CAN_ an example of nonclassical acoustic nonlinearity in solids

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

tpo61托福阅读全套解析阅读-1 (1)原文 (1)译文 (3)题目 (4)答案 (7)背景知识 (8)阅读-2 (10)原文 (10)译文 (12)题目 (13)答案 (17)背景知识 (18)阅读-3 (21)原文 (21)译文 (22)题目 (24)答案 (28)背景知识 (29)阅读-1原文Physical Properties of Minerals①A mineral is a naturally occurring solid formed by inorganic processes.Since the internal structure and chemical composition of a mineral are difficult to determine without the aid of sophisticated tests and apparatus,the more easily recognized physical properties are used in identification.②Most people think of a crystal as a rare commodity,when in fact most inorganic solid objects are composed of crystals.The reason for this misconception is that most crystals do not exhibit their crystal form:the external form of a mineral that reflects the orderly internal arrangement of its atoms.Whenever a mineral forms without space restrictions,individual crystals with well-formed crystal faces will develop.Some crystals,such as those of the mineral quartz,have a very distinctivecrystal form that can be helpful in identification.However,most of the time,crystal growth is interrupted because of competition for space,resulting in an intergrown mass of crystals,none of which exhibits crystal form.③Although color is an obvious feature of a mineral,it is often an unreliable diagnostic property.Slight impurities in the common mineral quartz,for example, give it a variety of colors,including pink,purple(amethyst),white,and even black. When a mineral,such as quartz,exhibits a variety of colors,it is said to possess exotic coloration.Exotic coloration is usually caused by the inclusion of impurities, such as foreign ions,in the crystalline structure.Other minerals—for example, sulfur,which is yellow,and malachite,which is bright green—are said to have inherent coloration because their color is a consequence of their chemical makeup and does not vary significantly.④Streak is the color of a mineral in its powdered form and is obtained by rubbinga mineral across a plate of unglazed porcelain.Whereas the color of a mineral often varies from sample to sample,the streak usually does not and is therefore the more reliable property.⑤Luster is the appearance or quality of light reflected from the surface of a mineral.Minerals that have the appearance of metals,regardless of color,are said to have a metallic luster.Minerals with a nonmetallic luster are described by various adjectives,including vitreous(glassy)pearly,silky,resinous,and earthy (dull).⑥One of the most useful diagnostic properties of a mineral is hardness,the resistance of a mineral to abrasion or scratching.This property is determined by rubbing a mineral of unknown hardness against one of known hardness,or vice versa.A numerical value can be obtained by using Mohs'scale of hardness,which consists of ten minerals arranged in order from talc,the softest,at number one,to diamond,the hardest,at number ten.Any mineral of unknown hardness can be compared with these or with other objects of known hardness.For example,a fingernail has a hardness of2.5,a copper penny5,and a piece of glass5.5.The mineral gypsum,which has a hardness of two,can be easily scratched with your fingernail.On the other hand,the mineral calcite which has a hardness of three, will scratch your fingernail but will not scratch glass.Quartz,the hardest of the common minerals,will scratch a glass plate.⑦The tendency of a mineral to break along planes of weak bonding is called cleavage.Minerals that possess cleavage are identified by the smooth,flat surfaces produced when the mineral is broken.The simplest type of cleavage is exhibited by the micas.Because the micas have excellent cleavage in one direction,they break to form thin,flat sheets.Some minerals have several cleavage planes,which produce smooth surfaces when broken,while others exhibit poor cleavage,andstill others exhibit no cleavage at all.When minerals break evenly in more than one direction,cleavage is described by the number of planes exhibited and the angles at which they meet.Cleavage should not be confused with crystal form.When a mineral exhibits cleavage,it will break into pieces that have the same configuration as the original sample does.By contrast,quartz crystals do not have cleavage,and if broken,would shatter into shapes that do not resemble each other or the original crystals.Minerals that do not exhibit cleavage are said to fracture when broken.Some break into pieces with smooth curved surfaces resembling broken glass.Others break into splinters or fibers,but most fracture irregularly.译文矿物的物理性质①矿物质是由无机过程形成的天然固体。

2025年全国大学英语CET六级考试模拟试卷及解答参考一、写作（15分）Task 1: Writing (30 minutes)Part AWrite an email to your friend about a recent movie you watched. In your email, you should:1.Briefly introduce the movie and its main theme.2.Share your personal feelings about the movie.3.Recommend the movie to your friend, explaining why you think they would enjoy it.You should write about 100 words on the ANSWER SHEET 2.Do not sign your own name at the end of the letter. Use “Li Ming” in stead. Do not write the address.Example:Dear [Friend’s Name],I hope this email finds you well. I wanted to share with you a movie I recently watched that I thought you might find interesting.The movie I’m talking about is “Inception,” directed by Chris topher Nolan.It revolves around the concept of dream manipulation and the layers of reality. The story follows Dom Cobb, a skilled thief who specializes in extracting secrets from within the subconscious during the dream state.I was deeply impressed by t he movie’s intricate plot and the exceptional performances of the cast. The visual effects were breathtaking, and the soundtrack was perfectly matched to the action sequences. The movie made me think a lot about the nature of reality and the power of dreams.I highly recommend “Inception” to you. I believe it will be a captivating experience, especially if you enjoy films that challenge your perceptions and make you think.Looking forward to your thoughts on this movie.Best regards,Li MingAnalysis:This example follows the structure required for Part A of the writing task. It starts with a friendly greeting and a brief introduction to the subject of the email, which is the movie “Inception.”The writer then shares their personal feelings about the movie, highlighting the plot, the cast’s performances, the visual effects, and the soundtrack. This personal touch helps to engage the reader and provide a more authentic recommendation.Finally, the writer makes a clear recommendation, explaining that theybelieve the movie would be enjoyable for their friend based on itsthought-provoking nature and entertainment value. The email concludes with a friendly sign-off, maintaining a warm and inviting tone.二、听力理解-长对话（选择题，共8分）第一题听力原文：M: Hi, Lisa. How was your trip to Beijing last weekend?W: Oh, it was amazing! I’ve always wanted to visit the Forbidden City. The architecture was so impressive.M: I’m glad you enjoyed it. By the way, did you manage to visit the Great Wall?W: Yes, I did. It was a long journey, but it was worth it. The Wall was even more magnificent in person.M: Did you have any problems with transportation?W: Well, the subway system was very convenient, but some of the bus routes were confusing. I ended up getting lost a couple of times.M: That’s a common problem. It’s always a good idea to download a map or use a GPS app.W: Definitely. I also found the people in Beijing to be very friendly and helpful. They spoke English well, too.M: That’s great to hear. I’m thinking of visiting Beijing next month. Arethere any other places you would recommend?W: Oh, definitely! I would suggest visiting the Summer Palace and the Temple of Heaven. They are both beautiful and culturally significant.M: Thanks for the ti ps, Lisa. I can’t wait to see these places myself.W: You’re welcome. Have a great trip!选择题：1、Why did Lisa visit Beijing?A. To visit the Great Wall.B. To see her friends.C. To experience the local culture.D. To study Chinese history.2、How did Lisa feel about the Forbidden City?A. It was boring.B. It was too crowded.C. It was impressive.D. It was not as beautiful as she expected.3、What was the biggest challenge Lisa faced during her trip?A. Finding accommodation.B. Getting lost.C. Eating healthy food.D. Visiting all the tourist spots.4、What other places does Lisa recommend visiting in Beijing?A. The Summer Palace and the Temple of Heaven.B. The Great Wall and the Forbidden City.C. The National Museum and the CCTV Tower.D. The Wangfujing Street and the Silk Market.答案：1、C2、C3、B4、A第二题Part Two: Listening ComprehensionSection C: Long ConversationsIn this section, you will hear one long conversation. At the end of the conversation, you will hear some questions. Both the conversation and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C), and D).1.What is the main topic of the conversation?A) The importance of cultural exchange.B) The challenges of teaching English abroad.C) The experiences of a language teacher in China.D) The impact of language barriers on communication.2.Why does the speaker mention studying Chinese?A) To show his respect for Chinese culture.B) To express h is gratitude for the Chinese students’ hospitality.C) To emphasize the importance of language learning.D) To explain his reasons for choosing to teach English in China.3.According to the speaker, what is one of the difficulties he faced in teaching English?A) The students’ lack of motivation.B) The limited resources available.C) The cultural differences between Chinese and Western students.D) The high expectations from the school administration.4.How does the speaker plan to overcome the language barrier in his future work?A) By learning more Chinese.B) By using visual aids and non-verbal communication.C) By collaborating with local language experts.D) By relying on his previous teaching experience.Answers:1.C2.C3.C4.B三、听力理解-听力篇章（选择题，共7分）第一题Passage:A new study has found that the way we speak can affect our relationships and even our physical health. Researchers at the University of California, Los Angeles, have been investigating the connection between language and well-being for several years. They have discovered that positive language can lead to better health outcomes, while negative language can have the opposite effect.The study involved 300 participants who were monitored for a period of one year. The participants were asked to keep a daily diary of their interactions with others, including both positive and negative comments. The researchers found that those who used more positive language reported fewer physical symptoms and a greater sense of well-being.Dr. Emily Thompson, the l ead researcher, explained, “We were surprised to see the impact that language can have on our health. It’s not just about what we say, but also how we say it. A gentle tone and supportive language can make a significant difference.”Here are some examples of positive and negative language:Positive Language: “I appreciate your help with the project.”Negative Language: “You always mess up the project.”The researchers also looked at the effects of language on relationships. They found that couples who used more positive language were more likely toreport a satisfying relationship, while those who used negative language were more likely to experience relationship stress.Questions:1、What is the main focus of the study conducted by the University of California, Los Angeles?A) The impact of diet on physical health.B) The connection between language and well-being.C) The effects of exercise on mental health.D) The role of social media in relationships.2、Which of the following is a positive example of language from the passage?A) “You always mess up the project.”B) “I can’t believe you did that again.”C) “I appreciate your help with the project.”D) “This is a waste of time.”3、According to the study, what is the likely outcome for couples who use negative language in their relationships?A) They will have a more satisfying relationship.B) They will experience fewer physical symptoms.C) They will report a greater sense of well-being.D) They will likely experience relationship stress.Answers:1、B2、C3、D第二题Passage OneIn the United States, there is a long-standing debate over the best way to educate children. One of the most controversial issues is the debate between traditional public schools and charter schools.Traditional public schools are operated by government and are funded by tax dollars. They are subject to strict regulations and are required to follow a standardized curriculum. Teachers in traditional public schools are typically unionized and receive benefits and pensions.On the other hand, charter schools are publicly funded but operate independently of local school districts. They are free to set their own curriculum and teaching methods. Charter schools often have a longer school day and a more rigorous academic program. They are also subject to performance-based evaluations, which can lead to their closure if they do not meet certain standards.Proponents of charter schools argue that they provide more choices for parents and that they can offer a more personalized education for students. They also claim that charter schools are more accountable because they are subject to more direct oversight and can be closed if they fail to meet their goals.Opponents of charter schools argue that they take resources away fromtraditional public schools and that they do not provide a level playing field for all students. They also claim that charter schools can be more selective in their admissions process, which may lead to a lack of diversity in the student body.Questions:1、What is a key difference between traditional public schools and charter schools?A) Funding sourceB) CurriculumC) Teacher unionsD) Academic rigor2、According to the passage, what is a potential advantage of charter schools?A) They are subject to fewer regulations.B) They offer more choices for parents.C) They are more likely to receive government funding.D) They typically have a shorter school day.3、What is a common concern expressed by opponents of charter schools?A) They are less accountable for their performance.B) They may lead to a lack of diversity in the student body.C) They are more expensive for local taxpayers.D) They do not follow a standardized curriculum.Answers:1、B) Curriculum2、B) They offer more choices for parents.3、B) They may lead to a lack of diversity in the student body.四、听力理解-新闻报道（选择题，共20分）第一题News ReportA: Good morning, everyone. Welcome to today’s news broadcast. Here is the latest news.News Anchor: This morning, the World Health Organization (WHO) announced that the number of confirmed cases of a new strain of the H1N1 flu virus has reached 10,000 worldwide. The WHO has declared the outbreak a public health emergency of international concern. Health officials are urging countries to take immediate measures to contain the spread of the virus.Q1: What is the main topic of the news report?A) The announcement of a new strain of the H1N1 flu virus.B) The declaration of a public health emergency.C) The measures taken to contain the spread of the virus.D) The number of confirmed cases of the new strain.Answer: BQ2: According to the news report, who declared the outbreak a public health emergency?A) The World Health Organization (WHO)B) The Centers for Disease Control and Prevention (CDC)C) The European Union (EU)D) The United Nations (UN)Answer: AQ3: What is the main purpose of the health officials’ urging?A) To increase awareness about the flu virus.B) To encourage people to get vaccinated.C) To take immediate measures to contain the spread of the virus.D) To provide financial assistance to affected countries.Answer: C第二题News Report 1:[Background music fades in]Narrator: “This morning’s top news includes a major announcement from the Ministry of Education regarding the upcoming changes to the College English Test Band Six (CET-6). Here’s our correspondent, Li Hua, with more details.”Li Hua: “Good morning, everyone. The Ministry of Education has just announced that starting from next year, the CET-6 will undergo significant modifications. The most notable change is the inclusion of a new speaking section, which will be mandatory for all test-takers. This decision comes in response to the increasing demand for English proficiency in various fields. Let’s goto the Education Depar tment for more information.”[Background music fades out]Questions:1、What is the main topic of this news report?A) The cancellation of the CET-6 exam.B) The addition of a new speaking section to the CET-6.C) The difficulty level of the CET-6 increasing.D) The results of the CET-6 exam.2、Why has the Ministry of Education decided to include a new speaking section in the CET-6?A) To reduce the number of test-takers.B) To make the exam more difficult.C) To meet the demand for English proficiency.D) To replace the written test with an oral test.3、What will be the impact of this change on students preparing for the CET-6?A) They will need to focus more on writing skills.B) They will have to learn a new type of test format.C) They will no longer need to take the exam.D) They will be able to choose between written and oral tests.Answers:1、B2、C3、B第三题You will hear a news report. For each question, choose the best answer from the four choices given.Listen to the news report and answer the following questions:1、A) The number of tourists visiting the city has doubled.B) The city’s tourism revenue has increased significantly.C) The new airport has attracted many international tourists.D) The city’s infrastructure is not ready for the influx of tou rists.2、A) The government plans to invest heavily in transportation.B) Local businesses are benefiting from the tourism boom.C) The city is experiencing traffic congestion and overcrowding.D) The city is working on expanding its hotel capacity.3、A) Th e city’s mayor has expressed concern about the impact on local culture.B) The tourism industry is collaborating with local communities to preserve traditions.C) There are concerns about the negative environmental effects of tourism.D) The city is implementing strict regulations to control tourist behavior.Answers:1.B) The city’s tourism revenue has increased significantly.2.C) The city is experiencing traffic congestion and overcrowding.3.B) The tourism industry is collaborating with local communities to preserve traditions.五、阅读理解-词汇理解（填空题，共5分）第一题Read the following passage and then complete the sentences by choosing the most suitable words or phrases from the list below. Each word or phrase may be used once, more than once, or not at all.Passage:In the past few decades, the internet has revolutionized the way we communicate and access information. With just a few clicks, we can now connect with people from all over the world, share our thoughts and experiences, and even conduct business transactions. This rapid advancement in technology has not only brought convenience to our lives but has also raised several challenges and concerns.1、_________ (1) the internet has made it easier for us to stay connected with friends and family, it has also led to a decrease in face-to-face interactions.2、The increasing reliance on digital devices has raised concerns about the impact on our physical and mental health.3、Despite the many benefits, there are also significant_________(2) associated with the internet, such as privacy breaches and cybersecuritythreats.4、To mitigate these risks, it is crucial for individuals and organizations to adopt robust security measures.5、In the future, we need to strike a balance between embracing technological advancements and maintaining a healthy lifestyle.List of Words and Phrases:a) convenienceb) challengesc) privacy breachesd) physicale) significantf) mentalg) privacyh) embracei) reliancej) face-to-face1、_________ (1)2、_________ (2)第二题Reading PassagesPassage OneMany people believe that a person’s personality is established at birthand remains unchanged throughout life. This view is supported by the idea that personality is determined by genetic factors. However, recent studies have shown that personality can be influenced by a variety of environmental factors as well.The word “personality” can be defined as the unique set of characteristics that distinguish one individual from another. It includes traits such as extroversion, neuroticism, and agreeableness. These traits are often measured using psychological tests.According to the passage, what is the main idea about personality?A. Personality is solely determined by genetic factors.B. Personality remains unchanged throughout life.C. Personality is influenced by both genetic and environmental factors.D. Personality is determined by a combination of psychological tests.Vocabulary Understanding1、The unique set of characteristics that distinguish one individual from another is referred to as ________.A. personalityB. genetic factorsC. environmental factorsD. psychological tests2、The view that personality is established at birth and remains unchanged throughout life is ________.A. supportedB. challengedC. irrelevantD. misunderstood3、According to the passage, traits such as extroversion, neuroticism, and agreeableness are part of ________.A. genetic factorsB. environmental factorsC. personalityD. psychological tests4、The passage suggests that personality can be influenced by ________.A. genetic factorsB. environmental factorsC. both genetic and environmental factorsD. neither genetic nor environmental factors5、The word “personality” is best defined as ________.A. the unique set of characteristics that distinguish one individual from anotherB. the genetic factors that determine personalityC. the environmental factors that influence personalityD. the psychological tests used to measure personalityAnswers:1、A2、A3、C4、C5、A六、阅读理解-长篇阅读（选择题，共10分）First QuestionPassage:In the digital age, technology has transformed almost every aspect of our lives, including education. One significant impact technology has had on learning is through online platforms that offer a wide variety of courses and educational materials to anyone with internet access. This democratization of knowledge means that individuals no longer need to rely solely on traditional educational institutions for learning. However, while online learning provides unprecedented access to information, it also poses challenges such as ensuring the quality of the content and maintaining student engagement without the structure of a classroom setting. As educators continue to adapt to these changes, it’s clear that technology will play an increasingly important role in s haping the future of education.1、According to the passage, what is one major advantage of online learning?A) It guarantees higher academic achievements.B) It makes educational resources more accessible.C) It eliminates the need for traditional learning methods entirely.D) It ensures that all students remain engaged with the material.2、What challenge does online learning present according to the text?A) It makes it difficult to assess the quality of educational content.B) It increases the reliance on traditional educational institutions.C) It decreases the amount of available educational material.D) It simplifies the process of student engagement.3、The term “democratization of knowledge” in this context refers to:A) The ability of people to vote on educational policies.B) The equal distribution of printed books among citizens.C) The process by which governments control online information.D) The widespread availability of educational resources via the internet.4、How do educators respond to the changes brought about by technology in education?A) By rejecting technological advancements in favor of conventional methods.B) By adapting their teaching practices to incorporate new technologies.C) By insisting that online learning should replace traditional classrooms.D) By ignoring the potential benefits of online learning platforms.5、Based on the passage, which statement best reflects the future outlook for education?A) Traditional educational institutions will become obsolete.B) Technology will have a diminishing role in the education sector.C) Online learning will complement but not completely replace traditional education.D) Students will no longer require any form of structured learning environment.Answers:1.B2.A3.D4.B5.CThis is a fictional example designed for illustrative purposes. In actual CET exams, the passages and questions would vary widely in topic and complexity.第二题Reading PassagesPassage OneGlobal warming is one of the most pressing environmental issues facing the world today. It refers to the long-term increase in Earth’s average surface temperature, primarily due to human activities, particularly the emission of greenhouse gases. The consequences of global warming are far-reaching, affecting ecosystems, weather patterns, sea levels, and human health.The Intergovernmental Panel on Climate Change (IPCC) has warned that if global warming continues at its current rate, we can expect more extreme weather events, such as hurricanes, droughts, and floods. Additionally, rising sealevels could displace millions of people, leading to social and economic instability.Several measures have been proposed to mitigate the effects of global warming. These include reducing greenhouse gas emissions, transitioning to renewable energy sources, and implementing sustainable agricultural practices. However, despite the urgency of the situation, progress has been slow, and many countries have failed to meet their commitments under the Paris Agreement.Questions:1、What is the primary cause of global warming according to the passage?A、Natural climate changesB、Human activitiesC、Ecosystem changesD、Increased carbon dioxide levels in the atmosphere2、Which of the following is NOT mentioned as a consequence of global warming?A、Extreme weather eventsB、Rising sea levelsC、Improved crop yieldsD、Increased global biodiversity3、What is the IPCC’s main concern regarding the current rate of global warming?A、It is causing a decrease in Earth’s average surface temperatu re.B、It is leading to more extreme weather events.C、It is causing the Earth’s magnetic field to weaken.D、It is causing the ozone layer to thin.4、What are some of the proposed measures to mitigate the effects of global warming?A、Reducing greenhouse gas emissions, transitioning to renewable energy sources, and implementing sustainable agricultural practices.B、Building more coal-fired power plants and expanding deforestation.C、Increasing the use of fossil fuels and reducing the number of trees.D、Ignoring the issue and hoping it will resolve itself.5、Why has progress in addressing global warming been slow, according to the passage?A、Because it is a complex issue that requires international cooperation.B、Because people are not concerned about the consequences of global warming.C、Because scientists do not have enough information about the issue.D、Because the Paris Agreement has not been effective.Answers:1、B2、C3、B4、A5、A七、阅读理解-仔细阅读（选择题，共20分）First QuestionPassage:In the age of rapid technological advancement, the role of universities has shifted beyond traditional academic pursuits to include fostering innovation and entrepreneurship among students. One such initiative taken by many institutions is the integration of technology incubators on campus. These incubators serve as platforms where students can turn their innovative ideas into tangible products, thereby bridging the gap between theory and practice. Moreover, universities are increasingly collaborating with industry leaders to provide practical training opportunities that prepare students for the challenges of the modern workforce. Critics argue, however, that this shift might come at the cost of undermining the foundational academic disciplines that have historically formed the core of higher education.Questions:1、What is one key purpose of integrating technology incubators in universities according to the passage?A) To reduce the cost of university education.B) To bridge the gap between theory and practice.C) To compete with other universities.D) To focus solely on theoretical knowledge.Answer: B) To bridge the gap between theory and practice.2、According to the text, how are universities preparing students for the modern workforce?A) By isolating them from industry professionals.B) By providing practical training through collaboration with industry leaders.C) By discouraging entrepreneurship.D) By focusing only on historical academic disciplines.Answer: B) By providing practical training through collaboration with industry leaders.3、What concern do critics raise about the new initiatives in universities?A) They believe it will enhance foundational academic disciplines.B) They fear it could undermine the core of higher education.C) They think it will make universities less competitive.D) They are worried about the overemphasis on practical skills.Answer: B) They fear it could undermine the core of higher education.4、Which of the following best describes the role of universities in the current era as depicted in the passage?A) Institutions that strictly adhere to traditional teaching methods.B) Centers that foster innovation and entrepreneurship among students.C) Organizations that discourage partnerships with industries.D) Places that prevent students from engaging with real-world challenges.Answer: B) Centers that foster innovation and entrepreneurship among students.5、How does the passage suggest that technology incubators benefit students?A) By ensuring they only focus on theoretical studies.B) By giving them a platform to turn ideas into products.C) By limiting their exposure to practical experiences.D) By encouraging them to avoid modern workforce challenges.Answer: B) By giving them a platform to turn ideas into products.This set of questions aims to test comprehension skills including inference, detail recognition, and understanding the main idea of the given passage. Remember, this is a mock example and should be used for illustrative purposes only.Second QuestionReading Passage:The Future of Renewable Energy SourcesIn recent years, there has been a growing interest in renewable energy sources due to their potential to reduce dependency on fossil fuels and mitigate the effects of climate change. Solar power, wind energy, and hydropower have all seen significant advancements in technology and cost-efficiency. However, challenges remain in terms of storage and distribution of these energy sources. For solar energy to become a viable primary energy source worldwide, it must overcome the limitations posed by weather conditions and geographical location. Wind energy faces similar challenges, particularly in areas with low wind speeds. Hydropower, while more consistent than both solar and wind energies, is limited。

大学英语17音体美本科阅读理解SectionCpassageone试题及参考答案17级音体美本科阅读理解Section C Passage One试题17级音体美阅读理解Section C Passage One试题第一套Section CDirections: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D . You should decide on the best choice and mark the corresponding letter on Answer Sheet 2 with a single line through the centre.Passage One.There is no denying that students should learn something about how computers work，just as we expect them at least to understand that the internal-combustion engine(内燃机)has something to do with burning fuel，expanding gases and pistons (活塞)being driven. For people should have some basic idea of how the things that they use do what they do. Further，students might be helped by a course that considers the computer‘s impact on society. But that is not what is meant by computer literacy. For computer literacy is not a form of literacy (读写能力);it is a trade skill that should not be taught as a liberal art.Learning how to use a computer and learning how to program one are two distinct activities. A case might be made that the competent citizens of tomorrow should free themselves from their fear of computers. But this is quite different from saying that all ought to know how to program one. Leave that to people who have chosen programming as a career. While programming can be lots of fun，and while our society needs some people who are experts at it，the same is true of autorepair and violin-making.Learning how to use a computer is not that difficult，and it gets easier all the time as programs become mor e “user-friendly”。

论证举例英语作文模板及范文英文回答：Assertion: Argumentation by example is a type of inductive reasoning in which a generalization is made based on specific instances.Evidence:The statement "All birds fly" is an example of argumentation by example. This generalization is based on the observation of many specific instances of birds flying.Another example is the statement "All dogs bark." This generalization is based on the observation of many specific instances of dogs barking.Explanation:Argumentation by example is a valid form ofreasoning when the instances used to support the generalization are representative of the population as a whole.However, argumentation by example can be flawed if the instances used to support the generalization are not representative.中文回答：论证举例模板。

论证举例是一种归纳推理，根据具体事例得出概括性结论。

论证举例英语作文模板英文回答：Introduction。

Argumentation is a crucial aspect of academic writing and everyday communication. It involves presenting a logical and persuasive case to support a particular point of view. To effectively construct an argument, it is essential to provide evidence and examples that reinforce the claims being made. This essay provides a comprehensive template for writing an exemplary argumentative essay, incorporating examples and evidence to bolster the argument's credibility.Step 1: Formulate a Clear Thesis Statement。

The thesis statement is the cornerstone of any argumentative essay. It should concisely state the central argument or claim that the essay will endeavor to support.A strong thesis statement is specific, arguable, and focused. For example: "Technology has had a transformative impact on modern society, both positively and negatively."Step 2: Gather Credible Evidence。

a r X i v :a s t r o -p h /0403324v 3 13 A p r 20042Varun Sahni1Dark MatterObservations of the cosmic microwave background(CMB)and the deuterium abundance in the Universe suggest thatΩbaryon h2≃0.02,orΩbaryon≃0.04 if the current Hubble expansion rate is h=H0/100km/sec/Mpc=0.7.Al-thoughΩbaryon is much larger than the observed mass in stars,Ωstars≃0.005 1,it is nevertheless very much smaller than the total energy density in the universe inferred from the observed anisotropy in the cosmic microwave back-ground[193]Ωtotal≡8πGρtotal=0,(4)2where U≃−GM2/R is the potential energy of a cluster of radius R,K≃3M v2r /2is the kinetic energy and v2r 1/2is the dispersion in the line-of-sight velocity of cluster galaxies.(Clusters in the Abell catalogue typically have R≃1.5h−1Mpc.)This relation allows us to infer the mean gravitationalDark Matter and Dark Energy3 potential energy if the kinetic energy is accurately known.The mass-to-light ratio in clusters can be as large as M/L≃300M⊙/L⊙.However since most of the mass in clusters is in the form of hot,x-ray emitting intracluster gas, the extent of dark matter in these objects is estimated to be M/M lum≃20, where M lum is the total mass in luminous matter including stars and gas.Fig.1.The observed rotation curve of the dwarf spiral galaxy M33extends consid-erably beyond its optical image(shown superimposed);from Roy[164].In individual galaxies the presence of dark matter has been convincingly established through the use of Kepler’s third lawv(r)= r(5)to determine the‘rotation curve’v(r)at a given radial distance from the galactic center.Observations of galaxies taken at distances large enough for there to be no luminous galactic component indicate that,instead of declining at the expected rate v∝r−1/2true if M≃constant,the velocity curves flattened out to v≃constant implying M(r)∝r(seefig1).This observation suggests that the mass of galaxies continues to grow even when there is no luminous component to account for this increase.Velocity curves have been compiled for over1000spiral galaxies usually by measuring the21cm emission line from neutral hydrogen(HI)[148,191].The results indicate that M/L= (10−20)M⊙/L⊙in spiral galaxies and in ellipticals,while this ratio can increase to M/L≃(200−600)M⊙/L⊙in low surface brightness galaxies4Varun Sahni(LSB’s)and in dwarfs.For instance,a recent measurement of the Draco dwarf spheroidal galaxy located at a distance of only79kpc from the Milky Way shows the presence of a considerable amount of dark matter M/L|Draco=440±240M⊙/L⊙[97]!It is interesting that the total mass of an individual galaxy is still somewhat of an unknown quantity since a turn around to thev∝r−1/2law at large radii has not been convincingly observed.An important difference between the distribution of dark matter in galax-ies and clusters needs to be emphasised:whereas dark matter appears toincrease with distance in galaxies,in clusters exactly the reverse is true,the dark matter distribution actually decreases with distance.Indeed,for certain dwarfs(such as DD0154)the rotation curve has been measured to almost15optical length scales indicating that the dark matter surrounding this object is extremely spread out(see alsofigure1).A foreground cluster,on the otherhand,acts as a gravitational lens which focuses the light from background ob-jects such as galaxies and QSO’s thereby allowing us to determine the depth of the cluster potential well.Observations of strong lensing by clusters indicatethat dark matter is strongly concentrated in central regions with a projected mass of1013−1014M⊙being contained within0.2-0.3Mpc of the central region.As we shall see later,this observation may prove to be problematic foralternatives to the dark matter hypothesis such as the Modified Newtonian Dynamics(MOND)approach of Milgrom[122].As discussed earlier,the fact that only4%of the cosmic density is bary-onic suggests that the dark matter which we are observing could well be non-baryonic in origin.The need for non-baryonic forms of dark matter gets indi-rect support from the fact that baryonic modelsfind it difficult to grow struc-ture from small initial conditions and hence to reconcile the existence of a well developed cosmic web offilaments,sheets and clusters at the present epoch with the exceedingly small amplitude of density perturbations(δρ/ρ∼10−5 at z≃1,100)inferred from COBE measurements and more recent CMB ex-periments.Indeed,it is well known that,if the effects of pressure are ignored, linearized density perturbations in a spatiallyflat matter dominated universe grow at the rateδ∝t2/3∝(1+z)−1,where1+z=a0/a(t)is the cosmolog-ical redshift.(Contrast this relatively slow growth rate with the exponential√‘Jeans instability’of a static matter distributionδ∝expDark Matter and Dark Energy5 a universe with a substantial non-baryonic component can give rise to the structure which we see today from smaller initialfluctuations.The growth of structure via gravitational instability depends both uponthe nature of primordial perturbations(adiabatic/isocurvature)and upon whether the dark matter species is hot or cold.The issue of density per-turbations has been discussed in considerable detail by Ruth Durrer at this school and I shall not touch upon this important topic any further.Let me instead say a few words about hot and cold dark matter.Non-baryonic HotDark Matter(HDM)particles are assumed to have decoupled from the rest of matter/radiation when they were relativistic and so have a very large veloc-ity dispersion(hence called‘hot’).Cold Dark Matter(CDM)particles,on theother hand,have a very small velocity dispersion and decouple from the rest of matter/radiation when they are non-relativistic.The free-streaming(collision-less phase mixing)of non-baryonic particles as they travel from high density to low density regions(and vice versa)introduces an important length scale called the‘free-streaming distance’λfs–which is the mean distance travelledby a relativistic particle species until its momentum becomes non-relativistic. In both HDM and CDM the processedfinal spectrum of density perturbations differs from its initial form.In the case of HDM this difference arises becausefluctuations on scales smaller thanλfs are wiped out due to free streaming with the result that the processedfinal spectrum has a well defined cutoffonscales smaller thanλ∼λfs.Perhaps the best example of HDM is provided by a light neutrino of mass about30eV.In this caseλfs≃41(30eV/mν) Mpc with the result that large proto-pancakes having masses comparable tothose of rich clusters of galaxies M∼1015M⊙are thefirst objects to form in HDM.Smaller objects(galaxies)are formed by the fragmentation of the proto-pancake.This top-down scenario for structure formation was originallysuggested by Zeldovich and coworkers in connection with adiabatic baryonic models and subsequently applied to HDM.It has since fallen out of favour mainly due to the strong observational constraints on the mass of the neu-trino νi mνi<0.7eV and on the relic neutrino density10−3<∼Ωνh2<∼10−1 [61,193,63,123].It also faces considerable difficulty in forming structure suf-ficiently early to explain the existence of galaxies and QSO’s at high redshifts.In contrast to HDM,constituents of CDM have a much smaller free-streaming distance.Because of this small scales are thefirst to go non-linear and gravitational clustering proceeds in a bottom up fashion in this scenario.A key quantity defining gravitational clustering is the power spectrum of den-sity perturbations P(k)≡|δk|2,which is related to the mean square density fluctuation via δρ6Varun Sahniequality and other cosmological quantities.The final and initial spectra are related through a transfer functionP f (k )=P i (k )×T 2(k ).(7)CDM-typespectrahavethefollowing approximateformof thetransferfunc-tion[165,194,166]T (k )= 1+Ak 2ρ 2k ∼k 3P f (k )∝log 2k ,(9)which illustrates the fact that,although the smallest scales are the first to go non-linear,there is significant power to drive gravitational instability rapidly to larger scales in this model.Indeed,detailed N-body simulations of large scale structure show that filaments defining the cosmic web first form on the smallest scales.The scale-length characterizing the cosmic web grows as theDark Matter and Dark Energy7Fig.2.The power spectrum inferred from observations of large scale structure, the Lymanαforest,gravitational lensing and the CMB.The solid line shows thepower spectrum prediction for aflat scale-invariant LCDM model withΩm=0.28,Ωb/Ωm=0.16,h=0.72;from Tegmark et al.[200].universe expands,until at the present epoch the cosmic web consists of afully developed supercluster-void network with a scale-length of several tens of Megaparsec[181,183,119,206].Promising candidates for cold dark matter include a100−1000GeV parti-cle called a neutralino.The neutralino is a weakly interacting massive particle (WIMP).As its name suggests it is neutral and is a fermionic partner tothe gauge and Higgs bosons(usually called the‘bino,wino and higgsino’).It is believed that the lightest supersymmetric particle will be stable due to R-parity which makes the neutralino an excellent candidate for cold dark matter(see[163,89]for reviews of particle dark matter).A radically different particle candidate for cold dark matter is an ultra-light pseudo-Goldstone boson calledan axion with a mass of only m a∼10−5±1eV.Although ultralight,the axion is‘cold’because it was created as a zero-momentum condensate.Its existence is a by-product of an attempt to resolve QCD of what is commonly called the‘strong CP problem’which arises because non-perturbative effects in QCD8Varun Sahnigive rise to an electric dipole moment for the neutron–in marked contrastwith observations[101].Other candidates for non-baryonic cold dark matterinclude string theory motivated moduliifields[32];non-thermally produced super-heavy particles having a mass∼1014GeV and dubbed Wimpzillas[100];as well as axino’s and gravitino’s–superpartners of the axion and graviton respectively[163].Since WIMP’s cluster gravitationally,one should expect tofind aflux ofthese particles in our own solar system and attempts are being made to deter-mine dark matter particles by measuring the scattering of WIMP’s on targetnucleii through nuclear recoils.Now the earth orbits the sun with a velocity≃30km/sec,even as the sun orbits the galaxy with v M⊙≃220km/sec. Furthermore the plane of the Earth’s orbit is inclined at an angle of60◦tothe glactic plane,because of which the dark matterflux on Earth is expected to be larger in June(when the Earth’s velocity and the Sun’s velocity add together)than in December(when these two velocities subtract).The result-ing rate variation is about7%between theflux measured during summer and winter.Precisely such a signal was reported by the DAMA experiment whose data(collected since1996)appears to show a yearly modulation with greater events reported in June than in December[17].However results obtained by the DAMA group remain controversial since they have not been substanti-ated by other groups which report negative results for similar searches(see [129,95]for recent reviews on this subject).Fig.3.The and Munoz(2001).Despite the excellent agreement of LCDM with large scale observations, some concerns have recently been expressed about the ability of this model toDark Matter and Dark Energy9 account for a number of smaller scale observations which can be summarized as follows:•The substructure problem is used to describe the fact that the cold dark matter model(with or without a cosmological constant)predicts an ex-cessive number of dark matter subhaloes(or substructure)within a larger halo.If one(perhaps naively)associates each halo with a gravitation-ally bound baryonic object then the predicted number of dwarf-galaxy satellites within the local group exceeds the observed number by over an order of magnitude.Indeed,detailed N-body simulations as well as theoretical estimates predict around1000dark matter satellites in our local group which is much larger than the40or so observed at present [98,126,94,35,192,24,120,199,64].•The cuspy core problemCDM predicts a universal density profile for dark matter halos in the wide range107M⊙−1015M⊙which applies both to galaxy clusters as well as individual galaxies including dwarfs and LSB’s.2The density profile originally suggested by Navarro,Frenk and White[133]isρ(r)=ρ0(r s/r) 1+ r2Low Surface Brightness Galaxies(LSB’s)are dominated by their dark matter content and therefore provide particularly good astrophysical objects with which to test dark matter models.10Varun Sahnimatter halos of their baryonic content resulting in a large number of‘failed galaxies’and providing a possible resolution to the‘satellite catastrophe’. (The failed galaxies will act as gravitational lenses and should therefore be detectable through careful observations.)Other explanations include the ef-fects of tidal stripping recently discussed in[103].Likewise issues involving beam smearing,the influence of bars and the interaction of baryons and dark matter in the central regions of galaxies and clusters could be intricately linked with the central cusp issue and must be better understood if one wishes to seriously test the CDM hypothesis on small scales.In concluding this discussion on dark matter I would like to briefly mention Modified Newtonian Dynamics(MOND)which,in some circles,is regarded as an alternative to the dark matter hypothesis.As the name suggests,MOND is a modification of Newtonian physics which proposes to explain theflat rota-tion curves of galaxies without invoking any assumptions about dark matter. Briefly,MOND assumes that Newtons law of inertia(F=ma)is modified at sufficiently low accelerations(a<a0)toF=m aµ(a/a0),(11) whereµ(x)=x when x≪1andµ(x)=1when x≫1[122,180].It is easy to see that this results in the modification of the conventional formula for gravi-tational acceleration F=m g N,resulting in the following relation between the true acceleration and the Newtonian value:a=√To summarise,current observations make a strong case for clustered,non-baryonic dark matter to account for as much as a third of the total matterdensity in the UniverseΩm≃1/3.The remaining two-thirds is thought to reside in a relative smooth component having large negative pressure andcalled Dark Energy.2Dark Energy2.1The cosmological constant and Vacuum energyType Ia supernovae,when treated as standardized candles,suggest that theexpansion of the universe is speeding up rather than slowing down.The case for an accelerating universe also receives independent support from CMB and large scale structure studies.All three data sets can be simultaneously satified if one postulates that the dominant component of the universe is relatively smooth,has a large negative pressure andΩDE≃2/3.The simplest example of dark energy is a cosmological constant,intro-duced by Einstein in1917.The Einstein equations,in the presence of the cosmological constant,aquire the formR ik−1c4T ik+Λg ik.(13)Although Einstein originally introduced the cosmological constant(Λ)into the left hand side of hisfield equations,it has now become conventional to move theΛ-term to the RHS,treating it as an effective form of matter.In a homogeneous and isotropic Friedmann-Robertson-Walker(FRW)universe consisting of pressureless dust(dark matter)andΛ,the Raychaudhury equa-tion,which follows from(13),takes the form¨a=−4πG3.(14)Equation(14)can be rewritten in the form of a force law:F=−GM3R,(R≡a)(15) which demonstrates that the cosmological constant gives rise to a repulsive force whose value increases with distance.The repulsive nature ofΛcould be responsible for the acceleration of the universe as demonstrated in(14).Although introduced into physics in1917,the physical basis for a cosmo-logical constant remained a bit of a mystery until the1960’s,when it was realised that zero-point vacuumfluctuations must respect Lorenz invariance and therefore have the form T ik =Λg ik[214].As it turns out,the vacuum expectation value of the energy momentum is divergent both for bosonic andfermionicfields,and this gives rise to what is known as‘the cosmological constant problem’.Indeed the effective cosmological constant generated by vacuumfluctuations isΛk2+m2k2dk,(16)since the integral diverges as k4one gets an infinite value for the vacuum energy.Even if one chooses to‘regularize’ T ik by imposing an ultraviolet cutoffat the Planck scale,one is still left with an enormously large value for the vacuum energy T00 vac≃c5/G2 ∼∼1076GeV4which is123orders of magnitude larger than the currently observedρΛ≃10−47GeV4.A smaller ultraviolet cut-offdoes not fare much better since a cutoffat the QCD scale results inΛ4QCD∼10−3GeV4,which is still forty orders of magnitude larger than observed.In the1970’s the discovery of supersymmetry led to the hope that,since bosons and fermions(of identical mass)contribute equally but with opposite sign to the vacuum expectation value of physical quantities,the cosmological constant problem may be resolved by a judicious balance between bosons and fermions in nature.However supersymmetry(if it exists)is broken at the low temperatures prevailing in the universe today and on this account one should expect the cosmological constant to vanish in the early universe, but to reappear during late times when the temperature has dropped below T SUSY.This is clearly an undesirable scenario and almost the very opposite of what one is looking for,since,a large value ofΛat an early time is useful from the viewpoint of inflation,whereas a very small current value ofΛis in agreement with observations[172,171].In the absence of a resolution to the cosmological constant problem the following possibility connecting the vacuum energy with the SUSY and Planck scales may be worth exploring[172,171].The mass scale associated with the scale of supersymmetry breaking in some models,M SUSY∼1TeV,lies midway between the Planck scale and10−3eV.One could conjecture that the small observed value of the cosmological constantρΛ≃(10−3eV)4is associated with the vacuum in a theory which had a fundamental mass scale M X≃M2SUSY/M Pl,such thatρvac∼M4X∼(10−3eV)4.The cosmological constant is also relevant from the perspective of mod-els with spontaneous symmetry breaking[209].Indeed,if one examines the LagrangianL=12µ2φ2+1µ2/λ,therebybreaking the reflection symmetryφ↔−φpresent in the Lagrangian.ForV0=0this potential gives rise to a large negative cosmological constant Λeff=V(φ=σ)=−µ4/4λin the broken symmetry state.This embarassing situation can be avoided only if one chooses a value for V0which almostexactly cancelsΛeff,namely V0≃+µ4/4λso thatΛeff/8πG=V0−µ4/4λ≃10−47GeV4.The cosmological consequences of this rather ad-hoc‘regularization’ex-ercise are instructive.Unless the value ofΛeff lies in a very small window, the universe will be a very different place from the one we are used to.For instance a negative value of theΛ-termΛeff/8πG<−10−43GeV4will cause the universe to recollapse(the effect ofΛis attractive now instead of being repulsive)less than a billion years after the big bang–a period which is much too short for galaxies to form and for life(as we know it)to emerge.On the other hand a large positiveΛeff/8πG>10−43GeV4makes the universe accel-erate much before the present epoch,thereby inhibiting structure formation and precluding the emergence of life.The very small window inΛwhich allows life to emerge has led somecosmologists to propose anthropic arguments for the existence of a small cos-mological constant[20,118,76,210].One such possibility is the following“if our big bang is just one of many big bangs,with a wide range of vacuum en-ergies,then it is natural that some of these big bangs should have a vacuum energy in the narrow range where galaxies can form,and of course it is just these big bangs in which there could be astronomers and physicists wondering about the vacuum energy”[210].I will not discuss the anthropic argument any further in these lectures butwill point the interested reader to[118,76,210]for further discussion of this issue.It is important to note that there is no known fundamental symmetry innature which will set the value ofΛto zero.In its absence,the small observed value of the dark energy remains somewhat of a dilemma which remains to be fully understood and resolved.32.2Dynamical models of Dark EnergyThe cosmological constant is but one example of a form of matter(dark en-ergy)which could drive an accelerated phase in the history of our universe. Indeed,(14)is easily generalised to¨a3 i(ρi+3p i)=−4πG3The important role played by symmetries is illustrated by the U(1)gauge symme-try of electrodynamics whose presence implies a zero rest mass for the photon.No analogous symmetry exists for the neutrino and recent experiments do indicate that neutrino’s could have a small mass.Fig.4.Spontaneous symetry breaking in manyfield theory models takes the form of the Mexican top hat potential shown above.The dashed line shows the potential before the cosmological constant has been‘renormalized’and the solid line after. (From Sahni and Starobinsky2000.)H2≡ ˙a3 iρi−k= i(4πGρi2,(20) aH2whereΩi=8πGρi/3H2and we have assumed aflat universe withΩm+ΩX= 1(ΩX≡ΩDE).The condition for accelerated expansion(q<0)is equivalenttow X <−13for Ωm =0,(22)w <−12 3ct 2/3,(25)which smoothly interpolates between a matter dominated universe in the past (a ∝t 2/3)and accelerated expansion in the future (a ∝exp 3t ).We are now in a position to appreciate the evidence for an accelerating universe which originates in observations of the light flux from high redshift type Ia supernovae.Type Ia supernovae are extremely bright objects,(M B ≃−19.5)which makes them ideally suited for studying the properties of the universe at large distances.The light flux received from a distant supernova is related to its absolute luminosity L and its ‘luminosity distance’d L through the relationF =Lx 2+y 2+z 2.In general relativity,on the other hand,the geometry of space can be non-Euclidean,and the luminosity distance to an object located at redshift z will,in general,depend both upon the geometry of space as well as the expansion history of the universe.Indeed,it can be shown that in a spatially flat and expanding FRW universe,the luminosity distance has theformd L(z)=(1+z) z0dz′Λus to‘standardize’supernova light curves thereby reducing the scatter in their luminosities to∼12%which turns type Ia supernovae into very good standard candles.•Type Ia supernovae at higher redshifts are consistently dimmer than their counterparts at lower redshifts relative to what might be expected in SCDM cosmology.If type Ia supernovae are treated as standard candles then,assuming systematic effects such as cosmological evolution and dim-ming by intergalactic dust are either not vitally important or have been corrected for,the systematic dimming of high−z Sn can be interpreted as evidence for an accelerated expansion of the universe caused by a form of ‘dark energy’having large negative pressure.The evidence for an accelerating universe from high redshift type Ia super-novae has now received independent support from an analysis of CMBfluc-tuations together with the HST key project determination of the Hubble pa-rameter.Interestingly,the degeneracy in parameter space{Ωm,ΩΛ}arising from Sn observations is almost orthogonal to the degeneracy which arises from CMB measurements.This principle of‘cosmic complementarity’serves to sig-nificantly reduce the errors onΩm&ΩΛwhen the two sets of observations are combined,as shown infigure6.Fig.6.Constraints on the density of dark matterΩm and dark energy in the form of a cosmological constantΩΛ,determined using WMAP(upper left),WMAP+other CMB experiments(WMAPext;upper right),WMAPext+HST key project data (lower left)and WMAPext+HST+supernova data(lower right);from Spergel et al(2003).If dark energy is described by an unevolving equation of state w=p X/ρX, then the transition between deceleration and acceleration(¨a=0)occurs at the redshiftΩX(1+z a)−3w=−(1+3w)ΩX .(29) SubstitutingΩΛ=0.7,Ωm=0.3wefind z a≃0.73,z eq≃0.37for LCDM. The fact that the acceleration of the universe is a fairly recent phenomenon illustrates the‘cosmic coincidence’puzzle according to which we appear to live during a special epoch when the densities in dark energy and in dark matter are almost equal.A recent origin for the acceleration epoch is supported by supernova observations which suggest a decelerating universe at z>∼0.5[160]. It is important to note that dark enegy models with an unevolving equation of state need to have their initial conditions properly‘tuned’in order to dominate the universe at precisely the present epoch.This problem is most acute for the cosmological constant.Since the cosmological constant does not evolve while both matter and radiation evolve rapidly(ρm∝a−3,ρr∝a−4),it follows that the small current valueρΛ=Λ/8πG≃10−47GeV4impliesρΛ/ρr≃10−123 at the Planck time(when the temperature of the universe was T∼1019GeV), orρΛ/ρr≃10−55at the time of the electroweak phase transition(T∼100 GeV).Thus an extremefine-tuning of initial conditions is required in order to ensure thatρΛ/ρm∼1today!Thefine tuning problem which plaguesΛalso affects DE models in which w=constant=−1.A combined analaysis of CMB,galaxy clustering and supernovae data indicates that a constant equation of state for dark energy must satisfy w<−0.82at the95%confidence level[193,201],and it is easy to show that for these models thefine tuning(and cosmic coincidence) problems are almost as acute as they are for the cosmological constant.This constraint on w also virtually rules out two interesting DE candidates based on topological defect models:a tangled network of cosmic strings w≃−1/3 and domain walls w≃−2/3.2.3QuintessenceIt is interesting that thefine tuning problem facing dark energy models with a constant equation of state can be alleviated if we assume that the equation of state is time dependent.An important class of models having this property are scalarfields(quintessence)4which couple minimally to gravity so thattheir Lagrangian density and energy momentum tensor isL=12˙φ2+V(φ),p≡−Tαα=1to allow the universe to accelerate.Note that for quintessencefields the con-dition’s(22)&(23)translate intowφ<−12⇒˙φ2<28πλφ/M p)[157,213],where M p=1/√ρB+ρφ=3(1+w B)w(Cφ+D),(35) with suitably chosen values of C,D.Quintessence models can be divided into two categories:models which roll to large values ofφ/m P>∼1and models for whichφ/m P≪1at the present epoch.An important concern for the former is the effect of quantum corrections which,if large,could alter the shape of the quintessence potential [102,33,59,182].An important related issue is that the coupling between standard modelfields and quintessence must be small in order to have evaded detection.Moreover even small couplings between quintessence and standard modelfields can give rise to interesting changes in cosmology as shown in [6,114].V0exp(−λφ)Ratra&Peebles(1988),Wetterich(1988),Ferreira&Joyce(1998)m2φ2,λφ4Frieman et al(1995)V0/φα,α>0Ratra&Peebles(1988)V0exp(λφ2)/φαBrax&Martin(1999,2000)V0(coshλφ−1)p Sahni&Wang(2000)V0sinh−α(λφ)Sahni&Starobinsky(2000),Ure˜n a-L´o pez&Matos(2000) V0(eακφ+eβκφ)Barreiro,Copeland&Nunes(2000)V0(exp M p/φ−1)Zlatev,Wang&Steinhardt(1999)V0[(φ−B)α+A]e−λφAlbrecht&Skordis(2000)。

英语六级高分必备500关键句第222期:阅读理解(119)第222句：As an example of what's going on, consider U.S. Bancorp,which was recent sued for deceptive practices by the state of Minne80ta.作为现在正在发生的事情的例子，考虑一下最近被明尼苏达州以欺诈行为起诉的美国合众银行。

六级词汇讲解:本句中，as引导伴随状语；which引导定语从句，修饰U.S. Bancorp。

U.S. Bancorp即“美国合众银行”，其中Bancorp为bank 和corporation的合成。

sue意为“起诉；控告”，常用于sue sb. for sth.这一搭配。

如：I'll sue you for libel.我要以诽谤罪控告你。

六级考点归纳：deceptive是由动词deceit引申而来的形容词。

由deceit引申而来的词主要有：deceptive意为“迷惑的；虚伪的；诈欺的”。

如：Deceptive advertising have damaged the company's image among the consumers.虚假广告已损害了该公司在消费者心目中的形象。

deceptiveness意为“欺骗的性质或状态”。

如：Precisely because he can still deceive a number of people and hasa certain deceptiveness，he was still kept in the gang group.就是因为他还能欺骗一部分人，还有一点欺骗人的价值，所以他现在还是那一流氓团伙的成员。

deception意为“骗局，诡计”。

如：His pretended friendship was part of the deception.他伪装出来的友谊是骗局的一部分。

GRE写作是非题分析论证句式总结2016GRE写作是非题分析论证句式总结美丽是属于自信者的，从容是属于有备者的，奇迹是执着者造成的，成功是顽强者铸成的`!以下是小编带来的2016GRE写作是非题分析论证句式总结，希望对你有帮助。

1. Whereas other societies look to the past for guidance，we cast our nets forward(面向未来)2. It is the belief in a brighter future that gives us optimism.3. Even these days， when not all progress seems positive ，the belief remains that for every problem there is a rational solution.4. The job of the parents is to give the children every opportunity while they are growing up and then get out of their way.5. What deference people in authority do command is based on their actual powers rather than on their age， wisdom， or dignity.6. In a society that changes as fast as ours，experience simply does not have the value that it does in traditional societies.7. It has taken a long time to convince the public that free enterprise does not mean that a company should be free to pollute the air， foul the rivers， and destroy the forests.8. The assembly line reduced workers to cogs of machinery and made their jobs unutterably boring， but it produced goods fast.9. Food is prepackaged and shopping is impersonal，but the efficiency of the operation produces lower prices and less shopping time.11. In America，there are no such expressions such as inchina where “the fat pig gets slaughtered，” or in Japan，where “the nail that sticks out gets hammered down.”12. This freedom from the group has enabled the American to become “Economic Man”—one directed almost purely by profit motive， mobile and unencumbered(不受阻碍的)by family or community obligations.13. Equipped with the money， one can acquire the taste，style， and ideas that mark each class and launch a quick ascent of the social ladder.14. Actually， persons in status societies who are secure in their niches (适当的位置)are allowed more eccentricity than Americans， who rely heavily on signals that other people like them.15. When half the population goes to college， one cannot expect the colleges to maintain the same standards as in countries where only the elite attend.16. Just as not every Japanese is hardworking and deferential to superiors (长者、上司)， not every Chinese is devoted to family，not every American is ambitious or patriotic –or even unsophisticated.17. No one could seriously think that anyone who grows up poor，lives in a bad neighborhood，and attends an inferior school has an opportunity equal to that of someone more favored.18. Americans may not have achieved equality， but at least they aspire to it， which is more than many other nations can claim.19. In many countries，when jobs become available for young people in distant cities，when television begins to dominate home life， when ready – made foods appear in themarkets，the culture appears more “American” – although the resemblance could be entirely superficial.20. When the demand for something is greater than its supply，producers and suppliers will sense the possibility of making a profit –the excess of revenues over expenses is the profit.21. As the case illustrates， competition takes four general forms：pure competition，monopoly，monopolistic competition， and oligopoly(少数制造商对市场的控制).22. The classic example of pure competition occurs with a commodity， like wheat or corn， that has so many producers that no one of them can control its selling price.23. A monopoly occurs when one company alone offers a particular food or service and therefore controls the market and price for it.24. Private restaurants serve gourmet food for $70 per person; incentives boosted agricultural production 25 percent and industrial output 80 percent in just three years; farmers are encouraged to raise as much as they can on their own plots，and some become almost rich in the process.(注意本句中分号的使用)25. All these changes in China’s economic life have brought changes in China’s social and cultural life as well，many of which unwanted.。