lower hydration energies.Furthermore,the type of substitutions present and layer charge of a clay mineral can significantly influence its swelling characteris-tics.This is discussed in greater detail in Anderson et al.[8].4.Effects of clay on properties of concreteThere has long been concern that clay particles may be harmful to concrete because of their ability to absorb water and swell, which increases the water demand in fresh concrete.As early as 1933,Parsons[48]studied the effects of partially substituting clay for either10%by volume of cement or7.5%by volume offine aggregate,on the compressive strength,absorption,and perme-ability of concrete.Three different clays were used:red surface clay from Occoquan,blue clay from Baltimore,Maryland and yellow clay from Alexandria,Virginia,It was believed the clays were free from organic matter as they were used in brick manufacturing.It was observed that substituting10%of clay for cement by volume caused around0–10%decrease in compressive strength at ages be-yond three months,but there was no appreciable effect on perme-ability.Also,substituting clay for7.5%offine aggregate increased compressive strength by up to37%.The effects of clay on the water absorption,permeability,and resistance to freezing and thawing cycles of concrete were not significant.In1934,Lyse[37]reported that experimental work at Lehigh University supported the claim that severe limits on the contents offines in concrete were unnec-essary and even could become illogical when chemical admixtures are permitted.More recently,Solomon and Ekolu[60]investigated the incor-poration of clay soil into concrete mixtures as a means of making low-cost,low-strength construction materials for infrastructure in developing countries.Four control concrete mixtures with 350kg/m3of cement and water-to-cementitious content(w/cc)ra-tio of0.70,0.75;and with280kg/m3cementitious content with w/ cc=0.80and0.85were tested.Further mixtures had10%,20%,30%, 40%,and60%partial substitution of cement with local raw clay.It was found that clay–cement concrete mixtures with a maximum w/cc=0.80and20–30%clay replacement for cement can be suited to fulfil the strength and workability requirements for low-cost, low-strength applications including housing,roads and dams.Olanitori[47]reported that the higher the clay and silt content in sand,the higher was the cement dosage increment needed to maintain the compressive strength of concrete beyond20MPa, which is the value generally specified at28-d in Nigeria for a mix-ture ratio1:2:4.He recommended carrying out a comparative cost analysis between the cement dosage increments used for sand with a particular clay/silt content,and washing the sand to reduce the clay/silt content,so as to determine which is more cost-effec-tive to maintain20-MPa compressive strength.Li et al.[32]studied the workability,strength and modulus of elasticity,drying shrinkage and creep,freeze–thaw resistance and chloride ion permeability of C60high-performance concrete (HPC)made with manufactured sand(MS)containing 3.5–14% crushed limestone dust,versus that made with river sand(RS)with clay amounts of3%and5%.The clay content in MS decreased work-ability,increased drying shrinkage and accelerated freeze–thaw damage of the C60-HPC,but did not affect its compressive strength and chloride ion permeability.It was concluded that C60-HPC can be made with MS with a high content of crushed limestone dust, but the amount of clay in MS should be controlled.Norvell et al.[46]explored the effects of clay minerals present in natural aggregates versus that of clay-sized particles present in manufacturedfine aggregates on concrete performance by‘‘dop-ing’’micro-fine aggregates with clay minerals and non-clay con-taining particles of similar size.Specifically,they investigated the effects on water demand,water-reducing admixture demand,374M.L.Nehdi/Construction and Building Materials51(2014)372–382compressive strength and drying shrinkage.It was concluded that clays do increase the water and superplasticizer demand in accor-dance with their interlayer absorption and cation exchange capac-ity,respectively(Table1).However,clay-sized particles(particles of similar size to clay but with different mineralogy)did not signif-icantly affect the water and superplasticizer demands at the levels studied.At constant w/c,only smectite(montmorillonite)clay was found to decrease compressive strength and to increase drying shrinkage.Li et al.[33]explored the effects of the clay content and charac-teristics,methylene blue value(MBV ranging from0.35to2.5)of manufactured sand(MS)and the limestonefines content on the performance of concrete.Results showed that with an increase in MBV,the workability,flexural strength and7-d compressive strength of the MS concrete decreased,while the28-d compressive strength was not affected.Also,increasing MBV enhanced plastic and drying shrinkage cracking of the concrete and remarkably accelerated its freeze–thaw damage and abrasion loss.It was con-tended that the critical MBV was1.4;a value below which the per-formance of MS concrete is not significantly compromised by the presence of clay.Since different specifications and code provisions define various limits for thefine impurities content of the concrete coarse aggre-gate,Seleem and El-Hefnawy[56]evaluated the effects of different levels offine impurities normally found in coarse aggregates in Egypt on the compressive strength and dimensional stability of concrete.Based on their test results,a higher limit offine impuri-ties(5%)in coarse aggregate was suggested,particularly when the increase in shrinkage is overcome using a superplasticizer and low-er water-to-cement-ratio.Chan and Wu[14]argued that research has shown silts and clays to be deleterious because in the mixing of concrete con-taining silts and clays more water is added to achieve adequate workability.They reasoned that the use of a superplasticizer at similar w/c ratio to that of a control OPC concrete not containing silts and clays may provide good quality concrete.They con-ducted trial concrete mixtures with particles less than150l m in size consisting of silts and clays obtained from crushed gran-ite stone along with a sulphonated naphthalene superplasticizer. They concluded that durable concrete could be made with25% partial replacement of cement with silt and clay using a w/c ra-tio of0.5.However,Chan and Wu[14]explored workability, strength and permeability of the silt and clay concrete,but did not assess its dimensional stability,abrasion and freeze–thaw resistance.Courard et al.[18]investigated the effects of various limestone fillers on the fresh and hardened properties of self-compacting mortars.Six different limestonefillers were used at15%,25%and 35%partial mass replacement of cement.Thefillers incorporated clays and had methylene blue absorption values between0.7and 5.0.Among the sixfillers,two contained swelling clays.It was found that the water requirement of limestonefillers was primar-ily affected by their content of swelling clay.The water require-ment had a direct correlation with the methylene blue absorption and the BET specific surface of thefillers.The consis-tency of fresh mortars decreased with increasing swelling clay con-tent of the limestonefillers.It was argued that despite the effect on fresh mortar properties,no major influence of clays on the behav-iour of hardened mortars was observed.Even the swelling clays did not hinder the porosity of limestonefiller modified mortars.It was contended that should superplasticizers be used to solve rheologi-cal problems,fillers from the aggregate industry and stone sawing could be used in concrete manufacturing.Fernandes et al.[22]carried out an experimental study on clay–cement–sand composites.They compared the effects of pure quartz sand to that of two synthesized sands made by dry mixing of this pure sand with either20%by mass of kaolin or20%by mass of montmorillonite.They made various mortars with Type I OPC and variable sand types,water/cement ratios and sand/cement ratios.The28-d compressive strength was measured and X-ray diffraction was employed to examine whether any reactions between the clay and cement had oc-curred.A linear relationship existed between the amount of clay and corresponding amount of water needed to maintain certain workability.XRD analysis did not identify any secondary prod-ucts forming in the presence of clay.Moreover,the mixtures incorporating kaolin clay followed similar strength-w/c relation-ship to that of normal concrete,with lower strengths attributed to increased water demand and/or increased compaction diffi-culty,while those including montmorillonite followed a different relationship,suggesting that this clay had other deleterious ef-fects beyond the increased water demand.It was postulated that for the typical w/c and strength values of building materials in developing countries,satisfactory mortar and blocks can be made from clay-contaminated sand.However,the effect of the type of clay is significant and structural concrete made with such materials needs proper durability and dimensional stability investigation.The effects of coarse aggregate coatings on concrete proper-ties were explored by Muñoz et al.[43].Seven concrete mixtures were made with coarse aggregates containing two types of coat-ings:naturalfield-coated aggregates,and manufactured coated samples of dust and clayfines.The effects of these coatings on concrete performance were examined by comparing the relative changes in physical and mechanical properties of the concrete versus that of a control concrete made with washed aggregates. It was concluded that microfine coatings on coarse aggregates can influence the properties of fresh and hardened concrete even when their amount in the passing No.200sieve is less than 1.5%.The extent and nature of such influence depend on the quantity and type of the microfine.Thus,ASTM C117,which only accounts for the quantity of micro-fines present in the aggre-gates,was not considered an adequate monitoring tool for this problem.It was suggested that the product of MBV(methylene blue value)and P200(maximum percentage of material passing the No.200sieve),referred to as the MMBV was the best overall predictor.Table1Water and admixture demand with clay minerals and non-clay sized minerals (modified after[46].Type of Mineral Waterdemand Superplasticizer dosage (w/c=0.42)Control:granite sand0.47 4.5Clay mineral1%Kaolinite0.50 6.04%Kaolinite0.608.01%Illite0.49 5.54%Illite0.5110.01%Montmorillonite0.6218.54%Montmorillonite0.90186.0Clay sized particles1%Fine calcium carbonate(60%<2l m)0.48–4%Fine calcium carbonate(60%<2l m)0.48 4.01%Ultrafine calcium carbonate(90%<2l m)0.49–4%Ultrafine calcium carbonate(90%<2l m)0.49 4.01%Ground silica(96%<5l m)0.47–1%Ground silica(96%<5l m)0.47 2.5M.L.Nehdi/Construction and Building Materials51(2014)372–3823755.Effects of clay on chemical admixturesIt is believed that their ability to readily exchange cations is the most deleterious feature of clays in concrete.Cations are ex-changed in order to balance inherent electrical charges on the sur-face of clay particles.Such cations can be readily exchanged with organic materials such as water-reducing admixtures and superp-lasticizers.This high affinity to organic substances competes with the adsorption and dispersing mechanisms of chemical admixtures at the surface of cement and supplementary cementitious materi-als particles.Subsequently,as clay particles consume part of the chemical admixture,a higher dosage will be required to achieve certain workability.This not only has cost implications,but the very high admixture dosage can lead to excessively long setting time,delays in strength gain and formwork removal.Table1exhib-its the substantial effect observed by Norvell et al.[46]of swelling clay on the superplasticizer demand of concrete.In particular,there has been growing evidence that polycarbox-ilate-based superplasticizers(PCEs)are more sensitive to clays than poly-condensate superplasticizers.This is primarily due to their incorporation into the layered clay structure via their side chains,which impedes their dispersing ability.It was observed by several researchers(e.g.[55,31]that different types of PCEs show pronounced sensitivity to clay and their dispersing force de-creases significantly in its presence.The predominantly used side chain in PCE superplasticizers is poly(ethylene oxide),which is known to easily intercalate within alumosilicate layers of clays (e.g.[36].Montmorillonite(MMT)was found to be particularly harmful to concretefluidity compared to other clay minerals such as kaolinites(e.g.[27].This is caused by the expanding lattices of MMT,allowing intercalation,swelling and cation exchange[38].Li et al.[34]studied the influence of clay on the disperse-ability of polycarboxylate superplasticizers.They investigated thefluidity and viscosity of cement paste and examined the influence of clayfiltrate on the molecular structure and kinetics of adsorption of PCE on the surface of clay particles in a simu-lated alkaline environment consisting of saturated calcium hydroxide solution.Theirfindings indicate that PCE has no dis-persing effect on cement paste once the clay content reached 15%.Increasing the PCE dosage mitigated this negative effect of clay.Moreover,it was found that the clayfiltrate did not change the molecular structure of PCE nor did it affect its disperse-abil-ity.The kinetics of clay adsorption in the simulated alkaline environment on PCE was rapid,with an adsorption capacity about4times that on cement,with clay reaching its equilibrium adsorption within6min.Ng and Plank[44]tested PCEs consisting of methacrylic acid/ MPEG methacrylate-ester with molar ratios of6:1and1.5:1.They found that the tested PCEs sorb chemically and physically onto clay by amounts about100times higher than that on cement.Chemi-sorption appeared to take place via intercalation of the poly(ethyl-ene oxide)side chains into the interlayer region between alumos-ilicate layers,while physic-sorption occurred on positively charged clay surfaces through uptake of Ca2+.The type of sorption was dos-age dependent,with side chain intercalation dominating at higher PCE dosage,while electrostatic attraction via the clay surfaces an-ionic backbone prevailed at lower dosage.Since PCEs possessing high grafting density were more vulnerable to clay effects,it was argued that poly-glycols can be utilised as sacrificial agents when highly grafted PCEs are employed at high dosages.Lei and Plank[31]asserted that new PCE superplasticizers pos-sessing modified chemical structure for enhanced robustness to-wards clay need to be developed.Hence,they synthetized modified PCEs from methacrylic acid and hydroxyl-alkyl methac-rylate esters and tested their dispersion performance in cement with and without montmorillonite clay.The new PCE was found to disperse cement effectively in the presence of clay and was much less affected by clay than conventional PCEs.A mechanistic study including adsorption and XRD experiments revealed that the new PCE only adsorbs on the surface of clay and does not incor-porate into its layered structure,which explains its tolerance to clay contamination.6.Expansion of aggregates with clay bearing mineralsThe dimensional stability of aggregates versus moisture changes has been discussed in detail by Shayan[59].Generally, dense and un-weathered aggregates are not affected by changes in moisture content.Their water absorption is generally less than 1%by mass of rock.Hence they usually retain their dimensions un-der wet or dry conditions.However,some vesicular rocks may ex-hibit high water absorption,yet can remain dimensionally stable provided they are free of expansive clay minerals.Once altered or weathered,rocks can exhibit expansive minerals,yielding high water absorption due to the ability of clay minerals to accommo-date water in its interlayer spaces.The formation of expansive clay minerals has been reported by several authors in basaltic rocks and in granophyre(e.g.in[59];its effects on the properties of the rock as a source of concrete aggregate have also been well documented.Water absorption by clay minerals in aggregates can cause expansion of the granular matrix,hence causing expansion of the concrete.Drying can exhibit excessive shrinkage,possibly leading to cracking,especially under repeated wetting/drying conditions (e.g.[16,54].Water vapour and nitrogen absorption studies and measurements of internal and external surface area of basalts (e.g.[16,58]revealed a direct relationship between the length change of rock prisms subjected to wetting/drying cycles and their clay content.Similar relationships have also been established for granophyre and basalt[58,67].The dimensional stability and moisture sensitivity of rocks can be experimentally measured on prism specimens subjected to re-peated wetting–drying cycles and monitoring the associated length changes using accurate length measurement comparators (e.g.[16,57].Some indirect methods including correlating drying shrinkage with moisture absorption of aggregate or with adsorp-tion of other polar molecules such as methylene blue dye,have been used to predict the drying shrinkage of aggregates[59].In particular,the MBV value had a reasonable correlation with the clay content of tested materials and was successfully used to eval-uate a source rock for drying shrinkage before the development of a quarry at the site[57].Using124test specimens,a correlation was developed by Sha-yan[57]between drying shrinkage of aggregate and its MBV value. It was shown that MBV levels beyond1.75ml/g were associated with unacceptable aggregate drying shrinkage.Table2lists typical ranges of moisture-induced length changes measured on different rock prisms from Australian aggregate source rocks and reported by[59].It can be observed that andesitic tuffs,grey basalts and sandstones undergo significant length changes upon wetting and drying,at times exceeding1000micro-strains.Except grey basalt, substantial dimensional instability in rocks has been linked to higher clay content.Likewise,when clay occurred in the form of an interconnected network in basalt(e.g.[17]or in the form of veins in granophyre(e.g.[57],the length change was much larger than when a similar amount of clay was present in isolated patches or in vesicles.7.Test methods for clay in cement-based materialsConsidering the significant influence of the type and content of clay on the water and chemical admixture demand,mechanical376M.L.Nehdi/Construction and Building Materials51(2014)372–382。
NS2 概况
apt-get install build-essentia
apt-get install tcl8.4 tcl8.4-dev tk8.4 tk8.4-dev
apt-get install libxmu-dev
NS2安装
(3).输入cd命令，转到ns-allinone-2.31文件夹 下（我的路home/natalie/ns-allinone-2.31）； 输入./install，进行安装。
NS2 概述
大纲
• • • • Ns2介绍 Ns2安装 Ns2仿真基础 实例分析
NS2介绍
• NS 是Network Simulator 的英文缩写，字面翻译即为网络模 拟器，又称网络仿真器。NS2 则是网络仿真器的第2 版， 它是一种面向对象的网络仿真器，本质上是一个以离散事 件模拟器，其本身有一个虚拟的时钟，所有的仿真都是由 离散事件驱动的。 • 目前NS2可以用于仿真各种不同的通信网络。它功能强大， 模块丰富，已经实现的一些仿真模块有：网络传输协议， 如TCP和UDP；业务源流量产生器，如FTP、Telnet、Web CBR和VBR；路由队列管理机制，如Droptai、RED和CBQ； 路由算法，如Dijkstra，以及无线网络的WLAN，Ad hoc路 由，移动IP和卫星通信网络等。NS2也为进行局域网的仿 真而实现了多播以及一些MAC子层协议。
Tcl的面向对象扩展-OTcl
C++和Otcl两种语言来实现NS
C++和Otcl两种语言来实现NS
C++和Otcl的连接-类成员变量的绑定
C++和Otcl的连接-两种对象成员函数的对应
NS仿真原理-网络组件
分类器（Classifier）
介绍北欧两项英语作文
介绍北欧两项英语作文North European two events, also known as Nordic combined, is a winter sport that combines cross-country skiing and ski jumping. It requires a high level of skill and endurance, as athletes must excel in both disciplinesto succeed.The origins of North European two events can be traced back to the 19th century in Norway, where it was first introduced as a way to test the overall proficiency of skiers. Over time, it has evolved into a highly competitive sport with athletes from countries like Norway, Finland,and Germany dominating the international scene.One of the most thrilling aspects of North European two events is the ski jumping component, where athletes launch themselves off a ramp and soar through the air before landing gracefully on the snow below. It requires precision, balance, and nerves of steel to execute a perfect jump.On the other hand, the cross-country skiing portion of North European two events is a test of endurance and strength, as athletes must navigate through challenging terrain and varying weather conditions. It is a true test of physical and mental toughness.Overall, North European two events is a captivating and demanding sport that showcases the athleticism and skill of its participants. It is a true test of versatility and determination, making it a favorite among winter sports enthusiasts around the world.。
History-based
History-based route selection for reactive ad hoc routingprotocolsSirisha Medidi and Peter CappettoSchool of Electrical Engineering and Computer ScienceWashington State University,Pullman99164-2752,USAABSTRACTAd hoc networks rely on cooperation in order to operate,but in a resource constrained environment not all nodes behave altruistically.Selfish nodes preserve their own resources and do not forward packets not in their own self interest.These nodes degrade the performance of the network,but judicious route selection can help maintain performance despite this behavior.Many route selection algorithms place importance on shortness of the route rather than its reliability.We introduce a light-weight route selection algorithm that uses past behavior to judge the quality of a route rather than solely on the length of the route.It draws information from the underlying routing layer at no extra cost and selects routes with a simple algorithm.This technique maintains this data in a small table,which does not place a high cost on memory.History-based route selection’s minimalism suits the needs the portable wireless devices and is easy to implement.We implemented our algorithm and tested it in the ns2environment.Our simulation results show that history-based route selection achieves higher packet delivery and improved stability than its length-based counterpart.Keywords:ad hoc routing,selfish nodes,packet delivery,route stability1.INTRODUCTIONAd hoc networks function without pre-existing infrastructure and do not have centralized administration.This freedom permits a wide range of novel uses from battlefield coordination to disaster response.Ad hoc networks rely on cooperation to operate.In many ad hoc networks,the participating devices face resource constraints such as limited battery life and processing power.This altruistic behavior does not directly benefit intermediate nodes acting as forwarders;on the contrary,they expend their own resources on behalf of other nodes.Intermediate nodes can save their own resources by acting selfishly and dropping packets.Selfishness and other forms of packet loss hurts the network performance.Nodes drop packets for many reasons.Congested nodes run out of buffer space and must drop packets when their queues becomes full.Malfunctioning nodes drop packets because of software or hardware problems. In hostile environments enemy nodes actively drop packets through attacks such as the blackhole or grayhole attacks.1,2Spurious packet drops leads to decreased network performance.Judicious route selection accounting for misbehavior helps to mitigate the effects of misbehaving nodes as well as preserve resources.Direct observation of the offenders behavior helps source nodes identify offending nodes.Because wireless is an open medium,nodes are able to promiscuously listen to their neighbors’transmissions and detect misbehavior in their one-hop munication protocols also provide insight into node ing a protocol with acknowledgments lets the sender know that their packet arrived safely at the destination given; unacknowledged traffic does not have this luxury.Acknowledgments also show the nodes on that path have cooperated and attest their reliability.Other protocol information can also reflect the quality of nodes,for example,ICMP Destination Unreachable messages.Source nodes need not rely purely on their own ratings;they can incorporate outside knowledge.Second-hand information distribution,termed gossiping,allows a node to use other node’s ratings.A node will periodically distribute its assessment of others.The receiving nodes can incorporate these values with their own to form a broader picture of network ing second-hand information introduces some problems. Second-hand information increases the overhead due to the periodic rating distribution.Unscrupulous nodescan publish false values and spread bogus values to other nodes.Adversarial nodes can collude and boost each other’s ratings when in fact they are misbehaving.Once a node becomes misbehaving,the source node can take action to deal with the problem.After observing the node and evaluating it based on the misbehavior criteria,the systemflags the node as misbehaving.Many systems set a threshold value on their evaluation metric andflag the node when it exceeds that value.3,4Routes with the node can be removed entirely,or receive a low rating.Not all misbehaving nodes are malicious and may start to function correctly later.At this point,the rating system can begin a forgiveness process and allow the node to redeem itself from its past behavior.In this paper we propose a light-weight route selection method that only relies on information received from the routing layer.This approach only usesfirst-hand information and and does not require the participation of other nodes in misbehavior management.This follows the reasoning that not all nodes in the network cannot be trusted to run non-modified copies of the routing algorithm.History-based routing takes a light-weight approach and does not require intense computation,which suites the needs of energy constrained devices.It uses freely available routing information to base decisions and does not require significant modification to the underlying routing algorithm.The algorithm uses a small amount of memory per node to maintain a record of past behavior.We show that this method performs well under high mobility conditions.The paper takes the following structure.Section2introduces related work coming from differing perspectives. We describe our approach,history-based route selection,in Section3and illustrate the details behind the algorithm.Section4explains the goals behind experiments used to test the solution.It details and justifies the metrics used and explains the results.Section6presents our conclusions and future work.2.RELATED WORKDifferent approaches tackle mitigating misbehavior through diverse perspectives.Reputation systems assign nodes ratings based on their performance.Traditional wired network cryptographic techniques do not translate to wired networks well,so cryptographic approaches tend to use light weight algorithms to avoid the cost for complex calculations.Potlapally et al.5give an interesting study on energy usage of security protocols on portable devices and show the cost of asymmetric cryptography.Pre-established infrastructures like certificate authorities do translate well to the ad hoc environment.Others have based their methods on differentfields like game theory.6These share the common goal of maintaining good network performance in the presence of misbehaving nodes.2.1.Watchdog and PathraterMarti et al.3describe a misbehavior detection system that observes packet forwarding in its one hop neighbor-hood.Their system consists of two components:the watchdog and the pathrater.The watchdog stores packets and listens promiscuously for the next hop neighbor to forward the packet.It compares the transmission to the buffered copy of the packet and detects alteration of the packet.If a neighboring node exceeds a threshold value for dropped packets,then it becomesflagged as misbehaving.The pathrater component maintains ratings of nodes and bases routing selections based on these values.The watchdog and pathrater help to choose more reliable routes without misbehaving nodes,but others have criticized it for not punishing the offenders.4,72.2.CONFIDANTBuchegger and Le Boudec4present a reputation system addressing other facets of dealing with misbehavior. Their approach uses bothfirst-and second-hand information.Nodes compare their assessments of others with the second-hand information they received;the node will only use it if it does not deviate considerably from its own assement.Furthermore,the accepted second hand information only contributes slightly.These steps help to protect against lying nodes,but also help decrease the detection time of misbehaving nodes.Their system focuses more on recent behavior and introduces the idea of rating degregation.Fading gives misbehaving nodes an opportunity to redeem themselves.2.3.Virtual Currency:NugletsButtyan and Hubaux8take an approach inspired by economics and uses a virtual currency exchanged for packet forwarding.Each node in the network has a number of tokens called nuglets used for forwarding.They propose two variants of payment for forwarding.In one method the forwarding node pays the next hop along the route. The other method charges the next hop to forward the packet.The price depends on a number of factors including:current energy level,number of nuglets possessed,and the amount of energy required to transmit the packet.This approach rests on a number of assumptions.Each node has a security module responsible for storing, crediting,and deducting nuglets.It also holds:the nodes public and private keys,the manufacturers certicate and public key,as well as session keys.The security module resides in tamper proof hardware asssumed to be made from a handful of of manufacturers.2.4.A Cryptographic Approach:Secure Routing ProtocolThe Secure Routing Protcol(SRP)9uses security associations between source and destination nodes to protect the integrity of the route discovery process.SRP verifies the contents of route discovery packets with message authentication codes using the shared secret.This method has the benefit of not relying on pre-existing infras-tructure like certificate authorities and does not require intermediate node municating nodes create the message authentication codes with a shared secret obtained through methods like key exchange or loaded before deployment.This scheme works against many attacks launched by a single node,but does not ensure correctness against colluding nodes.This method only secures the route discovery process,but does not protect the communication afterwards.This still leaves the packets vulnerable to tampering by malicious nodes and spurious packet drops by misbehaving nodes.2.5.Artificial Immune SystemsLe Boudec and Sarafijanovic10model ad hoc networks as an artificial human immune system.Each part of the network corresponds to a component found in the immune system.The network consists of self cells and non-self cells,which are misbehaving nodes.This system observes DSR packet headers and treats them as antigens.It builds a list of behaviors witnessed over afixed period for each of its neighbors.Antibodies act as detectors and try to match non-self antigens.If an antibody matches an antigen in afixed period of time,the node is considered of be suspicious.Problematic nodes become monitored atfirst and deemed misbehaving after the probability they are misbehaving exceeds a threshold.3.HISTORY-BASED ROUTE SELECTION3.1.OverviewHistory-based route selection augments the underlying DSR11protocol with the ability to maintain past perfor-mance of nodes and choose routes based on these values.The original DSR protocol selects routes soley on the length of the path and has no recollection of whether nodes along that path have performed well in the past.It does not associate any form of quality with the nodes or routes.The quality of a node depicts the overall reliability of that node.If a node consistently drops packets,then it is unreliable.A high quality node forwards packets regularly and does not often drop packets.In selecting a route,nodes with a better track record of dutifully forwarding packets have more utility than nodes with a poor history.In order to evaluate the goodness or badness of a node,there must be a means to evaluate their performance.Our system uses packet counts to represent the performance of other nodes.Packet counts represent forwarder behavior well:a forwarder either forwarded the packet or it did not.These values are collected at no charge from the underlying routing layer.When a node along a path forwards a packet for the sender,it gives evidence of its good citizenship,and the node receives an increment in its Unacknowledged protocols like UDP do not have a feedback mechanism to alert the sender of a successful receipt by the destination,but other information availableTable1.History-Table FormatNode Id Good Bad...i th node##...to the host gives negative feedback,i.e.the packet did not reach the destination.In DSR,route error packets arise when this happens.Receipt of error packets add to the negative packet count for the node responsible for the error.These changes do not require heavy modification of the underlying routing layer.This system is suited for real world operation due to its simplicity and ease of implementation.3.2.History TableHistory-based routing maintains a structure called a history-table to record its experiences with other nodes. When a node joins the network,it has an empty history table and empty route cache.The table entries are indexed with the node id and have twofields:the number of good and bad forwards.A good forward represents the case where node successfully forwarded the packet to the next hop.A bad forward indicates the node dropped the packet.These two values constitute8bytes of storage per node,which does not place a heavy burden on the nodes memory.The history table grows as the node interacts with the network and gains routes.Nodes gain routes directly from route replies and secondarily from overheard packets.When it gains a new route,it adds the routes to its cache.New nodes receive an entry in the history-table and have an initial value of zero for both the number of good and bad forwards.Over time,the underlying routing layer removes routes from the cache,but the history table still holds the statistics for each of the nodes along the routes.Routes are removed for several reasons.When the route cache becomes full,the underlying protocol removes older,stale routes to make room for newer routes.The receipt of route errors also forces out all cached routes including the erroneous node.3.3.Rating SchemeThe route selection algorithm uses the history-table and the route cache to select the route with the best average rating.Each node receives a rating based algorithm1.This gives a rating between0.0and1.0where1.0 Algorithm1Node Rating Functionif∃node n thenreturn good forwards/total forwardselsereturn1.0end ifrepresents a100%delivery record.In the event the node just entered the table and has no past interaction,then it is assumed to be properly functiong until proven wrong.This is a simple rating scheme based on algebra,so it does not require intensive computation nor does it require much storage.Given these values,when the source requests a route from its cache,the cache performs the algorithm2.Once the route with the best rating has been selected,the sender credits each of the nodes along the route by incrementing the good forward count by one.Since this scheme works with an unacknowledged protocol,it does not know if the packet has arrived successfully at the destination.This scheme takes a innocent-until-proven-guilty approach and assumes the packet does indeed reach the destination unless it hears otherwise.Algorithm 2Route Selection Algorithmif ∃routes R to destination d thenbiggest =0.0for all routes r ∈R doH ←h 1,h 2,...,h n where h i is the i th hop of rrating ←P |H |i =1rating (h i )|H |if rating >=biggest thenbiggest ←ratingend ifend forreturn biggestelsereturn nullend if Table 2.S’s History TableGood Forwards Bad Forwards Rating A1146.95B00100C 91.9.........The source node penalizes intermediate nodes upon the receipt of packets containing route errors.For eachof the route errors contained in the packet,the sender determines the source of the error and increments the badforward table entry to reflect the misbehavior.Furthermore,since the sender assumed correct behavior whensending the packet along the route with the node,it also decrements the previously awarded good count.3.4.ExampleS ADB CFigure 1.Example Network TopologyConsider the network shown in Figure 1.In this scenario,node S wishes to establish a connection with nodeD.It has the values in its history table shown in table 2and routes to node D as shown in 3.It has not previouslyinteracted with node B,so it has a rating of 1.0.Routes (1)and (2)have an average intermediate node ratingof .95,but route (1)is the shortest so node S uses this route.Next,suppose that node A drops a packet.S removes route (1)and any other routes with node A.It has analternative route to node D,so it sends subsequent packets to D along route (2).As it sends packets along thisroute,the intermediate nodes receive credit in the good forward count.Table3.S’s Routes to Node DRoute Rating(1)S→A→D.95(2)S→B→C→D.95Table4.S’s history table after more timeGood Forwards Bad Forwards Rating A1147.942 B200100 C282.93.. .......S continues to send packets along this route until C drops a packet and it receives a route error from node B.After receiving the route error packet it removes route(2)from the cache and has no routes to D.It must initiate a route request tofind a new route.Both node A and C are working correctly,so they return the routes S→A→D and S→B→C→D,respectively.Node S bases its decision on4.Route(1)has a rating of.942 and route(2)has a rating of.967.Since route(2)has a better average node rating,S chooses this route.4.PERFORMANCE EV ALUATIONThere were two major thrusts in the simulation design.One set of experiments varied the percentage of misbe-having nodes from0%to40%at intervals of5%to test how our algorithm performed with varying degrees of misbehavior in the network.The other major set of experiments varied the time to investigate if more informa-tion leads to better route selection.Nodes in history-based DSR gather more information about the network as time progresses,so they will be able to make better informed choices about route selection.We conducted our simulations using the ns212simulator.The simulations occured in an1000x1000meter area with100nodes.Nodes started at randomly determined(x,y)coordinates.Node mobility followed the random waypoint model using maximum speeds of20m/s and5m/s.Each speed also had two pause times of 5s and30s.Each set of experiments also used either10or15connections of CBR traffic at several rates detailed in the following subsections.All connections started at time0and data gathering started at60s.This allowed routes to form and traffic to stabilize.These are reasonable conditions similar to those used by others and permit comparison.The misbehaving node behavior varied with the experiment goals.The misbehaving nodes all started at the start of the simulation.They dropped all packets except for those containing route replies and requests in order to place themselves along routes.The nodes were randomly chosen and placed throughout the network. The experiments concerning time used15%misbehaving nodes.This number of misbehaving nodes tested the algorithm while not completely degrading the network.Our discussion on the results focus on the scenarios with the most challenging conditions,because they reflect performance in the worst-case scenario.Higher mobility scenarios present more challenges to protocols because of their changing topology.4.1.MetricsWe evaluated history-based DSR on two sets of related metrics:general network performance and stability. Metrics like throughput and delay reflect the effectiveness of the network as a whole.A healthy network delivers packets in a timely fashion with a reasonable number of packet drops.Out of these measures,we particulary looked at the number of data packets received over the course of the simulation to represent the throughput. Both variants of the routing algorithm used the same traffic generator and same rate,so a higher count depicts more ability to receive data.Comparing the type and number of control packets shows the effects of the algorithm on network stability.A stable routing algorithm has less overhead because the routes it chooses are reliable.In this same vein,stable routes remain effective longer and produce fewer route errors.The percentage of control packets of theoverall traffic is also important.A higher percentage indicates the nodes must spend time processing protocolinformation rather than sending data packets on their way.4.2.Varying Degrees of Misbehavior200 400600 80010001200140016001800200022000 5 10 15 20 25 3035 40 45P a c k e t s /s Percentage of Misbehaving Nodes Standard History (a)Data Reception 1000 200030004000 5000 6000 70008000 0 5 10 15 20 25 30 35 40 45P a c k e t s /s Percentage of Misbehaving Nodes Standard History (b)OverheadFigure 2.Aggregate Network Data and Control Packet ReceptionProgressively increasing the number of misbehaving nodes tested the performance of both algorithms undera more hostile environment.As the percentage of misbehaving nodes grows,the chance to have a misbehavingnode along a route reply increases.Figures 2and 3represent simulation setup using 20m/s maximum speedand a 5s pause.This high mobility scenario changes the topology of the network more often than slower runs,which helps test the adaptibility of the algorithms.Our results show the history-based selection scheme having higher aggregate packet reception and less controlpackets.Both routing methods decreased their delivery effectiveness at roughly the same rate,but the history-based scheme had a markedly higher packet delivery than the standard counterpart.History-based routinginitiated fewer route queries.This indicates the routes it chose were more stable.Standard DSR also experiencedmore route errors than history-based routing.This indicates that it chose routes with nodes more prone to droppackets.4.3.Sensitivity to TimeHistory-based routing collects evidence of node performance over time,so it gains a better picture of the networkwith more time.Figure4shows performance improvement with longer simulation times.Initially both routingalgorithms behave similarly at 300seconds.History-based route selection starts to achieve higher aggregate datareception with time.The data points on Figure 4illustrate the difference between the two algorithms increaseswith longer simulations.At 15%misbehavior,both of the selection algorithms had comparable routing overhead.As the time increased,history-based selection avoided more packet drops than standard route selection.Thehistory-dependent scheme chose higher quality routes as evidenced by the figures.5.DISCUSSIONAt lower movement speeds,both algorithms behaved comparably in terms of both general performance andstability.This held true for longer pause times as well.In these conditions nodes remain in place more and donot move out of transmission range from their neighbors as often than a higher mobility scenario.Higher mobility resulted in history-based routing performing better than the standard algorithm.The scenariowith a maximum speed of 20m/s and 5s pause time exercised the algorithms the most,but the 5m/s and 5s0 100 200 300 400500 600 0 5 10 15 20 25 3035 40 45P a c k e t s Percentage of Misbehaving Nodes Standard History (a)Number of Route Requests200 4006008001000 12001400 0 5 10 15 20 25 30 35 40 45E r r o r s r e p o r t e d Percentage of Misbehaving Nodes Standard History(b)Number of Errors 0 1000200030004000500060007000 0 5 10 15 20 25 3035 40 45P a c k e t s Percentage of Misbehaving Nodes Standard History(c)Number of RepliesFigure 3.Route Control Packet Type Comparisonpause time case also created considerable mobility.The more mobile nodes move out of transmission range oftheir neighbors,more links break and result in route error generation.The changing topology places more ofdemand on the route selection algorithms since routes change more often.The introduction of misbehavingnodes complicates the already tenous network.The more interaction with nodes helps to make better route selections.Scenarios with longer duration showedan improvement in performance as time went on.The longer time allowed nodes to collect more packet countsand build their history-table.Results of trials with higher packet rates support this claim.Previous work withvarying the packet rate showed improvements in performance at higher rates.Our mechanism works with packetcounts,so the more packets observed by the sender help to build their view of the network.The lower number of control packets received demonstrated the stability of our algorithm.Routes that lastlonger have utility to both the sender and the network.The sender does not need to flood route request packetsas much,which saves the network from propagating the requests.Fewer requests translates to fewer replies;thisfurther reduces network control packet numbers.Stability also means fewer broken routes.Lower number ofroute errors helps the network from experiencing flooding associated with the query process.Our results showless overhead and higher data reception,which means that the nodes have spent more time transmitting datarather than control packets.6.CONCLUSIONIn this paper we have described a light-weight route selection algorithm augmenting existing reactive routingprotocols.It extracts and collects statistics from the underlying routing layer at no extra ing this3.S.Marti,T.J.Giuli,i,and M.Baker,“Mitigating routing misbehavior in mobile ad hoc networks,”in Mobile Computing and Networking,pp.255–265,2000.4.S.Buchegger and J.-Y.Le Boudec,“Self-Policing Mobile Ad-Hoc Networks by Reputation,”IEEE Com-munication Magazine43(7),p.101,2005.5.N.R.Potlapally,S.Ravi,A.Raghunathan,and N.K.Jha,“A study of the energy consumption character-istics of cryptographic algorithms and security protocols,”IEEE Transactions on Mobile Computing05(2), pp.128–143,2006.6.S.Zhong,J.Chen,and Y.R.Yang,“Sprite:A simple,cheat-proof,credit-based system for mobile ad-hoc networks,”in INFOCOM2003.Twenty-Second Annual Joint Conference of the IEEE Computer and Communications Societies,3,pp.1987–1997,2003.7.P.Dewan,P.Dasgupta,and A.Bhattacharya,“On using reputations in ad hoc networks to counter maliciousnodes,”in ICPADS’04:Proceedings of the Parallel and Distributed Systems,Tenth International Conference on(ICPADS’04),p.665,IEEE Computer Society,(Washington,DC,USA),2004.8.L.Buttyan and J.-P.Hubaux,“Nuglets:a Virtual Currency to Stimulate Cooperation in Self-OrganizedMobile Ad Hoc Networks,”tech.rep.,2001.9.P.Papadimitratos and Z.Haas,“Secure routing for mobile ad hoc networks.”10.J.L.Boudec and S.Sarafijanovic,“An artificial immune system approach to misbehavior detection in mobilead-hoc networks,”2003.11.D.Johnson,D.Maltz,and J.Broch,DSR The Dynamic Source Routing Protocol for Multihop Wireless AdHoc Networks,ch.5,pp.139–172.Addison-Wesley,2001.12.K.Fall and K.Varadhan,The ns Manual(formerly ns Notes and Documentation)./nsnam/ns/doc/index.html.。
牛津译林版英语八上Unit2《Schoollife》(welcome)说课稿
牛津译林版英语八上Unit 2《School life》（welcome）说课稿一. 教材分析《School life》是人教版初中英语八年级上册Unit 2的一篇阅读文章，主要介绍了英国学校的日常生活。
通过学习本节课，学生可以了解英国学校的概况，提高阅读理解能力，同时培养对不同文化背景的尊重和理解。
文章内容丰富，语言贴近学生生活，有利于激发学生的学习兴趣。
二. 学情分析根据初中英语课程标准，八年级的学生已经具备了一定的英语基础，能够运用简单的英语进行日常交流。
但在阅读理解、词汇积累以及文化背景知识方面，学生还存在一定的差距。
因此，在教学过程中，教师需要关注学生的个体差异，充分调动学生的积极性，引导他们主动参与课堂活动。
三. 说教学目标1.知识目标：学生能够掌握文章中的重点词汇和短语，如“schooluniform”、“host family”等；2.能力目标：学生能够运用所学知识进行简单的阅读理解和口语表达；3.情感目标：学生通过学习，培养对不同文化背景的尊重和理解，提高跨文化交际能力。
四. 说教学重难点1.重点：文章中的重点词汇和短语；2.难点：对文章中长难句的理解，以及文化背景知识的掌握。
五. 说教学方法与手段1.交际法：通过小组讨论、角色扮演等方式，让学生在实际语境中运用英语，提高口语表达能力；2.任务型教学法：通过完成具体任务，引导学生主动参与课堂活动，提高阅读理解能力；3.多媒体教学：利用多媒体课件，为学生提供丰富的视觉和听觉信息，增强课堂趣味性。
六. 说教学过程1.导入：教师通过提问，引导学生谈论自己喜欢的学校活动，激发学生对学校生活的兴趣；2.读前预测：教师展示文章标题和图片，让学生猜测文章内容，激发阅读欲望；3.快速阅读：学生快速阅读文章，回答简单问题，了解文章大意；4.细节理解：学生仔细阅读文章，回答具体问题，巩固重点词汇和短语；5.小组讨论：学生分组讨论，对比中英学校生活的异同，提高跨文化交际能力；6.角色扮演：学生分组进行角色扮演，模拟英国学校的日常生活，提高口语表达能力；7.总结：教师引导学生总结文章内容，回顾所学知识；8.作业布置：学生课后撰写一篇关于自己学校生活的短文，培养写作能力。
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2.LEACH（Low-Energy Adaptive Clustering Hierarchy）协议：
LEACH协议分为两个阶段操作，即类准备阶段(set-up phase)和就绪阶段(ready phase)。为了使能耗最小化，就绪阶段持续的时间比类准备阶段长。类准备阶段和就 绪阶段所持续的时间总和称为一轮(round) 在类准备阶段，LEACH协议随机选择一个传感器节点作为类头节点(cluster head node)，随机性确保类头与基站之间数据传输的高能耗成本均匀地分摊到所有传感器 节点。 具体的选择办法是：一个传感器节点随机选择0和1之间的一个值，如果选定的值小于 某一个阈值T(n)，那么这个节点 成为类头节点。T(n)值按右边公式计算： N：网络中传感器节点的总数； p：一轮中网络的类头节点数；r：己完成的轮数； Gr：在剩余的N/k-r个回合中未成为类头节点的传感器节点组成的集合； 在类头节点选定后，该类头节点对网络中所有节点进行广播，广播数据包含有该节点 成为类头节点的信息。一旦传感器节点收到广播数据包，根据接收到的各个类头节点 广播信号强度，该节点选择信号强度最大的类头节点加入，向其发送成为其成员的数 据包。类形成后，类头节点采用TDMA策略分配通道使用权给类内节点。 一旦处于就绪阶段，类头节点开始接收类内各节点采集的数据，然后采用数据融合和 数据压缩等技术进行汇聚，将整合后的数据传输给Sink节点。在就绪阶段持续了一段 时间后，网络又进入了另一次的类准备阶段。
Otcl是Tcl的面向对象（Object Oriented）的扩展，在 Otcl中加入了类的概念。 对象是类的实例，它有自己的属性（成员变量，InstVar ）和自己的内部操作（成员函数，InstProc）。 对象具有继承、封装、多态性和动态绑定等性质。 面向对象机制的加入使得原始的Tcl变得更加强大，更加 方便使用。 实际上，Tcl和OTcl的关系就像C和C++ 。因此，所有的 Tcl命令都可以在OTcl中使用。
无线传感器网络仿真平台NS2
计算机应用技术 张道远
内容
NS2介绍 OTcl语言简介 NS2的实现机制和体系结构 利用NS2模拟流程和注意事项 NS2—协议仿真
NS2介绍
NS2是面向对象的，离散事件驱动的网络环境模拟器，开发于 UC Berkeley，它可以模拟各种IP网络环境。 NS2实现了对许多网络协议的模拟，如TCP，UDP，和数据源 发生器（traffic source)如FTP，WWW，Telnet，Web，CBR和 VBR等。 NS2模拟了路由队列的管理机制，如Drop Tail，RED和VBR， 实现了Dijkstra和其他的路由算法。 NS2也实现了Multicasting和一些应用于局域网模拟的在MAC层 的协议。 NS2采用分裂对象模型的开发机制，由C++和Otcl（加上面向对 象特性的TCL脚本程序设计语言，开发于MIT）两种程序设计语 言实现。
节点存活率
节点能量消耗
数据包发送量
NS2的部分类结构
分类器——classifier是Ns-2基本网络组件的一个大类。 它的基本派生类有地址分类器（AddrClassifier）和多播 分类器（McastClassifier）等。基于分类器的基本网络 组件具有1个或多个可能的数据输出路径，属于交换 （Switch）设备（对应来说，连接器Connector只有一个 数据的输出路径）。 拓扑结点（Node）是由一个结点入口对象和若干个分类 器（Classifier）组成的一个符合对象。
C++程序模块的运行速度非常快，是强制类型的程序设 计语言（变量严格定义整型，浮点型和字符、字符串类 型），容易实现精确的、复杂的算法，但是修改和发现 、修正bug所花费的时间要长一些。适合对具体协议的模 拟和实现，因为它需要很有效率的处理字节（Byte）， 报头（Packet Header）等信息，需要应用合适的算法在 大量的数据集合上进行操作。 Otcl是脚本程序编写语言，是无强制类型的，比较简单 ，容易实现和修改，容易发现和修正bug，虽然它的运行 速度和C++的模块相比要慢很多。许多网络中的研究工 作都围绕着网络组件和环境的具体参数的设置和改变而 进行的，需要在短时间内快速的开发和模拟出所需要的 网络环境（scenarios），并且方便修改和发现、修复程 序中的Bug。这种环境的配置只需要一次。
NS2的实现机制和体系结构
N S 仿 真 试 图
NS是一种面向对象Tcl(OTcl)语言脚本解释器，它有一个事件调度器、一个网络组件 库。换句话说，使用NS时需要使用OTcl语言编写脚本文件。 事件调度器:事件在NS中是一个具有唯一ID号的数据包、数据包被处理的时间及处 理它的主对象的总称。事件调度器跟踪仿真的时间并且根据预定时间安排队列中的 事件，激活当前时间对应的处理该事件的网络对象。事件调度器维护一个排序的数 据结构（缺省情况下ns使用链表），对事件有序地执行、释放，并激活事件处理对 象。
NS由C++和OTcl写成：其中C++语言实现各种网络组件，这是为了提高效 率；OTcl语言编写脚本文件来建立网络和运行仿真，这样是为了简单而快速 地进行网络环境的建立。 编译过的C++对象只要通过链接，创建一个与之匹配的OTcl对象就可在OTcl 解释器中使用。
OTcl与C++的类对应示意图
OTcl语言简介
Tk是Tcl在X Window环境下的扩展，它包含了Tcl的全部的C库函 数，以及支持X Window的窗口、控件等C库函数，为用户开发 图形用户界面提供了方便。 Tcl是解释执行的脚本语言。它的实现依赖于Tcl内部的C函数库 。添加新的C函数就可以扩充Tcl的命令和功能，是扩展性非常强 的脚本程序设计语言。 Tcl解释器把用户输入的命令和程序语句进行初步分析，然后调 用C函数库里的相应函数来执行，输出结果。 Tcl是无强制类型的脚本语言，一切变量，不论整型，浮点型等 ，都以字符串的形式存储。
连接器——Connector是NS2基本网络组件中的另一个大类。 它的基本派生类对象包括缓冲队列（Queue）、延迟 （Delay）、各种产生和处理数据包的代理（Agent）和对象 的跟踪器（Trace）。基于连接器的基本网络组件只有一个可 能数据输出的路径，和分类器有1个或多个可能的数据输出 路径（Switch）是不同的。 拓扑结点连接类（Link）是NS2中另一个主要的复合组件对 象。一个结点和另一个结点之间的简单连接（simplex-link） 是单向的。一个最基本的简单连接由一个连接入口、包缓冲 队列、延迟处理对象、废弃处理对象和时间处理对象（TTL ）组成。
NS2的总体系结构
NS2的目录结构
ns-2.34:存放C++代码的地方； ns-2.34\tcl:存放OTcl代码的地方； Ns-2.34\tcl\lib:存放与组件（agent, node, link, packet, address, routing ） 实现有关的OTcl代码；在此目录下，有以下几个文件：ns-lib.tcl: Simulator 类定义与成员函数实现，如 run，simplexlink，flush-trace等；ns-default.tcl ：各种网络组件配置的缺省值。 ns-2.34\tcl\ex, ns-2.34\tcl\test: 存放一些例子脚本文件和验证结果。
2. 注意事项
Start NS有 吗 ？
No
Yes
需要修改 吗？
网上呢？
C++实 现
添加
Yes
配置场景
修改
编译调试 测试分析
编译调试
Ye s
TE(Minimum Transmission Energy)协议：
在MTE协议中，节点选择离自己平面距离 最近的节点进行路由中转 当且仅当如下公式满足时，节点A将会选择 B转发自己的数据到节点C
两个节点间数据包通信的实例
如何从OTcl来操纵NS2的C++对象, 这包括: 动态创建一个新的C++对象, 访问这个C++对象的属性, 调用该C++对象的方法.
利用NS2模拟流程和注意事项
1. 流程 整个模拟流程主要有三部分工作量：一是修改源代码，二是 编写Tcl模拟脚本，三是分析结果。 源代码在需要修改的时候才修改，注意修改C++代码时候，要修 改相应的OTcl代码 需要用awk语言对结果进行分析，用gnuplot作图或者用nam生 成动画 Gawk gnuplot Trace文件 tcl 脚本 ns-2 Nam文件 nam
LEACH模型
3.LEACH-C协议： LEACH-C引入中心控制机制，保证簇头较优地分布于网络中，从而优化网 络性能。 LEACH-C 协议也分为簇的建立和数据传输阶段。在簇的建立阶段，所有节 点都将自己的位置与能量信息传送给基站。基站计算出所有节点能量的平 均值，只有能量大于平均值的节点才有资格成为簇头。然后基站利用模拟 退火算法划分簇，选出簇头节点。然后向所有节点广播簇头节点的ID 信息 ，各个节点根据接收的消息判断自己的身份。如果ID 与自己的ID 信息相同 ，则成为簇头；否则，则根据自己所在的簇决定自己的数据传输TDMA 时 隙，并进入“睡眠”状态，直到传输数据的时隙到来。数据传输阶段， LEACH-C 与LEACH 机制相同。
仿真后生成 x.data,x.alive,x.energy等文件（x对应的为协 议名称），分别对应的为各个协议的数据包传送个数， 节点生存情况和节点能量消耗，用awk语言编写程序， 提取数据进行分析 在Cygwin中用gnuplot 作出分析结果曲线