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有关于月球或太空的科幻故事作文英语It was the year 2050 and humanity had finally achieved its long-held dream of establishing a permanent human settlement on the Moon. The lunar colony, known as Artemis, had grown steadily over the past decade, with a population of over 1,000 scientists, engineers, and support staff living and working on the lunar surface.The journey to this milestone had not been an easy one. There were countless technical and logistical challenges that had to be overcome - from the development of reliable life support systems capable of sustaining human life in the harsh lunar environment, to the complex task of transporting all the necessary equipment, supplies, and personnel to the Moon. But through determination, innovation, and a relentless pioneering spirit, the world's space agencies had persevered, turning the dream of a lunar settlement into a reality.For Lena, a young astrophysicist who had been part of the Artemis project since the beginning, this was the fulfillment of a lifelong ambition. As she gazed out of the pressurized observation dome at the desolate lunar landscape, she couldn't help but feel a profoundsense of wonder and accomplishment. After so many years of planning and preparation, she was now living and working on another world - a truly remarkable achievement.Lena's primary role was to help monitor and maintain the various scientific instruments and experiments that were being conducted on the lunar surface. This included remote-operated telescopes, geologic survey equipment, and specialized laboratories for studying the unique properties of the lunar environment. The data gathered from these experiments was then transmitted back to research centers on Earth, where it was analyzed by teams of scientists working to expand our understanding of the Moon and the solar system.One of Lena's favorite tasks was operating the lunar rover, a highly advanced and versatile vehicle that allowed the Artemis crew to explore the surrounding region in greater detail. The rover was equipped with a range of scientific instruments, including ground-penetrating radar, seismic sensors, and a suite of spectrometers for analyzing the chemical composition of the lunar soil and rocks. During her excursions, Lena would often stop to collect samples, taking great care to document their location and characteristics.But it wasn't just the scientific work that captivated Lena - it was the sheer beauty and majesty of the lunar environment itself. The vast,barren landscape, sculpted by billions of years of meteorite impacts, was a sight to behold. And the low-gravity conditions, which allowed her to bound effortlessly across the surface, never ceased to fill her with a sense of wonder and freedom.Perhaps most remarkable of all, though, were the views of Earth, visible as a magnificent blue-and-white orb hanging in the blackness of space. Lena never tired of gazing at her home planet, marveling at the fragility of the life that it sustained and the extraordinary journey that had brought humanity to this point.One day, as Lena was conducting a routine survey of the lunar surface, she noticed something unusual. Using the rover's high-resolution cameras, she observed what appeared to be a small, artificial structure nestled in a shallow crater near the colony's outskirts. Intrigued, she quickly reported her findings to the Artemis command center, and a team of engineers and scientists was dispatched to investigate further.As they approached the site, it became clear that the structure was not of human origin. It was a compact, angular device, seemingly constructed from a strange, metal-like material that Lena had never seen before. Scans revealed that it was powered by an unknown energy source and appeared to be transmitting a faint, pulsing signal.The team carefully examined the device, running a series of tests and analyses to determine its purpose and origin. After weeks of intensive study, they made a startling discovery: the structure was, in fact, an advanced alien communications relay, left behind by an extraterrestrial civilization that had visited the Moon centuries ago.The implications of this discovery were profound. It meant that humanity was not alone in the universe, and that there were other intelligent beings out there, with technologies and capabilities that far surpassed our own. It also raised a host of questions about the nature of this alien civilization, their intentions, and the extent of their presence in the solar system.As news of the discovery spread back to Earth, the world was gripped by a mixture of excitement, wonder, and trepidation. Some hailed it as the most significant scientific and technological breakthrough in human history, while others expressed concerns about the potential risks and challenges of making contact with an extraterrestrial civilization.For Lena and the rest of the Artemis crew, the discovery was both thrilling and humbling. It underscored the vastness of the universe and the possibility that humanity's place in it was just a small part of a much larger cosmic story. As they continued their work on the lunar surface, they couldn't help but wonder what other secrets theMoon might hold, and what other wonders and mysteries the cosmos might have in store.。
高三英语天文观测设备单选题50题1. An ______ is a building or place equipped with telescopes and other instruments for observing astronomical objects.A. observatoryB. laboratoryC. factoryD. library答案：A。
解析：本题考查名词词义辨析。
observatory意为天文台，是配备望远镜等仪器用于观测天文物体的建筑或场所，符合题意。
laboratory是实验室，主要用于科学实验；factory是工厂，用于生产制造；library是图书馆，用于藏书和供人阅读学习，这三个选项均不符合天文观测场景的描述。
2. The ______ is an important tool for astronomers to observe the stars and galaxies far away.A. microscopeB. telescopeC. magnifierD. binoculars答案：B。
解析：本题考查天文观测工具相关的名词。
telescope望远镜是天文学家观测遥远恒星和星系的重要工具。
microscope是显微镜，用于观察微小的物体，如细胞等；magnifier是放大镜，主要用于放大近距离的小物体；binoculars是双筒望远镜，虽然也可用于观测，但在天文观测中telescope更为专业和常用。
3. In the observatory, the ______ of the telescope needs to be adjusted precisely to get a clear view of the celestial bodies.A. lensB. buttonC. handleD. box答案：A。
解析：本题考查名词在天文观测设备中的部件。
现代无人机对现代农业的影响英语作文Modern agricultural drones have had a significant impact on modern agriculture, revolutionizing the way farmers manage their crops and increasing efficiency and productivity. There are several key ways in which agricultural drones have influenced modern agriculture.Firstly, agricultural drones have improved crop monitoring and management. With the help of advanced sensors and imaging technology, drones can capture high-resolution images of the entire field, allowing farmers to identify areas of stress or disease in the crops. This enables farmers to take targeted and timely action to address any issues, ultimately leading to higher crop yields and better quality produce.Secondly, agricultural drones have transformed the way farmers apply fertilizers and pesticides. Drones equipped with precision spraying systems can accurately and efficiently apply these chemicals to crops, reducing waste and minimizing environmental impact. This precise application also reduces the exposure of farm workers toharmful chemicals, improving overall safety in agricultural operations.Furthermore, agricultural drones have enhancedirrigation management. By using thermal and multispectral imaging, drones can assess the moisture levels of soil and crop health, enabling farmers to optimize their irrigation practices. This not only conserves water but also ensures that crops receive the right amount of water, leading to improved growth and yield.In addition, agricultural drones have streamlined the process of crop scouting and field mapping. Drones can quickly and easily survey large areas of land, providing farmers with detailed maps and data on crop health, soil conditions, and topography. This information is invaluable for making informed decisions about planting, harvesting, and land management.Moreover, agricultural drones have improved labor efficiency and reduced operational costs. Drones can cover large areas of farmland in a fraction of the time it would take for traditional methods, saving farmers time andresources. This allows farmers to focus on other important tasks and ultimately increases their overall productivity.Overall, the impact of modern agricultural drones on modern agriculture has been overwhelmingly positive. They have revolutionized the way farmers monitor and managetheir crops, leading to increased efficiency, productivity, and sustainability in agricultural practices.现代农业无人机对现代农业产生了重大影响，彻底改变了农民管理作物的方式，提高了效率和生产力。
浦东新区 2019 学年度第二学期后续教学质量检测高三英语试卷说明:(1)本场考试时间为 120 分钟，总分 140 分；(2)请认真答卷，并用规范文字书写。
I. Listening Comprehension(满分 25 分)Section A(共 10 题，每小题 1 分，满分 10 分)Directions:In Section A, you will hear ten short conversations between two speakers. At the end of each conversation, a question will be asked about what was said. The conversations and the questions will be spoken only once. After you hear a conversation and the question about it, read the four possible answers on your paper, and decide which one is the best answer to the question you have heard.1.A. A teacher.B. A salesman.C. A hotel manager.D. A policeman.【答案】D【解析】【原文】M: Could you still remember the exact time when the theft happened?W: Yes, of course.Q: What is probably the man?2.A. July 10.B. July 27.C. July 13.D. July 30. 【答案】B【解析】【原文】W: We had planned to set out for New York on July 13 but the weatherman said there would be a heavy rain on that day.M: Well, let’s delay the trip to July 30. But we have to book the air t icket three days in advance.Q: When does man propose to book the air ticket?3.A. He does not want any mixed grill.B. There is no more mixed grill left.C. Mixed grill is his favorite food.D. He orders the mixed grill for the woman.【答案】A【解析】【原文】W: Are you going to try some of the mixed grill?M: Well, to be honest, I have never been a big fan of meat.Q: What does the man imply?4.A. To appreciate famous sculptures.B. To learn skills of paintings.C. To look after her sister.D. To visit the modern art exhibition.【答案】C【解析】【原文】M: News comes that a modern art exhibition is being held and a variety of famous paintings and sculptures is on display. Would you like to go with me tomorrow? W: I’d love to, but I have to take care of my sister who is il l.Q: What is woman probably going to do tomorrow?5.A. The man should get up early in the morning.B. The man can find the time if he makes up his mind.C. It is a bad habit to learn English late in the evening.D. It really takes time to have a good command of English.【答案】B【解析】【原文】M: I want to practise my oral English but never seem to have the time. W: Why don’t you do i t the first thing in the morning?Q: What does the woman mean?6.A. Asking Simon and Sally for help.B. Decorating the house.C. Preparing for a party.D. Purchasing the food.【答案】C【解析】【原文】M: Have you got fully prepared for the party to celebrate your parents’ 20th wedding anniversary?W: Not yet. But everything is going on smoothly. Simon offers to help me with the decoration and Sally will care for the purchase of food.Q: What are the speakers talking about?7.A. 10.B. 11.C. 12.D. 13.【答案】B【解析】【原文】W: We had expected a dozen of guests to attend the lecture but Johnson called just now that he and his wife could not make it.M: All right. I’m just going to tell you I have invited Franklin.Q: How many guests are going to attend the lecture?8.A. She refuses to give free admission to the man.B. She asks the man to bring her some coins.C. She hesitates to give the man free admission.D. She thinks working in a bank has great benefits.【答案】A【解析】【详解】W: Now that you’ve got a job in the Disney Resort, can’t you bring me afree admission now and then?M: Certainly, if you bring me a few coins now and then from the bank where you work! Q: What does the man mean?9.A. The woman broke her arm while doing the project.B. The man expect the woman to go on with the project.C. It takes the doctor a month to cure the woman’s broken leg.D. The woman can now come back to do her unfinished project .【答案】B【解析】【原文】W: What bad news! The doctor says my broken leg has to be secured with bandage for another month.M: I am sorry to hear that. How I wish you could recover soon and continue the project with us.Q: What can you learn from the conversion?10.A. He has totally no idea of how to play games.B. He thinks the team has already been eliminated.C. He finds it hard to believe the team will enter the national game.D. He does not know whether the team enter the national game or not.【答案】D【解析】【原文】W: Did you hear if our school football team is going on to the national game or did they get eliminated halfway?M: To tell the truth, I haven’t been following their progress for years.Q: What does the man imply?Section B(共 10 题，每小题 1.5 分，满分 15 分)Directions: In Section B, you will hear two short passages and a longer conversation,and you will be asked some questions on the passages and the conversation. The passages and the conversation will be read twice, but the questions will be spoken only once. When you hear a question, read the four possible answers on your paper and decide which one is the best answer to the question you have heard. Questions are based on the following passage.11. A. 8:30. B. 9:00. C. 8:45. D. 9:15.12.A. When the interview begins, you should shake hands with the interviewer first.B. If you don’t understand a question, you should answ er it as quickly as possible.C. Your answer should contain all the skills you have to convince the interviewer.D. A good response can help you sell the interviewer on yourself as the best candidate.13.A. Ask the next step in the hiring process.B. Offer to shake hands with the interviewer again.C. Ask more questions about the position and the salary.D. Take the opportunity to catch your breath and stay calm.【答案】11. C 12. D 13. A【解析】【原文】As an HR manager who has been engaged in recruitment for 30 years, I would like to give you some tips on how to perform better in a job interview. First and foremost, arrive 15 minutes early prior to your interview. An interview is even more stressful than normal if you’re rushing to get there on time. Second, send a positive message through your body language. Shake hands firmly, but only if a hand is offered to you first. Always maintain eye contact and listen carefully. If you do not understand a question, ask the interviewer to either repeat or clarify the questions for you. Give honest, direct answers. However, be sure that your responses are focused on the questions and highlight the skills related to the job. Keep in mind that your responses are your sales pitch. You’re selling the interviewer on yourself as the best candidate for a second interview and for the job, so be sure you focus on yourrelevancy. Last but not least, towards the end of the interview, let the hiring manager know that you think the job is an excellent fit and that you are very interested in the job. It’s appropriate to ask what the next step in the hiring process will be and when you might expect to hear.Questions:If you have an interview at 9:00, when should you arrive according to the speaker’s advice?Which one of the following is TRUE according to the speaker’s advice? If you are the interviewee, what should you do towards the end of the interview according to the speaker’s advice?Questions are based on the following passage.14.A. Drinking a lot of alcohol.B. Going shopping in stores.C. Gathering around tables for hotpot.D. Eating fried food and barbecued meat.15.A. Movies are available to people in Shanghai at midnight.B. People in Hangzhou attach great importance to dinner.C. A total of nine online platforms provide data for the report.D. People in Beijing are most likely to order Starbucks in the afternoon.16.A. People’s eating habits in d ifferent regions of China.B. Th e impact of mobile payment on Chinese people’s lifestyle.C. The difference of nightlife among residents in Chinese cities.D. The pressure of urban life brought by the nightlife activities.【答案】14. D 15. A 16. C【解析】【原文】A new report driven by what people in eight Chinese cities buy on their phonesafter the night falls reveals just how different the nightlife is among Chinese urban dwellers. According to data gathered from Alibaba Group on payment services across eight platforms－including Alipay, food delivery unit Ele.me, as well as the video-streaming site Youku－Chinese people go to bed at 1 a.m. on average. Additionally, it also shows Beijingers order Starbucks after 6 p.m. the most, go to bed late and rise at the earliest times. Residents in Shanghai purchase movie tickets and pay the most hospital visits at midnight, and East China’s Nanjing city has the most bookstore visits. As for the night food orders, they start coming in at 9 p.m. with orders for fried chicke n and barbecued sticks of meat ranking as people’s favorites. Down southwest in Chengdu, people spend the most on dinner, gathering around tables for hotpot. Citizens in Hangzhou City in eastern China prefer drinks over food, with its highest sales of alcohol at night. Mobile payment has been an integrated part of people’s lives in China, as consumers can place a food order, shop online and also pay utility bills on their smartphone screens－no matter what time it is. However, the active nightlife also reflects the pressure of urban life. Questions:What is the favorite nightlife activity of people in Nanjing?Which of the following can be inferred from the report?What is the report mainly about?Questions are based on the following passage.17.A. People can drive their cars at a high speed on the PRT system.B. Each car on the PRT system can carry 300 passengers at a time.C. The cars running on the PRT system can be controlled by a wire.D. The power that sets the cars on the PRT system running comes from the sun.18.A. The traffic jam in Masdar City.B. Building more roads with wider lanes.C. Solutions to traffic jams.D. Encouraging people to cycle more.19.A. Taxi drivers.B. Shop assistants.C. Teachers and students.D. The elderly and the sick.20.A. The benefit of cycling lies in that more people can travel at the same time.B. The man thinks that building more roads with wider lanes is not a perfect solution.C. The woman disagrees with the second expert because riding is practical on rainy days.D. The woman agrees with the first expert because it is very expensive to build more roads.【答案】17. D 18. C 19. A 20. B【解析】【原文】M: The Nightly News made a special program on how to deal with traffic jams in big cities. Did you watch it?W: Not yet. Would you please tell me something about it?M: Certainly. The program began with an introduction of the PRT system in Masdar City. Controlled wirelessly and powered by solar energy, 300 highspeed driverless cars each carrying three passengers were running on it. Then, three experts were invited to work out a few possible solutions.W: Really? What are those solutions?M: Well, the solution proposed by the first expert involves engineering. This means building more roads with wider lanes so that more cars can travel at the same time. W: Hmm, don’t you think more roads may actually encourage more traffic? Besides, the cost is so high.M: You hit the point. The second expert criticized that solution and proposed that the government should encourage people to cycle more because this mode of transport has obvious health benefits and helps to reduce air pollution.W: Yeah. But is it practical in every climate? What’s more, riding can prove dangerous in heavy traffic.M: I agree with you. The solution put forward by the last expert is to increase taxon fuel so that people are more likely to think carefully about using cars. Do you think it really works?W: Not exactly. It can discourage people from driving to work to some extent. But how about people “driving for work” ? They will lose their jobs.M: All right. It seems that each of the solutions has its own advantages and disadvantages.Questions:Which one of following statements is TRUE about the PRT system in Masdar City? What did the experts in the TV program mainly discuss about ?If the government increases the tax on fuel, who will directly fall victim to it? According to the dialogue, which one of following statements is TRUE? II Grammar and Vocabulary(满分 20 分) Section A(共 10 题，每小题 1 分，满分 10 分) Directions: After reading the passages below, fill in the blanks to make the passagescoherent and grammatically correct. For the blanks with a given word, fill in each blank with the proper form of the given word; for the other blanks, use one word that best fits each blank.The rapid spread of new technology in Africa is changing the way people receive news and entertainment. Traditionally, vast numbers of Africans relied on radio to keep ___21___ (inform). So how is this medium coping ___22___the face of fast growing competition from mobile phone, Internet and television?If you want to get a sense of ___23___Africa is listening to, come with me to Kenya’s capital Nairobi. Over the past 20 years, the number of radio stations in Kenya ___24___ (grow) from 10 to more than 130. It’s a trend ___25___has been mirrored across Africa. Economic growth paired with ___26___new generation that’s more connected to the outside world and more diverse. Stations have become incredibly local producing programs in dozens of indigenous( 当地的)languages and increasingly global playing western music. Africa’s passion for radio remains insatiable(未被满足)___27___the growth of television. As not many of them ___28___afford a TV, thisrise in TV sales or TV numbers will never compare to radio at least for the next maybe decade or two.Commercial radio stations are what most people listen to. In Nairobi, I have interviewed a lot of people about their attitude towards radio. “Yeah, I love to listen to news. I like to hear what’s happening in people’s lives.” “Radio is much ___29___(cheap). I like listening to the music station.” “It’s so convenient. You can choose as many stations ___30___you like.” “It tells us the news of what is happening all over the world.” Therefore, it seems tha t radio is here to stay for a while.【答案】21. informed22. in 23. what24. has grown25. that/which26. a 27. despite28. can 29. cheaper30. as【解析】这是一篇说明文。
增加使用无人机的利弊英语作文The Pros and Cons of Increasing Drone UsageDrones, also known as unmanned aerial vehicles (UAVs), have gained significant popularity in recent years due to their versatility and accessibility. However, like any technology, the increasing use of drones comes with both advantages and disadvantages.On the positive side, drones offer efficient and cost-effective solutions for various applications. In agriculture, for example, drones equipped with sensors and cameras can monitor crop health, detect diseases, and even spray pesticides, significantly reducing labor costs and increasing efficiency. In the field of photography and videography, drones provide a unique perspective that was previously inaccessible or extremely difficult to capture. Furthermore, drones are invaluable in search and rescue missions, able to quickly survey large areas and locate missing persons or assess damage after natural disasters.However, the rise of drones also brings challenges. One significant concern is privacy. Drones equipped with high-resolution cameras can potentially invade people's privacy, especially in residential areas. Additionally, the noise generated by drones can be a nuisance, particularly in urban environments. There are also safety concerns, as drones have the potential to collide with manned aircraft or cause accidents if not operated properly.Moreover, the misuse of drones for illegal activities such as smuggling or spying is another worrying aspect. Regulatory frameworks are still evolving to address these issues, but it remains a challenge to enforce these regulations effectively.In conclusion, while drones offer remarkable benefits in various fields, their increasing use also poses significant challenges that need to be carefully managed. Balancing the benefits of drone technology with the potential risks it poses is crucial to ensure their safe and responsible integration into society.增加使用无人机的利弊近年来，无人机（也称为无人驾驶飞行器UAVs）由于其多功能性和易获取性而越来越受欢迎。
黑龙江省哈尔滨三中2024届高考最后冲刺模拟（二）英语试题请考生注意：1．请用2B铅笔将选择题答案涂填在答题纸相应位置上，请用0．5毫米及以上黑色字迹的钢笔或签字笔将主观题的答案写在答题纸相应的答题区内。
写在试题卷、草稿纸上均无效。
2．答题前，认真阅读答题纸上的《注意事项》，按规定答题。
第一部分（共20小题，每小题1.5分，满分30分）1．We ______ be careful with the words we say when we are angry.A．may B．can C．might D．should2．To tell the truth, I would rather I ________ the pain instead of you. You don’t know how worried I was.A．took B．had takenC．have taken D．should have taken3．Along with the email was my brother’s promise ______ I came first in the competitio n, he would buy me an MP4. A．what B．that C．that if D．whether4．According to the school rule, no child be allowed out of the school, unless accompanied by his or her own parents.A．should B．mustC．shall D．can5．_______child will find his own personal road to success.A．Each B．The otherC．Either D．Another6．—What did you say you were reluctant to risk just now?—_________ to high levels of radiation.A．Being exposed B．Having been exposedC．To be exposed D．Exposed7．The climate conference was attended by 11,000 people, it the largest UN gathering ever held.A．making B．to make C．made D．to be making8．He works very hard in order to get himself ______ into a key university.A．accepted B．received C．announced D．admitted9．---.We didn’t find t he Blacks during the lecture.--- No one had told them about _____ a lecture.A．there to be B．there being C．there be D．there was10．It is sometimes said that a society can be judged ____the way it cares ____its weakest members.A．on; about B．by; for C．under; with D．with; on11．The party last month really gave me a lot of fun. So can we have this month,Mr.James?A．any B．one C．another D．the other12．Mary_______ to writing classes every night since June and the course will end this week.A．had gone B．has been goingC．is going D．went13．Tom is proud and ________, never admitting he is wrong and always looking for someone else to blame.A．strict B．stubbornC．sympathetic D．sensitive14．The government has taken some measures to solve the shortage of electricity, but it will be some time_________ the situation improves.A．since B．whenC．unless D．before15．She then took the little key, and opened it, trembling, but could not at first see anything ________, because the windows were shut.A．plainly B．closely C．firmly D．frequently16．He messed the project up, but he behaved as if nothing ______.A．had happened B．happenedC．would happen D．would have happened17．Laughter produces short-term changes in the function of the heart and blood circulation,_________heart rate and oxygen consumption.A．increasing B．to increase C．having increased D．being increased18．--Can’t you stay a little longer? I really want to talk more with you.--Me, too. ________ I have to get home before 10 at night.A．But B．Since C．And D．For19．Linda realized she was in the wrong and promised to ________ a new leaf.A．take over B．turn over C．get over D．go over20．Nowadays, more and more young ladies, figures most are fine enough, are going on a diet.A．who B．whoseC．of whose D．of whom第二部分阅读理解（满分40分）阅读下列短文，从每题所给的A、B、C、D四个选项中，选出最佳选项。
嫦娥一号发射视频英语作文As the world watched with keen interest, China made a significant stride in its space exploration history with the launch of Chang'e 1, its first lunar orbiter. The event marked a new chapter in China's ambitious space program and was a source of national pride.On October 24, 2007, the Chang'e 1 spacecraft was launched from the Xichang Satellite Launch Center in Sichuan province. The launch was meticulously planned and executed, showcasing the country's advanced technological capabilities. The rocket carrying the spacecraft soared into the sky, leaving a trail of smoke and a thunderous roar that echoed across the launch site.The mission of Chang'e 1 was multifaceted. It aimed to map the lunar surface in detail, detect the elements and materials on the Moon, and provide valuable data for future lunar missions, including potential landing sites. The spacecraft was equipped with a suite of scientific instruments, including a high-resolution camera and a neutron spectrometer.The journey of Chang'e 1 to the Moon was not without its challenges. The spacecraft had to navigate the vast expanse of space, enduring the harsh conditions of the void. However, the team of scientists and engineers back on Earth worked tirelessly, guiding the spacecraft through its complextrajectory.Upon reaching the Moon, Chang'e 1 entered into a polar orbit, allowing it to survey the lunar surface comprehensively. The data sent back to Earth provided scientists with a wealth of information that has contributed to our understanding of the Moon's geology and composition.The success of the Chang'e 1 mission was a testament toChina's growing expertise in space technology. It not only positioned China as a key player in space exploration alongside the United States and Russia but also inspired a new generation of scientists and engineers to pursue careers in space research.In conclusion, the launch of Chang'e 1 was a historic moment for China and for the global space community. It signified a new era of lunar exploration and set the stage for further advancements in space technology. The images and data collected by Chang'e 1 have enriched our knowledge of the Moon and have paved the way for future missions that will delve even deeper into the mysteries of our nearest celestial neighbor.。
高三英语公众意识单选题50题1. In many cities, people are encouraged to use public transportation instead of private cars to reduce _____.A. air pollutionB. water pollutionC. noise pollutionD. soil pollution答案：A。
解析：本题考查名词短语的辨析以及公众的环保意识。
句中提到鼓励人们使用公共交通代替私家车，这一举措主要是为了减少空气污染。
选项A“air pollution”表示空气污染，符合题意。
选项B“water pollution”是水污染，与使用交通工具关系不大。
选项C“noise pollution”是噪音污染，虽然私家车也会产生噪音污染，但这里主要强调的是与公共交通相对比下对空气的影响。
选项D“soil pollution”是土壤污染，也与使用交通工具的关联较小。
2. Recycling is an important part of resource conservation. Which of the following items is the most difficult to recycle?A. Glass bottlesB. Plastic bagsC. NewspapersD. Aluminum cans答案：B。
解析：本题考查公众对不同物品可回收性的了解以及相关词汇。
在这四个选项中，塑料袋子是最难回收的。
选项A“Glassbottles”玻璃瓶相对容易回收利用。
选项C“Newspapers”报纸也是可回收材料。
选项D“Aluminum cans”铝罐也比较容易回收。
而塑料袋子由于材质薄、易破损、分类难等问题，导致其回收难度较大，这也体现了公众在资源保护方面需要意识到正确处理塑料袋子的重要性。
3. Many forests are being cut down for various reasons. What can ordinary people do to help protect the forests?A. Buy more wooden furnitureB. Use disposable chopsticksC. Support forest conservation organizationsD. Ignore the problem答案：C。
调查客人对酒店体验的四个方面英语作文回答1:Title: A Survey on Four Aspects of Guest Experience at HotelsIntroduction:The hospitality industry has always placed a lot of emphasis on guest satisfaction. In order to understand and improve the guest experience, it is important to conduct regular surveys. This article aims to present the findings of a recent survey that focused on four key aspects of guest experience at hotels.Findings from the Survey:The survey collected responses from a diverse group of guests who had recently stayed at various hotels. The four aspects of the guest experience that were explored are the check-in process, room cleanliness, amenities, and overall customer service.Check-in Process:The check-in process plays a crucial role in shaping the initial impression of a hotel. According to the survey, themajority of guests expressed satisfaction with the check-in process. They highlighted the importance of a smooth and efficient check-in, especially after long travels. However, some guests also pointed out the need for more personalized and welcoming check-in experiences.Room Cleanliness:When it comes to room cleanliness, the survey revealed that most guests expected a high standard of hygiene. The respondents emphasized the importance of spotless bathrooms, fresh linens, and tidy living spaces. Any shortcomings in this aspect were considered highly detrimental to the overall guest experience.Amenities:The availability and quality of amenities also featured prominently in the survey. Guests appreciated well-maintained facilities such as swimming pools, fitness centers, and spas. Several respondents also stressed the importance of complimentary items, including toiletries, Wi-Fi, and in-room entertainment options.Overall Customer Service:The final aspect of the survey focused on the overall customer service provided by hotel staff. This encompasses interactions with front desk personnel, housekeeping, dining staff, and other hotel employees. The responses indicated that friendly, attentive, and responsive customer service significantly enhanced the guest experience. On the other hand, any perceived rudeness or unprofessional behavior left a lasting negative impression.中文回答：引言：酒店业一直都非常重视客人的满意度。
a r X i v :a s t r o -p h /9807125v 1 13 J u l 1998A high-resolution radio survey of the Vela supernova remnant(To appear in The Astronomical Journal )D.C.-J.BockRadio Astronomy Laboratory,University of California,Berkeley,CA 94720;and School ofPhysics,University of Sydney,NSW 2006,Australia;dbock@and A.J.Turtle and A.J.Green School of Physics,University of Sydney,NSW 2006,Australia;turtle@.au,agreen@.au ABSTRACT This paper presents a high-resolution radio continuum (843MHz)survey of the Vela supernova remnant.The contrast between the structures in the central pulsar-powered nebula of the remnant and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class.The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula,and make possible a comparison of radio,optical and soft X-ray emission from the resolved shell filaments.The survey,made with the Molonglo Observatory Synthesis Telescope,covers an area of 50square degrees at a resolution of 43′′×60′′,while imaging structures on scales up to 30′.Subject headings:ISM:individual (Vela SNR,Vela X)—supernova remnants —pulsars:individual (PSR B0833-45)1.IntroductionThe Vela supernova remnant (G263.9−3.3)is one of the closest and brightest supernova remnants.Recent measurements support a distance of about 350pc (Dubner et al.1998and references therein).Estimates of its age range from a few thousand years (Stothers 1980)to 29,000yr (Aschenbach,Egger,&Tr¨u mper 1995)with a widely used value being that given by the characteristic age of its pulsar,11,400yr (Reichley,Downs &Morris 1970).Its brightness and large angular size (∼8◦)have made possible its study at many wavelengths.Yet it has been less intensively studied than other close remnants such as the plerionic Crab Nebula and the shell-type Cygnus Loop,although it is arguably the closest and a key member of the third major class of SNRs,the composite remnants.Among many controversies surrounding its nature hasbeen that of whether it is a shell or a composite remnant.This paper aims to show that the Vela SNR definitely can be seen as a composite remnant on morphological grounds and ought to be considered the Galactic archetype.Previous radio studies of the Vela SNR region have mainly used lower resolution single dish images over a frequency range from408MHz to8.4GHz(Milne1968a;Day,Caswell,&Cooke 1972,Milne1980;Milne1995;Duncan et al.1996).The earliest observations showed the Vela SNR to comprise three main areas of radio emission,called Vela X,Y,and Z,within a diameter of 5◦,corresponding roughly with the bright,filamentary structure of the nebula Stromlo16(Gum 1955;Milne1968b).Until recently,this5◦diameter was thought to indicate the extent of the remnant,with the nebula Vela X containing the pulsar(PSR B0833–45),offset to one side.This pulsar,discovered in1968,was immediately associated with the Vela supernova remnant(Large et al.1968).Calculations by Bailes et al.(1989)indicate that there is only a0.1%probability that the pulsar and the supernova remnant are in chance superposition.Kundt(1988)deduced from the408MHz survey of Haslam et al.(1982)that the Vela SNR might be much larger,in fact about8◦across,with the pulsar approximately at the center.ROSAT and radio observations (Aschenbach1992;Duncan et al.1996)reinforced this model.The discovery that the speed and direction of the pulsar’s proper motion indicates that it was born near the center of the8◦Vela SNR shell(Aschenbach et al.1995)solves the offset problem.This is one of only a few reliable SNR/pulsar associations(Kaspi1996).The most recent single-dish observations(Milne1980; Milne1995)began to resolve Vela X at higher frequencies(5–8.4GHz)and uncovered strongly linearly polarized structure.Higher resolution observations at327MHz with the Very Large Array (VLA)by Frail et al.(1997)showed a brightfilament near the center of Vela X,near the X-ray feature called a‘jet’by Markwardt&¨Ogelman(1995).This feature extends southwards from the pulsar,which is offset to the north of Vela X.The radio spectral index of Vela X isflatter than that of the rest of the remnant,leading to the remnant’s classification as a composite,with the Vela X nebula directly powered by the Vela pulsar(Dwarakanath1991;Weiler&Sramek1988).This conclusion has been controversial(Weiler &Panagia1980;Milne&Manchester1986;Weiler&Sramek1988).The Vela SNR lies closeto the Galactic Plane,leading to difficulties in estimating the baselevel both in single-dish and interferometer images.To provide thefirst evidence supporting the classification as a composite on morphological grounds,radio observations are presented in this paper at the highest resolution yet used to image the Vela X region.A subsequent paper will present a multi-wavelength study of Vela X and consider the nature of the central plerion in detail.These are thefirst high-resolution radio observations to cover a large fraction of the entire Vela SNR,and are thefirst radio observations of the Vela shell at a resolution compatible with currently available optical and X-ray images.Radio observations of the Vela shell published before the present work have been at relatively low resolution.For example,the observations of Duncan et al.(1996)have a resolution of10′,making them difficult to correlate with high resolution data in other spectral regimes.In this paper it is possible for thefirst time to present a multi-wavelengthstudy of part of a composite remnant’s shell at scales a small fraction of a parsec.2.ObservationsThe Molonglo Observatory Synthesis Telescope(MOST)is an east-west multi-element interferometer located in New South Wales,Australia(Robertson1991).It consists of twoco-linear cylindrical parabolas,each11.6m by778m.In a twelve-hour synthesis observation it images an ellipticalfield of size70′×70′cosec|δ|.1Sixty-three of these synthesis observations covering an area of almost50square degrees comprise this survey.The survey includes the regions of brightest radio emission from the Vela SNR and covers the majority of the X-ray remnant as seen by Aschenbach et al.(1995).The area close to the strong H ii region RCW38has been avoided,due to imaging artefacts.Each observation was made at a frequency of843MHz and a resolution of43′′×43′′cosec|δ|,receiving right-handed circular polarization in a bandwidthof3MHz.The observations were made over the period1984February3to1996February3. Complete coverage with the ellipticalfield shape necessitates substantial overlaps in the survey which have been used to refine the relative calibration betweenfields,based on the unresolved sources common to more than onefield.Twenty-seven of the earlier observations were made for the First Epoch Molonglo Galactic Plane Survey(Whiteoak et al.1989;Green,Cram,&Large 1998)and some of these data appear in the MOST supernova remnant catalogue(Whiteoak& Green1996).The remaining observations,which maintained the same basic grid separation of0.◦9, commenced on1992January17.Those observations initially made in the vicinity(within about1◦)of the Vela pulsar were severely limited in dynamic range by the presence of the pulsar in the primary beam.The pulsar is a strong,unresolved continuum source and is variable over time scales of seconds to hours. Its integrated pulsed emission in ungated observations was2.2±0.4Jy,averaged over the entire pulsar period.A source will appear in a MOST image with a symmetric point-spread function only if its intensity remains constant throughout the observation.Any time-dependent variation compromises sidelobe cancellation during synthesis,producing rays within the image emanating from the source,and confusing nearby faint features.To improve the imaging of this region a method of pulsar gating was used which was originally developed by J.E.Reynolds(personal communication,1996)for an observation in1986.To make the observations,a predicted pulse arrival time was used to generate a gating signal of width20ms in each pulsar period(∼89ms).2This was displayed on an oscilloscope simultaneously with the actual detected total power signal of the pulsar.The half-power pulsewidth of the pulsar signal was4.5ms,larger than the observed half-power width of2.3ms at 632MHz(McCulloch et al.1978)due to the dispersion(2ms)over the MOST’s bandwidth (following Komesaroff,Hamilton,&Ables1972)and to the effect of an integrating low passfilter present in the signal path before the detection point.The gating signal was adjusted to suppress data acquisition from5ms before until15ms after the peak of the pulse,to allow removal of almost all of the variable pulsed emission.Four observations were made,each with the pulsar near the edge of thefield to the north,south,east and west.These observations were incorporated in the complete mosaic in place of the non-gated data,for this part of the survey.The observations made with this procedure contain only a40mJy(2%)residual of the pulsed emission,sufficient to preclude associated imaging artefacts.However,some artefacts are present in more remote fields,mainly due to the grating response of the MOST to the pulsar.Further details of the pulsar gating procedure are given by Bock(1997).3.ImagingIndividual images were synthesized from each of the63(12hour)observations using the back-projection algorithm(Perley1979;Crawford1984)as implemented in the standard MOST reduction software.To provide initial calibration for the reduction process,several strong unresolved sources were observed briefly before and after each target observation.These provide a preliminary gain,phase and beamshape calibration.The images were deconvolved using the H¨o gbom CLEAN algorithm.Some images containing stronger sources were adaptively deconvolved as described by Cram&Ye(1995).This method is similar to self-calibration,but with a reduced set of free parameters.The residual images had pixel rms in the range1–6mJy beam−1.This range reflects the variation betweenfields which were essentially noise-limited and those which were dynamic-range limited.Preliminary position andflux calibration used short observations of a number(typically eight)of unresolved calibration sources before and after each Vela targetfield.These sources are a subset of the MOST calibrators from Campbell-Wilson&Hunstead(1994).A refined calibration was achieved using unresolved surveyfield sources which are located in the overlapped regions. Measurement of these sources produced small corrections that result in positions mostly consistent to better than1′′in right ascension and2′′in declination andflux densities accurate to within5%.3 The refining corrections could not be applied to somefields which had too few unresolved sources in common with nearbyfields(for example,those at the edge of the mosaic).The individualfields were mosaiced into ARC projection(Greisen&Calabretta1995),to facilitate comparison with optical surveys.The MOST is a redundant array sensitive to the full range of spatial frequencies within the limits set by its extreme spacings.The minimum geometric spacing(42.85λ),implies a maximum detectable angular scale of about1.3◦.However,it has been found empirically that the actual synthesized beam of the MOST is bestfit with a model including a effective minimum spacing of about70λ.This parameter varies between and during observations.Typically,angular scales less than about30′are well imaged.The MOST’s synthesized beam can also vary significantly during an observation due to environmental effects and minor telescope performance variations with the result that the theoretical beam used for deconvolution sometimes does not model well the actual beam of an observation.A combination of these effects produces a negative bowl artefact around bright extended sources.In the MOST Vela SNR survey,this effect causes a background level of about−10mJy beam−1around Vela X and Puppis A.Extended structure at levels as low as6mJy beam−1is clear in the images.Although the rms in individual pixels is around2mJy beam−1,typical extended structure covers many pixels and is reliably detected at lower levels than would usually be accepted for point sources.The confirmation of this low level structure in a VLA image of Vela X made at1.4GHz(Bock et al. 1998)validates similar emission seen at843MHz elsewhere in the survey.The most common artefacts present in the image are grating rings,which are due to the periodic nature of the MOST.They are sections of ellipses of dimension1.◦15×1.◦15cosec|δ|with a width dependent on the source producing them and are,in general,of variable amplitude since they pass through several individualfields where the grating rings have different relative gains. The morphology of these artefacts makes them easily distinguishable from the sky emission.Much of the survey is dynamic-range limited;in the less complicated regions the rms noise is of order 1–2mJy beam−1.An additional non-ideality comes from the mosaicing:the image from each of the63individual observations was deconvolved separately,yet structure outside a givenfield can contribute to sidelobes in thatfield.This manifests itself as discontinuities in the survey image,at the edges of component images or where regions containing artifacts have been masked.4.ResultsAn image of the complete MOST survey of the Vela SNR is shown infigure1.To assist in identifying the various objects and emission regions within the survey,a cartoon covering the same area is presented infigure2.Key characteristics of the survey are summarized in Table1.Morphologically,there are several distinct regions apparent in the image.Near the center is the bright nebula known as Vela X,which is thought to be powered by the Vela pulsar (PSR B0833−45:Large,Vaughan,&Mills1968).The nebula is composed of a network of complex filaments.Significant extended structure is also present but not detected by the MOST.This region is seen more clearly in subsequent images.Table1:Key parameters of the MOST Vela SNR surveyParameter ValueIn the north and east of the image there are severalfilaments from the shell of the Vela supernova remnant and at least one unrelated H ii region,RCW32(Rodgers,Campbell,& Whiteoak1960).There are also partial elliptical artefacts due to strong H ii regions outside the survey area.Broadly speaking,we can categorize the extended structure in this area on morphological grounds.To the north-east of the Galactic Plane,much of the structure is diffuse and randomly oriented and may be Galactic emission unrelated to the Vela SNR.Most of the extended emission between the Galactic Plane and the Vela X nebula is due to the Vela supernova event.Thesefilamentary features have some correspondence with opticalfilaments and X-ray emission in the area(§4.1).They are generally perpendicular to the direction to the center of the SNR and are presumably related to the shell.This is the area known in the literature as Vela Y(Dwarakanath1991;Milne1968a).Directly to the east of Vela X is the radio peak known as Vela Z.This area is confused by the elliptical sidelobe from the bright H ii region RCW38 (Rodgers et al.1960),which is not included in the survey.The area around RCW38is included in the First Epoch Molonglo Galactic Plane Survey(Green et al.1998).On the southern side of the central nebula,another region of shell-like emission(08h32h−49◦00′)is probably also part of the Vela SNR.This coincides approximately with the southern boundary of the8◦remnant (Aschenbach1992;Duncan et al.1996).The survey contains many unresolved and barely resolved sources,most of which are presumably background sources.4However,some may be density enhancements in the Vela emission or other Galactic objects,such as compact H ii regions,planetary nebulae,pulsars or small-diameter SNRs.Several of these sources have unusual coincidences with extended structures. From the survey it is unclear whether they are in fact background sources,or whether they are ‘knots’in the SNR emission.Follow-up VLA observations(Bock et al.1998)of four of these sources have not found evidence for a Galactic origin.The unrelated supernova remnant Puppis A is also contained within the survey.It is an oxygen-rich SNR of age about3700yr(Winkler et al.1988)at an accepted distance of2kpc (Arendt et al.1990).Puppis A has previously been imaged separately with the MOST(Kesteven &Caswell1987;Arendt et al.1990).It falls approximately on the8◦X-ray boundary of the Vela SNR.However,no Vela radio emission is obvious in the vicinity.4.1.The northern shellThe present survey of the Vela SNR covers much of the brightest region of the Vela shell. The image infigure3is part of the survey showing the northern section of the Vela SNR shell. The following discussion focuses on this area,where the radio emission from the shell is most prominent and not confused by emission from unrelated Galactic objects or by artefacts.The extended structure in this image is in a series offilamentary arcs across the image at position angles ranging from70◦to170◦.The structure is generally concave towards the center of the SNR:there are no significant radialfilaments.The majority of thefilaments are resolved by the MOST,with widths ranging from1′to6′and peak surface brightnesses up to20mJy beam−1. Thesefilaments generally have a sharp edge on the side away from the center of the remnant, while towards the remnant center they may fade over several arcminutes.The sharper outside profile is consistent with the‘projected sheet’picture offilamentary emission(Hester1987).The effect may also indicate that thefilaments are in fact edges,spatiallyfiltered by the MOST so that only the sharp transitions appear.4.1.1.A multi-wavelength comparisonThe availability of three datasets of comparable resolution at widely spaced wavelengths gives us an opportunity to understand the spatial relationship between the underlying physical processes.In addition to the843MHz survey with the MOST,Hαand soft X-ray data are available.The radio image shows primarily the non-thermal synchrotron emission,the optical filaments are line emission resulting from recombination in cooling processes,while the X-rays are shock heated thermal radiation.An Hαimage of the northern Vela shell is shown infigure4(a),overlaid with a contour(at approximately the3σlevel)from the radio image offigure3.This image is from a test observation (kindly made and reduced by M.S.Bessell)for the MSSSO Wide Field CCD HαImaging Survey (Buxton,Bessell,&Watson1998).The observation was made using a2048×204824µm pixel CCD through a400mm,f/4.5Nikkor-Q lens,at the16-inch(0.4m)telescope facility at Siding Springs Observatory.Pixel spacing in the image is12′′,giving afield size of7◦square.The portion of this image presented here is taken from the central(5◦×5◦)region,where vignetting in the1.5nmfilter is not significant.The image has been derived from two frames with a totalexposure time of1400s,which were bias-subtracted andflat-field corrected before averaging.No correction has been made for the effect of cosmic rays.No continuum observation was made for subtraction.Consequently,the image presented here contains stars and a continuum component in the extended emission.A coordinate system was applied to the image by comparison with a Digital Sky Survey image(Morrison1995)using the KARMA package(Gooch1996).The registration is within the resolution of the radio data.The Vela SNR was observed as part of the ROSAT All-sky Survey between1990October and1991January.An image of the Vela SNR(0.1–2.4keV,with angular resolution1′)from the survey has been presented by Aschenbach et al.(1995),and part is reproduced infigure4(b), overlaid with the same radio contour as infigure4(a).In thefigure,the top section of the X-ray image(black)is the Galactic background.The surface brightness at the edge of the SNR shell is 7×10−15erg cm−2s−1arcmin−2(Aschenbach et al.1995).To the south,the surface brightness increases by a factor of500to the brightest part(white),which is the most intense X-ray emission region in the entire SNR.Thefirst grey area(δ=−41◦40′)marks the edge of the main shock, seen in projection.4.1.2.Morphological analysisBy considering only the radio and Hαimages(figure4(a)),it is possible to see immediately the most striking aspect of the comparison,namely the contrast between the optical and radio emission regions.As will be discussed below,this has a simple theoretical basis,but is contrary to the picture seen in other SNRs in those cases where optical emission has been compared with well-resolved radio shell structure.The brightest radiofilaments are(as noted earlier) generally oriented perpendicularly to the direction to the SNR center and are without optical counterparts.Likewise,many of the opticalfilaments are without radio counterparts.However, one of the brightest opticalfilaments(with orientation similar to the radio structures),centered on08h36m−42◦50′,does have a faint radio counterpart.By contrast,the equally bright optical filaments in the south-west corner of the image are without radio counterparts in the MOST image.Thesefilaments are generally not oriented perpendicularly to the direction to the SNR center in the same way as the radiofilaments.In addition to the opticalfilamentary structure,diffuse optical emission is also present.This is concentrated to the eastern side of the image,in the general area of the strong radiofilaments, but there is no obvious correlation between the diffuse optical emission and the radiofilaments. No direct measure of the effect of extinction on the Hαimage is available.The complete X-ray image(Aschenbach et al.1995)shows by its near-circular shape that it delineates the projected edge of those parts of the main shock that are still expanding into a relatively homogeneous medium.The regions of optical and radio emission described so far are interior to this main X-ray shell.At the western side of the main X-ray boundary infigure4(b),we see significant optical and radio emission clearly present close to the X-ray edge.Here the radio and optical emission agree quite well,in an arc with apex at08h35m−42◦10′,just behind the outer edge of the X-ray emission.The X-ray emission is quite different in form to the emission we see in the optical and radio regimes.Apart from the main edge,it is relatively diffuse and smooth.By contrast,the radio and optical images are dominated byfilamentary structure.However,we note that the radio image has reduced sensitivity to smooth structure,due to the MOST’s spatial response.The bright opticalfilament at08h36m−42◦50′traces the exterior(with respect to the remnant expansion)of the brightest peaks of the X-ray emission.Yet not all the opticalfilaments exhibit this relationship.The diffuse optical component has no obvious X-ray counterpart and is strongest where the X-ray emission is not quite so bright,to the east.The radiofilaments are also partially correlated with the X-ray emission.Several follow changes in X-ray brightness.However,the most centralfilament(08h39m−43◦10′)is less well correlated:it crosses a bright region of X-ray emission.4.1.3.Radiation mechanismsIn SNRs,optical and X-ray emission are both typically due to thermal processes.However, quite different physical conditions are involved.Thermal X-ray emission is the result of fast shocks propagating through a rarefied medium,with density0.1–1cm−3,shocked to temperatures of 106–107K(Lozinskaya1992).The optical emission typically observed is produced by hydrogen recombination of cooling shocked gas at about104K,with density a few times102cm−3.One model which has had success explaining optical and X-ray observations of the Cygnus Loop(Hester&Cox1986;Graham et al.1995;Levenson et al.1996)invokes large(∼>1014m) molecular clouds with which the expanding shock is interacting.The optical emission comes from the shocked cloud,where the dense material is not heated to temperatures as high as those which are maintained in the less dense X-ray emitting regions.This emission is due to recombinative cooling after the passage of the shock.Behind the optical emission,the X-ray emission is further brightened by the passage of a reflected(or reverse)shock due to the density contrast between the cloud and the less dense inter-cloud material.Where the main shock does not encounter molecular clouds,we do not expect to see recombinative cooling.Instead the non-radiative shock may be traced by fainter Balmerfilaments(Hester,Raymond,&Blair1994).The present observations of the northern Vela shellfit nicely into this picture.If the majority of optical emission was from the main shock interacting with a relatively uniform medium,but seen here in projection,we would expect also to see it along the entire edge of the X-ray shell,where accentuation of sheet-like emission in projection would be strongest.This is not observed,implying the emission is localized and due to some interaction in density inhomogeneities with afilling factor much less than unity.The cloud interaction model is further supported by the presence ofX-ray brightened regions(figure4(b))immediately behind the bright opticalfilamentary structure centered on08h36m−42◦50′infigure4(a).We might be seeing this emission in projection, significantly in front of or behind the plane of the explosion center transverse to the line of sight. This would indicate local density enhancements very close to the main shock.Alternatively,it could be nearly in the plane of the explosion center,with a shock velocity significantly reduced by interactions with more dense material.Some of the emission could be from regions already passed and energized by the main shock.The digital60µm images in the IRAS Sky Survey Atlas(Wheelock et al.1994)support the thermal emission model for the X-ray emission.Much of the X-ray structure does have an infra-red counterpart.However,infra-red images are generally less useful thermal diagnostics than X-ray images near the Galactic Plane,since the infra-red observations are dominated by diffuse Galactic emission and confusion from other sources(White&Long1991).An alternative model for SNR optical/X-ray emission(McKee&Cowie1975),explains SNRs with centrally-peaked X-ray emission(White&Long1991).In this model cold dense clouds with a smallfilling factor have been passed by the main shock and are evaporating by conductive heating from the postshock gas.Both these models rely on molecular clouds to explain the observed features.Molecular clouds have been detected in the direction of the Vela SNR(May,Murphy,&Thaddeus1988).The initial survey was of12CO and13CO J=1→0line emission with a resolution of0.◦5.Higher resolution follow-up observations(Murphy&May1991)covered only the eastern part of the Vela SNR shell.A cloud with a barely resolved peak at08h41m−41◦20′is seen,with a distance estimated to be0.5–2.0kpc,i.e.immediately behind the Vela SNR.However,this cloud appears coincident with a bright H ii region seen optically to the north offigure4(a),and might not be responsible for the observed optical features in the Vela shell.H i may be a better tracer of density in the Vela shell region.Dubner et al.(1998)find a near-circular shell of H i surrounding the northern edge of the remnant,with column densities up to1021cm−2,and estimate the pre-shock gas to have had a density of1–2cm−3.The H i shell traces the X-ray edge of the remnant,enclosing the radio and opticalfilaments.In the simple radio emission model for the interaction of supernova explosions with the ISM (Woltjer1972),Vela is in the radiative or snowplow phase of evolution,having swept up significant matter and dissipated much of the original kinetic energy of the explosion.A cool dense shell surrounds a hot interior.This model can account for the faint radio emission seen just behind the X-ray edge,which indicates the presence of compressed magneticfields and accelerated particles, probably from the diffusive shock mechanism(Fulbright&Reynolds1990).It does not account for the brighter localizedfilaments apparently well behind the main shock.Duin&Van Der Laan(1975)present a consistent picture for the coincidence of radio and optical emission which is observed in“middle-aged”shell remnants.This model,based on observations of IC443,proposes that the magneticfield required for synchrotron emission is frozen。
