Theoretical study of the permeation of water through TiO2 nanotubes
2024年6月大学英语六级考试真题和答案(第1套)
2024年6月大学英语六级考试真题和答案（第1套）Part I Writing (30 minutes)Directions: For this part, you are allowed 30 minutes to write an essay that begins with the sentence “There is a growing awareness of the importance of digital literacy and skills in today’s world.” You can make comments, cite examples or use your personal experiences to develop your essay. You should write at least 150 words but no more than 200 words. You should copy the sentence given in quotes at the beginning of your essay.Part Ⅱ Listening Comprehension (30 minutes)Section ADirections:In this section, you will hear two long conversations. At the end of each conversation, you will hear four 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). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 1 to 4 are based on the conversation you have just heard.1. A) Reply to the man’s last proposal within a short time.B) Sign the agreement if one small change is made to it.C) Make a sponsorship deal for her client at the meeting.D) Give the man some good news regarding the contract.2. A) They are becoming impatient.B) They are afraid time is running out.C) They are used to making alterations.D) They are concerned about the details.3. A) To prevent geographical discrimination.B) To tap the food and beverage market.C) To avoid any conflict of interest.D) To reduce unfair competition.4. A) It is a potential market for food and beverage.B) It is very attractive for real estate developers.C) It is a negligible market for his company.D) It is very different from other markets.Questions 5 to 8 are based on the conversation you have just heard.5. A) They are thrilled by a rare astronomic phenomenon.B) They are celebrating a big event on mountain tops.C) They are enthusiastic about big science-related stories.D) They are joined by astronomers all across North America.6. A) It will be the most formidable of its kind in over a century.B) It will come closest to Earth in more than one hundred years.C) It will eclipse many other such events in human history.D) It will be seen most clearly from Denver’s mountain tops.7. A) A blur.B) Stars.C) The edge of our galaxy.D) An ordinary flying object.8. A) Use professional equipment.B) Climb to the nearby heights.C) Fix their eyes due north.D) Make use of phone apps.Section BDirections: In this section, you will hear two passages. At the end of each passage, you will hear three or four questions. Both the passage 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). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 9 to 11 are based on the passage you have just heard.9. A) Whether consumers should be warned against ultra-processed foods.B) Whether there is sufficient scientific consensus on dietary guidelines.C) Whether guidelines can form the basis for nutrition advice to consumers.D) Whether food scientists will agree on the concept of ultra-processed foods.10. A) By the labor cost for the final products.B) By the degree of industrial processing.C) By the extent of chemical alteration.D) By the convention of classification.11. A) Increased consumers’ expenses.B) Greater risk of chronic diseases.C) People’s misunderstanding of nutrition.D) Children’s dislike for unprocessed foods.Questions 12 to 15 are based on the passage you have just heard.12. A) They begin to think of the benefits of constraints.B) They try to seek solutions from creative people.C) They try hard to maximize their mental energy.D) They begin to see the world in a different way.13. A) It is characteristic of all creative people.B) It is essential to pushing society forward.C) It is a creative person’s response to limitation.D) It is an impetus to socio-economic development.14. A) Scarcity or abundance of resources has little impact on people’s creativity.B) Innovative people are not constrained in connecting unrelated concepts.C) People have no incentive to use available resources in new ways.D) Creative people tend to consume more available resources.15. A) It is key to a company’s survival.B) It shapes and focuses problems.C) It is essential to meeting challenges.D) It thrives best when constrained.Section CDirections: In this section, you will hear three recordings of lectures or talks followed by three or four questions. The recordings will be played only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 16 to 18 are based on the recording you have just heard.16. A) Because they are learned.B) Because they come naturally.C) Because they have to be properly personalized.D) Because there can be more effective strategies.17. A) The extent of difference and of similarity between the two sides.B) The knowledge of the specific expectation the other side holds.C) The importance of one’s goals and of the relationship.D) The approaches one adopts to conflict management.18. A) The fox.B) The owl.C) The shark.D) The turtle.Questions 19 to 21 are based on the recording you have just heard.19. A) Help save species from extinction and boost human health.B) Understand how plants and animals perished over the past.C) Help gather information publicly available to researchers.D) Find out the cause of extinction of Britain’s 66,000 species.20. A) It was once dominated by dinosaurs.B) It has entered the sixth mass extinction.C) Its prospects depend on future human behaviour.D) Its climate change is aggravated by humans.21. A) It dwarfs all other efforts to conserve, protect and restorebiodiversity on earth.B) It is costly to get started and requires the joint efforts of thousands of scientists.C) It can help to bring back the large numbers of plants and animals that have gone extinct.D) It is the most exciting, most relevant, most timely and most internationally inspirational.Questions 22 to 25 are based on the recording you have just heard.22. A) Cultural identity.B) Social evolution.C) The Copernican revolution.D) Human individuality.23. A) It is a delusion to be disposed of.B) It is prevalent even among academics.C) It is a myth spread by John Donne’s poem.D) It is rooted in the mindset of the 17th century.24. A) He believes in Copernican philosophical doctrines about the universe.B) He has gained ample scientific evidence at the University of Reading.C) He has found that our inner self and material self are interconnected.D) He contends most of our body cells can only live a few days or weeks.25. A) By coming to see how disruptive such problems have got to be.B) By realising that we all can do our own bit in such endeavours.C) By becoming aware that we are part of a bigger world.D) By making joint efforts resolutely and persistently.Part III Reading Comprehension (40 minutes)Section ADirections: In this section, there is a passage with ten blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before making your choices. Each choice in the bank is identified by a letter. Please mark the corresponding letter for each item on Answer Sheet 2with a single line through the centre. You may not use any of the words in the bank more than once.It’s quite remarkable how different genres of music can spark unique feelings, emotions, and memories. Studies have shown that music can reduce stress and anxiety before surgeries and we are all attracted toward our own unique life soundtrack.If you’re looking to____26____stress, you might want to give classical music a try.The sounds of classical music produce a calming effectletting____27____pleasure-inducing dopamine (多巴胺) in the brain thathelps control attention, learning and emotional responses.It can also turn down the body’s stress response, resulting in an overall happier mood. It turns out a pleasant mood can lead to____28____in a person’s thinking.Although there are many great____29____of classical music like Bach, Beethoven and Handel, none of these artists’ music seems to have the same health effects as Mozart’s does. According to researchers, listening to Mozart can increase brain wave activity and improve____30____function. Another study found that the distinctive features of Mozart’s music trigger parts of the brain that are responsible for high-level mental functions. Even maternity____31____use Mozart to help newborn babies adapt to life outside of the mother’s belly.It has been found that listening to classical music____32____reduces a person’s blood pressure. Researchers believe that the calming sounds of classical music may help your heart____33____from stress. Classical music can also be a great tool to help people who have trouble sleeping. One study found that students who had trouble sleeping slept better while they were listening to classical music.Whether classical music is something that you listen to on a regular basis or not, it wouldn’t____34____to take time out of your day to listen to music that you find____35____. You will be surprised at how good it makes you feel and the potentially positive change in your health.A) alleviateB) clarityC) cognitiveD) composersE) hurtF) inhibitingG) interrogationH) intrinsicallyI) looseJ) majesticK) mandatoryL) recoverM) significantlyN) soothingO) wardsSection BDirections: In this section, you are going to read a passage with ten statements attached to it. Each statement contains information given in one of the paragraphs. Identify the paragraph from which the information is derived. You may choose a paragraph more than once. Each paragraph is marked with a letter. Answer the questions by marking the correspondingletter on Answer Sheet 2.The Curious Case of the Tree That Owns ItselfA) In the city of Athens, Georgia, there exists a rather curious local landmark—a large white oak that is almost universally stated to own itself. Because of this, it is considered one of the most famous trees in the world. So how did this tree come to own itself and the land around it?B) Sometime in the 19th century a Georgian called Colonel William Jackson reportedly took a liking to the said tree and endeavored to protect it from any danger. As to why he loved it so, the earliest documented account of this story is an anonymously written front page article in the Athens Weekly Banner published on August 12, 1890. It states, “Col. Jackson had watched the tree grow from his childhood, and grew to love it almost as he would a human. Its luxuriant leaves and sturdy limbs had often protected him from the heavy rains,and out of its highest branches he had many a time gotten the eggs of the feathered singers.He watched its growth, and when reaching a ripe old age he saw the tree standing in its magnificent proportions, he was pained to think that after his death it would fall into the hands of those who might destroy it.”C) Towards this end, Jackson transferred by means of a deed ownership of the tree and a little land around it to the tree itself. The deed read, “W. H. Jackson for and in consideration of the great affection which he bears the said tree, and his great desire to see it protected has conveyed unto the said oak tree entire possession of itself and of all land within eight feet of it on all sides.”D) In time, the tree came to be something of a tourist attraction, known as The Tree That Owns Itself. However, in the early 20th century, the tree started showing signs of its slow death,with little that could be done about it. Father time comes for us all eventually, even our often long lived, tall and leafy fellow custodians (看管者) of Earth. Finally, on October 9,1942, the over 30 meter tall and 200-400 year old tree fell, rumor has it, as a result of a severe windstorm and/or via having previously died and its roots rotted.E) About four years later, members of the Junior Ladies Garden Club (who’d tended to the tree before its unfortunate death) tracked down a small tree grown from a nut taken from the original tree. And so it was that on October 9, 1946, under the direction of Professor Roy Bowden of the College of Agriculture at the University of Georgia, this little tree was transplanted to the location of its ancestor. A couple of months later, an official ceremony was held featuring none other than the Mayor of Athens, Robert L McWhorter, to commemorate the occasion.F) This new tree became known as The Son of the Tree That Owns Itself and it was assumed that, as the original tree’s heir, it naturally inherited the land it stood on. Of course, there are many dozens of othertrees known to exist descending from the original, as people taking a nut from it to grow elsewhere was a certainty. Thatsaid, to date, none of the original tree’s other children have petitioned the courts for their share of the land, so it seems all good. In any event, The Son of the Tree That Owns Itself still stands today, though often referred to simply as The Tree That Owns Itself.G) This all brings us around to whether Jackson ever actually gave legal ownership of the tree to itself in the first place and whether such a deed is legally binding.H) Well, to begin with, it turns out Jackson only spent about three years of his life in Athens,starting at the age of 43 from 1829 to 1832, sort of dismissing the idea that he loved the tree from spending time under it as a child and watching it grow, and then worrying about what would happen to it after he died. Further, an extensive search of land ownership records in Athens does not seem to indicate Jackson ever owned the land the tree sits on.I) He did live on a lot of land directly next to it for those three years, but whether he owned that land or not isn’t clear. Whatever the case, in 1832 a four acre parcel, which included the land the tree was on and the neighboring land Jackson lived on, among others, was sold to University professor Malthus A Ward. In the transaction, Ward was required to pay Jackson a sum of $1,200 (about $31,000 today), either for the property itself or simply in compensation for improvements Jackson had made on the lot. In the end, whether he ever owned the neighboring lot or was simply allowed to use it while he allegedly worked at the University, he definitely never owned the lot the tree grew on, which is the most important bit for the topic at hand.J) After Professor Ward purchased the land, Jackson and his family purchased a 655 acre parcel a few miles away and moved there. Ten years later, in 1844, Jackson seemed to have come into financial difficulties and had his little plantation seized by the Clarke County Sheriff’s office and auctioned off to settle the mortgage. Thus, had he owned some land in Athens itself, including the land the tree sat on, presumably he would have sold it to raise funds or otherwise had it taken as well.K) And whatever the case there, Jackson would have known property taxes needed to be paid on the deeded land for the tree to be truly secure in its future. Yet no account or record indicates any trust or the like was set up to facilitate this.L) On top of all this, there is no hard evidence such a deed ever existed, despite the fact that deed records in Athens go back many decades before Jackson’s death in 1876 and that it was supposed to have existed in 1890 in the archives according to the original anonymous news reporter who claims to have seen it.M) As you might imagine from all of this, few give credit to this sideof the story. So how did all of this come about then?N) It is speculated to have been invented by the imagination of the said anonymous author at the Athens Weekly Banner in the aforementioned 1890 front page article titled “Deeded to Itself”, which by the way contained several elements that are much more easily proved to be false. As to why the author would do this, it’s speculated perhaps it was a 19th century version of a click-bait thought exercise on whether it would be legal for someone to deed such a non-conscious living thing to itself or not.O) Whatever the case, the next known instance of the Tree That Owns Itself being mentioned wasn’t until 1901 in the Centennial Edition of that same paper, the Athens Weekly Banner. This featured another account very clearly just copying the original article published about a decade before, only slightly reworded. The next account was in 1906, again in the Athens Weekly Banner, again very clearly copying the original account, only slightly reworded, the 19th century equivalent of re-posts when the audience has forgotten about the original.36. Jackson was said to have transferred his ownership of the oak tree to itself in order to protect it from being destroyed.37. No proof has been found from an extensive search that Jackson had ever owned the land where the oak tree grew.38. When it was raining heavily, Jackson often took shelter under a big tree that is said to own itself.39. There is no evidence that Jackson had made arrangements to pay property taxes for the land on which the oak tree sat.40. Professor Ward paid Jackson over one thousand dollars when purchasinga piece of land from him.41. It is said the tree that owned itself fell in a heavy windstorm.42. The story of the oak tree is suspected to have been invented as a thought exercise.43. Jackson’s little plantation was auctioned off to settle his debt in the mid-19th century.44. An official ceremony was held to celebrate the transplanting of a small tree to where its ancestor had stood.45. The story of the Tree That Owns Itself appeared in the local paper several times, with slight alterations in wording.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 OneQuestions 46 to 50 are based on the following passage.It is irrefutable that employees know the difference between right and wrong. So why don’t more employees intervene when they see someone exhibiting at-risk behavior in the workplace?There are a number of factors that influence whether people intervene. First, they need to be able to see a risky situation beginning to unfold. Second, the company’s culture needs to make them feel safe to speak up. And third, they need to have the communication skills to say something effectively.This is not strictly a workplace problem; it’s a growing problem off the job too. Every day people witness things on the street and choose to stand idly by. This is known as the bystander effect—the more people who witness an event, the less likely anyone in that group is to help the victim. The psychology behind this is called diffusion of responsibility. Basically, the larger the crowd, the more people assume that someone else will take care of it—meaning no one effectively intervenes or acts in a moment of need.This crowd mentality is strong enough for people to evade their known responsibilities. But it’s not only frontline workers who don’t make safety interventions in the workplace. There are also instances where supervisors do not intervene either.When a group of employees sees unsafe behavior not being addressed at a leadership level it creates the precedent that this is how these situations should be addressed, thus defining the safety culture for everyone.Despite the fact that workers are encouraged to intervene when they observe unsafe operations, this happens less than half of the time. Fear is the ultimate factor in not intervening. There is a fear of penalty, a fear that they’ll have to do more work if they intervene. Unsuccessful attempts in the past are another strong contributing factor to why people don’t intervene—they tend to prefer to defer that action to someone else for all future situations.On many worksites, competent workers must be appointed. Part of their job is to intervene when workers perform a task without the proper equipment or if the conditions are unsafe. Competent workers are also required to stop work from continuing when there’s a danger.Supervisors also play a critical role. Even if a competent person isn’t required, supervisors need a broad set of skills to not only identify and alleviate workplace hazards but also build a safety climate within their team that supports intervening and open communication among them.Beyond competent workers and supervisors, it’s important to educate everyone within the organization that they are obliged to intervene ifthey witness a possible unsafe act, whether you’re a designated competent person, a supervisor or a frontline worker.46. What is one of the factors contributing to failure of intervention in face of risky behavior in the workplace?A) Slack supervision style.B) Unfavorable workplace culture.C) Unforeseeable risk.D) Blocked communication.47. What does the author mean by “diffusion of responsibility” (Line 4, Para. 3)?A) The more people are around, the more they need to worry about their personal safety.B) The more people who witness an event, the less likely anyone will venture to participate.C) The more people idling around on the street, the more likely they need taking care of.D) The more people are around, the less chance someone will step forward to intervene.48. What happens when unsafe behavior at the workplace is not addressed by the leaders?A) No one will intervene when they see similar behaviors.B) Everyone will see it as the easiest way to deal with crisis.C) Workers have to take extra caution executing their duties.D) Workers are left to take care of the emergency themselves.49. What is the ultimate reason workers won’t act when they see unsafe operations?A) Preference of deferring the action to others.B) Anticipation of leadership intervention.C) Fear of being isolated by coworkers.D) Fear of having to do more work.50. What is critical to ensuring workplace safety?A) Workers be trained to operate their equipment properly.B) Workers exhibiting at-risk behavior be strictly disciplined.C) Supervisors create a safety environment for timely intervention.D) Supervisors conduct effective communication with frontline workers.Passage TwoQuestions 51 to 55 are based on the following passage.The term “environmentalist” can mean different things. It used to refer to people trying to protect wildlife and natural ecosystems. In the 21st century, the term has evolved to capture the need to combat human-made climate change.The distinction between these two strands of environmentalism is thecause of a split within the scientific community about nuclear energy.On one side are purists who believe nuclear power isn’t worth the risk and the exclusive solution to the climate crisis is renewable energy. The opposing side agrees that renewables are crucial, but says society needs an amount of power available to meet consumers’ basic demands when the sun isn’t shining and the wind isn’t blowing. Nuclear energy, being far cleaner than oil, gas and coal, is a natural option, especially where hydroelectric capacity is limited.Leon Clarke, who helped author reports for the UN’s Intergovernmental Panel on Climate Change, isn’t an uncritical supporter of nuclear energy, but says it’s a valuable option to have if we’re serious about reaching carbon neutrality.“Core to all of this is the degree to which you think we can actually meet climate goals with 100% renewables,” he said. “If you don’t believe we can do it, and you care about the climate, you are forced to think about something like nuclear.”The achievability of universal 100% renewability is similarly contentious. Cities such as Burlington, Vermont, have been “100% renewable” for years. But these cities often have small populations, occasionally still rely on fossil fuel energy and have significant renewable resources at their immediate disposal. Meanwhile, countries that manage to run off renewables typically do so thanks to extraordinary hydroelectric capabilities.Germany stands as the best case study for a large, industrialized country pushing into green energy. Chancellor Angela Merkel in 2011 announced Energiewende, an energy transition that would phase out nuclear and coal while phasing in renewables. Wind and solar power generation has increased over 400% since 2010, and renewables provided 46% of the country’s electricity in 2019.But progress has halted in recent years. The instability of renewables doesn’t just mean energy is often not produced at night, but also that solar and wind can overwhelm the grid during the day, forcing utilities to pay customers to use their electricity. Lagging grid infrastructure struggles to transport this overabundance of green energy from Germany’s north to its industrial south, meaning many factories still run on coal and gas. The political limit has also been reached in some places, with citizens meeting the construction of new wind turbines with loud protests.The result is that Germany’s greenhouse gas emissions have fallen by around 11.5% since 2010—slower than the EU average of 13.5%.51. What accounts for the divide within the scientific community about nuclear energy?A) Attention to combating human-made climate change.B) Emphasis on protecting wildlife and natural ecosystems.C) Evolution of the term ‘green energy’ over the last century.D) Adherence to different interpretations of environmentalism.52. What is the solution to energy shortage proposed by purists’opponents?A) Relying on renewables firmly and exclusively.B) Using fossil fuel and green energy alternately.C) Opting for nuclear energy when necessary.D) Limiting people’s non-basic consumption.53. What point does the author want to make with cities like Burlington as an example?A) It is controversial whether the goal of the whole world’s exclusive dependence on renewables is attainable.B) It is contentious whether cities with large populations have renewable resources at their immediate disposal.C) It is arguable whether cities that manage to run off renewables have sustainable hydroelectric capabilities.D) It is debatable whether traditional fossil fuel energy can be done away with entirely throughout the world.54. What do we learn about Germany regarding renewable energy?A) It has increased its wind and solar power generation four times over the last two decades.B) It represents a good example of a major industrialized country promoting green energy.C) It relies on renewable energy to generate more than half of its electricity.D) It has succeeded in reaching the goal of energy transition set by Merkel.55. What may be one of the reasons for Germany’s progress having halted in recent years?A) Its grid infrastructure’s capacity has fallen behind its development of green energy.B) Its overabundance of green energy has forced power plants to suspend operation during daytime.C) Its industrial south is used to running factories on conventional energy supplies.D) Its renewable energy supplies are unstable both at night and during the day.Part IV Translation (30 minutes)Directions: For this part, you are allowed 30 minutes to translate a passage from Chinese into English. You should write your answer on Answer Sheet 2.中国的传统婚礼习俗历史悠久，从周朝开始就逐渐形成了一套完整的婚礼仪式，有些一直沿用至今。
伟大的头脑是天生的还是后天养成的英文文章
伟大的头脑是天生的还是后天养成的英文文章1. Introduction1.1 Statement of the issue1.2 Explanation of the significance of the issue1.3 Thesis statement2. Nature vs. Nurture Debate: The Origins of Great Minds2.1 Brief history of the nature vs. nurture debate2.2 Definitions of 'nature' and 'nurture' in the context of intelligence and greatness2.3 Overview of key arguments and evidence on both sides3. The Case for Nature: Innate Intelligence and Genetic Factors 3.1 The role of genetics in determining intelligence3.2 Evidence from twin and adoption studies3.3 Examples of prodigies and geniuses with exceptional abilities from a young age3.4 Scientific research on the heritability of intelligence4. The Case for Nurture: Environmental and Experiential Factors 4.1 The influence of education and upbringing on cognitive development4.2 Socioeconomic and cultural factors that contribute to or hinder intellectual growth4.3 Case studies of individuals who have ovee challenging circumstances to achieve greatness4.4 The impact of early childhood experiences on br本人n development5. The Interactionist Perspective: The Complex Interplay of Nature and Nurture5.1 The theory of gene-environment interaction5.2 The importance of both genetic predispositions and environmental influences5.3 Examples of research demonstrating thebined effects of nature and nurture on cognitive abilities5.4 Implications for education, parenting, and social policy6. Conclusion6.1 Restatement of the thesis6.2 Summary of key points6.3 Discussion of the implications for understanding and fostering greatness in individuals6.4 Suggestions for future research on the origins of great mindsGreat Minds: Nature or Nurture?The question of whether great minds are born or made has long been a topic of debate in the fields of psychology, genetics, and education. This essay will explore theplex interplay of genetic and environmental factors in the development of exceptional cognitive abilities, with a focus on the implications for understanding and fostering greatness in individuals.The nature vs. nurture debate has a rich and contentious history, with proponents on both sides presentingpelling arguments for their respective positions. On one hand, advocates of the'nature' side argue that intelligence is largely determined by genetic factors. Studies of twins and adopted siblings have provided convincing evidence for the heritability of intelligence, suggesting that genetic predispositions play a significant role in the development of cognitive abilities. Furthermore, the existence of prodigies and geniuses who exhibit exceptional talents from a young age supports the notion of innate intelligence.Conversely, proponents of the 'nurture' perspective emphasizethe crucial influence of environmental and experiential factors on cognitive development. Numerous studies have demonstrated the impact of education, socioeconomic status, and family upbringing on intellectual growth. Moreover, inspiring stories of individuals who have ovee adversity and achieved greatness through hard work and perseverance serve as powerful testaments to the potential for nurturing extraordinary minds.In reality, the origins of great minds are likely to be the result of aplex interplay of nature and nurture. The theory of gene-environment interaction suggests that genetic predispositions interact with environmental influences to shape cognitive abilities. This interactionist perspective underscores the importance of recognizing the multifaceted nature of human intelligence and the need to consider both genetic and environmental factors in understanding and fostering greatness.In conclusion, the origins of great minds are best understood as the result of the intricate interplay of nature and nurture. Genetics may provide a foundational predisposition for cognitive abilities, but environmental and experiential factors also play a crucial role in shaping and fostering greatness inindividuals. Recognizing the dynamic interplay of genetic and environmental influences has important implications for education, parenting, and social policy, as well as for the ongoing pursuit of knowledge in the field of psychology. Continued research into the origins of great minds will further our understanding of theplex factors that contribute to exceptional cognitive abilities and guide efforts to nurture and support the development of greatness in individuals.。
Theoretical prevision of physical chemical properties of amino acids from genetic code
order in the tensoring procedure. However, it is well-known (see Table 1) that in a multiplet of codons relative to a specific amino acid, the first two bases constituent of a codon are “relatively stable”, the degeneracy being mainly generated by the third nucleotide. Considering the tensor product
1 U ≡ (− 2 , +1 ) 2
G ≡ (+ 1 , −1 ) 2 2
1 1 A ≡ (− 2 , −2 )
(1)
Iare built as composite states of the nucleotide states by tensoring
1 1 three such ( 2 , 2 ) representations. Note that the crystal basis, which exists in the limit q → 0 of the q -deformed universal enveloping algebra Uq (G) for any semi-simple Lie algebra G, is the only way to provide such composite states as pure states, and to ensure the existence of an
1 1 , 1) ⊗ (2 , 2 ) = (1, 1) ⊕ (1, 0) ⊕ (0, 1) ⊕ (0, 0) (1 2 2
托福(阅读)历年真题试卷汇编4(题后含答案及解析)
托福（阅读）历年真题试卷汇编4(题后含答案及解析) 题型有： 3. Reading ComprehensionSections Three：Reading ComprehensionEarly Theories of Continental DriftP1: The idea that the geography of Earth was different in the past than it is today is not new. As far back as 1620, Francis Bacon spotted that the west coast of Africa and the east coast of South America looked as if they would fit together, like pieces of a jigsaw puzzle. Between then and 1912, other people identified further similarities between other continental coastlines. But because much of the early support for mobilism was based on far-flung intercontinental similarities, geologists tended to be skeptical of the fieldwork of others.P2: During the late nineteenth century, Austrian geologist Eduard Suess proposed the name “Gondwanaland”in his book The Face of the Earth (1885) and gave far greater emphasis to the evolutionary nature of the earth and he noted the similarities among the Late Paleozoic plant fossils of India, Australia, South Africa, and South America. Based upon glossopteris fern fossils in such regions, he explained that the three land masses were once connected in a supercontinent which he names Gondwanaland, and that the ocean flooded the spaces currently between those lands. Thus, in his view, the similarities of fossils on these continents could be accounted for by postulating the concept of a land bridge that existed once but subsided later.P3: Later, a number of refinements to Suess’s theory were made. The American geologist Frank Taylor published a pamphlet in 1910 presenting his concept of “horizontal displacement”. He explained the formation of mountain ranges as a result of the lateral movements of continents. With the earth’s capture of the moon, the gravitational forces between them generated a pull towards lower latitudes where they thickened and formed folded mountain belts especially in middle latitudes. Although we now know that Taylor’s explanation of continental drift is erroneous, one of his most significant contributions was his suggestion that the Mid-Atlantic Ridge—an underwater mountain range discovered by the 1872-1876 British HMS Challenger expeditions—might mark the site at which an ancient continent broke apart, forming the present-day Atlantic Ocean.P4: However, it is Alfred Wegener, a German meteorologist, who is generally credited with developing the hypothesis of continental drift. In his monumental book, The Origin of Continents and Oceans (1915), Wegener theorized that a single supercontinent he called “Pangaea”existed sometime between 350 million to 225 million years ago. Wegner portrayed his grand concept of continental movement in a series of maps showing the breakup of Pangaea and the movement of various continents to their present-day locations. What evidence did Wegener use to support his hypothesis of continental drift? First, Wegener noted that there is geographical similarity along both the coasts of the Atlantic Ocean. The opposing coasts of the Atlantic can be fitted together in the same way as two cut off pieces of wood can be refitted. Furthermore, mountain ranges and glacial deposits seem tomatch up in such a way that suggests continents could have once been a single landmass. Finally, many of the same fossils and vegetative remains are found today on widely separated continents, indicating that the continents must have been in proximity at one time. During his days, Wegener was regarded as an advocate rather than as an impartial scientific observer, appearing to ignore vast evidence unfavorable to his ideas and distort other evidence to bring it into harmony with the theory.P5: After Wegener’s death, a South African geologist Alexander Du Toit continued to assemble fossil evidence for Pangaea. He noted that fossils of the now extinct reptile “Mesosaurus”occur in rocks of the same age in both Brazil and South Africa. Because the physiology of freshwater and marine animals is completely different, it is hard to imagine how a freshwater reptile could have swum across the Atlantic Ocean and then found a freshwater environment nearly identical to its former habitat. Moreover, if Mesosaurus could have swum across the ocean, its fossil remains should be widely dispersed. It is more logical to assume that Mesosaurus lived in lakes in what were once adjacent areas of South America and Africa when it was united into a single continent. Notwithstanding all of the empirical evidence in favor of continental drift theory presented here, most geologists at the time refused to entertain the idea.P6 :The debate over continental drift has the same role and stature in the history of the earth sciences as the debate over Darwinian evolution in the history of life sciences and the debates over relativity and quantum theory in the history of physics. In the largest sense, the history of earth science, the history of biology, and the history of physics in the 20th century are all histories of the consolidation of opinion and the formation of broad consensus—that these theories were the best way to organize and advance these sciences.P5: After Wegener’s death, a South African geologist Alexander Du Toit continued to assemble fossil evidence for Pangaea.■He noted that fossils of the now extinct reptile “Mesosaurus” occur in rocks of the same age in both Brazil and South Africa.■Because the physiology of freshwater and marine animals is completely different, it is hard to imagine how a freshwater reptile could have swum across the Atlantic Ocean and then found a freshwater environment nearly identical to its former habitat. ■Moreover, if Mesosaurus could have swum across the ocean, its fossil remains should be widely dispersed. It is more logical to assume that Mesosaurus lived in lakes in what were once adjacent areas of South America and Africa when it was united into a single continent. ■Notwithstanding all of the empirical evidence in favor of continental drift theory presented here, most geologists at the time refused to entertain the idea.1．According to paragraph 2, Eduard Suess believed that similarities of plant and animal fossils on the southern continents were due toA．living in the southern climateB．crossing the land bridgesC．fossilization in the coal layersD．movements of the supercontinent正确答案：B解析：【事实信息题】题目问动植物化石的相似性是因为什么，文中提到“the similarities of fossils on these continents could be accounted for by”所以原因是之前有陆桥后来消失了，答案是B。
中国地质大学(北京)考博专业英复习材料
晶） is said to have a porphyritic texture（斑状结构）. The classification of fine-grained rocks, then, is based on the proportion of minerals which form phenocrysts and these phenocrysts （斑晶）reflect the general composition of the remainder(残留) of the rock. The fine-grained portion of a porphyritic（斑岩） rock is generally referred to as the groundmass（基质） of the phenocrysts. The terms "porphyritic" and "phenocrysts" are not restricted to fine-grained rocks but may also apply to coarse-grained rocks which contain a few crystals distinctly larger than the remainder. The term obsidian(黑曜岩) refers to a glassy rock of rhyolitic（流纹岩） composition. In general, fine-grained rocks consisting of small crystals cannot readily be distinguished from③ glassy rocks in which no crystalline material is present at all. The obsidians, however, are generally easily recognized by their black and highly glossy appearanceass of the same composition as obsidian. Apparently the difference between the modes of formation of obsidian and pumice is that in pumice the entrapped water vapors have been able to escape by a frothing（起泡） process which leaves a network of interconnected pore（气孔） spaces, thus giving the rock a highly porous （多孔的）and open appearance（外观较为松散）. ④ Pegmatite（结晶花岗岩） is a rock which is texturally（构造上地） the exact opposite of obsidian. ⑤ Pegmatites are generally formed as dikes associated with major bodies of granite （花岗岩） . They are characterized by extremely large individual crystals （单个晶体） ; in some pegmatites crystals up to several tens of feet in length（宽达几十英尺）have been identified, but the average size is measured in inches （英寸） . Most mineralogical museums contain a large number of spectacular（壮观的） crystals from pegmatites. Peridotite（橄榄岩） is a rock consisting primarily of olivine, though some varieties contain pyroxene（辉石） in addition. It occurs only as coarse-grained intrusives（侵入）, and no extrusive（喷出的） rocks of equivalent chemical composition have ever been found. Tuff （凝灰岩）is a rock which is igneous in one sense （在某种意义上） and sedimentary in another⑥. A tuff is a rock formed from pyroclastic （火成碎 屑的）material which has been blown out of a volcano and accumulated on the ground as individual fragments called ash. Two terms（igneous and sedimentary） are useful to refer solely to the composition of igneous rocks regardless of their textures. The term silicic (硅质 的)signifies an abundance of silica-rich（富硅） and light-colored minerals（浅 色矿物）, such as quartz, potassium feldspar（钾长石）, and sodic plagioclase （钠长石） . The term basic （基性） signifies （意味着） an abundance of dark colored minerals relatively low in silica and high in calcium, iron, and
英语翻译中的长难句结构分析（2）
41. The most thrilling explanation is, unfortunately,a little defective. Some economists argue that powerful structural changes in the world have upended the old economic models that were based upon the historical link between growth and inflation. [参考译⽂]很不幸，这最令⼈震惊的解释有⼀点缺陷。
⼀些经济学家认为世界经济结构的强有⼒的变化已经结束了那个以经济增长和通货膨胀的历史关联为基础的旧的经济模式。
42. The Aswan Dam, for example, stopped the Nile flooding but deprivedEgypt of the fertile silt that floods left-all in return for a giant reservoir of disease which is now so full of silt that it barely generates electricity.[参考译⽂]例如，阿斯旺⼤坝使得尼罗河不再洪⽔泛滥，但是它也夺去了埃及以前所享有的洪⽔留下的肥沃淤泥--这些换宋的就是这么个疾病滋⽣的⽔库，现在这个⽔库积满了淤泥，⼏乎不能发电了。
43. New ways of organizing the workplace--all that re-engineering anddownsizing--are only one contribution to the overall productivity of an economy, which is driven by many other factors such as joint investment in equipment and machinery, new technology, and investment in education and training,[参考译⽂]企业重组的新⽅法--所有那些重新设计、缩⼩规模的做法--只是对⼀个经济的整体⽣产⼒做出了⼀⽅⾯的贡献。
Abstract
Compare the results, according to the equations (1), (2), (3), (4), defining inhibition type is competitive one.
EI的文摘长度一般不超过150 words，或1500字母。 美国物理学会Style Manual, 不 超过500个单词。
对实验结果可用现在时（表示客观真理）或 现在完成时（已取得的阶段性成果）。
• 关于结构式文摘
据统计，目前世界上约有60％的核心生物医学期刊采用 结构式摘要，但此种摘要不适合综述之类的文章。 结构式文摘是按Objective（目的）、Methods（方法）、 Results（结果）和Conclusions（结论）逐一阐述论文 的梗概。在Objective项，可直接用动词不定式的一般 式主动语态，如To provide, To explore, …; Methods和 Results 项，可用一般过去时（有时也用现在完成时） 及其被动语态；Conclusions 则用一般现在时(参见： 韩仲琪，李炳汝，王庆法. 医学论文英文摘要格式及 其写作问题. 编辑学报，2002，14（6）：412)
Abstract
1 基本特性 2 时态 3 语态 4 语法修辞 5 一个典型示例 6 化学常用句式
1 基本特性
具有独立性和自明性，它是通篇文章的概 括和总结，应该反映文章的全貌，因此 一篇英文摘要应该用简明、精炼、确切 的文字向广大读者提供尽可能多的定性 和定量的信息。
简要陈述研究工作的宗旨与解决的问题， 说明理论或实验方案，概述基本发现， 并指出主要结论。切勿对结论做自我评 价。综述的摘要应阐述评述的话题、范 围和评述的资料来源以及结论。 摘要应确系反映文章的内容。 摘要应便于读者明了这篇文章的性质与 范围，有助于编者为存储和检索来确认 文章的关键特征。
C4_旋转对称光子晶体平板中的对称保护连续谱束缚态
第40卷第3期Vol.40㊀No.3重庆工商大学学报(自然科学版)J Chongqing Technol &Business Univ(Nat Sci Ed)2023年6月Jun.2023C4旋转对称光子晶体平板中的对称保护连续谱束缚态张铭洋重庆工商大学数学与统计学院,重庆400067摘㊀要:在光子晶体平板中,连续谱束缚态关于C2和C6旋转对称的依赖性已经在数值上进行了广泛研究,但是缺少严格的理论分析过程,此外还缺少对C4旋转对称的研究,鉴于此,构建了系统分析连续谱束缚态关于所有旋转对称的依赖性的理论,并且重点研究了C4旋转对称的情况;首先,通过分析具有旋转对称的结构中麦克斯韦方程组特征解的性质,将连续谱束缚态的存在性问题转变为旋转矩阵的特征值是否与一个简单代数方程的解相同的问题;其次,给出了C4旋转对称的结构中连续谱束缚态存在时所对应的条件;然后,证明了破坏C4旋转对称保持C2旋转对称时,连续谱束缚态依然存在;最后,利用有限元软件FreeFEM 进行了大量的数值验证;上述理论可适用于所有旋转对称的情况,深入揭示了旋转对称对连续谱束缚态存在的重要性,深入揭示了高阶旋转对称性与低阶旋转对称性之间的依赖关系,为连续谱束缚态的实际应用提供了理论指导㊂关键词:光子晶体;旋转对称;连续谱束缚态中图分类号:O436㊀㊀文献标识码:A㊀㊀doi:10.16055/j.issn.1672-058X.2023.0003.09㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀收稿日期:2022-05-13㊀修回日期:2022-06-20㊀文章编号:1672-058X(2023)03-0064-07基金项目:重庆市自然科学基金面上项目(CSTC2019JCYJ -MSXMX0717).作者简介:张铭洋(1997 ),女,重庆忠县人,硕士研究生,从事光子晶体㊁麦克斯韦方程组数值计算研究.引用格式:张铭洋.C4旋转对称光子晶体平板中的对称保护连续谱束缚态[J].重庆工商大学学报(自然科学版),2023,40(3):64 70.ZHANG Mingyang.Symmetry-protected bound states in the continuum in C4rotationally symmetric photonic crystal plates J .Journal of Chongqing Technology and Business University Natural Science Edition 2023 40 3 64 70.Symmetry-protected Bound States in the Continuum in C 4Rotationally Symmetric Photonic Crystal Plates ZHANG MingyangSchool of Mathematics and Statistics Chongqing Technology and Business University Chongqing 400067 ChinaAbstract The dependence of bound states in the continuum BICs on C2and C6rotational symmetry in photonic crystalplates has been extensively studied numerically.However a rigorous theoretical analysis process is lacking and there is alack of studies on C4rotational symmetries.In view of this a theory of systematic analysis of the dependence of BICs on all rotational symmetries was constructed and the case of C4rotational symmetry was mainly studied.Firstly by analyzingthe characteristic solutions of Maxwell s equations with rotationally symmetric structure the problem of the existence of BICs was transformed into the question of whether the eigenvalue of the rotation matrix was the same as the solution of asimple algebraic equation.Secondly the conditions for the existence of BICs in C4rotationally symmetric structures weregiven.Then it was proved that the BICs still existed when C4rotation symmetry was destroyed and C2rotatory symmetrywas maintained.Finally the finite element software FreeFEM was used to do a lot of numerical verifications.The abovetheory can be applied to all cases of rotational symmetries revealing the importance of rotational symmetry for the existenceof BICs.The dependence between high-order and low-order rotational symmetries was revealed providing theoretical guidance for applying BICs.Keywords photonic crystal rotational symmetry bound states in the continuum第3期张铭洋,等:C4旋转对称光子晶体平板中的对称保护连续谱束缚态1㊀引㊀言光学连续谱束缚态(bound states in the continuum, BIC)是指位于连续谱中的导模,其不能与辐射场耦合,没有能量辐射,被完美地束缚在结构中[1-3]㊂数学上,光学连续谱束缚态是指开结构中麦克斯韦方程组的一类频率位于连续谱内的平方可积特征解㊂通常,导模(即平方可积特征解)的特征频率位于连续谱外㊂1929年冯诺依曼等[4]从数学模型上发现在一些特殊的结构中存在特征频率位于连续谱内的导模㊂直到1985年文献[5]才构造出具有连续谱束缚态的真实物理系统㊂2008年,文献[3]研究了光子晶体结构中的连续谱束缚态㊂此后,连续谱束缚态受到广泛关注,与之有关的研究快速发展㊂目前,连续谱束缚态的概念和研究已推广到水波㊁声波等其他波动现象[1]㊂连续谱束缚态可看成为品质因子为无穷大的共振,只存在于若干离散的频率上㊂连续谱束缚态由共振模式所包围㊂通过扰动波矢,可在连续谱束缚态附近找到任意大小品质因子的共振模式[6]㊂此性质使得连续谱束缚态在光学㊁光子学等领域都拥有广阔的应用前景㊂目前,连续谱束缚态已在波导㊁光栅㊁光子晶体及超材料等结构中被广泛研究[7],光子晶体中的连续谱束缚态现在已经被用于传感器,激光器和滤波器的设计当中[8-10]㊂通常,共振模式的品质因子与波矢之差的平方成反比㊂文献[6]证明了存在特殊的连续谱束缚态使得附近共振模式的品质因子与波矢之差的四次方和六次方成反比,并给出了两类特殊连续谱束缚态的条件㊂从实际应用角度来讲,在这些特殊的连续谱束缚态附近更容易构造出高品质因子的共振模式㊂连续谱束缚态可以大致分为两类:对称保护的连续谱束缚态[11-15]和非对称保护的连续谱束缚态[2,16-19]㊂对称保护的连续谱束缚态(Symmetry Protected Bound states in the continuum,SPBIC)的机理是:在对称结构中,布洛赫模的对称性与结构中辐射场的对称性不相容,从而与辐射场不耦合,变成一个连续谱束缚态[3]㊂而非对称保护连续谱束缚态的存在机理是:共振模式的辐射场之间发生干涉相消现象,造成没有辐射,成为连续谱束缚态[3]㊂连续谱束缚态的存在性与结构的对称性具有密切联系㊂早期研究结果都是在对称结构中研究连续谱束缚态,学术界一度认为连续谱束缚态只存在于对称结构中㊂目前数学上还没有非对称保护连续谱束缚态的存在性理论㊂非对称保护连续谱束缚态关于结构对称性的依赖关系非常复杂㊂文献[20-23]从数值和实验上演示了破坏二维结构的C2旋转对称性后,连续谱束缚态演化为共振模式㊂这间接说明了结构的对称性对非对称保护连续谱束缚态的存在性具有重要影响㊂但是破坏对称性后连续谱束缚态是否一定会演化为共振模式并没有明确的结论㊂最近,文献[24-26]证明了只要引入足够多的结构扰动参数,连续谱束缚态可以连续存在于非对称的结构中,且对于不同类型的连续谱束缚态,所需要引入的最小参数的数量是不同的㊂上述结论表明,非对称保护连续束缚态可以存在于非对称结构中,只要结构的自由参数足够多㊂对称保护连续谱束缚态只存在于对称结构中㊂光子晶体平板可具有四类旋转对称性:C2㊁C3㊁C4和C6旋转对称性,即分别旋转180㊁120㊁90和60度后结构不变㊂文献[11-12]首先从数学理论上证明了在具有C2旋转对称的二维介质结构中对称保护连续谱束缚态的存在性,在非对称结构中一定不存在对称保护连续谱束缚态㊂研究对称保护连续谱束缚态对上述四种不同类型对称性的连续依赖性具有十分重要的意义㊂文献[21]研究了C6旋转对称性对具有拓扑电荷为q=-2的对称保护连续谱束缚态存在性的影响㊂通过数值计算发现破坏C6对称保持C2对称,对称保护连续谱束缚态依然存在,但是变成拓扑电荷q=-1;破坏C6对称保持C3对称,对称连续谱束缚态演化为共振模式,而且会产生两个非对称保护连续谱束缚态㊂上述研究结果给出了一种产生非对称保护连续谱束缚态的方法㊂目前,对于拓扑电荷为q=-1或q=1的对称保护连续谱束缚态关于结构对称性的依赖关系没有进行系统讨论,缺乏严格系统的依赖性理论㊂研究C4旋转对称结构中对称保护连续谱束缚态关于对称性的依赖关系㊂建立了严格数学理论证明破坏C4对称保持C2对称,对称保护连续谱依然存在㊂并利用有限元软件FreeFEM进行数值验证㊂相比于以前的研究,研究既有严格的数学理论,又有数值验证㊂研究成果具有一般性,可推广到分析对称保护连续谱束缚态关于C6对称性的依赖性,有利于深入理解连续谱束缚态关于对称性的依赖关系,为其实际应用提供理论指导㊂2㊀连续谱束缚态考虑一个在x与y方向为周期,在z方向上厚度有限的光子晶体平板㊂光子晶体平板通过在平板上构造正方形空气柱晶格所构成㊂设平板厚度为2D,晶格常数为L,平板的介电常数为ε1,空气的介电常数为ε0= 1㊂记整个结构的介电常数为ε(r),其中r=(x,y,z),则z>D时有ε(r)=1,且ε(r)满足ε(r)=ε(x+mL,y+nL,z)(1)其中,m与n为任意整数㊂设光子晶体平板是无磁性㊁各向同性的,由麦克斯56重庆工商大学学报(自然科学版)第40卷韦方程组可知,具有时间依赖e -iwt 的时谐波的电场E 满足如下的控制方程:∇ˑ∇ˑE -k 2εE =0∇㊃(εE )=0其中k =ωc为真空中的波速,ω为角频率,c 为真空中的光速㊂光子晶体平板中的布洛赫模(即麦克斯韦方程组的特征解)可写成:E (r )=Φ(r )e ik ㊃r其中,k =(α,β,0)为布洛赫波矢,实数α与β分别为x 与y 方向的布洛赫波速,Φ(r )满足周期条件式(1)㊂由于在z >D 时,结构是均匀的,由傅立叶展开式与分离变量法可知,满足向外辐射条件的布洛赫模可以展开为[18]E (r )=ð+ɕm ,n =-ɕd ʃm ,neik ʃm ,n㊃r ʃz >D (2)其中,常数向量d ʃm ,n满足d ʃm ,n ㊃k ʃm ,n =0,k ʃm ,n=(αm ,βn ,ʃγm ,n ),αm =α+2m πL ,βn =β+2n πL,γm ,n =k 2-α2m -β2n ㊂若结构是无耗散的,即ε(r )为非负实函数,则布洛赫模可以分为三类:导模㊁共振以及连续谱束缚态㊂(1)若k 为实数,则布洛赫模为导模㊂可以证明k 为实数等价于E (r )满足lim z ңɕE (r )=0,即没有能量辐射,没有能量损失㊂当波速和布洛赫波矢满足条件0<k <α2+β2时,导模关于α与β连续存在㊂在上述条件下,γm ,n 的虚部都大于0,所以展开式(2)中每一个平面波都在无穷远出衰退到0,即E (r )自动满足lim z ңɕE (r )=0,从而是一个导模㊂(2)若k 为复数,则布洛赫模为共振模式㊂共振模式的波速k 满足[Re(k )]2-[lm(k )]2>α2+β2㊂由于共振的波速k 为复数且满足向外辐射条件,共振满足条件lim z ңɕE (r )=ɕ,即在空间上是无限增大,但随时间指数衰退㊂共振波速k (或共振频率ω)的虚部小于零,即lm(k )<0,它表示共振随着时间衰退的速度㊂共振的品质因子Q 定义为Q =-12Re(k )lm(k ),表示共振模式的振幅衰退到原来的e -1时所需要的振荡周期㊂共振模式关于α与β也是连续存在的㊂(3)若k 为实数且满足k >α2+β2,则布洛赫模是一个连续谱束缚态㊂连续谱束缚态可以看成是一个Q 因子为无穷大的共振,只在离散的(α,β)点上存在,在连续谱束缚态的附近,通过调整α与β可以获得任意大小Q 因子的共振㊂由于k 为实数等价于条件limz ңɕE (r )=0,在展开式(2)中,若lm(γm ,n )ȡ0,则e ikm ,n㊃r可向z ңɕ辐射能量,(m ,n )是对应一个开放的辐射通道㊂若lm(γm ,n )<0,则eik ʃn ,m ㊃r在z ңɕ时衰退到零,对应一个关闭的辐射通道㊂若Re(k )>α2+β2,则至少有lm(γ0,0)ȡ0,即(0,0)处辐射通道是开放的㊂记Z 0表示所有开放的辐射通道,即Z 0=(m ,n )lm(γm ,n )ȡ0{},则条件lim z ңɕE (r )=0等价于d ʃm ,n=0,∀(m ,n )ɪZ 0(3)式(3)是布洛赫模的一个附加条件,在一般情况下,连续谱束缚态不容易存在㊂3 对称保护连续谱束缚态当光子晶体平板具有旋转对称性时,可能存在对称保护连续谱束缚态㊂下面给出具有C n 旋转对称的光子晶体平板中对称保护连续谱束缚态的定义,并分析其关于对称性的依赖关系㊂利用旋转对称性下布洛赫模的性质,将连续谱束缚态的存在性问题转变为旋转矩阵的特征值是否与一个简单代数方程的解相同的问题;其次,给出了C4旋转对称的结构中连续谱束缚态存在时所对应的条件;然后,证明了破坏C4旋转对称保持C2旋转对称时,连续谱束缚态依然存在;具有C n 旋转对称性结构的介电函数ε(r )满足条件ε(r )=ε(T -1r )其中,T =cos φ-sin φ0sin φcos φ0001éëêêêùûúúú表示旋转矩阵,φ=2πn ,只考虑n =2与n =4的情况㊂其理论可推广到n =3与n =6的情况㊂C n 旋转对称光子晶体平板中的布洛赫模具有以下性质[24]:若E (r )=Φ(r )e ik ㊃r 是一个对应于波矢k =(α,β,0)和波速k 的布洛赫模,则TE (T -1r )是一个对应于波矢Tk 和波速k 的布洛赫模㊂特别地,取α=β=0,即k =(0,0,0),有Tk =k ,此时E (r )与TE (T -1r )是对应同一个波矢与波速的两个布洛赫模㊂若特征值问题是非退化的,则E (r )与TE (T -1r )线性相关,即存在常数τ使得:TE (T -1r )=τE (r )(4)由于任何结构旋转n 次2πn角度(即2π)后都不变,有T n=I ,其中I 表示单位算子㊂所以有τn=1,即τ=e i 2πn j,j =0,1,2, ,n -1㊂更具体地,当n =2时,τ=ʃ1;当n =4时,τ=ʃ1,ʃi ㊂注意到τ的取值对应于C n 点群的不可约表示的特征㊂设布洛赫模的波矢为k =(0,0,0)且频率满足0<Re(k )ε0<2πL,即只有(0,0)处辐射通道是开放的,则当n =2时,对应于τ=1以及当n =4时,对66第3期张铭洋,等:C4旋转对称光子晶体平板中的对称保护连续谱束缚态应于τ=ʃ1的布洛赫模一定是连续谱束缚态,称为对称保护连续谱束缚态㊂在上述条件下,布洛赫模是一个连续谱束缚态的充要条件是d ʃ0,0=0㊂下面证明当n =2时,τ=1以及当n =4时,τ=ʃ1,有d ʃ0,0=0㊂将展开式(2)代入条件式(4)得:Td ʃ0,0=τd ʃ0,0(5)令,d ʃ0,0=d ʃx ,d ʃy ,d ʃz []T ,T ^=cos φ-sin φsin φcos φéëêêùûúú,d ʃʅ=d ʃx ,d ʃy []T 表示d ʃ0,0的x 与y 分量所构成的向量㊂由d ʃ0,0㊃k ʃ0,0=0且α=β=0,知d ʃz k =0,即d ʃz =0㊂所以d ʃ0,0=0等价于d ʃʅ=0㊂由式(5)得:T ^d ʃʅ=τd ʃʅ若τ不是T ^的特征值,则必有d ʃʅ=0㊂当n =2时,T ^=-100-1éëêêùûúú,T ^只有一个特征值-1㊂所以当τ=1时,有d ʃʅ=0㊂当n =4时,T ^=0-110éëêêùûúú,此时T ^的特征值为ʃi ㊂所以当τ=ʃ1时有d ʃʅ=0㊂由上面的证明过程可知,条件d ʃ0,0=0是由C n 对称性所保证的㊂在具有C4旋转对称的结构中,对称保护连续谱束缚态对应的τ=1或-1㊂注意到无论是τ=1还是-1,都有τ2=1,即这些连续谱束缚态也同时由C2旋转对称所保护㊂有以下结论:具有C4旋转对称结构中的对称保护连续谱束缚态都是由C2旋转对称所保护的,即破坏C4旋转对称,保持C2旋转对称,这些连续谱束缚态依然存在㊂4㊀拓扑电荷连续谱束缚态对应于动量空间中辐射场的漩涡,因此其存在性与拓扑性质有关㊂前面提到了布洛赫模是一个连续谱束缚态的充要条件是d ʃ0,0=0,通过d ʃ0,0的x 与y 分量可以计算得到辐射场的极化角㊂极化椭圆的长轴与y 轴的夹角称之为极化角度,记为θ㊂θ可以看成是α与β的函数,即θ=θ(α,β)㊂在αβ平面上,任意给定一条曲线Γ,让(α,β)沿着Γ绕一圈重新定义θ,使其为连续函数㊂拓扑电荷的定义为q =12πɥΓd θ=12πɥΓ∇θ㊃ n d s拓扑电荷q 表示αβ上的一点绕Γ走一圈后,极化角度旋转了q 圈,q 是一个整数㊂若Γ所围区域内无圆极化与连续谱束缚态,则q =0;若Γ所围区域内有且仅有一个连续谱束缚态则q =ʃ1,ʃ2,ʃ3, ;若Γ所围区域内只有一个圆极化,则q =ʃ12㊂需要注意的是圆极化和连续谱束缚态是αβ平面中的一个极化奇点㊂5㊀数值实验由于辐射边界条件下的特征值问题定义在无穷区间上,无法用数值方法来计算㊂所以在实际计算连续谱束缚态的时候,可以用完美匹配层的方法来将无穷区域截断为有限区域㊂用完美匹配层截断后的特征值问题是原特征值问题的一个近似,它们之间的误差关于完美匹配层的参数σ∗㊁H 2-H 1(即完美匹配层的厚度)指数衰退到零㊂所以只需要选择合适的σ∗与H 2-H 1,便可以得到足够精确的特征解,即可以计算得到连续谱束缚态的频率㊂相对于拟周期边界条件,在有限元方法中周期边界条件更容易实现㊂用有限元方法求解偏微分方程最重要的是弄清楚解空间和变分形式㊂在用有限元求解时,变分问题被近似为下列代数方程的特征值问题:A Φ=k 2B Φ其中,A 与B 为矩阵㊂考虑如图1所示的具有正方形晶格空气柱的光子晶体平板,其俯视图如图2所示㊂平板是由空气所包围的㊂平板的厚度为2D =0.5L ,介电常数为ε1=4,空气中的介电常数ε0=1㊂空气柱体横截面参数分别为w =0.2L ,a =w2㊂若h 1=h 2,则结构具有C4旋转对称性㊂若h 1ʂh 2,则结构只有C2旋转对称性㊂为了验证前面得到的理论,用完美匹配层[27]的方法将无穷区域上的特征值问题转化为有限区域上的特征值问题,并用有限元[28]的方法求解㊂数值计算时,需要用完美匹配层方法将z 方向截断为-H 2,H 2[],如图3所示㊂取完美匹配层的厚度为H 2-H 1=L ,σ∗=18ˑm +1β0(H 2-H 1)[29],β0=k 20ε0-α2-γ2,m =3㊂其中H 1-D 表示完美匹配层的远近㊂采用基于FreeFEM 软件的有限元方法来数值求解特征值问题,以计算对称保护连续谱束缚态的频率㊂计算时在平板的每个边界的离散点个数取N =10,PML 层的离散点个数也取N =10㊂考虑如此复杂结构的原因是为了避免其他对称性(例如镜面反射对称)对结果的影响㊂ε=ε0ε=ε0z =D z =-Dzxy图1㊀光子晶体平板结构图Fig.1㊀Structure diagram of photonic crystal plates76重庆工商大学学报(自然科学版)第40卷h 2h 1h 1h 2L Lαωωxy图2㊀光子晶体平板结构的俯视图Fig.2㊀Top view of the photonic crystal flat plate structurez=H2z=H1z=D z=-Dz=-H1z=-H2ε=εε=εzxy 图3㊀PML截断后的计算区域Fig.3㊀Computation region after PML truncation 若取h1=h2=0.15L,这时结构具有C4旋转对称性㊂通过数值计算,可以找到5个TM-Like模式下(即E z是z变量的奇函数)的对称保护连续谱束缚态,其频率如表1的第2列所示㊂图4(a) 图8(a)分别是SPBIC1-SPBIC5在具有C4旋转对称的结构中log10Q 关于α与β的值㊂可以通过观察得到当(α,β)ң(0, 0)时,Q的值趋近于无穷大㊂图4(c) 图8(c)分别是SPBIC1到SPBIC5在C4旋转对称结构中的磁场z分量H z在z=0时的场图㊂从下面的场图可以观察得到, SPBIC1与SPBIC5对应于τ=1,其他3个对称保护连续谱束缚态对应于τ=-1㊂表1的最后一列表示为对称保护连续谱束缚态的拓扑电荷㊂若保持h1=0.15L,令h2=0.1L,参数扰动后结构的C4旋转对称性被破坏,但保持了C2旋转对称性㊂通过数值计算表明,SPBIC1-SPBIC5在扰动后的结构中依然存在,其频率如表1的第三列所示,可以发现两种结构下连续谱束缚态的频率近乎相等㊂图4(b) 图8(b)分别是SPBIC1到SPBIC5在具有C2旋转对称的结构中log10Q关于α与β的值㊂可以通过观察得到当(α,β)ң(0,0)时,Q的值趋近于无穷大,并且可以发现两种结构下,log10Q关于α与β的值很相近㊂图4(d) 图8(d)分别代表的是扰动后SPBIC1-SPBIC5在C2旋转对称结构中的磁场z分量H z在z=0时的场图㊂从下面的场图可以观察得到,SPBIC1与SPBIC5仍然对应于τ=1,其他3个对称保护连续谱束缚态也依旧对应于τ=-1㊂通过对比,可以发现两种结构下的场图几乎一模一样,并且可以发现结构扰动不改变对称保护连续谱束缚态的拓扑电荷㊂表1㊀C4与C2旋转对称结构中对称保护连续谱束缚态的频率ωL2πc的值Table1㊀Value ofωL2πc the frequency of symmetrically protected bound states in the continuum in the rotationallysymmetric structure of C4and C2C4C2q SPBIC10.61590.6101+1 SPBIC20.63670.6282-1 SPBIC30.85690.8485-1 SPBIC40.93830.9338-1 SPBIC50.95140.9492+10.05-0.05-0.0500.05βL/(2π)Q f a c t o rαL/(2π)8640.05-0.05-0.0500.05αL/(2π)864βL/(2π)Q f a c t o r㊀㊀(a)(b )0.5-0.5-0.500.5y/LR e/H zx/L0.5-0.5-0.500.5R e/H zx/L㊀㊀(c)(d)图4㊀SPBIC1的Q因子图和场图Fig.4㊀Q factor diagram and field diagram of SPBIC10.05-0.05-0.0500.05βL/(2π)Q f a c t o rαL/(2π)8765430.05-0.05-0.0500.05αL/(2π)βL/(2π)Q f a c t o r876543㊀㊀(a)(b)86第3期张铭洋,等:C4旋转对称光子晶体平板中的对称保护连续谱束缚态0.50-0.5-0.50.5y /LR e /H zx /L0.5-0.5-0.50.5y /LR e /H zx /L㊀㊀(c )(d )图5㊀SPBIC2的Q 因子图和场图Fig.5㊀Q factor diagram and field diagram of SPBIC20.010-0.01-0.010.01βL /(2π)Q f a c t o rαL /(2π)8765430.010-0.01-0.0100.01αL /(2π)βL /(2π)Q f a c t o r76543㊀㊀(a )(b )0.5-0.5-0.50.5y /LR e /H zx /L0.5-0.5-0.50.5y /LR e /H zx /L㊀㊀(c )(d )图6㊀SPBIC3的Q 因子图和场图Fig.6㊀Q factor diagram and field diagram of SPBIC30.010-0.01-0.010.01βL /(2π)Q f a c t o rαL /(2π)76540.010-0.01-0.0100.01αL /(2π)βL /(2π)Q f a c t o r7654㊀㊀(a )(b )0.5-0.5-0.50.5y /LR e /H zx /L0.5-0.5-0.50.5y /LR e /H zx /L㊀㊀(c )(d )图7㊀SPBIC4的Q 因子图和场图Fig.7㊀Q factor diagram and field diagram of SPBIC40.020-0.02-0.0200.02βL /(2π)Q f a c t o rαL /(2π)8640.020-0.02-0.0200.02αL /(2π)βL /(2π)Q f a c t o r6543㊀㊀(a )(b )0.5-0.5-0.50.5y /LR e /H zx /L0.5-0.5-0.500.5y /LR e /H zx /L㊀㊀(c )(d )图8㊀SPBIC5的Q 因子图和场图Fig.8㊀Q factor diagram and field diagram of SPBIC5经过数值计算,从扰动前后不同结构下对称保护连续谱束缚态的频率以及对比分析它们的Q 因子图和场图可以观察得到具有C4旋转对称结构的光子晶体平板中的对称保护连续谱束缚态都是由C2旋转对称性所保护的㊂即若破坏C4旋转对称但保持C2旋转对称,原有的对称保护连续谱束缚态依然存在㊂进一步反映了C4旋转对称与C2旋转对称之间的依赖关系㊂6㊀结束语构建了系统分析连续谱束缚态关于旋转对称性的依赖理论,并且重点研究了C4旋转对称的情况,分别从理论和数值两个方面证明了具有C4旋转对称光子晶体平板中的对称保护连续谱束缚态都是由C2旋转对称性所保护的㊂即破坏C4旋转对称但是保持C2旋转对称性,原对称保护连续谱束缚态依然存在㊂虽然只考虑了C4旋转对称光子晶体平板中的对称保护连续谱束缚态,但提出的理论和数值分析方法都可以用于研究具有C6旋转对称的光子晶体平板,不过由于此结构同时具有C2与C3旋转对称性,对称保护连续谱束缚态与对称性的依赖关系可能会更加复杂㊂提出的理论分析方法也可以适用于所有旋转对称的情况㊂由于是从麦克斯韦方程组出发,没有引入模型近似,并且分析过程根据严格㊂研究结果有利于深入理解对称保护连续谱束缚态的性质,为其理论分析和实际应用提供指导㊂96重庆工商大学学报(自然科学版)第40卷参考文献References1 ㊀HSU C W ZHEN B STONE A D et al.Bound states in thecontinuum J .Nature Reviews Materials 2016 1 9 1 13.2 ㊀HSU C W ZHEN B LEE J et al.Observation of trappedlight within the radiation continuum J .Nature 2013 4997457 188 191.3 ㊀MARINICA D C BORISOV A G SHABANOV S V.Boundstates in the continuum in photonics J .Physical Review Letters 2008 100 18 1 4.4 ㊀NEUMANN J WIGNER E P.Über merkwürdige diskreteEigenwerte M .Berlin Heidelberg Springer 1993.5 ㊀FRIEDRICH H WINTGEN D.Interfering resonances andbound states in the continuum J .Physical Review A 198532 6 3231 3239.6 ㊀YUAN L LU Y Y.Bound states in the continuum on periodicstructures surrounded by strong resonances J .Physical Review A 2018 97 4 1 8.7 ㊀AZZAM S I KILDISHEV A V.Photonic bound states in thecontinuum from basics to applications J .Advanced Optical Materials 2020 9 1 1469 1477.8 ㊀KODIGALA A LEPETIT T GU Q et sing action fromphotonic bound states in continuum J .Nature 2017 5417636 196 199.9 ㊀JIN J YIN X NI L et al.Topologically enabled ultrahigh-Qguided resonances robust to out-of-plane scattering J .Nature 2019 574 7779 501 504.10 HAN S CONG L SRIVASTAVA Y K et al.All-dielectricactive terahertz photonics driven by bound states in the continuum J .Advanced Materials 2019 31 37 1 28.11 BONNET-BENDHIA A S STARLING F.Guided waves byelectromagnetic gratings and non-uniqueness examples for the diffraction problem J .Mathematical Methods in the Applied Sciences 1994 17 5 305 338.12 VENAKIDES S SHIPMAN S P.Resonance and bound statesin photonic crystal slabs J .SIAM Journal on Applied Mathematics 2003 64 1 322 342.13 SHIPMAN S VOLKOV D.Guided modes in periodic slabsexistence and nonexistence J .SIAM Journal on Applied Mathematics 2007 67 3 687 713.14 LEE J ZHEN B CHUA S L et al.Observation anddifferentiation of unique high-Q optical resonances near zero wave vector in macroscopic photonic crystal slabs J .Physical Review Letters 2012 109 6 1 5.15 HU Z LU Y Y.Standing waves on two-dimensional periodicdielectric waveguides J .Journal of Optics 2015 176065601 065608.16 YANG Y PENG C LIANG Y et al.Analytical perspective for bound states in the continuum in photonic crystal slabs J . Physical Review Letters 2014 113 3 1 5.17 YUAN L LU Y Y.Propagating bloch modes above the lightline on a periodic array of cylinders J .Journal of Physics B Atomic Molecular and Optical Physics 2017 505 1 5.18 KANG M ZHANG S XIAO M et al.Merging bound states in the continuum at off-high symmetry points J .Physical Review Letters 2021 126 11 1 7.19 YUAN L LU Y Y.Conditional robustness of propagating bound states in the continuum in structures with two-dimensional periodicity J .Physical Review A 2021 1034 1 10.20 OVERVIG A C MALEK S C CARTER M J et al.Selection rules for quasibound states in the continuum J .Physical Review B 2020 102 3 1 30.21 YODA T NOTOMI M.Generation and annihilation of topologically protected bound states in the continuum and circularly polarized states by symmetry breaking J .Physical Review Letters 2020 125 5 1 12.22 LI S ZHOU C LIU T et al.Symmetry-protected bound states in the continuum supported by all-dielectric metasurfaces J . Physical Review A 2019 100 6 1 6.23 LI L LI Y ZHU Y et al.Rotational symmetry of photonic bound states in the continuum J .Scientific Reports 2020 101 1 8.24 SAKODA K.Optical properties of photonic crystals M . Berlin Springer Science&Business Media 2004.25 YUAN L LU Y Y.Parametric dependence of bound states in the continuum on periodic structures J .Physical Review A 2020 102 3 1 9.26 YUAN L LUO X LU Y Y.Parametric dependence of bound states in the continuum in periodic structures vectorial cases J .Physical Review A 2021 104 2 1 11.27 LU Y Y.Minimizing the discrete reflectivity of perfectly matched layers J .IEEE Photonics Technology Letters 2006 18 3 487 489.28 LI Y J JIN J M.Fast full-wave analysis of large-scale three-dimensional photonic crystal devices J .JOSA B 2007 249 2406 2415.29 ZHEN B HSU C W LU L et al.Topological nature of optical bound states in the continuum J .Physical Review Letters 2014 113 25 1 20.责任编辑:田㊀静07。
汉译英_高级职称
The mistake escaped my notice.
9.只有在显微镜下才能看见红血球。
A microscope is needed (for us) to see red cells.
10.2000年奥运会将在悉尼举行。
Sydneywill host (be the host city for) the 2000 Olympic Games.
After a careful check of the blueprint, they made comments on his design.
6.据说在质量方面这种仪器是优越的。
It is said that this instrument is high in quality.
2.不同国家的社会习俗往往大相径庭。
Social customs are usually different from country to country.
3.我们应该尽我们最大的努力防止这类事故再次发生。
We should do our best to prevent this kind of accident from happening again.
At the end of this century, the world population will be over six billion.
2.去年，这个国家的工农业总产值为两千亿美元。
Last year, the general output value of industry and agriculture of this country was two hundred billion dollars.
Study on the properties of percolative conductors
Study on the properties of percolativeconductorsIntroductionPercolation theory provides a useful framework for understanding the behavior of materials that conduct electricity. A percolative conductor is a material that has a random network of conductive pathways, allowing for the flow of current. In this article, we will explore the properties of percolative conductors and the factors that affect their behavior.ConductivityThe primary property of percolative conductors is conductivity, which is a measure of the ability of a material to conduct electricity. The conductivity of a percolative conductor is determined by the density and connectivity of the network of conductive pathways. As the density of the network increases, so does the conductivity of the material.Another important factor that affects conductivity is the shape of the conductive pathways. The more tortuous the pathways, the lower the conductivity of the material. This is because the electrons have a longer path to travel, and thus encounter more resistance.ResistanceThe resistance of a material is the inverse of its conductivity and is a measure of the opposition to the flow of current. The resistance of a percolative conductor is determined by the density and connectivity of the network of conductive pathways as well as the shape of the pathways.In general, as the density of the network of conductive pathways increases, the resistance of the material decreases. Similarly, as the connectivity of the network increases, the resistance decreases. However, the shape of the pathways can have asignificant impact on the resistance of the material, with more tortuous pathways leading to higher resistance.Percolation ThresholdThe percolation threshold is the point at which the network of conductive pathways becomes connected, allowing for the flow of current. Below this threshold, the material is insulating, and above it, the material is conducting.The percolation threshold is determined by a number of factors, including the size and shape of the conductive particles, the nature of the insulating material, and the concentration of the conductive particles. In general, smaller particles lead to lower percolation thresholds, and more spherical particles lead to higher percolation thresholds.Temperature DependenceOne of the key factors that affect the conductivity of percolative conductors is temperature. In general, as the temperature increases, the conductivity of the material increases. This is because the higher temperature allows for more energy to be available for the flow of current.However, there are limits to this effect, and at some point, the temperature will become too high, and the conductivity will decrease due to other factors such as thermal expansion and changes in the material structure.ApplicationsPercolative conductors have a wide range of applications, including in the electronic and optoelectronic industries. They are used in the production of printed circuit boards, organic solar cells, and transparent conductive coatings.ConclusionThe study of percolative conductors provides a useful framework for understanding the behavior of materials that conduct electricity. The conductivity, resistance, percolation threshold, and temperature dependence are all important properties that affectthe behavior of these materials. By understanding these properties, researchers can develop new and improved materials for a wide range of applications.。
Numerical Methods for Incompressible Viscous Flow
Hans Petter Langtangen∗ Kent-Andre Mardal Dept. of Scientific Computing, Simula Research Laboratory and Dept. of Informatics, University of Oslo Ragnar Winther Dept. of Informatics, University of Oslo and Dept. of Mathematics, University of Oslo
Re = U d/ν , where U is a characteristic velocity of the flow and d is a characteristic length of the involved geometries. The basic Navier-Stokes equations describe both laminar and turbulent flow, but the spatial resolution required to resolve the small (and important) scales in turbulent flow makes direct solution of the Navier-Stokes equations too computationally demanding on today’s computers. As an alternative, one can derive equations for the average flow and parameterize the effects of turbulence. Such common models models for turbulent flow normally consist of two parts: one part modeling the average flow, and these equations are very similar to (1)–(2), and one part modeling the turbulent fluctuations. These two parts can at each time level be solved sequentially or in a fully coupled fashion. In the former case, one needs methods and software for the system (1)–(2) also in turbulent flow applications. Even in the fully coupled case the basic ideas regarding discretization of (1)–(2) are reused. We also mention that simulation of turbulence by solving the basic Navier-Stokes equations on very fine grids, referred to as Direct Numerical Simulation (DNS), achieves increasing importance in turbulence research as these solutions provide reference databases for fitting parameterized models. In more complex physical flow phenomena, laminar or turbulent viscous flow is coupled with other processes, such as heat transfer, transport of pollution, and deformation of structures. Multi-phase/multi-component fluid flow models often involve equations of the type (1)–(2) for the total flow coupled with advection-diffusion-type equations for the concentrations of each phase or component. Many numerical strategies for complicated flow problems employ a splitting of the compound model, resulting in the need to solve (1)–(2) as one subset of equations in a possibly larger model involving lots of partial differential equations. Hence, it is evident that complex physical flow phenomena also demand software for solving (1)–(2) in a robust fashion. Viscous flow models have important applications within the area of water resources. The common Darcy-type models for porous media flow are based on averaging viscous flow in a network of pores. However, the averaging introduces the permeability parameter, which must be measured experimentally, often with significant uncertainty. For multi-phase flow the ad hoc extensions of the permeability concept to relative permeabilities is insufficient for satisfactory modeling of many flow phenomena. Moreover,
核专业英语背诵材料2.0
Unit 1Helium---------------------氦uranium------------铀Gaseous state-----------气态的artificially------------人工的The perfect gas law------理想气体定律Boltzmann constant--- 玻尔兹曼常数neutrons --------------中子electrostatic -------静电的，静电学的Specific heat capacity--- 比热容Plank constant---------普朗克常量Fission----------------裂变fusion-----------------聚变Maxwellian distribution--麦克斯韦分布microscopic------------微观的Macroscopic-----------宏观的quantum number-------量子数Laser-----------------激光deuterium--------------氘Tritium----------------氚deuteron---------------氘核Trition----------------氚核atomic mass unit------原子质量单位Avogadro’s number----阿伏伽德罗常数binding energy----------结合能Substance-------------物质internal-----------------内部的Spontaneously --------自发地circular-----------------循环的Electronic ------------电子的neutral-----------------中性的Qualitative -----------定性的dissociation-------------分解分离Disrupt--------------使分裂A complete understanding of the microscopic structure of matter and the exact nature of the forces acting (作用力的准确性质) is yet to be realized. However, excellent models have been developed to predict behavior to an adequate degree of accuracy for most practical purposes. These models are descriptive or mathematical often based on analogy with large-scale process, on experimental data, or on advanced theory.一个完整的理解物质的微观结构和力的确切性质(作用力的准确性质)尚未实现。
水资源专业单词表
AbsoluteThe micron rating of a filter. It indicates that any particle larger than a specific size will be trapped within the filter.AbsorptionWhen a solid takes up molecules into its structure.Acid aerosolVery small liquid or solid particles that are acidic and are small enough to become airborne.Acidic waterAcid neutralizing capacityMeasure of the buffering capacity of water; the ability of water to resist changes in pH.Acid rainRain that has a flamboyantly low pH, due to contact with atmospheric pollutants such as sulphuric oxides.AcidityThe quantitative capacity of water to neutralize a base, expressed in ppm or mg/L calcium carbonate equivalent. The number of hydrogen atoms that are present determines this. It is usually measured by titration with a standard solution of sodium hydroxide.Activated coalThis is the most commonly used adsorption medium, produced by heating carbonaceous substances or cellulose bases in the absence of air. It has a very porous structure and is commonly used to remove organic matter and dissolved gases from water. Its appearance is similar to coal or peat. Available in granular, powder or block form; in powder form it has the highest adsorption capacity.Activated sludgeOxygen dependent biological process that serves to convert soluble organic matte r to solid biomass, that is removable by gravity or filtration.Active groupsReally fixed ions bolted on to the matrix of an ion exchanger. Each active group must always have a counter-ion of opposite charge near itself.AdsorptionSeparation of liquids, gases, colloids or suspended matter from a medium by adherence to the surface or pores of a solid.More info on adsorptionAdvanced oxidation processOne of several combination oxidation processes. Advanced chemical oxidation processes use (chemical) oxidants to reduce COD/BOD levels, and to remove both organic and oxidisable inorganic components. The processes can completely oxidise organic materials to carbon dioxide and water, although it is often not necessary to operate the processes to this level of treatment.A wide variety of advanced oxidation processes are available:- Chemical oxidation process using hydrogen peroxide, ozone, combined ozone & peroxide, hypochlorite, Fenton's reagent, etc.- Ultra-violet (UV) enhanced oxidation such as UV/ ozone, UV/ hydrogen, UV/air- Wet air oxidation and catalytic wet air oxidation (where air is used as the oxidant)More info on advanced oxidationAdvanced water treatmentThe level of water treatment that requires an 85-percent reduction in pollutant concentration, also known as tertiary treatment.Advanced Wastewater TreatmentAny treatment of sewage water that includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids.Aerated lagoonA water treatm ent pond that speeds up biological decomposition of organic waste by stimulating the growth and activity of bacteria, which are responsible for the degradation.AerationTechnique that is used w ith water treatment that demands oxygen supply, commonly known as aerobic biological water purification. Either water is brought into contact with water droplets by spraying or air is brought into contact with water by means of aeration facilities. Air is pressed through a body of water by bubbling and the water is supplied with oxygen.More info on aerationAeration tankA tank that is used to inject air into water.AerobicA process that takes place in the presence of oxygen, such as the digestion of organic matter by bacteria in an oxidation pond.AerosolVery small liquid or solid particles dispersed in air.AffinityThe keenness with which an ion exchanger takes up and holds on to a counter-ion. Affinities are very much affected by the concentration of the electrolyte surrounding the ion exchanger.AgglomerationA process of bringing smaller particles together to form a larger mass.Aggressive waterWater that is soft and acidic and can corrode plumbing, pipes and appliances.AlgaeSingle- or multi-celled organisms that are commonly found in surface water, such as duckweed. They produce their own food through photosynthesis. The algae population is divided up into green algae and blue algae, of which the blue algae are very damageable to human health. Excessive algae growth may cause the water to have undesirable odours or tastes. Decay of algae diminishes oxygen supplies in the water.Algal bloomsPeriods of enlarged algal growths that affect water quality. Algal blooms indicate potentially hazardous changes in the chemistry of water.AliquotA measured portion of a sample taken for analysis. One or more aliquots make up a sample.AlkalinityAlkalinity means the buffering capacity of water; the capacity of the water to neutralize itself. It prevents the water pH levels from becoming too basic or acid. It also adds carbon to water. Alkalinity stabilizes water at pH levels around 7. However, when the acidity is high in water the alkalinity decreases, which can cause harmful conditions for aquatic life.In water chemistry alkalinity is expressed in ppm or mg/L of equivalent calcium carbonate. Total alkalinity of water is the sum of all three sorts of alkalinity; carbonate, bicarbonate and hydroxide alkalinity.AlluviumSediments deposited by erosion processes, usually by streams.AnaerobicA process that takes place in the absence of oxygen, such as the digestion of organic matter by bacteria in a UASB-reactor.AnionA negatively charged ion that results from the dissociation of salts, acids or alkali's in solution.AnodeA site in electrolysis where metal goes into solution as a cation leaving behind an equivalent of electrons to be transferred to an opposite electrode, called a cathode.AquaticGrowing in water, living in water, or frequenting water.AqueousSomething made up of water.Aqueous solubilityThe maximum concentration of a chemical that dissolves in a given amount of water.AquiferA layer in the soil that is capable of transporting a significant volume of groundwater.AromaticsA type of hydrocarbon that contains a ring structure, such as benzene and toluene. They can be found for instance in gasoline.AssimilationThe ability of water to purify itself of pollutants.Assimilative CapacityThe capacity of natural water to receive wastewaters or toxic materials without negative effects and without damage to aquatic life or humans who consum e the water.AtomThe smallest unit of matter that is unique to a particular element. They are the ultimate building blocks for all matter.Atomic numberA specific number that differs for each element, equal to the number of protons in the nucleus of each of its atoms.AttenuationThe process of reduction of a compound's concentration over time. This can be through absorption, adsorption, degradation, dilution or transformation.AttritionThe action of one particle rubbing against the other in a filter media or ion exchange bed that can in time cause breakdown of the particles.Available chlorineA measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials.BackflowThe flow of water in a medium in a direction opposite to normal flow. Flow is often returned into the system by backflow, if the wastewater in a purification system is severely contaminated.Back PressurePressure that can cause water to backflow into the water supply when a user's waste water system is at a higher pressure than the public system.Back siphonageReverse seepage of water in a distribution system.BackwashingReversing the flow of water back through the filter media to remove entrapped solids.BacteriaMicroscopically small single-cell organisms, that reproduce by fission of spores.Bacterial water contaminationThe introduction of unwanted bacteria into a water body.BaseAn alkaline substance that has a pH that exceeds 7,5.Bed LoadSediment particles resting on or near the channel bottom that are pushed or rolled along by the flow of water.Benthic zoneThe lower region of a body of water including the bottom.BicarbonatesSalts containing the anion HCO3-. When acid is added, this ion breaks into H2O and CO2, and acts as a buffer.BinderChemicals that hold short fibres together in a cartridge filter.BioaccumulantionThe increase in concentration of a substance in living organisms, as they take in contaminated air, water, or food, due to slow metabolization and excretion.Biochemical Oxygen Demand (BOD)The amount of oxygen (measured in mg/L) that is required for the decomposition of organic matter by single-cell organisms, under test conditions. It is used to measure the amount of organic pollution in wastewater.More info on BOD and waste water treatmentBiocideA chemical that is toxic to microrganisms. Biocides are often used to eliminate bacteria and other single-cell organisms from water.Biodegradable pollutantsPollutants that are capable of decomposing under natural conditions.BiofilmPopulation of various microrganisms, trapped in a layer of slime and excretion products, attached to a surface.Biological contaminantsLiving organisms such as viruses, bacteria, fungi, and mammal and bird antigens that can cause harmful health effects to humans.Biologically activated carbonActivated carbon that supports active microbial growth, in order to aid in the degradation of organics that have been absorbed on its surface and in its pores.Biological oxidationDecomposition of complex organic materials by microrganisms through oxidation.BiomonitoringThe use of living organisms to test the suitability of effluents for discharge into receiving waters and to test the quality of such waters downstream from the discharge.BioremediationThe biological treatment of wastewater and sludge, by inducing the breakdown of organics and hydrocarbons to carbon dioxide and water.BiotaAll living organism s in a region or ecosystem.BiotransformationConversion of a substance into other compounds by organisms; including biodegradation.BlackwaterWater that contains waste of hum ans, animals or food.Blind spotsAny place on a filter medium where fluids cannot flow through.BlindingA build-up of particles in a filter medium, that prevents fluids from flowing through.BOD5The amount of dissolved oxygen consumed in five days by bacteria that perform biological degradation of organic matter.Boiling pointThe temperature at which the vapour pressure of a liquid equals the pressure of its surface. The liquid will than vaporize If the pressure of the liquid varies, the actual boiling point varies. For water the boiling point is 100 degrees Celsius.Bottled waterWater that is sold in plastic containers for drinking water and/ or domestic use.Brackish waterWater that is neither falls in the category of salt water, nor in the category of fresh water. It holds the middle between either one of the categories.Breakpoint chlorinationAddition of chlorine to water until there is enough chlorine present for disinfection of water.BreakthroughCrack or break in a filter bed that allows the passage of floc or particulate matter through a filter.BrineHighly salty and heavily mineralised water, containing heavy metal and organic contaminants.BufferA substance that reacts with hydrogen or hydroxyl ions in a solution, in order to prevent a change in pH.CakeSolid dewatered residue on a filter media after filtration.Calcium hypo chloriteA chemical that is widely used for water disinfection, for instance in swimming pools or water purification plants. It is especially useful because it is a stable dry powder and ca n be made into tablets.Candle filterA relatively coarse aperture filter, designed to retain a coat of filter m edium on an extended surface.Capillary actionWater that at some point rises higher than that portion of its surface, not in contact with the solid surface. This is due to adhesion, cohesion and surface tension where later touches a solid.Cappilary membranesMembranes about the thickness of a human hair, used for Reverse Osmosis, nanofiltration, ultrafiltration and microfiltrtion.Capillary zoneSoil area above the water table where water can rise up slightly through the cohesive force of capillary action.CarcinogenAny dissolved pollutant that can induce cancer.Cartridge filterDisposable filter device that has a filter range of 0.1 micron to 100 microns.More info on cartridge filtersCarbonatesChemical compounds related to carbon dioxide.Carbonate hardnessHardness of water caused by carbonate and bicarbonate by-products of calcium and magnesium.CatalysesChemical that increases the rate of a reaction but does not take a direct part in the reaction, so that it is still intact after the reaction has taken place.Catch basinA sedimentation area designed to remove pollutants from runoff before being discharged into a stream or pond.CathodeA site in electrolysis where cations in solution are neutralized by electrons that plate out on the surface or produce a secondary reaction with water.CationA negatively charged ion, resulting from dissociation of mole cules in solution.CentrifugationA separation process, which uses the action of centrifugal force to promote accelerated settling of particles in a solid-liquid mixture.More info on centrifugationCFUColony Forming Units. This is a measure that indicates the number of microrganisms in water.Check valveA valve that allows water to stream in one direction and will then close to prevent development of a back-flow.Chelating agentsOrganic compounds that have the ability to draw ion from their water solutions into soluble complexes.Chemical Oxygen Demand (COD)The amount of oxygen (measured in mg/L) that is consumed in the oxidation of organic and oxidasable inorganic matter, under test conditions. It is used to measure the total amount of organic and inorganic pollution in wastewater. Contrary to BOD, with COD practically all compounds are fully oxidized.Chemical pollutionIntroduction of chemical contaminants into a water body.Chemical weatheringDissolving of rock by exposure to rainwater, surface water, oxygen, and other gases in the atmosphere, and compounds secreted by organisms.ChloraminesA chemical complex that consists of chlorine and ammonia. It serves as a water disinfectant in public water supplies in place of chlorine because chlorine can combine with organics to form dangerous reaction products. In which forms chloramines exist depends on the physical/ chemical properties of the water source.Chlorinated hydrocarbonsHydrocarbons that contain chlorine. These include a class of persistent insecticides that accumulate in the aquatic food chain. Among them are DDT, aldrin, dieldrin, heptachlor, chlordane, lindane, endrin, Mirex, hexachloride, and toxaphene.Chlorinated solventAn organic solvent containing chlorine atoms that is often used as aerosol spray container, in highway paint, and dry cleaning fluids.ChlorinationA water purification process in which chlorine is added to water for disinfection, for the control of present microrganisms. It is also used in the oxidation of compound impurities in water.Chlorine-contact chamberThe part of a water treatm ent plant where effluent is disinfected by chlorine.ClarityThe clearness of a liquid.CoagulationDestabilisation of colloid particles by addition of a reactive chemical, called a coagulant. This happens through neutralization of the charges.More info on coagulationCoalescenceLiquid particles in suspension that unite to create particles of a greater volume.Coastal zoneLands and waters near the coast, whose uses and ecology are affected by the sea.Coliform bacteriaBacteria that serve as indicators of pollution and pathogens when found in water. These are usually found in the intestinal tract of humans and other warm-blooded animals.Coliform indexA rating of the purity of water based on a count of coliform bacteria.Collector sewersPipes to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.ColloidsMatter of very small particle size, in the range of 10-5 to 10-7 in diameter.Combined sewerA sewer system that carries both sewage and rain water runoff.Composite sampleA series of water samples taken over a given period of time and weighted by flow rate.CompoundsTwo or more different elements held together in fixed proportions by attractive forces called chemical bonds.ConcentrateThe totality of different substances that are left behind in a filter medium afte r filtration.ConcentrationThe amount of material dissolved in a unit of solution, expressed in mg/L.Concentration processThe process of increasing the number of particles per unit volum e of a solution, usually by evaporating the liquid.CondensateWater obtained by condensation of water vapour.CondensationThe change of state from a gas to a liquid.ConductivityThe amount of electricity the water can conduct. It is expressed in a che mical magnitude. Please use also our information about TDS and conductivity.ConduitA natural or artificial channel through which fluids may be transported.Consumptive water useWater removed from available supplies without return to a water resources system; water used in manufacturing, agriculture, and food preparation.Contact timeThe length of time a substance is in contact with a liquid, before it is removed by filtration or the occurrence of a chemical change.ContaminantAny foreign component in a substance, for example in water.Conventional sewer systemsSystems that were traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant, before discharge on receiving surface waters.Conveyance lossWater loss in pipes and channels by leakage or evaporation.Cooling towerLarge tower used to transfer the heat in cooling water from a power or industrial plant to the atmosphere either by direct evaporation or by convection and conduction.CorrosivityAbility of water to dissolve or break down certain substances, particularly metals.Cross flow filtrationA process that uses opposite flows across a membrane surface to minimize particle build-up.CryptosporidiumA microorganism in water that causes gastrointestinal illness in humans. It is commonly found in untreated surface water and can be removed by filtration. It is resistant to disinfectants such as chlorine.Cultural eutrophicationDecline of the oxygen rate in water, which has serious consequences for aquatic life, caused by humans.CurrentThe portion of a stream or body of water, which is moving much faster than the rest of the water. The progress of the water is principally concentrated in the current.CycleThe length of time a filter can be used before it needs cleaning, usually including cleaning time.DealkalinisationAny process that serves to reduce the alkalinity of water.DecarbonationThe process of removing carbon dioxide from water, using contact towers or air scrubbers.DecantTo draw off the upper layer of liquid after the heaviest material (a solid or another liquid) has settled.DecompositionThe break down of organic matter by bacteria and fungi, to change the chemical structure and physical appearance of matter.DefluoridationThe removal of fluoride from drinking water to prevent teeth damage.De-foaming agentsChemicals that are added to wastewater discharges to prevent the water from foaming when it is discharged into a receiving water body.DegasificationThe process of removing dissolved gasses from water, using vacuum or heat.DeionisationProcess that serves to remove all ionised substances from a solution. Most commonly is the exchange process where cations and anions are removed independently of each other.DemineralisationProcesses to remove minerals from water, usually the term is restricted to ion exchange processes.DemiwaterDemineralised water. Water that is treated to be contaminant-, mineral- and salt free.DenitrificationRemoval of nitrate and nitrate product from water to produce a quality that answeres common water standards.DensityThe weight of a certain amount of water. It is usually expressed in kilograms per cubic metre.Depression storageThe storage of water in low areas, such as ponds, and wetlands.Depth filtrationTreatm ent process in which the entire filter bed is used to trap insoluble and suspended particles in its voids as water flows through it.DesalinationThe removal of salt from seawater or brackish water to produce drinking water, using various techniques.DesorptionThe opposite of adsorption; the release of matter from the adsorption medium, usually to recover material.Detention timeThe actual time that a small amount of water is in a settling basin or flocculating basin. In storage reservoirs, it means the length of time water will be stored.DetergentA water-soluble cleansing agent, other than soap.DewaterThe separation of water from sludge, to produce a solid cake.DiffuserA component of the ozone contacting system in an ozone generator that allows diffusion of an ozone containing gas.DiffusionThe movement of gas molecules or aerosols into liquids, caused by a concentration gradient.DigesterA closed tank for wastewater treatment, in which bacterial action is induced to break down organic matter.Diluting waterDistilled water that has been stabilized, buffered, and aerated. It is often applied in the BOD tests.Direct run-offWater that flows from the ground surface directly into streams, rivers, and lakes.DischargeFlow of surface water in a stream or canal.DisinfectantsFluids or gasses to disinfect filters, pipelines, systems, etc.DisinfectionThe decontamination of fluids and surfaces. To disinfect a fluid or surface a variety of techniques are used, such as ozone disinfection. Often disinfection means eliminating the present microrganisms with a biocide.More info on disinfectionDissolveThe process during which solid particles mix molecule by molecule with a liquid and appear to become part of the liquid.Dissolved air flotation (DAF)A procedure of induced flotation with very fine air bubbles or 'micro bubbles',of 40 to 70 microns.Dissolved oxygenThe amount of oxygen dissolved in water at a certain time, expressed in ppm mg/L. Dissolved solidsSolids material that totally dissolves in water and can be removed by means of filtration. DistillationWater treatment method where water is boiled to steam and condensed in a separate reservoir. Contaminants with higher boiling points than water do not vaporize and remain in the boiling flask.DredgingCleaning, deepening, or widening of a waterway, using a machine (dredge) that removes materials by means of a scoop or a suction device.DroughtTerm applied to periods of less than average precipitation over a certain period of time.DuplicatesTwo separate samples with separate containers taken at the same time and at the same place.Dystrophic lakesAcidic bodies of water that contain many plants but few fish, due to the presence of great amounts of organic matter.EffluentThe outlet or outflow of any system that deals with water flows, for an oxidation pond for biological water purification. It is the product water of the given system.EjectorA device used to inject a chemical solution into wastewater during water treatment.Electrical chargeThe charge on an ion, declared by its number of electrons. A Cl- ion is in fact a Cl atom which has acquired an electron, and a Ca++ ion is a Ca atom, which has lost two electrons.ElectrolyteSubstance that dissociates into ions when it dissolves in water.ElectrodialysisA process that uses electrical currents, applied to permeable membranes, to remove minerals from water.ElectrolysisProcess where electrical energy will change in chemical energy. The process happens in an electrolyte, a watery solution or a salt melting which gives the ions a possibility to transfer between two electrodes. The electrolyte is the connection between the two electrodes, which are also connected to a direct current. If you apply an electrical current, the positive ions migrate to the cathode while the negative ions will migrate to the anode. At the electrodes, the cations will be reduced and the anions will be oxidated.ElectronsNegatively charged building blocks of an atom that circle around the nucleus.ElementsThe distinctive building blocks of matter that make up every material substance.ElutriationFreeing sludge of its mother liquor by washing it with water.EmulsifierA chemical that helps suspending one liquid in another.EmulsionDispersion of one liquid in another liquid, occurs when a liquid in insoluble.End-of-pipe techniquesTechniques for water purification that serve the reduction pollutants after they have formed.EnrichmentWhen the addition of nutrients, such as nitrogen and phosphorus, from sewage effluent or agricultural runoff to surface water, greatly increases algal growth.ErosionThe wearing away of the land surface by wind, water, ice or other geological agents. Erosion occurs naturally from weather or runoff but is often intensified by human land use practices.Eschericha coli (E. coli)Coliform bacterium that is often associated with human and animal waste and is found in the intestinal court. It is used by health departments and private laboratories t measure the purity of water.EstuaryRegion of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Therefore estuaries mainly consist of brackish water.EutrophicReferring to water that is rich in nutrients such as nitrogen and phosphorous.EutrophicationEnrichment of water, which causes excessive growth of aquatic plants and increasing activity of anaerobic microrganisms. As a result the oxygen levels in the water quickly decline and the water chokes, making life impossible for aerobic water organisms.EvaporationThe process of the passage of water from liquid to vapour.Evaporation pondsAreas where sewage sludge is dumped and dried.EvapotranspirationThe loss of water from the soil through vaporizing, both by direct evaporation and by transpiration from plants.Facultative bacteriaBacteria that can live under aerobic or anaerobic conditions.FermentationThe conversion of organic matter to methane, carbon dioxide and other molecules by anaerobic bacteria.Filter mediumThe permeable material that separates solids from liquids passing through it.FiltrateA liquid that has passed through the filter medium.FiltrationSeparation of a solid and a liquid by using a porous substance that only lets the liquid pass through.First drawThe water that comes out when a tap is first opened. It is likely that is has the highest level of lead contamination from weathering of pipelines.FissionReproduction of microrganisms by means of cell division.。
Theoretical evidence for the superluminality of evanescent modes
Theoretical evidence for the superluminality of evanescentmodesZhi-Yong Wang, Cai-Dong XiongSchool of Physical Electronics, University of Electronic Science and Technology of China, Chengdu610054, CHINAThough both theoretical and experimental investigations have revealed the superluminal behavior of evanescent electromagnetic waves, there are many disputes about the physical meaning and validity of such superluminal phenomenon, which is due to the fact that the traditional investigations are based on the theory of tunneling time, and concerned with the problem of what the group velocity of evanescent waves means. In this paper, by studying the quantum probability amplitude for photons to propagate over a spacelike interval along an undersized waveguide, we present theoretical evidence for such superluminality.PACS number(s): 03.65.Xp, 41.20.Jb, 42.50.Nn, 03.65.PmI. INTRODUCTIONFrom the point of view of classical electromagnetic field theory, inside an undersized waveguide evanescent waves have support everywhere (through exponential damping) along the undersized waveguide, and "the propagation of evanescent modes" is not a well-defined concept; but, from the quantum-mechanical viewpoint, there exists a physical process that photons propagate through an undersized waveguide (i.e., the so-called photon tunneling phenomenon), and then we can study the propagation of evanescent modes in the sense of quantum mechanics. To do so, traditionally, people have applied a formal analogy between the Helmholtz equation describing evanescent modes and the nonrelativistic Schrödinger equation for a particle tunneling through a potential barrier [1-2], and by whichthe theory of tunneling time is applied to reveal the superluminal behavior of evanescent waves. However, such an analogy is appropriate in mathematics, not in physics, because the photon’s equation of motion is relativistic while the Schrödinger equation is not. Moreover, time in quantum mechanics has been a controversial issue since the advent of quantum theory, and there are a lot of theoretical models of tunneling time [3-6]. As a consequence, in spite of the fact that theoretical and experimental studies had obtained the same conclusion that photons inside an undersized waveguide propagate superluminally [7-13], many papers disproving this conclusion have been published recently [14-20], they are mainly based on reinterpreting the physical meaning of the evanescent waves’ group velocity.A proper description for the propagation of evanescent modes should be based on the photon’s quantum theory itself rather than just via a quantum-mechanical analogy. Therefore, in this paper we will try to study the propagation of photons inside an undersized waveguide at the level of quantum field theory of photons. That is, by studying the quantum probability amplitude for photons to propagate along an undersized waveguide, we present theoretical evidence for the superluminal behavior of evanescent modes. What we study is the superluminality of evanescent modes (i.e., to show that photons’ motion through an undersized waveguide is a spacelike one), and have nothing to do with the controversy about how to interpret the physical meaning of the evanescent waves’ group velocity. This paper does not study whether a signal (information) can propagate superluminally, this issue can be found in Refs. [21, 22], where QED-based studies of evanescent modes are given, and a successful test of these predictions with experimental data has been presented.In the following, the natural units of measurement (1c ===) is applied, repeated indices must be summed according to the Einstein rule, and the space-time metric tensor is chosen as , diag(1,1,1,1)g μν=−−−,0,1,2,3μν=, (,)x x t μ==x , and so on.II. SPACElike BEHA VIORS OF PHOTONS INSIDE AN UNDERSIZED WA VEGUIDELet ()x ϕ represent a field operator and 0 denote the field’s vacuum state. According to quantum field theory, the quantity ()0()()D x y x y ϕϕ−≡0 represents a transition probability amplitude from the quantum state ()0y ϕ to the quantum state ()0x ϕ, such that 2()D x y − is related to the probability for a particle to propagate from 0(,)y y μ=y to . If 0(,)x x μ=x ()x ϕ is the Klein-Gordon field, then ()D x y − represents the probability amplitude for a scalar particle to propagate from y to x [23]. In particular, if its mass vanishes (m =0), one can obtain (see, for example, Ref. [23] with the replacements and 00(,)(,)p p k k μμ=→=pk p E ω=→= 33d 1()0()()0exp[i ()]2(2π)k D x y x y k x y ϕϕω−==−⋅−∫, (1) where ()(k x y k x y μ)μμ⋅−=− (and so on), is the four-dimensional (4D) momentum of the scalar particle and 0(,)k k μ=k ω=. Now, let denote the 4D momentum of photons in free vacuum, 0(,)k k μ=k 0 denote the photons’ vacuum state, and denote the 4D electromagnetic potential. In quantum field theory, plays the role of the field operator. In Lorentz gauge condition, it is well known that satisfies (()A x μ()A x μ()A x μ,0,1,2,3μν=):()0()()0(R x y A x A y g D x y μνμνμν−≡=−−)), (2) where is the space-time metric tensor and is given by diag(1,1,1,1)g μν=−−−(D x y −Eq. (1) with being reinterpreted as the 4D momentum of photons.0(,)k k μ=k In a Cartesian coordinate system spanned by an orthonormal basis with , we assume that a hollow metallic waveguide is placed along the direction of , and the waveguide is a straight rectangular pipe with the cross-sectional dimensions and , let without loss of generality. Then the cutoff frequency of the waveguide is 123{,,}e e e 31=×e e e 223e 1b 2b 1b b<c rs ω=0,1,2,...=(r , 1,2,3...s =). For simplicity, we shall restrict our discussion to the lowest-order cutoff frequency c πb 2ω=. It is also assumed that the waveguide is infinitely long and its conductivity is infinite, and the electromagnetic source is localized at infinity. In the present case, as for the 4D momentum of photons in the free space inside the waveguide, its first the second components are fixed: and 0(,)k k μ=k 10k =2πk =2), such that the function (D x y − presented in Eq. (2) becomes:31223300333d 1()()(π)exp[i ()2(2π)d 1 exp[i ()i ()]2π2k D x y k k b k x y k P x y k x δδωω]y ω−=−−⋅−=−−+−∫∫ , (3)where 0k ω== is the frequency of photons and 2222exp[i (π)()](2π)P b x y =− is a phase factor. Because is not an observable, to study the superluminal behavior of photons inside an undersized waveguide in a strict manner, our discussion will be based on field intensities (they are observables). For example, in terms of the electric field intensity ()A x μ00i i i E A A =∂−∂ (it is an operator in the second-quantization sense), one can analyze ()0()()0ij i j S x y E x E y −≡ without loss of generality (). Likewise, the function ,1,2,i j =3)(ij S x y − is related to the probability amplitude for photons to propagate from y to x along the waveguide, it can also be regarded as a correlation function for the electromagnetic field. Therefore, in the sense of quantumfield theory, one can study the propagation of evanescent modes via the function ()ij S x y −. If for a spacelike interval ()ij S x y −≠0)(x y − along the undersized waveguide, then evanescent modes have superluminal behavior. Substituting 00i i i E A =∂−∂A ) into , one can obtain(ij S x y − 2220()0()()0()(ij i j ij i j S x y E x E y D x y x x x δ∂∂−≡=−−∂∂∂)). (4) For our purpose, we will only consider the component 11(S x y − without loss of generality.As for photons inside the undersized waveguide, one has 0c ωω<=<, which implies that , where 3i k =q c c q ωω−<<. Because the waveguide is placed along the third axes, one can take and (0,0,0,0)y =(,0,0,)x t r = (for simplicity let ), and then in Eq. (3) the factor ,t r ≥021(2π)P =. Moreover, Eq. (3) shows that the function (D x y )− is independent of 1x and 1y , such that 10D x ∂∂=. Using 10D x ∂∂= and taking , (0,0,0,0)y =(,0,0,)x t =r ), the function 111111()()(,S x y S x S t r −== becomes:222112221()()()()S x D x D x x t t∂∂∂=−=−∂∂∂, (5) By substituting , (0,0,0,0)y =(,0,0,)x t r =, 3i k q =and 0c ωω<=< into Eq.(3), one can obtain [for convenience the constant factor 21(2π)P = isomitted]c0())D x qr ω=−∫−. (6) Here, it is necessary to point out that, if photons propagating along an undersized waveguide from A to B correspond to evanescent waves, then photons propagating along the undersized waveguide from B to A would correspond to antievanescent waves. Obviously, along the direction of A →B, the amplitudes of the evanescent waves are exponential damping, while those of the antievanescent waves are exponential increasing.Because our study is focused on the probability amplitude for photons to propagate from to (0,0,0,0)y =(,0,0,)x t =r , Eq. (6) does not contain the contribution of the anti-evanescent waves propagating from (,0,0,)x t r = to (0,0,0,0)y =, and then the integrating range in Eq. (6) is taken as c (0,)ω rather than c c (,)ωω−. Note that c π2ω= is the lowest-order cutoff frequency, and Eqs. (1)-(4) are written in an arbitrary inertial frame of reference.In order to evaluate the integral Eq. (6), for timelike interval , let 220x x x t r μμ==−>2t φ=and r φ=, and there is always an inertial frame in which 0r =; for spacelike interval , let 20x<t φ=and r φ=, and there is always an inertial frame in which . As 0t =φ varies in [0,)+∞, 2x is Lorentz invariant, then for convenience we will take 0φ→. Furthermore, the integral representation of the Hankel function of the second kind is useful:π(2)002()d exp(i sin )πH z z θθ=−∫. (7) The Hankel function behaves for large arguments z as(2)()i(π2π4)]H z z νν∼−−−, z →+∞. (8) From Eq. (6) one can obtain(2)20(2)201(0,8()1(i 0.8H x D x H x ωω⎧>⎪⎪=⎨⎪−<⎪⎩ (9) The Hankel functions satisfy the recurrence relations (2)(2)1()d[()]d z H z z H z z νννν−−+=−. Applying Eqs. (5) and (9), consider that the relations (2)(2)10()d[()]d H z H z =−z and1(2)1(2)21()d[()]d z H z z H z z −−=−, where z ω=, one can obtain:(2)(2)21c2c11(2)(2)212(( for 0,()(i(i for 0.H tH xS xH tH xωωωω−>=−−−<(10) Equation (8) implies that for large timelike interval () one has2x→+∞11()exp(iS xω∼−; for large spacelike interval () one has2x→−∞11()exp(S xω∼−. To be specific, consider the fact that for timelike interval , there is always an inertial frame in which2220x t r=−>0r=; for spacelike interval , there is always an inertial frame in which2220x t r=−<0t=, one can deduce theasymptotic behaviors of as follows:11()S x1222c113222c()exp(i), as timelike interval ,()()exp(), as spacelike interval .t t x tS xr r x rωω−−⎧−=⎪∼⎨−=⎪⎩→+∞−→−∞(11)It is very important to note that, because the evanescent waves oscillate with time as exp(i)tω−, as observed in an inertial frame of reference moving relative to the waveguide, the evanescent waves can propagate with a velocity 1v c<=, which is related to the Lorentz transformation of tω presented in the factor of exp(i)tω−. Therefore, though for timelike interval , its physical meaning is trivial. On the other hand, the propagation of evanescent waves through the waveguide is characterized by an exponential damping factor, and Eqs. (10)-(11) show that such a damping propagation is actually a spacelike (i.e., superluminal) one.11()0S x≠20x>III. CONCLUSIONS AND DISCUSSIONSAs discussed before, according to quantum field theory, the function given by Eq. (5) is related to the probability amplitude for photons to propagate fromto11()S x(0,0,0,0)y= (,0,0,)x t=r along the undersized waveguide. Using Eqs. (10) and (11) one can showthat for timelike intervals (), the function are the oscillating ones slowly decreasing in amplitude owing to the power-law factor, this behavior is just related to the fact that the evanescent waves contain the factor of 2220x t r =−>11()S x exp(i )t ω− and its physical meaning is trivial. For spacelike intervals (2220x t r =−<), the function rapidly fall to zero according to the exponential function (with the scale being set by the inverse cutoff frequency of the waveguide), this behavior corresponds to the propagation of photons through the undersized waveguide. In other words, the propagation of photons along the undersized waveguide is superluminal.11()S x The superluminal behavior of photons through an undersized waveguide is due to a purely quantum-mechanical effect, and it preserves weak causality that has been discussed in Refs. [24-27], where in Refs. [24-26] weak causality is discussed on a single particle level, while in Ref. [27] weak causality is discussed for ensembles of particles in field theory . In our case, the superluminal behavior preserves Einstein causality for expectation values or ensemble average only, not for individual process (in the sense of which weak causality can also be called quantum-mechanical causality). Within local quantum field theory a rigorous proof of weak causality for local observables has been given in the previous literatures [27]. To avoid a possible causality paradox, one can also resort to the particle-antiparticle symmetry. The process of a particle created at x and annihilated at y as observed in a frame of reference is identical with that of an antiparticle created at y and annihilated at x as observed in another frame of reference [28]. In our case, the antiparticle of the photon is the photon itself. Therefore, the process that a photon propagates superluminally from A to B as observed in a frame of reference is equivalent to one wherethe photon propagates superluminally from B to A as observed in another frame of reference, where causality is preserved provided that every observer has a consistent causal history locally. As we know, in total internal reflection, photons lie in evanescent modes and are actually virtual photons that describe the excitations of coupled modes of photons with matter [29, 30]. These virtual photons are the carrier of electromagnetic interaction in the quantum regime, and lie outside the ordinary photon dispersion relation and cannot be observed outside of the interacting system, but can be observed inside the system by means of a destructive measurement via a direct interaction with a probe [30]. On the other hand, Feynman has presented another way of looking at the guided waves [31], by which one can show that inside an undersized waveguide photons are also virtual photons. ACKNOWLEDGMENTSThe first author (Z. Y. W.) would like to thank Professor G. Nimtz for helpful discussions. This work was supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050614022) and by the National Natural Science Foundation of China (Grant No. 60671030).[1] M. Campi and M. Harrison, Am. J. Phys. 35, 133 (1967).[2] A. Enders and G. Nimtz, Phys. Rev. E 48, 632 (1993).[3] E. H. Hauge and J. A. Støvneng, Rev. Mod. Phys. 61, 917 (1989).[4] R. Landauer and Th. Martin, Rev. Mod. Phys. 66, 217 (1994).[5] J. G. Muga, R. Sala and I. L. Egusguiza, Time in Quantum Mechanics (Springer-Verlag, Berlin,2002).[6] V. S. Olkhovsky, E. Recami and J. Jakiel, Phys. Rep. 398, 133 (2004).[7] A. M. Steinberg, P. G. Kwiat, and R. Y. Chiao, Phys. Rev. Lett.71, 708 (1993).[8] Ch. Spielmann, R. Szipöcs, A. Stingl, and F. Krausz, Phys. Rev. Lett. 73, 2308 (1994).[9] Ph. Balcou and L. Dutriaux, Phys. Rev. lett.78, 851 (1997).[10] G. Nimtz and W. Heitmann, Prog Quant Electr. 21, 81 (1997).[11] G. Nimtz, A. Haibel, and R.-M. Vetter, Phys. Rev. E 66, 037602 (2002).[12] A. P. Barbero, H. E. Hernández-Figueroa and E. Recami, Phys. Rev. E 62, 8628 (2000).[13] S. Longhi, P. Laporta, M. Belmonte, and E. Recami, Phys. Rev. E 65, 046610 (2002).[14] A. D. Jackson, A. Lande, and B. Lautrup, Phys. Rev. A 64, 044101 (2001).[15] H.G. Winful, Nature (London) 424, 638 (2003).[16] H. G. Winful, Phys. Rev. Lett. 90, 023901 (2003).[17] H. G. Winful, Phys. Rev. E 68, 016615 (2003).[18] H. G. Winful, Phys. Rev. E 72, 046608 (2005).[19] H. G. Winful, Phys. Reports. 436, 1 (2006).[20] D. Sokolovski, A. Z. Msezane, and V. R. Shaginyan, Phys. Rev. A 71, 064103 (2005).[21] A.A. Stahlhofen and G. Nimtz, Europhys. Lett. 76, 189 (2006).[22] G. Nimtz, Do Evanescent Modes Violate Relativistic Causality, in: Special Relativity, Will itSurvive the Next 101 Years edited by J. Ehlers and C. Lämmerzahl, Lecture Notes in Physics (Springer-Verlag, Berlin, 2006), V ol. 702, pp. 506-531.[23] M. E. Peskin and D. V. Schroeder, An Introduction to Quantum Field Theory (Addison-Wesley,New York , 1995), p. 27.[24] J. S. Toll, Phys. Rev. 104, 1760 (1956).[25] H. M. Nussenzveig, Causality and Dispersion Relations (Academic Press, New York, 1972).[26] J. G. Cramer, Phys. Rev. D 22, 362 (1980).[27] G. C. Hegerfeldt, Ann. Phys. (Leipzig) 7, 716 (1998).[28] S. Weinberg, Gravitation and Cosmology (Wiley, New York 1972), Sec. 2-13.[29] C. K. Carniglia and L. Mandel, Phys. Rev. D 3, 280 (1971).[30] M. Ohtsu and H. Hori, Near-Field Nano-Optics (Kluwer Academic/plenum Publishers, NewYork, 1999).[31] R. P. Feynman, R. B. Leighton, and M. Sands, Feynman Lectures on Physics (Addison-Wesley,New York, 1964), V ol. 2, Chap. 24-8.11。
Theoretical approaches to heterogeneous catalysis
Theoretical approaches toheterogeneous catalysisHeterogeneous catalysis refers to chemical reactions where the reactants are in different phases, such as a gas and a solid. These reactions play a crucial role in the chemical and pharmaceutical industries, as they allow efficient production of complex molecules under mild conditions. Despite their practical importance, the underlying mechanism of heterogeneous catalysis is still not fully understood. In this article, we will discuss some of the theoretical approaches that have been developed to explain these reactions.One of the earliest models in heterogeneous catalysis is the Langmuir-Hinshelwood (LH) mechanism, which states that the reaction takes place on the surface of the catalyst through a series of adsorption and desorption steps. According to the LH model, the first step is the adsorption of the reactants onto the catalyst surface. This is followed by the formation of an activated complex, which has higher energy than both the reactants and the products. Finally, the complex dissociates to yield the products. The rate of the reaction is determined by the rate of the slowest step, which is usually the formation of the activated complex.The LH model provides a useful framework for understanding heterogeneous catalysis, but it has some limitations. For example, it does not account for the presence of spectator species, which can influence the reaction rate by blocking or enhancing certain sites on the catalyst surface. It also assumes that the catalyst surface is homogeneous and does not consider the effects of structural defects or dopants.To address these shortcomings, a number of more advanced models have been developed. One such model is the Mars-van Krevelen (MvK) mechanism, which takes into account the role of oxygen in redox reactions. The MvK model proposes that the reaction occurs through a series of interactions between the catalyst surface and oxygenmolecules. These interactions can lead to the formation of oxygen vacancies, which can then react with the adsorbed reactants to form the desired products.Another important model in heterogeneous catalysis is the Sabatier principle. The Sabatier principle states that the optimal catalyst for a given reaction is one that has a binding energy that is just strong enough to hold the reactants in place, but not so strong that it prevents their reaction. This principle has been used to design new catalysts for a variety of reactions, including the hydrogenation of carbon dioxide to produce methanol and the selective oxidation of methane to methanol.More recently, density functional theory (DFT) has emerged as a powerful tool for understanding heterogeneous catalysis at the molecular level. DFT allows researchers to calculate the electronic and geometric properties of catalyst surfaces and predict their reactivity towards different reactants. DFT has been used to study a wide range of reactions, from the activation of small molecules such as hydrogen and oxygen to the selective oxidation of hydrocarbons.In conclusion, while there is still much to learn about heterogeneous catalysis, the toolkit of theoretical approaches available to researchers is constantly expanding. From the early models of LH and MvK to the more recent use of DFT, each approach provides a unique perspective on the mechanisms that govern heterogeneous catalytic reactions. By combining these approaches, researchers can gain a deeper understanding of the complex and multifaceted nature of catalytic processes and design new catalysts with improved activity, selectivity, and stability.。
采用压缩感知的阵列失效单元诊断方法
2018年4月第45卷第2期西安电子科技大学学报（自然科学版）J O U R N A L OF X ID IA N U N IV E R S IT YApr. 2018Vol. 45 No. 2do i ： 10.3969/j. i s s n. 1001-2400.2018.02.027采用压缩感知的阵列失效单元诊断方法李玮1邓维波〃，杨 强1索莹MIGLIORE Marco Donald3(1.哈尔滨工业大学电子与信息工程学院，黑龙江哈尔滨150001; 2.信息感知技术协同创新中心，黑龙江哈尔滨150001 ; 3.意大利卡西诺大学电信与信息工程学院，意大利卡西诺03043)摘要：针对现有阵列单元故障诊断方法随阵元数目增多而存在的采样数量大、诊断时间长、计算复杂度高等缺陷，提出了一种采用压缩感知理论的故障诊断方法.该方法基于故障单元数目固有的稀疏性，利用完好阵列和实际阵列激励的差值构造稀疏信号.根据目标方位信息设计测量矩阵的网格划分准则，并通过测量矩阵以随机欠采样方式获取少量测量数据.结合平行坐标下降算法对该稀疏信号进行精确重构，从而实现故障单元的准确诊断.理论分析和仿真实验表明，文中提出的方法不仅明显减少了采样数量，有效缩短了诊断时间，大幅降低了计算复杂度，而且进一步提高了故障信息的重构精度.关键词：阵列诊断；压缩感知；傅里叶变换子矩阵；稀疏恢复；迭代收缩算法中图分类号：TN957 文献标识码：A 文章编号：1001-2400(2018)02-0160-06Diagnosis method for defective array elementsbased on compressive sensingLI W ei1'2 , DENG Weibo1'2 , YANG Qiang^ ,SUO Ying1,2 , MIGLIORE Marco Donald^(1. School of Electronics and Information Engineering, Harbin Institute of Technology, Harbin 150001, China;2. Collaborative Innovation Center of Information Sensing and Understanding, Harbin 150001, China;3. Schoolof Telecommunications and Information Engineering, Univ. of Cassino, Cassino 03043, Italy)Abstract：As the number of elements of the array increases, huge sampling data, long measurement timeand high computation costs arc several features of existing array fault diagnosis methods. Therefore， adiagnosis approach based on Compressive Sensing is investigated in this paper. The proposed methodutilizes the sparsity of the number of failed elements and the sparse signal derives from difference incentivesof reference array and the array under test. The criterion for grid division of the measurement matrix isdesigned according to the target direction in the spatial domain and a small number of measurement data arcthen obtained in the far field radiation pattern via a random under-sampling strategy. The ParallelCoordinate Decent Algorithm is used to implement fault diagnosis by reconstructing this sparse signal.Theoretical analysis as well as simulation results indicate that the proposed method not only reduces theamount of spatial sampling data, truncates the diagnosis time and abates the computational complexitysignificantly , but also improves the accuracy of recovered information on defective elements.Key Words：array diagnosis; compressive sensing; fouricr transform submatrix; sparse recovery; iterativeshrinkage algorithm收稿日期=2017-06-22 网络出版时间：2(H7-09-28基金项目：哈尔滨工业大学博士生国外短期访学资助项目（AUDQ9802200116);国家自然科学基金青年基金资助项目（61501145);中央高 校基本科研业务费专项资金资助项目（HIT. MKSTISP. 201613)作者简介：李玮（1988—)，男，哈尔滨工业大学博士研究生，E-mail: hit_14B905002@163. com.网络出版地址：http://kns. enki. net/kcms./detail/61. 1076. TN. 20170928. 2210. 054. html第2期李玮等采_用_展論感知的阵射失效单无爹新方法161随着阵元数量的増多、系统复杂度的提高以及工作环境的恶化，阵列单元将不可避免地存在失效问题. 当苦干天线单元发生失效启，将会引起包括最大副瓣电平（Peak SideLobe Level，P S LL)利零陷深度（N u ll D印th Level,W頂,)等辐射特性的改变》影_:雷达技战术性能的进常发挥.在乘取措施修正辐射方向圏之前，首先需要快速定位失效单元的位置*实现对失效单元的诊断.作为当前学术界研究的热点问题之一 •阵列失效单元诊断方法受到各[国学者的广泛关注.裔典的诊断方 法包括全息诊断方法程序控制方法[l fi]以及模式识别方法&4.上述方法要求探头以半波长为步进间隔 爲空间采祥数量不低于单元数目，因而，随着单元数量的增大存在采样数量大、测量时间长、诊断效率低等缺 陷.压缩感知理论（Compressive Sensing)的出现为这一领域提供了全新的思路，意大利卡西诺大学Marco Donald M ig lio re教授首次将压缩感知理论用于阵列天线失效单元诊断中•有效减少了采样数目和诊断时 闻.该,国特论托太学Giacomo OUiTOii激授首家将雇叶辦錄_感知蓮论(Bg^esiait Compr喊dve Sess_g)遽顧 于本领域[11] •不仅实现了失效单元的定位，而且给出了诊断的可信程度.土耳其学者T aner l nce提出了一种 采用k(0 <,1)范数的非凸压缩感知方法对阵列失效单元进行诊断^]，进一步减少了空间采样数B s 现有基于压缩感知理论的诊断模型中，均假设探头以等间隔扫描的方式在远场区域对静态方向图进行 采样，从而获取测量数据.然而这一假设很难符合实际情况，例如爾波束通过扫描方式在空域内搜索目标或 者对f扰进行自适应抑制时.最大方向并不一定出现在阵列的法线方向.因此•这类等间隔均匀采样策略所 构造的测量矩阵忽略I目标方位不'同对其性能的彰响.为此•笔者提出了 一种非均匀随机欠采样策略，理论 分析和仿真实验证明了所提方法的优越性和JE确性.1数学模型设有一均句翁阵會有N=2M+1个单元，对称雄鹫在轴]&：?砗元伺距c?=a.5A，i=2rc/i,是自由空饲 波数，A为波长.第《个天线单元电流幅度为是与阵列波束指向有关的各单元相位加权值.各单元正常工作时，阵列方向图函数为M MFE (6) = ^]I n exp(jna ) expCj^^：,, s'md) = ^]I n exp(j 厶sin沒），O )n=—M n=—M其中•夂=4exp(j逝 >，称为单元复电流.阵列单元发生失效时<将导致单元复电流发生变化，定义为〗；；.失效 模式具体分为两种：当匕=〇时，表征第《个单元发生“硬故障”，除此之外的失效模式.即单元的幅度或者相 位偏移正常值定义为“软故障”，因此，存在失效单元时的阵列（简称失效阵列）方向图函数为MFa(0=2I：exP()kz… s'm d) .(2)n =—M由于均匀线阵方向图函数与离散傅里叶变换对在数学关系上存在词构•因此通过特定空间角度上的远 场采样值可重建阵列口面场幅相分布，实现对畸变方向图中失效单元的检测.利用完好阵列方向图与失效阵列方向图F A(0)构造差异性阵列方向图A_F(0)，即MA F(0) = F e (6)—F a (6) =•exp(j々2：…sin沒）.(3)n=—M在通常情况下，失效单元的数鬣S远小于单元总数N(S《N)，因此差异性阵列单元复电流=1…—1；：构成稀疏信号.其中非零元素所在的位置对应失效单元的位置，非零元素的数量代表失效单元的数量，因此 对失效单元进行诊断的问题可转化为差.异性阵列单元复电流这一稀疏信号的重构问题.在已知完好阵列单 元复电流以及完好阵列和失效阵列远场采样数据的条件下，求解式（3)中的即可实现诊斯失效单元，进 一步通过反解得到失效阵列的口面场分布1:=^一乙…，从而实现对失效信息的重构.为了求解；… •通常将式（3)_示为矩阵形式：Y=A W，(4)其中，r6C NX1，表示差异性阵列方向图中的i V个采样数据;W =7:=J•忍=妒•忍6C NX1，表示差异性阵列单元复电流;A6C NXN，表示傅里叶变换矩阵，其元素表示为、.… =e x p(0、s i n〇(1 <<iV).162西安电子科技大学学报（自然科学版)第45卷2诊断方法2. 1测量矩阵的设计与优化在压缩感知理论中测量矩阵少实现对稀疏信号的压缩测量，因此其性能的优劣直接决定信号的线性投 影能否保持其原始结构.引人行随机抽取矩阵T ，构造测量矩阵0=T A =i I A ，即傅里叶变换矩阵按行以随 机方式抽取得到的K K N (K 《N )维子矩阵，定义为傅里叶变换子矩阵（Fourier Transform S ubm atrix )，exp(j k z x sin ^ ) ••• exp(jBind 1)0= \ ;， (5)exp (j 々之工sin 久） … exp (j 々霉w sin 久）K X N 其中，表示第z 个单元位置坐标表示采样角度位置.欠采样得到的K 个采样值记为P ={3^ ：y2，…，3^丨6 Ck ，则新的测量方程表7K 为P = T Y = T A W =n A W I n = 〇W I n = O W . (6)失效单元数目的稀疏性为降低空间采样数量创造了有利条件，加之^为稀疏信号，当选取少时，互相关系数/^(少，少）=l /iV1/2,这是互相关目前能够达到的理论最小值_，因此使最大程度地降低空间 采样数量成为可能.更一般的，考虑零均值，标准差为a 的复高斯噪声e ，则式(6)表示为P = OW + € , (7)在压缩感知理论中，测量矩阵少需要满足约束等距性（Restricted Isom etry P roperty ,R IP )准则，可通过 计算其各列的正交性进行验证.由于文中设计的测量矩阵与标准流行矩阵存在转置关系，因此R IP 的验证 转化为计算少中任意两行的正交性.在阵列形式确定后，少矩阵的行正交性仅与角度6的选取方式有关，不 同的采样策略将引起测量矩阵0正交性的差异.现有文献中均匀采样策略并不总能保证测量矩阵任意两行 间最优的正交性，这时根据目标在空间的方位信息寻找最优的采样策略进而构造对应的测量矩阵，对于提高 失效信息的重构精度具有重要意义.为此笔者提出了 |种类芷弦采样策略.具体来说，根据目标空间方位信 息的差异，在[一90°〜90°]的采样空域内实现了一种新的非均匀采样方式，如式（8)所示，有效地提高了失效 信息的重构精度.sin 沒=«(8)(sin 汐—1 ， 0。
The Application of Cohesion and Coherence Theory i
Journal of Literature and Art Studies, May 2021, Vol. 11, No. 5, 314-319doi: 10.17265/2159-5836/2021.05.008The Application of Cohesion and Coherence Theory inAdvanced College English TeachingCHEN Ying, WU Huan-diSchool of Foreign Languages, Gannan Normal University, Ganzou, ChinaIn 1976, Halliday and Hassan put forward the concept of cohesion and coherence theory for the first time in theirbook English Cohesion and discussed five types of cohesion: reference, substitution, omission, conjunction andlexical cohesion. Some scholars enriched and expanded cohesion and coherence from the perspective of cohesionconditions, phonology, structural relations at the level of meaning and discourse. Predecessors pay much attentionto the theoretical discussion, while from the perspective of the theoretical application, the cohesion and coherencetheory is used for analyzing the advanced college English textbook to provide the guidance for teachers andstudents in teaching and learning-teachers can judge and adopt appropriate teaching methods according to thecohesion and coherence theory; Students can understand cohesion and coherence in the text as well as theinfluencing factors, and adequately use the cohesion and coherence mechanism in listening, speaking, reading andwriting.All Rights Reserved.Keywords: cohesion and coherence theory, theoretical application, the advanced college English textbooks,teaching guidanceI. The Formulation and Development of the Cohesion and Coherence TheoryHalliday and Hasan firstly put forward the idea of cohesion in the book Cohesion in English (Halliday & Hassan, 2001) in 1976.At the semantic level of a discourse, the relationship between meanings constitutes cohesion. Cohesion exists when the meaning of one component needs to be interpreted by the other (Halliday & Hassan, 2001).Halliday and Hasan mainly discuss the five Cohesion types of Cohesion: reference, substitution, omission, conjunction and lexical cohesionin Cohesion in English (Halliday & Hassan, 2001). Hasan expands the scope ofcohesion to the structural relations in text in the level of meaning in Language, Context and Text (Halliday &Hassan, 2001, p. F32). Zhuanglin Hu further expands the scope of cohesion in his monograph Cohesion andCoherence of Texts 1994 (Halliday & Hassan, 2001, p. F32). Firstly, the transitive structural relations are takenas a cohesive mean. Secondly, the cohesive device is put forward in the phonological layer and classifies thephonetic pattern into the cohesion range.CHEN Ying, Ph.D. candidate, Associate Professor, School of Foreign Languages, Gannan Normal University.WU Huan-di, Postgraduate, Postgraduate, Department of English language and literature, Gannan Normal University.THE APPLICATION OF COHESION AND COHERENCE THEORY IN ADVANCED COLLEGE ENGLISH TEACHING 315Cohesion and coherence go hand in hand. Cohesion mechanisms and patterns are used to achieve logical coherence. Delu Zhang (1992, 1993, 1994) studies the coherence conditions in this paper and discusses thelimiting effects of context, information structure, thematic structure and junctions on the coherence (Halliday &Hassan, 2001, p. F32). Besides these, the scope of cohesion mechanism and its relationship with discoursecoherence are studied. The concept of external reference cohesion, which is regarded as the cohesion between thetext and the discourse, and the one of the implicit cohesion are put forward. From this perspective, the externalcohesion and the implicit cohesion will contribute to the text’s coherence.II. The Theoretical Application in Advanced College English Textbook.To achieve the goal of textual coherence, cohesive mechanisms in a text is critical important. There are two kinds of cohesive mechanisms: overt and covert mechanisms. Explicit cohesion is expressed through surfacestructure, and the semantic relationship is clear. Explicit cohesion can be achieved by the grammatical devices:reference, substitutes, ellipsis, and conjunctions and lexical devices.In Language Context Discourse, published by Halliday and Hassan in 1985, Hassan expanded the definition of cohesion and classified cohesion into structural cohesion and non-structural cohesion. The non-structuralcohesion contains the cohesion of component relations and the cohesion of organic relations. The cohesion ofconstituent relations includes four of the five cohesive elements in Halliday and Hasan (1976): reference,substitution, ellipsis and lexical cohesion (Halliday & Hassan, 2001, p. F32). It corresponds to the lexical devicesand lexical devices in the categorization of explicit cohesion.The analysis follows about the grammatical devices-reference, substitutes, omission, conjunctions and All Rights Reserved.lexical device of explicit mechanisms, taking Ships in the Desert (Zhang & Wang, 2010) in advanced Englishtextbooks as the example.A．Grammar Devices1. ReferenceReference refers to the relationship between one linguistic element in a text and another that can be mutually interpreted (Zhu, 2001, p. 14). Halliday and Hasan classified the reference three categories: personal reference,indicative reference and comparative reference (Hu, 2001, p. 37).1a. Industry meant coal, and later oil, and we began to burn lots of it—bringing rising levels of carbon dioxide, with its ability to trap more heat in the atmosphere and slowly warm the earth (Zhang & Wang, 2010, p. 27)1b. 工业意味着煤而后是石油的消耗，我们开始燃烧大量的煤和石油---导致大气层中二氧化碳含量增加，而二氧化碳会使更多的热量停留在大气层中，进而使地球慢慢变暖。
人教版高中英语词汇经典例句整理----选修七
选修7( 本单元由：知福、黄婧、张丽、水梅、婷娣负责)Unit 1Disability n. 伤残；无力；无能a physical or mental condition that means you cannot use a part of your body completely or easily, or that you cannot learn easily1、As a matter of fact, many people have a disability.事实上，许多人身体都有某种缺陷。
2、A good deal of disability and grief could be avoided.许多无能为力和悲伤就可以避免。
3、Buster retired on disability.巴斯特因伤残退了休。
Disabled adj.伤残的unable to use a part of your body completely or easily because of a physical condition, illness, injury, etc.;1、Now that he was disabled , his house had become a prison to him.因为他残废了，他的房子就成了他的牢笼。
2、The soldier disabled by wounds in his leg is buried in sadness.那个腿部受伤致残的士兵正沉浸在悲哀之中。
3、The disabled ship coasted the island, looking for a harbor.那艘损坏的船只在海岛沿岸航行以寻找港口。
Hearing n. 听力；听觉the ability to hear1、Hearing the hiss of gas, he rushed in and turned it off.听到煤气的嘶嘶声，他冲进来把它关掉。
he own study of explosives -回复
he own study of explosives -回复题目：研究爆炸物的一步一步回答引言：在现代科学技术的迅猛发展下，爆炸物作为一种既危险又重要的物质得到了广泛应用。
本文将一步一步回答关于研究爆炸物的一些基本问题，包括研究的背景和意义、研究的方法和实验、可能的结果以及对社会的影响等方面进行探讨。
一、背景和意义1. 什么是爆炸物？爆炸物是一种能够迅速释放巨大能量、产生爆炸反应的物质。
根据其性质和用途的不同，爆炸物可以分为高炸药、弹药、烟火和火焰等。
2. 为什么要研究爆炸物？爆炸物是军事和民用领域中必不可少的物质，研究爆炸物可以提高其临界性能、减少安全风险，增强军事防御能力，并为工程爆破、火灾灭火和烟火表演等方面提供技术支持。
二、研究方法和实验1. 爆炸物的化学分析方法是什么？爆炸物的化学分析常采用色谱质谱联用技术、红外光谱和核磁共振等方法，通过检测物质的成分和结构，确定其性质和稳定性。
2. 如何进行爆炸物的性能测试？对爆炸物性能的测试可以通过测量爆炸物的爆炸速度、燃速、爆热、敏感性和稳定性等指标来实现。
常用的方法包括撞击感度测试、加热感度测试、静电放电感度测试等。
3. 如何模拟爆炸事故进行实验研究？在研究爆炸事故时，可以通过建立数值模型或搭建实验装置，模拟爆炸发生的环境和过程，分析爆炸波传播规律、碎片飞溅及能量释放等参数。
实验参数的准确测试是保证研究结果准确性的关键。
三、可能的结果1. 研究爆炸物可以带来哪些成果？研究爆炸物可以帮助设计和生产更安全、稳定、高效的爆炸物品，提高其威力和使用效能，减少对环境和人体的伤害，从而提升军事和民用领域的安全水平和发展水平。
2. 实验结果如何评估其可靠性？实验结果的可靠性需要通过多次重复实验和与理论模型计算结果的对比来评估。
另外，进行交叉验证和参与科学同行评议也是评估实验结果可靠性的有效方法。
四、对社会的影响1. 为什么研究爆炸物对社会有重要意义？研究爆炸物既关乎国家安全和军事力量的发展，也涉及到生产安全和人员伤亡的风险。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
Full Terms & Conditions of access and use can be found at/action/journalInformation?journalCode=tmph20Download by: [Sichuan University]Date:15 January 2016, At: 22:50Molecular PhysicsISSN: 0026-8976 (Print) 1362-3028 (Online) Journal homepage: /loi/tmph20Theoretical study of the permeation of waterthrough TiO 2 nanotubes using molecular dynamics simulationWeihu Yang , Jiajia Fang , Peng Liu , Junfeng Li & Kaiyong CaiTo cite this article: Weihu Yang , Jiajia Fang , Peng Liu , Junfeng Li & Kaiyong Cai (2011)Theoretical study of the permeation of water through TiO 2 nanotubes using moleculardynamics simulation, Molecular Physics, 109:6, 969-974, DOI: 10.1080/00268976.2011.561809To link to this article:/10.1080/00268976.2011.561809Published online: 18 Mar 2011.Submit your article to this journalArticle views: 274View related articlesCiting articles: 2 View citing articlesMolecular PhysicsVol.109,No.6,20March 2011,969–974RESEARCH ARTICLETheoretical study of the permeation of water through TiO 2nanotubes usingmolecular dynamics simulationWeihu Yang ab *,Jiajia Fang ab ,Peng Liu ab ,Junfeng Li c and Kaiyong Cai abaKey Laboratory of Biorheological Science and Technology for Ministry of Education,Chongqing 400044,PR China;bCollege of Bioengineering,Chongqing University,Chongqing 400044,PR China;c Institute of Materials Scienceand Technology,Chengdu University of Technology,Chengdu 610059,PR China(Received 22November 2010;final version received 31January 2011)In this study,the theoretical structures of armchair (6,6)and zigzag (12,0)TiO 2nanotubes (TiNTs)were constructed by rolling the (101)layer of an anatase TiO 2crystal.The (101)layer was made using Materials Studio (MS)by cutting the cleave plane (101)of the anatase TiO 2crystal.Based on these structures,the basic properties of TiO 2nanotubes were investigated using MS.Molecular dynamics simulations were performed using the software NAMD to investigate the status and permeation of water through the TiO 2nanotubes.Structure analysis shows that both the inner and outer walls of the structures were terminated with oxygen atoms.Thethicknesses of single tube walls are smaller than that of a perfect triple layer (2.20A)in bulk anatase TiO 2.With regard to the bulk Ti–O bond length,the Ti–O bonds in the outer layer are elongated,and are shortened in the inner layer.Molecular dynamics simulation shows that the water molecules in the nanotubes move back and forth,as in one-dimensional Brownian motion.Moreover,the penetration properties of TiNTs are associated with their radii,with the TiNT with larger radii having better penetration properties.Thus,when used in drug delivery or filtration systems,armchair TiNT has a better effect than zigzag TiNT.Keywords:TiO 2nanotube;molecular dynamics;water permeation;theoretical structure1.IntroductionTubular inorganic nanostructures offer great potential for use in sensors,heterojunction solar cells,water photolysis,fuel cells,molecular filtration,and tissue engineering [1].Over the last decade,titanium dioxide (TiO 2)nanotubes have received special attention due to their unique functional properties,such as increased photo-corrosion resistance [2],high photo-conversion efficiency [3],and their suitability as a material for purification of water and air [4].As hydrogen sensors,TiO 2nanotube arrays possess such excellent photo-catalytic properties that they are able to self-clean from environmental contamination by exposure to ambient light [1,5].Photoanodes with a TiO 2nanotube array can enhance the photocleavage of water,perform as a superior electrocatalyst for methanol oxidation,and have been successfully used as photoanodes in dye-sensitized solar cells [1,6].Furthermore,TiO 2nanotubes can be used in the biomedical field as an adhesion and growth support platform for bone and stem cells,as well as their use in drug delivery and enhancing blood clotting for control of hemorrhage [7,8].At present,most efforts are focused on the various synthetic techniques and routes for forming TiO 2nanotubes and nanotube arrays.Most methods for producing TiO 2nanotubes can be classified into (a)replica processes,(b)the chemical approach,and (c)the template method [9–11].Other processes include anodic oxidation for nanotube arrays using a self-assembled template from the sol–gel polymerization of fibrous TiO 2,and treating TiO 2powder in basic aqueous solution [12,13].A limited number of theoretical studies have investigated the theoretical structure and basic properties of TiO 2nanotubes.The permeation of water through TiNTs has significance in biomedicine and environmental protec-tion.Previous studies have explored the use of TiNTs for filtration and separation applications.Shankar et al .[14]have discussed the use of TiNTs as transporters of water–formamide mixtures.Pettibone et al .[15]and Choi et al .[16]have investigated the*Corresponding author.Email:yangweihu@ISSN 0026–8976print/ISSN 1362–3028online ß2011Taylor &FrancisDOI:10.1080/00268976.2011.561809D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016applications of TiNTs for the adsorption of low-molecular-weight organic contaminants and toxins from water.The dynamics of water across nanochan-nels has significant implications for both the under-standing of biological activity and the design of novel nanofluidic devices or machines,which have a wide range of potential applications.The permeation of water through nanotubes is a complicated process that cannot be investigated in detail experimentally.Hence,the theoretical simulation of this process is a promising method.Molecular dynamics simulations were used in previous studies to investigate the transport properties of pristine single-walled carbon nanotubes (SWCNTs)and more elab-orate models based on SWCNTs as nanoscale channels have been proposed [17,18].Moreover,based on the molecular dynamics method,simple nanochannels with appropriate radii have also been utilized as model systems in the exploitation of the primary behaviour of complex biological water channels [19].Most inorganic nanotubes can be viewed as the rolling up of layered structures analogous to graphite sheet(s)[20].Therefore,in this study,we constructed TiO 2nanotubes,including zigzag and armchair nano-tubes,from an anatase TiO 2crystal.Molecular dynamics simulations were performed using NAMD to investigate the permeation process of water through these TiO 2nanotubes.2.Models and computational details2.1.Structure and simulation method of TiO 2nanotubesIn the conventional method,atomic models of nano-tubes may be obtained by simply rolling atomic sheets into seamless cylinders.Together with primitive vec-tors a 1and a 2,a fragment of the crystal structure of anatase TiO 2is shown in Figure 1,which is further used to design the corresponding nanotube.Based on this structure,we can construct the TiO 2nanotube in a standard way by rolling the molecular monolayer into a cylinder like a graphene sheet to form a carbon nanotube.As in the case of single-walled carbon nanotubes,three groups of TiO 2nanotubes can be designed depending on the rolling direction.These TiO 2nano-tubes may be described in terms of the primitive 2D hexagonal lattice vectors a 1and a 2and two integer indices n and m ,C h ¼n a 1þm a 2,and classified into three groups:n ¼m ‘armchair’,n ¼0,m ¼0‘zigzag’,and n ¼m ‘chiral’NTs [21–23].The structures of prototypical single-walled TiO 2nanotubes,namely armchair (6,6)and zigzag (12,0),are simulated inthis work.The structure file of anatase TiO 2(database code:amcsd 0010735)was obtained from the American Mineralogist Crystal Structure Database,and the (101)layer of the anatase structure was constructed using Materials Studio 4.0by cutting the cleave plane (101)with a non-bonded cut-off distance of 9.5A.After completing the energy minimization,the surface struc-ture was converted into a non-periodic superstructure with vectors 6and 6,as shown in Figure 2,then the armchair (6,6)TiO 2nanotube was generated by rolling up the (101)molecular monolayer.The zigzag (12,0)TiO 2nanotube was constructed using the same method.2.2.Method and details of calculationIn this study,MD simulations were performed at 300K using the NAMD software with theCHARMMFigure 1.Crystal structure of anatase TiO 2.Figure 2.Cleave plane (101)of anatase TiO 2.970W.Yang et al.D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016(Chemistry at Harvard Macromolecular Mechanics)force field,which was developed by the Theoretical and Computational Biophysics Group at the Beckman Institute for Advanced Science and Technology,University of Illinois at Urbana-Champaign.To evaluate the permeation of water from TiO 2nano-tubes,the armchair (6,6)and zigzag (12,0)TiNTs simulated by MS were dissolved in a water ball,as shown in Figure 3.Before the non-equilibrium MD simulations were performed,energy minimization and equilibrium MD runs were carried out.The simula-tions were carried out with a time step of 2fs.The cut-off distance for the non-bonding interactions betweenwater and TiNT was set at 12A.All simulations were performed at a constant temperature (NVT)of 300K.A permeation event is defined as a water molecule entering from one end of a nanotube and leaving from the other end,therefore traversing the entire length of the nanotube.To make the simulations faster and the analysis simpler,all atoms in the nanotubes are fixed,with only the water molecules being able to move.MD simulations were then carried out again.After the MD simulations,the output dcd files were analysed in VMD.In this study,each water molecule in the system has a label,which has five possible values:2,–2,1,–1and 0.These values represent,respectively,above the nanotube layer,below the nanotube layer,inside the nanotube layer from the upper surface,inside the nano-tube layer from the lower surface and inside the nanotube layer from the beginning.For each frame,the label of each water molecule is determined,and compared with its label in the previous frame.If the new label is þ2(or –2)and the old label is –1(or þ1),the water molecule has traversed the nanotube,thus a permeation event is reported and counted.If a watermolecule is inside the nanotube layer in the current frame,its label will be determined by its old label [24].3.Results and discussion3.1.Structure analysis of TiO 2nanotubesThe atomic structures of two representative nanotubes,armchair (6,6)and zigzag (12,0),are shown in Figure 4.At the end of the rolling up and optimization process,the inner and outer walls of both structures were terminated with oxygen atoms.The wall thickness was determined as the distance between the outer wall and the inner wall oxygen atoms.The Ti–O bond length was changed slightly because of the curvature effect during the formation of the tubular structure.The thicknesses of single tube walls are smaller thanthat of a perfect triple layer (2.20A)in bulk anatase TiO 2.In this study,the optimized wall thicknesses for armchair (6,6)and zigzag (12,0)nanotubes were 3.157and 3.209A,respectively.In general,the thickness of the tube wall increases with increasing tube diameter.From Figure 4the radii of the armchair (6,6)andzigzag (12,0)structures are 5.706and 6.170A,respectively.With regard to the bulk Ti–O bond length,the Ti–O bonds in the outer layer are elongated,and shortened in the inner layer,similar to a previous finding for MoTe 2nanotubes.For the zigzag (12,0)tube,the Ti–O bond lengths are 2.158, 2.154,and2.152Ain the outer layer and 1.938,1.978,and 1.986A in the inner layer.For the armchair (6,6)tube,the Ti–O bond lengths are 2.157,2.150,and1.880Ain the outer layer and 1.502,1.351,and1.325Ain the inner layer.Moreover,the Ti–O bond lengths decrease with increasing tube diameter.The Ti–O bonds in theouterFigure 3.An armchair (6,6)TiO 2nanotube surrounded by its water ball.Molecular Physics 971D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016layer are longer than those in bulk TiO 2,whereas those in the inner layer can be either elongated or compressed compared with their bulk counterparts,depending on the tube chirality as well as the angle between the Ti–O bond and the tube ually,the bonds normal to the axis of an armchair tube are elongated and the bonds along the axis direction are shortened for zigzag nanotubes [25–28].Anatase TiO 2is one of the three mineral forms of titanium dioxide,the other two being brookite and rutile.Of these forms,the crystals of anatase are very distinctive and are not easily confused with the others.They form an eight-faced tetragonal dipyramid with sharp elongated points.The elongation is sufficiently pronounced to distinguish this crystal form from octahedral crystals.Anatase TiO 2is commonly regarded as having a tetragonal 4/m crystal structure with spacegroup I41/amd.Figure 5shows the XRD pattern of anatase and simulated zigzag (12,0)TiNT.The characteristic peak of the (101)plane of anataseTiO 2can be seen at 25 in Figure 5(a).However,this characteristic peak is shifted to 24 from 25 in Figure 5(b).Compared with anatase TiO 2,in the structure of the zigzag (12,0)TiO 2nanotube,thelatticeFigure 4.Structures of simulated TiNT.Left:armchair (6,6).Right:zigzag (12,0).Cross-sectional (top)and side (bottom)views.Figure 5.XRD patterns of (a)anatase TiO 2and (b)zigzag (12,0)TiNT.972W.Yang et al.D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016parameters and cell volume are increased.This is the main reason for the shift of the (101)plane peak.3.2.The permeation of water through TiO 2nanotubesFigure 6shows an instantaneous snapshot of the trajectory of an MD simulation in equilibrium,which indicates free water diffusion through the nanotube.We can see from the figure that water molecules in the same nanotube are all aligned along the same direction with their oxygen atoms up and hydrogen atoms down.The water molecules are arranged in a very ordered fashion where water layers form a spiral-like chain of water molecules along the TiNT axis.Furthermore,both oxygens and hydrogens tend to be located at the centre of the TiNTs.This is logical since the Lennard–Jones parameter does not allow these atoms to approach the TiNT closer than a certain distance.Since Ti–O 4 Ti–H and O–O 4 O–H ,the hydrogen atoms can approach closer to the wall of TiNT than the oxygens [29–35].Finding all permeation events in the trajectory is tedious,especially in a long trajectory.Therefore,we made a script according to Zhu [32]to simplify the process.To observe the direction of water movement in the nanotubes in the trajectory,the water molecules in the nanotubes move back and forth,as in one-dimensional Brownian motion.During the whole simulation process,for the armchair (6,6)TiNT,the total number of permeation events in the þz direction was 59and the total number of permeation events in the –z direction was 62.However,for the zigzag (12,0)structure,the numbers of permeation events in the þz and –z directions were 75and 73,respectively.As discussed above,the radii for the armchair (6,6)and zigzag (12,0)structures are 5.706and 6.170A,respectively.These results indicate that the penetration properties of TiNTs are associated with their radii,the TiNT with the larger radius having the better penetra-tion property.When used in drug delivery or a filtration system,the armchair TiNT has a better effect than the zigzag structure.4.ConclusionsIn this study,the theoretical structures of armchair (6,6)and zigzag (12,0)TiO 2nanotubes were constructed using Materials Studio by rolling the (101)plane of an anatase TiO 2crystal.At the end of the rolling up and optimization process,the inner and outer walls of both structures were terminated with oxygen atoms.Structure analysis shows that the thicknesses of single tube walls are smaller than thatof a perfect triple layer (2.20A)in bulk anatase TiO 2.With regard to the bulk Ti–O bond length,the Ti–O bonds in the outer layer are elongated,and are shortened in the inner layer.Molecular dynamics simulation shows that the water molecules in the nanotubes move back and forth,as in one-dimensional Brownian motion.Moreover,the penetration proper-ties of TiNTs are associated with their radii,the TiNT with the larger radius having the better penetration property.Thus,when used in drug delivery or a filtration system,armchair TiNT has a better effect than the zigzag structure.AcknowledgementsProject No.CDJZR10230004supported by the Fundamental Research Funds for the CentralUniversities.Figure 6.Water molecules inside a (6,6)TiNT;radial (left)and axial (right)views.Molecular Physics 973D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016References[1]M.Paulose,K.Shankar,S.Yoriya,H.E.Prakasam,O.K.Varghese,G.K.Mor,tempa,A.Fitzgerald and C.A.Grimes,J.Phys.Chem.B 110,16179(2006).[2]D.Wang,T.Hu,L.Hu,B.Yu,Y.Xia,F.Zhou andW.Liu,Adv.Mater.19,1920(2009).[3]F.Mura, A.Masci,M.Pasquali and A.Pozio,Electrochim.Acta 55,2246(2010).[4]A.W.Morawski,M.Janus and B.Tryba,Pol.J.Chem.Tech.11,46(2009).[5]C.A.Grimes and G.K.Mor,TiO 2Nanotube Arrays:Synthesis,Properties and Applications (Springer,New York,2009).[6]F.Sauvage, F.Di Fonzo, A.Li Bassi, C.S.Casari,V.Russo,G.Divitini, C.Ducati, C.E.Bottani,te and M.Graetzel,Nano lett.10,2562(2010).[7]S.Yoriya and C.A.Grimes,Langmuir 26,417(2010).[8]Y.Hong,X.Chen,X.Jing,H.Fan,Z.Gu andX.Zhang,Adv.Funct.Mater.20,1503(2010).[9]H.Shin,D.K.Jeong,J.Lee,M.M.Sung and J.Kim,Adv.Mater.16,1197(2004).[10]Y.Zhang,D.Wang,S.Pang,Y.Lin,T.Jiang andT.Xie,Appl.Surf.Sci.256,7217(2010).[11]S.Rani,S.C.Roy,M.Paulose,O.K.Varghese,G.K.Mor,S.Kim,S.Yoriya,Tempa and C.A.Grimes,Phys.Chem.Chem.Phys.12,2780(2010).[12]Z.Tang and N.A.Kotov,Adv.Mater.17,951(2005).[13]W.Zhu,G.Wang and X.Hong,Electrochim.Acta 55,480(2009).[14]K.Shankar,G.K.Mor,A.Fitzgerald and C.A.Grimes,J.Phys.Chem.C 111,21(2007).[15]J.M.Pettibone, D.M.Cwiertny,M.Scherer andV.H.Grassian,Langmuir 24,6659(2008).[16]H.Choi,S.R.Al-Abed and D.D.Dionysiou,Sustain.Sci.Eng.2,229(2010).[17]M.Esai Selvan,D.J.Keffer and S.Cui,Mol.Simul.36,568(2010).[18]S.Joseph and N.R.Aluru,Nano Lett.8,452(2008).[19]R.R.Johnson,A.T.Charlie Johnson and M.L.Klein,Nano Lett.8,69(2008).[20]A.N.Enyashin and A.L.Ivanovskii,Mater.Lett.62,663(2008).[21]A.N.Enyashin and A.L.Ivanovskii,Phys.E 30,164(2005).[22]V.V.Ivanovskaya,A.N.Enyashin and A.L.Ivanovskii,Mendeleev Commun.23,5(2003).[23]J.Wang,L.Wang,L.Ma,J.Zhao, B.Wang andG.Wang,Phys.E 41,838(2009).[24]F.Q.Zhu and K.Schulten,Biophys.J.85,236(2003).[25]F.M.Hossain,A.V.Evteev and I.V.Belova,Comput.Mater.Sci.48,854(2010).[26]G.Mogilevsky,Q.Chen and A.Kleinhammes,Chem.Phys.Lett.460,517(2008).[27]A.V.Bandura and R.A.Evarestov,Surf.Sci.603,L117(2009).[28]R.A.Evarestov, A.V.Bandura,M.V.Losev,S.Piskunov and F.Yu.Zhukovskii,Zhukovskii,Phys.E 43,266(2010).[29]B.Liu,X.Li,B.Li,B.Xu and Y.Zhao,Nano lett.9,1386(2009).[30]A.S.Brady-Estevez,S.Ang and M.Limelech,Small.4,481(2008).[31]X.Gong,J.Li,H.Zhang,R.Wan,H.Lu,S.Wang andH.Fang,Phys.Rev.Lett.101,257801(2008).[32]X.Li,G.Zhu,J.S.Dordick and P.M.Ajayan,Small.3,595(2007).[33]K.S.Walton,lward,D.Dubbeldam,H.Frost,J.J.Low,O.M.Yaghi and R.Q.Snurr,J.Am.Chem.Soc.130,406(2008).[34]A.Z.Panagiotopoulos,Int.J.Thermophys.15,1057(1994).[35]V.A.Bakaev and W.A.Steele,Langmuir.8,1372(1992).974W.Yang et al.D o w n l o a d e d b y [S i c h u a n U n i v e r s i t y ] a t 22:50 15 J a n u a r y 2016。