The Evolution of Stellar Populations
2024届高三下学期英语培优外刊阅读学案 年度人物话题
高三英语培优外刊阅读班级：____________学号：____________姓名：____________外刊精选｜《时代》2023年度人物：泰勒·斯威夫特近日，美国流行音乐歌手泰勒·斯威夫特当选为《时代》杂志2023年度人物，成为近百年以来第一位单独拥有这一称号的艺人，也是该杂志第一位两次获评年度人物的女性。
2023年，泰勒·斯威夫特的时代（Eras）巡回演唱会在全球掀起追捧热潮，其个人净资产也高达11亿美元。
这位歌手到底有着怎样的魅力？她曾经历过怎样的人生低谷，又如何脱胎换骨，成为更强大的自己？Taylor Swift named Time Magazine's person of the yearBy Mark SavageTaylor Swift has capped off a stellar 2023 by being named Time Magazine's person of the year. The award goes to an event or person deemed to have had the most influence on global events over the past year.Already a superstar before 2023, her career has reached new heights thanks to the Eras tour -which sees the singer perform a career-spanning 45-song set every night. In Seattle, her concerts generated seismic activity equivalent to a 2.3 magnitude earthquake."It feels like the breakthrough moment of my career, happening at 33," she told Time. "And for the first time in my life, I was mentally tough enough to take what comes with that."Swift's imperial phase comes after a period where she was vilified for her positions on feminism - although her silence stemmed from nothing more sinister than a lack of confidence. After speaking out against Donald Trump and in favour of abortion rights, she hit a creative purple patch with the pandemic-era albums Folklore and Evermore.Time editor-in-chief Sam Jacobs said the US pop icon was "the rare person who is both the writer and hero of her own story", adding that Swift had "found a way to transcend borders and be a source of light".【词汇过关】请写出下面文单词在文章中的中文意思。
GRE阅读高频机经原文：蓝脱序星的两种形成过程
GRE阅读高频机经原文：蓝脱序星的两种形成过程gre阅读是许多考生难以攻克的大山，下面先来看看GRE阅读高频机经原文：蓝脱序星的两种形成过程，一起来学习吧！GRE阅读高频机经原文：蓝脱序星的两种形成过程蓝脱序星blue straggler的两种形成过程Vampires and collisions rejuvenate starsUsing the NASA/ESA Hubble Space Telescope, astronomers have uncovered two distinct kinds of "rejuvenated" stars in the globular cluster Messier 30. A new study shows that both stellar collisions and a process sometimes called vampirism are behind this cosmic "face lift". The scientists also uncover evidence that both sorts of blue stragglers were produced during a critical dynamical event (known as "core collapse") that occurred in Messier 30 a few billion years ago.Stars in globular clusters [1] are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they seem to have been left behind by the stars that followed the normal path of stellar evolution and became red giants, have been dubbed blue stragglers [2]. Blue stragglers appear to regress from "old age" back to a hotter and brighter "youth", gaining a new lease on life in the process. A team of astronomers used Hubble to study the blue straggler star content in Messier 30, which formed 13 billion years ago and was discovered in 1764 by Charles Messier. Located about 28 000 light-years away from Earth, this globular cluster — a swarm of several hundred thousand stars — is about 90 light-years across.Although blue stragglers have been known since the early 1950s, their formation process is still an unsolved puzzle in astrophysics. "It’s like seeing a few kids in the group picture of arest-home for retired people. It is natural to wonder why they are there," says Francesco Ferraro from the University of Bologna in Italy, lead author of the study that will be published this week in Nature [3]. Researchers have been studying these stars for many years and knew that bluestragglers are indeed old. They were thought to have arisen in a tight binary system [4]. In such a pair, the less massive star acts as a "vampire", siphoning fresh hydrogen from its more massive companion star. The new fuel supply allows the smaller star to heat up, growing bluer and hotter — behaving like a star at an earlier stage in its evolution.The new study shows that some of the blue stragglers have instead been rejuvenated by a sort of "cosmic facelift", courtesy of cosmic collisions. These stellar encounters are nearlyhead-on collisions in which the stars might actually merge, mixing their nuclear fuel andre-stoking the fires of nuclear fusion. Merged stars and binary systems would both be about twice the typical mass of individual stars in the cluster."Our observations demonstrate that blue stragglers formed by collisions have slightly different properties from those formed by vampirism. This provides a direct demonstration that the two formation scenarios are valid and that they are both operating simultaneously in this cluster," says team member Giacomo Beccari from ESA.Using data from the now-retired Wide Field Planetary Camera 2 (WFPC2) aboard Hubble, astronomers found that these "straggling" stars are much more concentrated towards the centre of the cluster than the average star. "This indicates that blue stragglers are more massive than the average star in this cluster," says Ferraro. "More massive stars tend to sink deep into the cluster the way a billiard ball would sink in a bucket of honey."The central regions of high density globular clusters are crowded neighbourhoods where interactions between stars are nearly inevitable. Researchers conjecture that one or two billion years ago, Messier 30 underwent a major "core collapse" that started to throw stars towards the centre of the cluster, leading to a rapid increase in the density of stars. This event significantly increased the number of collisions among stars, and favoured the formation of one of the families of blue stragglers. On the other hand, the increase of stellar crowding due to the collapse of the core also perturbed the twin systems, encouraging the vampirism phenomenon and thus forming the other family of blue stragglers. "Almost ten percent of galactic globular clusters have experienced core collapse, but this is the first time that we see the effect of the core collapse imprinted on a stellar population," says Barbara Lanzoni, University of Bologna."The two distinct populations of blue stragglers discovered in Messier 30 are the relics of the collapse of the core that occurred two billion years ago. In a broad context our discovery is direct evidence of the impact of star cluster dynamics on stellar evolution. We should now try to see if other globular clusters present this double population of blue stragglers," concludes Ferraro.GRE阅读词汇精选之渗透douse v.把…浸入水中，用水泼drenched adj.湿透的soak v.浸泡，渗透soaked adj.湿透的sodden adj.浸透了的soggy adj.湿透的，濡湿的souse v.浸在水中，使湿透steep v.浸泡，浸透logged adj笨重的，湿透的immerse v.浸入，沉浸于immersion n.沉入，浸入macerate v.浸软，消瘦GRE阅读表示选择的逻辑词汇总逻辑词条词性例句选择otherwiseadv.You need to work hard. Otherwise, you will fail.选择or (else)conj.You need to work hard, or (else) you will fail.选择lestconj.You need to work hard, lest you fail the exam.选择in caseconj.You need to work hard, in case the exam is hard. GRE阅读表示转折的逻辑词汇总逻辑词条词性例句转折butconj.I worked hard, but I failed.转折howeveradv.I worked hard. However, I failed.转折neverthelessadv.I worked hard. Nevertheless, I failed.转折stilladv.I worked hard. Still, I failed.转折nonethelessadv.I worked hard. Nonetheless, I failed.转折thoughadv.I worked hard. I failed, though.。
22年高考英语试卷
22年高考英语试卷22年高考英语试卷 1年普通高等学校招生全国统一考试英语这篇论文一共10页，满分120分。
考试需要120分钟。
注意事项：1. 答卷前，考生务必用黑色字迹钢笔或签字笔将自己的姓名、考生号、考场号和座位号填写在答题卡上。
用2B铅笔将试卷类型(A)填涂在答题卡相应位置上。
将条形码横贴在答题卡右上角“条形码粘贴处”。
因笔试不考听力，选择题从第二部分的“阅读”开始，试题序号从“21”开始。
2. 作答选择题时，选出每小题答案后，用2B铅笔把答题卡上对应题目选项的答案信息点涂黑;如需改动，用橡皮擦干净后，再选涂其他答案，答案不能答在试卷上。
3. 非选择题必须用黑色字迹钢笔或签字笔作答，答案必须写在答题卡各题目指定区域内相应位置上;如高改动，先划掉原来的答案，然后再写上新的答案;不准使用铅笔和涂改液，不按以上要求作答的答案无效。
考生一定要保持答题卡的清洁:考试结束后，将试卷和答题卡一起交回。
第一部分听力第一节(共5小题；每小题1.5分，满分7.5分)听下面5段对话。
每段对话后有一个小题，从题中所给的A、B、C三个选项中选出最佳选项。
听完每段对话后，你都有10秒钟的时间来回答有关小题和阅读下一小题。
每段对话仅读一遍。
1.What will the speakers do next?A. Check the map.B.Leave the restaurant.C.Park the car.2.Where are the speakers?A.Ata bus stop.B.At home.C.At the airport.3.What did the speakers do last week?A. They had acelebration dinner.B.They went to see a newbornbaby.C.They sent a mail to their neighbors.4. Why does the man make the phone call?A. To cancel a weekend trip.B. To make anappointment.C. To get some information.5.What does the man probably want to do?A. Do some exercise.B. Getan extrakey.C. Order room service.第二节(共15小题；每小题1.5分，满分22.5分)听下面5段对话或独白。
TPO听力题目
What does the professor say about Frantzen’s painting of a farm scene? It resembles a photograph. It may be Frantzen’s best-know painting. It was painted in the Impressionist style. It was painted while Frantzen lived abroad. Why did Frantzen go to the Sales Barn? To study human form and movement To earn money by painting portraits To paint farm animals in an outdoor setting To meet people who could model for her paintings What does the professor imply about the painting of the young woman surrounded by pumpkins? It was painted at an art fair. It combines Impressionism with Realism. It convinced Frantzen that she was a good illustrator. It was originally meant to be used in an advertisement. What does the professor discuss Frantzen’s difficulties as a young painter? He wants to point out mistakes that young artists commonly make. He thinks her example can inspire the students in their own lives. Her difficulties remind him of the difficulties he himself experienced as a young artist. Her difficulties are the subject of some of the paintings in the gallery that the students will visit. What does the professor imply when he says this: The students can understand Frantzen’s art without knowing about her life. The students should pay very close attention to what he is going to say. Some of his students are already familiar with Frantzen’s life story. Some of his students may not appreciate Frantzen’s work. Answers: CCABBA
银河系漫游指南英文版pdf
银河系漫游指南英文版pdfHere is the English essay with a word count of over 1000 words, as requested:The Milky Way Galactic OdysseyEmbark on a captivating journey through the vast expanse of the Milky Way Galaxy, a celestial wonder that has captivated the human imagination for millennia. As we delve into the mysteries and marvels of this galactic realm, prepare to be awestruck by the sheer scale and beauty of the cosmos that lies beyond our earthly confines.Let us begin our odyssey by venturing to the heart of the Milky Way, where the supermassive black hole known as Sagittarius A* resides. This gravitational behemoth, nearly 4 million times the mass of our Sun, anchors the center of our galaxy and exerts a powerful influence on the surrounding stars and stellar matter. As we approach this enigmatic cosmic phenomenon, we will witness the intricate dance of stars and gas clouds as they are drawn inexorably towards the event horizon, their fate forever sealed within the crushing grip of the black hole.Venturing outwards from the galactic center, we will encounter the diverse and vibrant neighborhoods that make up the Milky Way. Spiral arms, such as the Orion Arm in which our Solar System resides, are vast regions of star formation, with newborn stars and stellar nurseries dotting the landscape. We will marvel at the brilliant nebulae, glowing clouds of gas and dust that serve as the birthplaces of these young celestial bodies, their ethereal hues and intricate structures a testament to the dynamic processes that shape the galaxy.As we traverse the spiraling arms, we will come across the globular clusters – ancient, densely packed collections of stars that orbit the galactic center. These spherical assemblages, some of the oldest objects in the Milky Way, harbor valuable insights into the early history and evolution of our galaxy, their stars dating back to a time when the universe was a mere fraction of its current age.Amidst the stellar tapestry, we will discover the diverse array of stellar populations that call the Milky Way home. From the towering red giants, their brilliant crimson hues a testament to their advanced age and increased size, to the compact and enigmatic neutron stars, the collapsed remnants of once-mighty suns. Each type of star, with its unique properties and life cycle, contributes to the rich tapestry of the galactic landscape.But the Milky Way is not merely a collection of stars – it is a dynamic and ever-changing system, influenced by the complex interplay of gravity, stellar evolution, and the ever-present threat of cosmic catastrophes. We will explore the regions where massive stars meet their explosive demise, supernovae that briefly outshine entire galaxies and leave behind the dense, spinning neutron stars known as pulsars. These cataclysmic events not only shape the galactic environment but also provide the building blocks for new generations of stars and planets.As we venture deeper into the Milky Way, we will encounter the harrowing regions where the fabric of space-time is stretched and distorted by the intense gravitational fields of neutron stars and black holes. Here, we will witness the bizarre and mind-bending phenomena predicted by Einstein's theory of general relativity, from the warping of spacetime to the accretion disks that feed these cosmic monsters.Throughout our journey, we will be in awe of the sheer scale and majesty of the Milky Way. The galaxy, spanning nearly 100,000 light-years in diameter, is home to an estimated 200 to 400 billion stars, each one a unique and fascinating world unto itself. We will ponder the possibility of life elsewhere in this vast cosmic tapestry, wondering if intelligent civilizations have arisen on distant worlds and if they, too, gaze up at the night sky, marveling at the splendorof our shared galactic home.As our odyssey draws to a close, we will reflect on the profound impact that the study of the Milky Way has had on our understanding of the universe. From the groundbreaking work of pioneering astronomers to the cutting-edge research conducted with the most advanced observational tools, the Milky Way has been a constant source of fascination and discovery. And as we look to the future, we know that there are countless more secrets and mysteries waiting to be unveiled, beckoning us to continue our exploration of this awe-inspiring celestial realm.So let us embark on this Milky Way galactic odyssey, armed with a sense of wonder and a thirst for knowledge. For in unraveling the mysteries of our galactic home, we may just find the answers to some of the most profound questions that have puzzled humanity since the dawn of time.。
河北省英语中考2025年仿真试卷与参考答案
2025年河北省英语中考仿真试卷与参考答案一、听力部分（本大题有20小题，每小题1分，共20分）1、You will hear a short conversation between two students about their plans for the weekend. Listen to the conversation and choose the correct option.Conversation:“Hey Tom, what are you up to this weekend?”“I’m planning to visit the new art exhibition downtown. How about you, Sarah?”“I’ll probably just catch up on some reading at home.”Question: What is Tom planning to do?A)Visit a friend.B)Go to an art exhibition.C)Catch up on some reading.Answer: B) Go to an art exhibition.Explanation: In the dialogue, Tom explicitly states that he’s planning to visit the new art exhibition downtown, making option B the correct answer.2、Listen to a short weather forecast and determine what the weather will be like tomorrow afternoon in the city center.Forecast:“Good evening, folks. Looking ahead to tomorrow, we can expect mostly sunny skies in the morning, but clouds will start rolling in by noon. By mid-afternoon, there’s a high chance of showers in the city center and surrounding areas.”Question: What will the weather be like tomorrow afternoon in the city center?A)Sunny all day.B)Cloudy with a chance of showers.C)Rainy from morning till night.Answer: B) Cloudy with a chance of showers.Explanation: The forecast indicates that while the morning will be mostly sunny, by mid-afternoon there is a high chance of showers in the city center, which matches option B.This section tests the students’ ability to comprehend spoken English and extract specific information from a conversation and a forecast.3、What are the speakers discussing?A)The weather forecast for the next week.B)The importance of exercise for health.C)The latest movie releases.Answer: B) The importance of exercise for health.Explanation: The conversation between the two speakers focuses on the benefits of regular exercise and how it contributes to overall health, which indicates that the topic is related to exercise and not weather or movies.4、How does the woman suggest the man improve his productivity at work?A)By taking longer breaks.B)By working longer hours.C)By organizing his workspace.Answer: C) By organizing his workspace.Explanation: The woman advises the man to organize his workspace to improve his efficiency and productivity, suggesting that a cluttered or disorganized environment might be hindering his work performance.5、You will hear a short conversation between two friends. Listen carefully and choose the best answer to the following question.Question: What is the man’s favorite sport?A. BasketballB. FootballC. TennisD. None of the aboveAnswer: C. TennisExplanation: In the conversation, the man says, “I really enjoy playing tennis. It’s my favorite sport.” Therefore, the correct answer is C. Tennis.6、You will hear a news report about a recent event. Listen carefully and answer the following question.Question: What happened during the event?A. A fire broke out at the shopping center.B. A group of people gathered for a protest.C. An accident occurred on the highway.D. A festival was held in the park.Answer: B. A group of people gathered for a protest.Explanation: The news report states, “Today, a group of p eople gathered in the city center to protest against the new policy.” Therefore, the correct answer is B. A group of people gathered for a protest.7.Listen to the following dialogue and choose the best answer to the question.A. They are discussing a book.B. They are planning a trip.C. They are comparing their diets.Answer: BExplanation: The dialogue focuses on the speakers’ plans for their upcoming vacation, which indicates they are planning a trip.8.Listen to the following passage and answer the question.Question: What is the main purpose of the passage?A. To describe a new product.B. To provide information about a famous person.C. To explain the benefits of exercise.Answer: CExplanation: The passage discusses the various health benefits of regular physical activity, making option C the correct answer. The other options are not supported by the content of the passage.9、You will hear a conversation between two friends, Tom and Lucy. Listen carefully and choose the best answer to the question.What is the main topic of their conversation?A. Tom’s new job.B. Lucy’s birthday party.C. Tom’s weekend plans.Answer: BExplanation: The conversation is mainly about Lucy’s birthday par ty. They discuss the location, time, and activities planned for the party.10、You will hear a short passage about climate change. Listen carefully and answer the question.Which of the following is NOT mentioned in the passage?A. The increase in global temperatures.B. The melting of polar ice caps.C. The rise in sea level.Answer: BExplanation: The passage mentions the increase in global temperatures, the rise in sea level, and the negative effects of climate change. However, the melting of polar ice caps is not mentioned in the passage.11.You will hear a short conversation between two students about their weekend plans. Listen carefully and choose the best answer to the question.What does the woman plan to do on Saturday?A)Visit her grandparents.B)Go shopping.C)Study for an exam.D)Travel to another city.Answer: C) Study for an exam.Explanation: The woman mentions that she has a big exam coming up on Monday, which suggests that her weekend plans include studying.12.You will hear a news report about a new health initiative in a major city. Listen carefully and answer the following question.What is the main goal of the new initiative?A)To reduce traffic congestion.B)To promote healthy eating habits.C)To increase public awareness about mental health.D)To encourage more people to walk or cycle to work.Answer: B) To promote healthy eating habits.Explanation: The news report states that the initiative aims to provide more fresh food options in urban areas and educate residents about the importance of a balanced diet.13.You will hear a short conversation between two friends about their weekend plans. Listen carefully and answer the question.Question: What does Mark plan to do this weekend?A) Go hikingB) Visit his grandparentsC) Stay at home and relaxAnswer: CExplanation: In the conversation, Mark says, “I think I’ll just stay at homethis weekend and relax. I’ve been really busy lately.”14.You will hear a radio announcement about the weather forecast for the next three days. Listen carefully and answer the question.Question: What will the weather be like on Tuesday?A) Sunny with a high of 75°FB) Rainy with a low of 50°FC) Cloudy with a high of 65°FAnswer: AExplanation: The radio announcement states, “On Tuesday, we’ll have a sunny day with a hi gh of 75 degrees Fahrenheit.”15.You will hear a conversation between two friends discussing their weekend plans. Listen and answer the following question.Question: What does Sarah plan to do on Saturday afternoon?A) Go shoppingB) Watch a movieC) Visit a museumD) Go for a hikeAnswer: B) Watch a movieExplanation: In the conversation, Sarah mentions, “I’m thinking of watching a new movie at the cinema on Saturday afternoon.” Therefore, the correct answer is B) Watch a movie.16.Listen to a short passage about a famous author and answer the followingquestion.Question: What is the author known for?A) Writing a popular mystery novelB) Writing a science fiction novelC) Writing a historical fiction novelD) Writing a fantasy novelAnswer: C) Writing a historical fiction novelExplanation: The passage states, “The author, known for her historical fiction novels, has won numerous awards for her captivating storytelling.” Therefore, the correct answer is C) Writing a historical fiction novel.17.Listen to the following conversation and choose the best answer.A. The man is asking for directions to the library.B. The woman is looking for a book about history.C. The man is helping the woman find the nearest post office.D. The woman is inquiring about the opening hours of the museum.Answer: BExplanation: The woman mentions that she needs a book about history, which indicates that she is looking for a book related to that subject.18.Listen to the following news report and answer the question.What is the main topic of the news report?A. A new shopping center opening soon.B. A severe storm hitting the city.C. A famous singer performing in the city.D. A new law passed to improve traffic conditions.Answer: BExplanation: The news report discusses a severe storm that has hit the city, including details about the weather and the impact it has had on local residents. This indicates that the main topic is the storm itself.19.You will hear a conversation between two friends at a bookstore. Listen to the conversation and answer the following question.Question: What book is the woman looking for?A) A science fiction novel.B) A history book.C) A cookbook.D) A mystery novel.Answer: C) A cookbook.Explanation: The woman mentions that she needs a cookbook for her new cooking class, which indicates that she is looking for a cookbook.20.You will hear a short lecture about the effects of climate change on wildlife. Listen to the lecture and answer the following question.Question: What is one of the main effects of climate change mentioned in the lecture?A) Increased number of polar bears.B) Decline in bee populations.C) Enhanced plant growth in deserts.D) Increase in the salinity of freshwater lakes.Answer: B) Decline in bee populations.Explanation: The lecture discusses how climate change is affecting various species, and it specifically mentions the decline in bee populations due to changes in their habitats and food sources.二、阅读理解（30分）Title: The Birth of a New SpeciesReading Passage:In the small town of Greenfield, scientists have made an extraordinary discovery. For years, the local wildlife had been changing, and the townsfolk had noticed that the animals seemed to be evolving at an unprecedented rate. The town’s most famous naturalist, Dr.Evelyn Carter, decided to investigate this phenomenon. After months of research, she and her team uncovered the secret: a previously undiscovered mineral, known as “Evolium,” found deep within the town’s forest, was causing the animals to evolve rapidly.Dr. Carter’s findings were groundbreaking. The mineral seemed to stimulate the animals’ DNA, leading to genetic mutations that enhanced their physical and cognitive abilities. The most remarkable of these mutations was the appearance of a new species of bird, which Dr. Carter named the “Greenfield Glider.” These birds had longer wings, sharper beaks, and an enhanced abilityto navigate complex environments. The Gliders were soon becoming a symbol of hope and innovation in the town.Questions:1.What was the main focus of Dr.Evelyn Carter’s research?A) The impact of the new mineral on the local wildlife.B) The evolution of the town’s human population.C) The economic benefits of the new mineral.D) The history of the town of Greenfield.2.What effect did the Evolium mineral have on the animals in Greenfield?A) It caused them to become extinct.B) It made them more aggressive.C) It stimulated their DNA, leading to genetic mutations.D) It had no effect on their evolution.3.What is the significance of the Greenfield Glider?A) It is a rare bird species that is on the brink of extinction.B) It is the town’s mascot, representing its hope for innovation.C) It is the first bird to be discovered in the town’s history.D) It has no special features and is no different from other birds.Answers:1.A) The impact of the new mineral on the local wildlife.2.C) It stimulated their DNA, leading to genetic mutations.3.B) It is the town’s mascot, representing its hope for innovation.三、完型填空（15分）Complete the following passage with the most appropriate options.In the small town of Greenfield, the local library was facing a dilemma. For years, it had been a cherished community hub, but now, its aging building was in dire need of repairs. The mayor, Mr. Thompson, convened a meeting with the library board and community leaders to discuss the best course of action.The first option presented was to [] the existing building, which would cost a considerable amount of money. However, this solution was met with skepticism from some board members who feared that [] would result in the loss of the library’s unique charm.The second option was to [] a new, modern library on the outskirts of town, which would offer more space and amenities. This idea was more popular with the younger generation, but it raised concerns about the [] of the older residents who preferred to stay close to their homes.A third suggestion was made by Mrs. Jenkins, a long-time library volunteer. She proposed [] a partnership with a local university to create a [] library that would combine the resources of the library and the university, thereby providing a unique educational experience for students and the community.The mayor listened to all the proposals a nd then asked the group, “What do you think will be the most beneficial for Greenfield in the long run?”1.A. rebuild2.A. preserving3.A. construction4.A. establish5.A. hybridAnswer Key:1.A. rebuild2.A. preserving3.A. construction4.A. establish5.A. hybrid四、语法填空题（本大题有10小题，每小题1分，共10分）1、In the_______(1) place, I prefer staying at home rather than going out on weekends.答案：first解析：此处需要填入一个表示顺序的形容词，根据句意“首先”，应该使用“first”。
不同星族恒星的Sc和Mn元素丰度分析
不同星族恒星的Sc和Mn元素丰度分析摘要恒星元素丰度是从观测上追踪银河系结构和化学演化的很好探针。
随着天文观测技术和仪器的改进和提高，近年来人们积累了大量的恒星光谱数据，分析得到了恒星中许多元素的丰度，为我们研究不同类型恒星的化学演化提供了支持。
本文我们以F和G 型矮星作为研究对象，分析这些恒星中Sc和Mn这两种元素的丰度趋势。
为了得到更具普遍性的观测结果，我们采用大样本恒星的统计分析，所选择的样本有2个来源：第一个来源是选择了从2000年以来一直到2011年的11个大样本恒星的观测结果，第二个来源是使用中国科学院国家天文台兴隆观测站的2.16米望远镜，观测得到的15颗F和G型矮星的元素丰度。
总共获得了798颗恒星的元素丰度，包括367颗薄盘星，303颗厚盘星和128颗晕星。
论文首先介绍了银河系的旋臂结构、成分结构，综述了对恒星Sc和Mn元素丰度的观测研究和分析结果；第二部分是星族的分类，用纯运动学来划分薄盘星、厚盘星和晕星；第三部分是我们的光谱观测和丰度分析结果，观测并分析了15颗贫金属矮星的元素丰度；第四部分多样本统计分析，包括样本的选取和完备性分析；最后一部分详细讨论了不同星族恒星的Sc和Mn元素的丰度演化趋势。
通过大样本恒星的统计分析，得到了以下重要结果：（1）Sc元素丰度的演化趋势：贫金属星中[Sc/Fe] 总体上是相对超丰，而且随[Fe/H]的增加呈下降趋势，但在整个金属丰度范围内[Sc/Fe]并不是单一斜率下降，[Sc/Fe]随金属丰度[Fe/H]的演化趋势在薄盘星、厚盘星和晕星中是不完全相同的。
在薄盘恒星（[Fe/H] > -0.8）中[Sc/Fe] 随[Fe/H]的增加呈线性下降趋势，这一特性和α元素很相似，因此Sc有时被称为“类α元素”；在厚盘恒星中当[Fe/H]<-0.5 时[Sc/Fe]随[Fe/H]的增加是线性上升的，但当[Fe/H]达到-0.5后继续增加[Sc/Fe]转而变为线性下降的趋势；在晕族恒星中，[Sc/Fe]的弥散变得较大，且[Sc/Fe] 几乎与[Fe/H]的变化无关。
散发光 成为光英语作文
散发光成为光英语作文Radiating Light: The Luminary of the Universe.In the vast expanse of the cosmos, countless celestial bodies emit radiant energy, illuminating the darkness and illuminating our understanding of the universe. Among these luminous celestial objects, stars reign supreme as the primary source of light, energy, and awe for observers both on Earth and beyond.Stars, the building blocks of galaxies, are incandescent beacons of plasma held together by their own gravitational forces. Within their nuclear furnaces, the fusion of hydrogen atoms into helium releases prodigious amounts of energy, a process that sustains their brilliance for billions of years. This energy manifests as electromagnetic radiation, which travels through space as a spectrum of light waves.The light emitted by stars encompasses a vast range ofwavelengths, from short-wavelength gamma rays to long-wavelength radio waves. However, the human eye is only capable of perceiving a narrow band within this spectrum, known as visible light. Visible light ranges from violet to red, with each wavelength corresponding to a different color.Stars exhibit a remarkable diversity in their light output, ranging from faint and barely visible to dazzling and brilliant. The brightness of a star, as perceived by an observer on Earth, depends on several factors, includingits size, temperature, and distance from Earth.Large stars, with greater masses and hence more fuel to burn, typically emit more light than smaller stars. Temperature also plays a crucial role in determining astar's luminosity. Hotter stars emit blue and white light, while cooler stars radiate yellow or red light.The distance between a star and Earth also influences its apparent brightness. Stars that are closer to Earth appear brighter than those that are farther away. This isbecause the inverse square law of light dictates that the intensity of light decreases with the square of the distance from the source.The light of stars serves as a valuable tool for astronomers and astrophysicists. By analyzing the spectrum of light emitted by stars, scientists can determine their temperature, chemical composition, and other physical characteristics. This information helps us understand the evolution of stars, the nature of stellar populationswithin galaxies, and the history of the universe itself.Moreover, the light of stars provides a celestial beacon for navigators and explorers. For centuries, seafarers relied on the positions of stars to guide their ships across vast oceans. Even today, spacecraft venturing into the depths of space utilize star charts and celestial navigation to determine their location and trajectory.Beyond its practical applications, the light of stars also holds profound aesthetic and philosophical significance. Throughout human history, stars have capturedthe imagination of poets, artists, and philosophers. Their twinkling radiance has inspired countless works of art, literature, and music. Stars have also been associated with spirituality, divinity, and the pursuit of knowledge and enlightenment.In conclusion, the light of stars permeates our existence, providing both practical and profound benefits. It illuminates the darkness, guides our paths, and fuels our understanding of the universe. As we continue to explore the cosmos and unravel its mysteries, the light of stars will forever remain a constant and awe-inspiring source of wonder and inspiration.。
stars1
• We will cover this in stellar evolution, but much of the heavy elements in our Universe today is created when a giant star end its life in a supernova（超新星）. The intense heat for this creates in the upper atmosphere （高层大气）of stars much of the elements we know - like iron, gold, even fluoride（氟化物） (yes, the same stuff in your toothpaste). • These elements disperse themselves to nearby molecular clouds. （分子云）When that cloud undergoes contraction（收缩） and give birth to a new star, the end result is a Population I star - one that is now metal rich. • One consequence of a metal rich star is that they are likely to contain a system of planets（行星）!
星团 球状星团
、
open clusters.
疏散星团
Globular Clusters
They are generally comprised of old, metal poor stars that is contain little elements heavier than helium(氦). This means globular clusters formed a long time ago, before our galaxy contained more heavy stars.
托福备考托福阅读34套TPO样题+解析+译文30—2 The Pace of Evolutionary Change
托福考试 复习TPO 30—2 The Pace of Evolutionary Change原文：【1】A heated debate has enlivened recent studies of evolution. Darwin's original thesis, and the viewpoint supported by evolutionary gradualists, is that species change continuously but slowly and in small increments. Such changes are all but invisible over the short time scale of modern observations, and, it is argued, they are usually obscured by innumerable gaps in the imperfect fossil record. Gradualism, with its stress on the slow pace of change, is a comforting position, repeated over and over again in generations of textbooks. By the early twentieth century, the question about the rate of evolution had been answered in favor of gradualism to most biologists' satisfaction.【2】Sometimes a closed question must be reopened as new evidence or new arguments based on old evidence come to light. In 1972 paleontologist Stephen Jay Gould and Niles Eldredge challenged conventional wisdom with an opposing viewpoint, the punctuated equilibrium hypothesis, which posits that species give rise to new species in relatively sudden bursts, without a lengthy transition period. These episodes of rapid evolution are separated by relatively long static spans during which a species may hardly change at all.【3】The punctuated equilibrium hypothesis attempts to explain a curious feature of the fossil record—one that has been familiar to paleontologist for more than a century but has usually been ignored. Many species appear to remain unchanged in the fossil record for millions of years—a situation that seems to be at odds withDarwin's model of continuous change. Intermediated fossil forms, predicted by gradualism, are typically lacking. In most localities a given species of clam or coral persists essentially unchanged throughout a thick formation of rock, only to be replaced suddenly by a new and different species.【4】The evolution of North American horse, which was once presented as a classic textbook example of gradual evolution, is now providing equally compelling evidence for punctuated equilibrium. A convincing 50-million-year sequence of modern horse ancestors—each slightly larger, with more complex teeth, a longer face, and a more prominent central toe—seemed to provide strong support for Darwin's contention that species evolve gradually. But close examination of those fossil deposits now reveals a somewhat different story. Horses evolved in discrete steps, each of which persisted almost unchanged for millions of years and was eventually replaced by a distinctive newer model. The four-toed Eohippus preceded the three-toed Miohippus, for example, but North American fossil evidence suggests a jerky, uneven transition between the two. If evolution had been a continuous, gradual process, one might expect that almost every fossil specimen would be slightly different from every year.【5】If it seems difficult to conceive how major changes could occur rapidly, consider this: an alteration of a single gene in files is enough to turn a normal fly with a single pair of wings into one that has two pairs of wings.【6】The question about the rate of evolution must now be turned around: does evolution ever proceed gradually, or does it always occur in short bursts? Detailedfield studies of thick rock formations containing fossils provide the best potential tests of the competing theories.【7】Occasionally, a sequence of fossil-rich layers of rock permits a comprehensive look at one type of organism over a long period of time. For example, Peter Sheldon's studies of trilobites, a now extinct marine animal with a segmented body, offer a detailed glimpse into three million years of evolution in one marine environment. In that study, each of eight different trilobite species was observed to undergo a gradual change in the number of segments—typically an increase of one or two segments over the whole time interval. No significant discontinuous were observed, leading Sheldon to conclude that environmental conditions were quite stable during the period he examined.【8】Similar exhaustive studies are required for many different kinds of organisms from many different periods. Most researchers expect to find that both modes of transition from one species to another are at work in evolution. Slow, continuous change may be the norm during periods of environmental stability, while rapid evolution of new species occurs during periods of environment stress. But a lot more studies like Sheldon's are needed before we can say for sure.题目：1.The word "innumerable" in the passage is closest in the meaning toA.countless.B.occasional.rge.D.repeated.2.According to paragraph 1, all of the following are true EXCEPTA.Darwin saw evolutionary change as happening slowly and gradually.B.Gaps in the fossil record were used to explain why it is difficult to see continuous small changes in the evolution of species.C.Darwin's evolutionary thesis was rejected because small changes could not be observed in the evolutionary record.D.By the early twentieth century, most biologists believed that gradualism explained evolutionary change.3.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage paragraph 2 ? Incorrect choices change the meaning in important ways or leave out essential information.A.The punctuated equilibrium hypothesis challenged gradualism, which holds that species evolve in relatively sudden bursts of brief duration.B.The punctuated equilibrium hypothesis developed by Stephen Jay Gould and Niles Eldredge was challenged in 1972.C.In 1972 Stephen Jay Gould and Niles Eldredge challenged gradualism by positing that change from one species to another cannot occur without a lengthy transition period.D.The punctuate equilibrium hypothesis, in opposition to gradualism, holds that transitions from one species to another occur in comparatively sudden burst.4.According to paragraph 1 and paragraph 2, the punctuated equilibriumhypothesis and the gradualism hypothesis differed aboutA.Whether the fossil record is complete.B.Whether all species undergo change.C.Whether evolution proceeds an a constant rate.D.How many new species occur over long periods of time.5.According to paragraph 3, the lack of intermediate fossils in the fossil record of some speciesA.has been extensively studied by paleontologist for over a century.B.contradicts the idea that most species have remained unchanged for millions of years.C.challenges the view that evolutionary change is gradual.D.is most common in the fossil records of clam and coral species.6.The word "compelling" in the passage paragraph 4 is closest in the meaning toA.surprising.B.persuasive.C.controversial.D.detailed.7.Paragraph 4 mentions that North American horses have changed in all the following ways EXCEPT inA.the number of toes they have.B.the length of their face.C.their overall size.D.the number of years they live.8.The word "alteration" in the passage paragraph 5 is closest in meaning toA.imperfection.B.replacement.C.change.D.duplication.9.According to paragraph 7, Peter Sheldon's studies demonstrated which ofthe following about trilobites?A.They underwent gradual change over a long time period.B.They experienced a number of discontinuous transitions during their history.C.They remained unchanged during a long period of environmental stability.D.They evolved in ways that cannot be counted for by either of the two competing theories.10.The word "occasionally" in the passage paragraph 7 is closest in meaning toA.undoubtedly.B.basically.C.once in a while.D.to some extent.11.The main purpose of paragraph 7 is toA.Describe one test of the competing theories.B.Provide an example of punctuated equilibrium.C.Describe how segmented animals evidence both competing theories.D.Explain why trilobites became extinct.12. Look at the four squares [■] that indicate where the following sentence can be added to the passage.Where could the sentence best fit? They believe that environmental conditions may play a crucial role in determining which of the two modes will be in operation over a given period.■【A】Similar exhaustive studies are required for many different kinds of organisms from many different periods. ■【B】Most researchers expect to find that both modes of transition from one species to another are at work in evolution.■【C】Slow, continuous change may be the norm during periods of environmental stability, while rapid evolution of new species occurs during periods of environment stress. ■【D】But a lot more studies like Sheldon's are needed before we can say for sure.13.Directions: selected from the seven phrases below the phrases that correctly characterize punctuated equilibrium and the phrases that correctly characterize gradualism. Two of the phrases will not be used. This question is worth 3 points.A.States that new species emerge from existing species during relatively brief period of time.B.Was first formulated by Charles Darwin.C.Explain why North American horses have become smaller over time.D.States that new species evolve slowly and continuously from existing species.E.Explain the lack of intermediate fossil forms in the fossil record of many species.petition is usually strongest when the density of the competing populations is the same.G.States that a species will not change unless its environment changes.1 ）GradualismA B C D E F G2 ）punctuated equilibriumA B C D E F G答案：1.innumerable是不可计数的，A是无数的，B是偶然的，C是大的，D是重复的。
小学下册C卷英语第二单元寒假试卷
小学下册英语第二单元寒假试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.I _____ (play/learn) the guitar.2.I love to play games with my ________ (家人).3.The pyramids were built more than _______ years ago. (4000)4. A liquid that can dissolve other substances is called a ______.5.The symbol for titanium is _______.6.What do we call a person who creates films?A. DirectorB. ProducerC. ActorD. WriterA7.The _____ (考拉) sleeps most of the day in trees.8.What is the term for the region of space where two galaxies collide?A. Collision ZoneB. Intergalactic SpaceC. Merger ZoneD. Cosmic Collision9.I can ______ (应用) my knowledge in real-life situations.10.What do we call the area of land situated between two rivers?A. DeltaB. ValleyC. PeninsulaD. BasinD11.My cousin is a great ____ (athlete).12.What is the term for a young monkey?A. KidB. PupC. InfantD. BabyD Baby13.I can tell stories with my ________ (玩具).14.The Ptolemaic model placed Earth at the center of the ______.15.The Earth's core is very ______.16.The octopus is known for its problem-solving ______ (能力).17.What is the name of the famous mountain range in Asia?A. HimalayasB. RockiesC. AndesD. AlpsA18.My dad inspires me to be __________ (勇敢的) in life.19.The capital of Finland is __________.20.The __________ was a significant time of exploration in the 15th century. (大航海时代)21.The Great Lakes are located in __________.22.What is the opposite of heavy?A. LightB. DenseC. SolidD. ThickA23.Gardening can provide fresh ______ for your meals. (园艺可以为你的餐点提供新鲜的食材。
The outer Galaxy stellar populations and dark matter
a rXiv:as tr o-ph/73365v114Mar27**FULL TITLE**ASP Conference Series,Vol.**VOLUME**,**YEAR OF PUBLICATION****NAMES OF EDITORS**The outer Galaxy:stellar populations and dark matter Gerry Gilmore Institute of Astronomy,Cambridge,UK Abstract.The Galaxy’s stellar populations are naturally classified into six ‘types’,of which five have been observed.These are the thin disk (Pop I in the historical scheme),a discrete thick disk (Pop I.5),the metal-rich bulge,which was not named in the Baade sequence,the rare field halo (Pop II),a population currently being accreted into the very outer halo filed (Pop Sgr?)and a hard to discover initial enriching Pop III.Each of these forms a group with astonishly tight correlations between chemical element ratios and other parameters.It is very hard to understand how the observed properties of any one of these populations can be the sum of many discrete histories,except for the minor continuing outer halo accretion.All these stellar populations are embedded in dark-matter,and allow the properties of dark matter to be measured on small scales.Intriguing and unexpected consistencies in the properties of this dark matter are being revealed.1.Stellar Population Types In the Milky Way we can identify five stellar populations with properties that constrain the star formation history,the chemical evolution history (flows,feed-back..)and the mass assembly history of the Galaxy.There may even be a sixth type,sometimes called Pop III,as yet undetected directly but postulated to provide the first chemical enrichment .•The thin disk,also known as Baade’s Population I.This is composed of stars and gas on high angular momentum orbits,moving about the center with close to the circular velocity,and thus with only low amplitude ran-dom motions.Such a cold thin system presumably formed by dissipational collapse of gas,in a potential that is changing slowly,and conserved angu-lar momentum to spin-up as it collapsed (see Fall &Efstathiou 1980;Mo,Mao &White 1998).The origins of disks are however not clear:hierarchi-cal merging models predict significant angular momentum transport and generate disks that are too small (Navarro &Steinmetz 1997).Appeal to some suitable process of ‘feedback’can be implemented to prevent much of the angular momentum losses from the proto-disk,but at the expense of delaying the collapse to centrifugal equilibrium (e.g.Eke,Efstathiou &Wright 2000)and thus predicting few old stars in disks,and no extended high-redshift te perturbations to the thin disk cannot be too strong,or the disk will be destroyed (e.g.Ostriker 1990).The properties of stars in the thin disk are important tests of merging histories and en-ergetic dynamical processes.The age and metallicity distributions of the disk,well-defined only at the solar neighbourhood,point to extended in-12Gerry Gilmorefall of metal-poor gas,and steady star formation from a redshift of∼1.5(e.g.Binney et al.2000)to the present.•The thick disk-this was identified as a separate component some25years ago(Gilmore&Reid1983).The dominant population is old,as old as the globular cluster47Tuc,∼12Gyr,and of intermediate metallicity in the mean,[F e/H]∼−0.6,with a significant spread.The chemical enrichment history revealed by the pattern of element ratios is distinct from that of stars in the thin disk(Bensby et al.2007,this meeting).A plausible origin for the thick disk is a moderately violent dynamical event such asa minor merger;the old mean age for the thick disk limits such events tohave occurred only long ago,an important constraint–and a problem, if found to be a typical result–for CDM models.Thick disks are often observed in resolved stars in other galaxies(e.g.Mould2005;Yoachim& Dalcanton2005)but their properties remain to be robustly determined.•The central bulge-interestingly,though probably most stars in the Uni-verse are in spheroids,this was not in the classic Baade list of stellar populations.The dominant stellar population in the bulge of the Milky Way is old and metal-rich,with a broad spread in metallicities.Elemental abundances are available for remarkably few stars,given the capabilities of current telescopes,but where available point to a fairly rapid enrichment, being dominated by products of Type II supernovae.This,together with the old age and high(phase-space)density,point to in situ formation,in a‘starburst’,though a star formation rate of∼10M⊙yr−1is all that is required,at high redshift.In some way,this is connected to the formation of the supermassive black hole at the Galactic Center.The relationships between the overlapping‘bulge’,‘bar’and the thin and thick disks in the inner kpc or so remain unclear.•The stellar halo,also known as Baade’s Population II.This is a domi-nantly old and metal-poor component,with Type II dominated element ratios,indicating a short duration of star formation in each of the star-forming entities that created the halo.The negligible scatter in the ratio of alpha elements to iron for stars with a range in Galactocentric orbits of some tems of kpc is startling,and suggests in situ formation from a single well-mixed ISM over scales of that size during halo formation.Accretion to the dominant inner Population II halo can only have occured at early times(Unavane,Wyse&Gilmore1996).The bulk of the Population II halo may be connected to the stellar bulge;one can tie gas outflow from halo star-forming regions,required to provide the low mean metallicity, to gas inflow to the central regions to form the bulge.The low angular momentum of proto-halo material means that it will only come into cen-trifugal equilibrium after collapsing in radius by a significant factor.The predicted mass ratio of bulge to halo is around a factor of ten,just as would be expected,and the specific angular momentum distributions of stellar halo and bulge match(Wyse&Gilmore1992;see Figure1here).•The outer parts of the halo,although containing only a small fraction of even the rare halo stars,have a more complex structure and history(e.gThe Outer Galaxy3 the‘Field of Streams’,Belokurov etal2006).There are clear indications of significant accretion,most dramatically due to the Sagittarius dwarf (Ibata,Gilmore&Irwin1994)which is currently populating the outer halo with mostly intermediate-age and metal-rich members.It is quite unclear what the progenitor of Sgr would have looked like a few Gyr ago.•Population III–which we take to mean stars formed from primordial gas, precursers to‘galaxy’formation.Where are the low-mass Pop III stars?On-going searches for extremely low metallicity stars in the Galactic halo have not found any strong indications of a separate population(e.g.Beers et al.2005),but have identified a few stars with extreme deficiencies in iron,and relatively strong carbon(e.g.Aoki et al.2007).The origins of this abundance pattern are unclear.There is little observational evidence in favour of significant variations in the stellar IMF for any of the components discussed above,but there is theoretical prejudice that primordial stars might form with a narrow range of masses,around∼200M⊙(e.g.Bromm &Larson2004).The supernovae from such stars would provide elemental abundance patterns in the stars they enrich that do not match those of the extremely metal-poor stars,indicating that much remains to be learned.•Population Zero:the dark matter2.Dark Matter on small scalesThe Milky Way satellite dwarf spheroidal(dSph)galaxies are the smallest dark matter dominated systems in the universe.Several groups have underway dy-namical studies of the dSph to quantify the shortest scale lengths on which Dark Matter is distributed,the range of Dark Matter central densities,and the den-sity profile(s)of DM on small scales.An updated overview of results will be presented in Gilmore et al(2007).All mass distribution analyses based on the Jeans’equations-as most are to date-involve an inherent degeneracy between mass and(stellar tracer)orbital anisotropy.Nonetheless,the observed properties of all the dSph studied to date, including their half-light radii,the amplitude of their central velocity disper-sions,and theflatness of their velocity dispersion profiles,require,purely from observations,a quite remarkable similarity among the least luminous galaxies, even though they exist over several magnitudes in absolute magnitude.Exploiting this similarity in both optical sizes and kinematic properties, there is a simple consistency argument which links the observed distribution of sizes of small galaxies,the clear distinction in size and phase-space density between star clusters and galaxies of the same total luminosity,and all the available dSph galaxy dynamical analyses.Our current results suggest some surprising regularities:the central dark matter density profile is typically cored, not cusped,with scale sizes never less than one hundred pc;the central densities are typically10−20GeV/cc if the mass is cored,and less than∼1TeV/cc even if the dark matter is cusped.No galaxy is found with a dark mass halo less massive than∼107M⊙.All the dSph analysed by all groups to date show very similar,and sur-prisingly low,central dark matter mass densities,with a maximum value of4Gerry GilmoreFigure1.Adapted from Wyse&Gilmore1992,their Figure1.Angularmomentum distributions of the bulge(solid curve),the stellar halo(short-dashed/dotted curve),the thick disk(long-dashed/dotted curve)and the thindisk(long-dashed curve).The bulge and stellar halo have similar distribu-tions,as do the thick and thin disks.Does this hold for external galaxies,pointing to fundamental relationships between bulge and halo,and thick andthin disks?∼0.5M⊙pc−3,equivalent to∼20GeV/cc,if the mass profile really is cored. Interestingly,the rank ordering of the central densities,though not robustly determined,seems in inverse order to system total luminosity,with the least luminous galaxies being the most dense.This is of the opposite sign to some CDM predictions.The low maximum mass density is also intriguing,given that some currently favoured dark matter candidate particles are of Higgs scale,TeV mass-their corresponding volume density must be very low indeed.These consistencies were suspected,largely based on the results of Figure2 here,before the recentflurry of discoveries of several very low luminosity dSph galaxies,and the availability of several new kinematic studies.Interestingly,the validity of the conclusions is becoming stronger as the sample and the dynamic range are improved,suggesting some underlying general properties of dark mat-ter on the smallest scales are within observational reach(Gilmore etal2007 -submitted)We are discovering many more dSphs,which we and other groups are analysing to test the generality of these results.The Outer Galaxy5Figure2.Derived inner mass distributions from Jeans’eqn analyses for fourdSph galaxies.Also shown is a predicted r−1density profile.The modelling isreliable in each case out to radii of log(r)kpc∼0.5.The unphysical behaviourat larger radii is explained in the text.The general similarity of the four innermass profiles is striking.Acknowledgments.This review is based on joint work with many collab-orators,much also summarised in Wyse and Gilmore2006(astroph-0604130), in Gilmore et al2006(astroph-0608528),and in a larger analysis presented in Gilmore etal2007(ApJ-submitted).ReferencesAoki,W.et al.,2007,ApJ in press astro-ph/0609702Beers,T.et al.2000,AJ,119,2866Belokurov,V.et al2006ApJL642L137Bensby,T.,Zenn,A.,Oey,M.S.,&Feltzing,S.2007this volumeBinney,J.,Dehnen,W.&Bertelli,G.2000,MNRAS,318,658Bromm,V.&Larson,R.2004,ARAA,42,79Eke,V.,Efstathiou,G.&Wright,L.2000,MNRAS,315,L18Fall,S.M.&Efstathiou,G.1980,MNRAS,193,189Gilmore,G.&Reid,I.N.1983,MNRAS,202,1025Ibata,R.,Gilmore,G.&Irwin,M.1994,Nature,370,194Mo,H.,Mao,S.&White,S.D.M.1998,MNRAS,295,319Mould,J.2005,AJ,129,698Navarro,J.&Steinmetz,M.1997,ApJ,478,136Gerry GilmoreOstriker,J.P.1990,in‘Evolution of the Universe of Galaxies’,ASP Conference proceed-ings volume10,p25Unavane,M.,Wyse,R.F.G.&Gilmore,G.1996,MNRAS,278,727Wyse,R.F.G.&Gilmore,G.1992,AJ,104,144Yoachim,P.&Dalcanton,J.2005,ApJ,624,701。
人类该不该进行太空探索英语作文
人类该不该进行太空探索英语作文Humanity has always been driven by a deep-seated curiosity to explore the unknown and push the boundaries of our understanding of the universe. The quest for space exploration has been a part of this innate human desire to discover and unravel the mysteries that lie beyond our planet. As we stand at the cusp of a new era of space exploration, the debate on whether humans should continue to pursue this endeavor has become increasingly contentious. While some argue that the resources and efforts invested in space exploration could be better utilized to address pressing issues on Earth, others believe that the potential benefits of space exploration far outweigh the costs.One of the primary arguments in favor of continued space exploration is the potential for scientific and technological advancements. The research and development required for space missions have often led to groundbreaking discoveries and innovations that have had a profound impact on our daily lives. For instance, the development of satellite technology has revolutionized our communication systems, weather forecasting, and navigationcapabilities. Additionally, the study of microgravity and the unique conditions of space have led to advancements in fields such as medicine, materials science, and energy production.Moreover, space exploration has the potential to uncover new resources and habitable environments that could be crucial for the long-term survival and expansion of the human species. As the Earth's resources become increasingly strained, the exploration of other celestial bodies, such as asteroids or the Moon, could provide access to valuable minerals, water, and even potential sites for future human settlements. This could not only alleviate the strain on Earth's resources but also pave the way for the establishment of extraterrestrial colonies, ensuring the continued survival and progress of humanity.Another compelling argument in favor of space exploration is the potential for scientific discoveries that could fundamentally change our understanding of the universe and our place within it. The exploration of distant planets, stars, and galaxies can provide insights into the origins and evolution of the cosmos, as well as the potential for the existence of extraterrestrial life. These discoveries could have profound implications for our philosophical and religious beliefs, as well as our scientific understanding of the universe.Furthermore, space exploration can serve as a catalyst forinternational cooperation and collaboration. The development of space programs often requires the pooling of resources, expertise, and technological capabilities from various nations, fostering a sense of global unity and shared purpose. This collaboration can help to bridge cultural and political divides, promoting peaceful coexistence and the exchange of ideas and knowledge.However, critics of space exploration argue that the resources and funding directed towards these endeavors could be better utilized to address pressing issues on Earth, such as poverty, disease, and environmental degradation. They contend that the vast sums of money invested in space exploration could be more effectively allocated to improving the quality of life for people around the world.Additionally, some argue that the environmental impact of space exploration, particularly the launch of rockets and the disposal of space debris, can be detrimental to the Earth's ecosystems. They assert that the resources and energy consumed by space programs could be better directed towards the development of sustainable and eco-friendly technologies that could benefit the planet.While these concerns are valid, proponents of space exploration argue that the long-term benefits of continued exploration can outweigh the short-term costs. They believe that the knowledge and technological advancements gained through space exploration canultimately lead to solutions for many of the challenges facing humanity on Earth.Moreover, the exploration of space can serve as a source of inspiration and motivation for future generations, sparking their curiosity and fostering a sense of wonder and awe. This can inspire young people to pursue careers in science, technology, engineering, and mathematics, ultimately contributing to the advancement of human knowledge and the betterment of society.In conclusion, the debate on whether humans should continue to pursue space exploration is a complex and multifaceted issue. While there are valid arguments on both sides, the potential benefits of space exploration, including scientific and technological advancements, the discovery of new resources and habitable environments, and the promotion of international cooperation, suggest that the pursuit of space exploration is a worthwhile endeavor. As we navigate the challenges and uncertainties of the future, the continued exploration of the cosmos can provide us with the knowledge, resources, and inspiration needed to ensure the long-term survival and progress of humanity.。
高一年级英语宇宙探索与科学发现对人类生活的影响单选题40题
高一年级英语宇宙探索与科学发现对人类生活的影响单选题40题1. The first human to orbit the Earth was Y uri Gagarin from the Soviet Union. His achievement had a great impact on the Soviet people's view of themselves. Which of the following best reflects this impact?A. It made them feel more inferior in the face of the vast universe.B. It strengthened their confidence in their own national strength and scientific capabilities.C. It made them believe that they should rely more on foreign help in space exploration.D. It led them to think that space exploration was a waste of resources.答案：B。
解析：尤里·加加林是苏联宇航员，他成为第一个进入太空绕地球轨道飞行的人类，这一壮举是苏联在航天领域取得巨大成功的标志，这极大地增强了苏联人民对自己国家实力和科学能力的信心，而不是让他们感到自卑（A选项）；苏联一直致力于独立的航天探索，并不认为要依靠外国帮助（C选项）；这一伟大成就不会让他们觉得太空探索是浪费资源（D选项）。
2. When Neil Armstrong landed on the moon as an American astronaut, it had a profound influence on American culture. What was one of the main cultural concepts that emerged?A. A sense of superiority over other countries in all fields.B. An increased emphasis on individual heroism and the Americandream.C. A belief that the United States should stop exploring space and focus on domestic issues.D. A feeling that space exploration was only for the rich.答案：B。
随着人越来越多我们要去别的星球住英语作文
随着人越来越多我们要去别的星球住英语作文As the population of Earth continues to explode, the question of whether we should seek new habitats on other planets becomes increasingly urgent. With finite resources and limited space, the Earth's ability to sustain humanlife is being stretched to its limits. In this essay, we will explore the reasons why interstellar migration may become necessary, the challenges we face in achieving it, and the potential benefits it could bring to humanity.Firstly, the population growth on Earth is exponential, with the global population expected to reach over 9 billion by 2050. This rapid growth is putting immense pressure on the planet's natural resources, leading to issues such as climate change, water scarcity, and food insecurity. As these problems worsen, the viability of sustaining human life on Earth becomes increasingly questionable.Secondly, the search for alternative habitats is motivated by the desire for human survival and progress. As a species, we have always been explorers and pioneers, pushing the boundaries of what is possible. Interstellarmigration would be a巨大leap forward in our evolutionary journey, allowing us to expand our horizons and potentially discover new sources of energy, minerals, and even life itself.However, the challenges of interstellar migration are numerous and daunting. The technology required to travel to other planets is still in its infancy, and the costs are astronomical. Additionally, the physical and psychological toll on astronauts during such long journeys is a major concern. Furthermore, the political and ethicalimplications of colonizing other planets are complex and controversial.Despite these challenges, the potential benefits of interstellar migration are immense. It could provide a new home for humanity, relieving the pressure on Earth's resources and environment. It could also lead to new scientific discoveries and technological advancements,推动人类文明的进步和发展。
高一宇宙探索英语阅读理解30题
高一宇宙探索英语阅读理解30题1<背景文章>The solar system is a fascinating place. It consists of the sun, eight planets, moons, asteroids, comets, and other celestial bodies. The sun is at the center of the solar system and is a massive ball of hot gas. It provides light and heat to all the planets.The eight planets in the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Each planet has its own unique characteristics. Mercury is the closest planet to the sun and is very hot during the day and very cold at night. Venus is known as the Earth's sister planet because it is similar in size and composition. However, it has a thick atmosphere of carbon dioxide, which makes it very hot.Earth is the only planet known to support life. It has a moderate climate and a large amount of water. Mars is often called the Red Planet because of its reddish color. It has a thin atmosphere and evidence of past water.Jupiter is the largest planet in the solar system. It has a thick atmosphere of hydrogen and helium and many moons. Saturn is known for its beautiful rings. Uranus and Neptune are ice giants and have very cold temperatures.The planets in the solar system are in different positions. They orbit the sun in elliptical paths. The distance between the planets and the sun varies, which affects their temperatures and climates.1. The sun is at the center of the solar system and is a massive ball of ___.A. waterB. gasC. rockD. ice答案：B。
高一年级英语宇宙探索与科学发现对人类生活的影响分析单选题40题
高一年级英语宇宙探索与科学发现对人类生活的影响分析单选题40题1. Before Copernicus proposed the heliocentric theory, most people believed that the Earth was the center of the universe. What was the main reason for this belief?A. Lack of scientific explorationB. Religious influenceC. Limited astronomical observation toolsD. All of the above答案：D。
解析：在哥白尼提出日心说之前，大多数人认为地球是宇宙的中心。
选项A，当时缺乏科学探索，人们对宇宙的认识有限，这是一个原因。
选项B，宗教在当时有着极大的影响力，宗教教义倾向于地球为中心的观念。
选项C，当时天文观测工具有限，难以获取准确的宇宙信息，也导致人们只能基于有限的认知认为地球是中心。
所以以上三个选项都是人们有这种观念的原因。
2. Copernicus' heliocentric theory first challenged which traditional human thought?A. The omnipotence of GodB. Man's superiority in the universeC. The static view of the universeD. The connection between heaven and earth答案：C。
解析：哥白尼的日心说首先挑战的是传统人类对宇宙静态的看法。
在日心说之前，人们认为地球是宇宙中心且宇宙是静态的，哥白尼的理论提出地球绕着太阳转，打破了这种静态的宇宙观。
选项A，日心说不是首先挑战上帝的全能性。
邀请你校外国交换生参加国际爱鸟日英语作文
邀请你校外国交换生参加国际爱鸟日英语作文全文共6篇示例，供读者参考篇1Dear International Friends,I am so excited to invite all of you to join us for International Bird Day next month! This is one of my favorite events of the whole year. As an elementary school student, I really love birds and learning about them. International Bird Day is the perfect chance for us to celebrate these amazing creatures together.First, let me tell you a bit about what International Bird Day is all about. Every year on the same day, people all over the world take time to appreciate birds. We learn about the different species, their behaviors, their habitats, and how important they are to the environment. It's a day to have fun while also raising awareness about protecting birds.Our school always goes all out for International Bird Day. In the weeks leading up to it, we study different birds in class. We learn their calls, what they look like, where they live, and other cool facts. My favorite part is making bird feeders out of recycledmaterials to hang up around the school grounds. Seeing all the birds come eat from them makes me so happy!On the actual day, we have a huge Bird Day celebration at school. We start by going on a bird watching hike first thing in the morning. Our teachers bring binoculars and guidebooks to help us spot and identify as many different species as we can. I've gotten really good at recognizing birds just by their sounds and colorings.After the hike, we have a Bird Day assembly where each class performs a skit, poem, or song all about our feathered friends. I was a blue jay in my class's skit last year – we even made costumes with construction paper feathers! Some kids also share reports they've worked on about their favorite birds. We learn so much from each other.The best part though is the afternoon Bird Day festival on the playground. Teachers and parents run all kinds ofbird-themed games, crafts, and activities. There's a bird calling contest, where we see who can mimic bird calls the best. I won second place last year for my stellar robin impression! You can also decorate bird houses, make bird feeders, play bird bingo, and do a scavenger hunt. And of course, there are lots of tasty snacks and desserts shaped like birds.At the end of the festival, we release a flock of doves as a symbol of peace and appreciation for nature. It's such a beautiful sight to see all those white birds soaring up into the sky. We cheer them on and make wishes for the birds and the environment to stay healthy and protected. After that, we sing one of the Bird Day songs we learned as they fly away. I get chills every year!International Bird Day is tons of fun, but it's also a great way to learn about the importance of conserving bird species. Through all the activities, we learn why birds are so vital to ecosystems around the world. They pollinate plants, disperse seeds, control pest populations, and their migratory patterns can even help scientists study the effects of climate change.Sadly, many bird species are endangered due to habitat loss, pollution, illegal hunting and other human activities. That's why raising awareness through celebrations like International Bird Day is so important. We have to protect these amazing animals and their homes. Otherwise, future generations may never get to see certain bird species in the wild.My favorite bird that I learned is endangered is thespoon-billed sandpiper. This little shorebird has a very rare spoon-shaped beak and its numbers have dropped a lot due tohabitat loss in the areas it migrates through. I just think it looks so silly and unique! After learning about it for Bird Day, I did a whole report on the spoon-billed sandpiper and why we need to protect the areas it lives in. I really hope conservation efforts are able to help this funny little bird survive.So you can see why I absolutely love International Bird Day! It combines my favorite things: learning about amazing animals, doing creative activities, spending time outside in nature, and hanging out with all my friends. And on top of it all, we're celebrating something truly important for the whole planet.That's why I really, really hope all of you international exchange students will join us for the big Bird Day festivities at our school next month. It will be such an enriching experience for all of us to come together and bond over our shared appreciation for birds. We can learn so much from each other's cultures, backgrounds and perspectives. Plus, it will just be a total blast!I can't wait to hear your bird call impressions, see your awesome bird-themed crafts and outfits, and work together to protect our feathered friends. Having students from all over the world participate will make Bird Day even more special. We'llshow how uniting for a common cause like conservation can bring people together in such a joyous way.Getting to share my love of birds with friends from around the globe? That's about as cool as spotting an endangered species itself! I know we're all going to have a wild time. Let's fly into Bird Day together and keep our winged buddies soaring for generations to come!Can't wait to see you all there,[Your Name]篇2Dear International Friends,Hi there! My name is Emma, and I'm a 10-year-old student at Oakwood Elementary School here in the beautiful city of Greenville. I'm so excited to invite all of you, our wonderful international exchange students, to join us for a very special event – International Bird Day!Let me tell you a little bit about this amazing day. Every year, on the first Saturday of May, people from all around the world come together to celebrate and appreciate the incredible feathered creatures that share our planet with us – birds! It's aday filled with fun activities, educational workshops, and most importantly, a chance to learn about and protect our feathered friends.Now, you might be wondering, "Why should I care about birds?" Well, let me tell you, birds are some of the coolest animals out there! Have you ever seen a hummingbird hovering in mid-air, its wings beating so fast they're just a blur? Or a majestic eagle soaring high above the clouds? Birds come in all shapes, sizes, and colors, and each one is unique and amazing in its own way.But birds aren't just pretty to look at – they play a vital role in our ecosystem. They help pollinate plants, spread seeds, and control insect populations. Without birds, our world would be a very different place.That's why International Bird Day is so important. It's a chance for us to learn about the challenges birds face, like habitat loss, pollution, and climate change, and what we can do to help protect them. And trust me, there are so many fun ways to get involved!Imagine going on a guided bird-watching hike through one of our local nature preserves, where you might spot a brilliant red cardinal or a majestic great blue heron. Or maybe you'd liketo attend a workshop on building your very own birdhouse or feeder to attract feathered visitors to your backyard. There will even be a special presentation by a renowned ornithologist (that's a fancy word for a bird scientist!) who will teach us all about the incredible migration patterns of some of the world's most amazing birds.But that's not all! We'll also have a bird-themed arts and crafts station, where you can create your own colorful bird masks or paint a beautiful bird mural. And let's not forget the delicious bird-themed snacks – who's up for some "bird's nest" cookies or "owl" cupcakes?I can't wait for you all to experience the magic of International Bird Day with me and my classmates. It's going to be a day filled with learning, laughter, and a whole lot of feathered fun!So, what do you say, international friends? Will you join us in celebrating these amazing creatures and doing our part to protect them? I promise, it's going to be a hoot! (That's a bird pun – get it?)I'll be waiting eagerly for your response. I hope you'll all flock to this event and spread your wings with us for a day of avian adventure!Your friend,Emma篇3Dear International Friends,I can't wait to invite you all to the best day of the year - International Bird Day! Every spring, my school celebrates this awesome event, and we get to learn about the amazing world of birds from around the globe. But this year is even more special because you'll be here to join in the fun!First of all, let me tell you why birds are just the coolest. They can FLY! How amazing is that? With their lightweight, hollow bones and aerodynamic feathered bodies, they soar through the sky with such grace and freedom. Whenever I see a bird gliding effortlessly above me, I dream of having wings so I could experience that incredible feeling too.But birds aren't just awesome because they can fly. They come in so many dazzling colors and patterns that make them true artists of nature. My favorite is the male ruby-throated hummingbird with his iridescent red throat that glistens like a jewel. And have you seen a peacock's tail feathers? They're like arainbow exploded into one of the most breathtaking designs imaginable! Birds are walking, flying canvases painted by the most creative force in the universe.That's just the beginning of why birds totally rock. Their songs are like little musical melodies that brighten up even the dreariest day. From the cheerful trill of a house wren to the haunting coo of a mourning dove, every bird voice is unique and special. Listening to them chirping and whistling outside my window in the morning is my favorite way to start the day.Then there are the incredible bird behaviors that continue to surprise scientists. I recently learned that arctic terns fly over 50,000 miles every year during their annual migrations! That's like going around the world twice. No human could ever do that! Some birds are such genius builders too - just look at the intricately woven nests that birds like bald eagles craft to cradle their precious eggs. It's astounding what they can create using only their beaks and talons.But as amazing as birds are, that's what makes it so devastating that many species face huge threats like habitat loss, pollution, and climate change. That's why celebrating International Bird Day is so important - it's a chance for everyone to learn how to protect and preserve our feathered friends. Byworking together globally, we can create a brighter future for birds everywhere.So get ready, because our International Bird Day celebration is going to be epic! First, we'll kick things off with aneye-opening viewing of the acclaimed documentary "Winged Planet" in our school auditorium. Watching those breathtaking aerial shots of birds in flight against the backdrop of our majestic Earth is an experience you'll never forget.After the movie, we have tons of awesome activities lined up. You can visit our "Birds of the World" exhibit to see life-sized models, nests, eggs, and feather samples from hundreds of different species. The super cool VR station will let you virtually soar like an eagle over mountain peaks. Don't miss the live bird show with hawks, owls, and falcons too - those majestic raptors will blow you away!Back at school, you can enter the "Beak Challenge" to see which tasty treat you can extract fastest using different beak tools. Or test your crafting skills by building your own bird house or feeder to attract birds to your own backyard. Get ready for some friendly competition in the bird call imitation contest too - the winner gets a free book about birds!But the highlight of the day will be the international Bird Day parade through downtown. We'll all dress up like our favorite birds in amazing handmade costumes and march together spreading the message of bird conservation. Get ready to 'caw' like a crow, 'hoot' like an owl, and flap your wings in celebration of our flying friends!After the parade, the party continues with an ethnic food fair featuring bird-themed dishes from cultures around the world. You'll get to sample tasty treats like roasted quail with lingonberry sauce from Sweden, Vietnamese gà kho gùng, and chicken biryani from India. For dessert, check out the bird nest cookies and lovebird cake pops - they're almost too cute to eat (almost)!To wrap up our global Bird Day festivities, we'll release majestic butterflies and doves as symbols of peace and harmony between all the nations represented by our international Student body. As they take flight and soar into the dusk sky, we'll make a unified vow to protect these extraordinary creatures that make our planet so vibrant.So get ready to let your inner bird nerd soar, my friends! With your help, our International Bird Day is going to be thebiggest and best ever. Can't wait to see you all there as we celebrate the amazing feathered wonders of our world!Your friend,[Your name]篇4Dear friends,My name is Lily, and I'm a fourth-grader at Sunshine Elementary School. I'm writing to invite all of you, our international exchange students, to join us for a super fun and exciting event – International Bird Day!First, let me tell you what International Bird Day is all about. It's a special day celebrated every year on the first Saturday of May. On this day, people from all over the world come together to learn about, appreciate, and protect our feathered friends –the birds!You might be wondering, "Why birds?" Well, let me explain. Birds are amazing creatures that can fly high up in the sky, build cozy little nests, and sing the most beautiful songs. They come in all shapes, sizes, and colors, and each one is unique and special in its own way.But did you know that many bird species are facing threats like habitat loss, pollution, and climate change? That's why International Bird Day is so important. It's a chance for us to learn more about these incredible animals and find ways to help them thrive.Now, let me tell you about the fun-filled activities we have planned for International Bird Day at our school!First up, we're going to have a bird-watching adventure in our school's nature trail. We'll bring binoculars and field guides, and see how many different types of birds we can spot. Who knows, we might even catch a glimpse of a rare or endangered species!Next, we'll have a special guest speaker – a bird expert from the local nature center. They'll teach us all about the amazing things birds can do, like migrate thousands of miles and navigate using the stars. We'll also learn about the different types of bird calls and how to identify them.After that, we'll have a bird-themed arts and crafts session. We'll make our own bird feeders out of recycled materials, so we can attract more feathered friends to our school. We'll also create beautiful bird-themed paintings and drawings to decorate our classrooms.But that's not all! We're also going to have a fun bird quiz, with prizes for the winners. How much do you know about our feathered friends? This is your chance to show off your bird knowledge!And finally, we'll end the day with a special bird-themed movie screening. We'll cuddle up with our blankets and snacks, and watch an amazing documentary about the incredible lives of birds.Doesn't that sound like an awesome day? I can't wait to learn more about birds and how we can help protect them. And what better way to do that than with all of you, our international friends from different countries and cultures?Together, we can learn about the diverse bird species from around the world, and share our own experiences and stories about the birds in our home countries. It'll be a day of learning, sharing, and most importantly, having fun!So, what do you say? Are you ready to spread your wings and join us for International Bird Day? I promise it'll be a day you'll never forget!Let's show our feathered friends some love and appreciation, and do our part to make sure they can continue to soar freely in our skies for generations to come.I can't wait to see you all there!Your friend,Lily篇5Title: An Exciting Invitation to Celebrate International Bird Day!Hey there, my feathered friends! It's me, your pal, Emily, and I've got some exciting news to share with you all. Get ready to spread your wings and let your spirits soar because we're celebrating International Bird Day in a big way!First things first, let me tell you about this incredible day. International Bird Day is a special occasion when people from all around the world come together to appreciate and protect the amazing birds that share our planet. It's a day filled with fun activities, educational events, and plenty of opportunities to learn more about these fascinating creatures.Now, you might be wondering, "Why should I care about birds?" Well, let me tell you, my friends, birds are some of the coolest animals out there! They come in all shapes, sizes, and colors, and they can do incredible things like fly high up in the sky and sing the most beautiful songs.But that's not all! Birds play a crucial role in our ecosystems. They help pollinate plants, disperse seeds, and keep insect populations in check. Without them, our world would be a much less colorful and exciting place.That's why it's so important to celebrate and protect them, and that's exactly what we're going to do on International Bird Day!So, my dear international exchange students, I'm extending a special invitation to you to join us in this fantastic celebration. Whether you're from near or far, we want you to be a part of this unforgettable event.Imagine the fun we'll have! We'll have bird-watching tours, where we'll venture into local parks and nature reserves to spot all kinds of beautiful birds in their natural habitats. You'll get to see them up close and learn about their unique behaviors and habits. Who knows, you might even spot a rare species!But that's not all! We'll also have arts and crafts activities where we can make our own bird feeders and birdhouses. You'll get to unleash your creativity while doing something good for our feathered friends. Plus, it's a great way to take a piece of this special day home with you as a memory.And let's not forget about the educational presentations and workshops! You'll have the chance to learn from experts who will teach us all about bird conservation, migration patterns, and the importance of protecting their habitats. It's the perfect opportunity to expand your knowledge and become a true bird enthusiast.But wait, there's more! We'll also have a special photo booth where you can dress up like your favorite bird and strike a pose. Imagine yourself as a majestic eagle, a colorful parrot, or even a cute little hummingbird! It'll be a blast, and you'll have some fantastic memories to take back home with you.So, what do you say, my international friends? Are you ready to join us in this incredible celebration of our feathered companions? Trust me, it's going to be an experience you'll never forget!Just think about it – you'll get to learn new things, make new friends, and most importantly, you'll be doing your part to raiseawareness and protect the amazing birds that share our world. It's a win-win situation!Don't miss out on this incredible opportunity! Mark your calendars and get ready to spread your wings and soar with us on International Bird Day. I can't wait to see you all there, celebrating and appreciating the beauty and wonder of our feathered friends.Let's make this International Bird Day one for the books! Who's with me?篇6Title: Feathered Friends and Fun: An Invitation to Join International Bird DayHey there, my feathery friends! I'm Lily, a third-grader at Sunny Hill Elementary School, and I've got an exciting invitation for all you international exchange students out there!Get ready to spread your wings and soar into the wonderful world of birdwatching because International Bird Day is just around the corner, and we're gearing up for a day filled with feathery fun and educational adventures!Now, you might be wondering, "What's so special about International Bird Day?" Well, let me tell you, it's a day where we celebrate our feathered friends and learn all about their amazing lives, migrations, and the important role they play in our ecosystems.Can you imagine a world without the melodic chirping of birds in the morning or their colorful feathers fluttering through the sky? No, thank you! Birds are a crucial part of our planet, and it's our job to protect and cherish them.That's why our school is hosting a fantastic event to mark International Bird Day, and we want you, our international exchange students, to join us in this feathery fiesta!Picture this: a sunny day in the great outdoors, surrounded by lush trees and blooming flowers, with the sound of birds serenading us from every branch. We'll have expert birdwatchers on hand to teach us how to identify different species by their calls, colors, and behaviors.But that's not all! We'll also get to make our very own bird feeders and birdhouses, which we can take home and hang up in our backyards or gardens. Imagine the joy of watching our feathered friends flock to your creation for a tasty snack or a cozy nesting spot!And if that's not enough to ruffle your feathers, we've got a special surprise in store – a visit from a real-life falconer! That's right, you'll get to see these magnificent birds of prey up close and learn about their hunting techniques and incredible eyesight.But wait, there's more! We'll also have educational booths set up where you can learn about bird migration patterns, the importance of preserving their habitats, and how we can all do our part to protect these amazing creatures.Now, I know what you're thinking: "Lily, this sounds like a lot of work!" Don't worry, my feathery friends, because we'll have plenty of fun activities to keep your wings flapping with excitement!We'll have bird-themed games, arts and crafts stations, and even a bird-calling contest (get ready to show off your best chirps and tweets!). And let's not forget about the delicious picnic lunch we'll all enjoy together, surrounded by the sights and sounds of nature.So, what do you say? Are you ready to join us for this feathery extravaganza? Trust me; it's an opportunity you won't want to miss! Not only will you have a blast learning about ourfeathered friends, but you'll also get to meet new people from around the world and make unforgettable memories.Plus, who knows? You might even discover a newfound passion for birdwatching or become an expert at identifying different species by their calls and colors.So, mark your calendars, spread the word, and get ready to take flight with us on International Bird Day! Let's celebrate our feathered friends together and show the world how much we care about protecting these incredible creatures.See you there, my fellow bird enthusiasts! Let's make this International Bird Day one to remember!。
牡丹江“PEP”2024年11版小学第十二次英语第三单元暑期作业
牡丹江“PEP”2024年11版小学英语第三单元暑期作业考试时间：90分钟（总分:140）B卷考试人：_________题号一二三总分得分一、选择题(共计20题，共40分)1、What do you use to write on a blackboard?A. PenB. CrayonC. ChalkD. Marker2、What is 4 + 4?A. 6B. 7C. 8D. 93、Which of these is a type of tree?A. RoseB. OakC. DaisyD. Tulip4、What do we call a young deer?A. FawnB. CalfC. KidD. Pup5、What is the process called when a star collapses under its own gravity?A. SupernovaB. Black Hole FormationC. Red Giant PhaseD. Stellar Evolution6、What is the name of the largest planet in our Solar System?A. SaturnC. EarthD. Mars7、选择题：What do you call the natural satellite of the Earth?A. SunB. MoonC. StarD. Planet8、What is the name of the fairy tale character who had a magic mirror?A. CinderellaB. Snow WhiteC. RapunzelD. Belle9、What is the first letter of the alphabet?A. AB. BC. CD. D10、How many months are there in a year?A. 10B. 12C. 14D. 1111、选择题：What is the name of the famous scientist who developed the theory of relativity?A. Isaac NewtonB. Albert EinsteinC. Galileo GalileiD. Stephen Hawking12、How many legs does a spider have?A. 6B. 8C. 10D. 1213、What is the name of the famous river in the United States?A. MississippiB. AmazonD. Yangtze14、What are the two main types of telescopes?A. Optical and RadioB. Digital and AnalogC. Reflector and RefractorD. Infrared and X-ray15、What is the name of the galaxy that is colliding with the Milky Way?A. AndromedaB. TriangulumC. WhirlpoolD. Sombrero16、What do you call the place where you can watch movies?A. TheaterB. CinemaC. AuditoriumD. Gallery17、How do you say "friend" in German?A. FreundB. AmigoC. PalsD. Compagnon18、What is the term for the brightest part of the shadow during an eclipse?A. PenumbraB. UmbraC. EclipseD. Shadow19、What animal is known for having a long neck?A. ElephantB. GiraffeC. TigerD. Kangaroo20、选择题：What do you call the process of a plant growing?A. GerminationB. PhotosynthesisC. DigestionD. Respiration二、听力题(共计20题，共40分)1、听力题：Comets have long, bright ______ when close to the sun.2、听力题：The puppy is ___ around. (running)3、听力题：The ______ is known for his bravery.4、听力题：A solution is a mixture where one substance ______ in another.5、听力题：The _____ (ball/box) is round.6、听力题：The ______ is a talented athlete.7、听力题：The chemical formula for silver nitrate is _____.8、听力题：The chemical formula for silver acetate is _______.9、听力题：The ______ loves to cook healthy meals.10、听力题：The sky is blue and ___. (clear)11、听力题：The soup is ________ and healthy.12、听力题：The chemical symbol for cerium is ______.13、听力题：I enjoy ______ with my friends at the mall. (hanging out)14、听力题：I want to _____ (eat) ice cream.15、听力题：A _______ can symbolize love and beauty.16、听力题：I have a _____ (plan) for the weekend.17、听力题：A precipitate is a solid that forms during a _____ reaction.18、听力题：I want to ________ my toys.19、听力题：A mixture that appears uniform is called a ______ mixture.20、听力题：The chemical symbol for lanthanum is ______.三、填空题(共计20题，共10分)1、填空题：The antelope runs very _________. (快)2、填空题：A sheep provides us with ________________ (羊毛).3、填空题：I have a close _____ (同学).4、填空题：The ________ was a famous sculpture in ancient Greece.5、填空题：The ______ (小鱼) swims with its friends.6、填空题：The ______ (植物纤维) can be used for making clothes.7、填空题：The mouse is afraid of the _________ (猫).8、填空题：A kitten loves to explore new ______ (地方).9、填空题：Today is a sunny day, and I am very excited. I wake up early in the morning and lookoutside my window. The sky is ______ (1) and the birds are singing. I quickly get dressed and have ______ (2) with my family. My mom makes delicious pancakes, and10、填空题：A ________ (植物采集活动) can educate people.11、sh Inquisition started in ________ (1478). 填空题：The Span12、填空题：My friend loves to take care of her ______ (小猫).13、填空题：A ______ (绿色的) environment is beneficial.14、填空题：A ____(partnership) collaborates for mutual benefit.15、填空题：I play the _______ (piano/guitar).16、填空题：We are planting ________ (树) in the park.17、填空题：My cousin has a __________狗. (可爱的)18、填空题：I like to sing ______ songs with my family.19、填空题：The sun is _______ today.20、填空题：The _____ (树冠) provides shelter for birds.。
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a rXiv:as tr o-ph/13221v114Mar21The Evolution of Stellar Populations Discussion Session Angeles I.D´ıaz Departamento de F´ısica Te´o rica,C-XI,Universidad Aut´o noma de Madrid,28049Madrid,Spain Eduardo Hardy ∗National Radio Astronomy Observatory (NRAO)Casilla 36-D,Santiago,Chile Abstract.We summarize the discussion section on “Evolution of Stellar Populations”we led on May 27,2000in Granada,Spain,as part of the Euroconference on The Evolution of Galaxies.I-Observational Clues .The discussion was organized around two groups of topics.In the first,Population Synthesis ,the accent was partially placed on the use of tools and techniques centered around the question of the unicity of the models,their sensitivity to input and the question of the age-metallicity degeneracy.In the second group,Stellar Systems a stronger accent was placed on astrophysical questions,although we included there the need for “truth tests”that apply spectral synthesis techniques to objects for which there is detailed a priori knowledge of their stellar populations.We also provide a partial comparison between the present knowledge of these topics and that which existed at the time of the Crete Conference of 1995. 1.Introduction Five years ago,in October 1995,a conference was held in Crete which brought together in a friendly environment observers and theoreticians working in the field of galaxy evolution.A substantial part of that meeting was devoted to the study of the stellar populations of galaxies and its different analytical and observational tools.The overall results were summarized,as was also the case in this conference,by JohnHuchra (ASP Conferences Series,vol.98,1996).The Crete conference established a reference baseline for what was known about our subject at that time,and a natural starting point to evaluate progress since then.The reader is invited to examine the excellent summary men-tioned above and compare it with the present one with a question in mind:What has changed since Crete?At Crete it was recognized that the existing stellar libraries were good only over a limited spectral and chemical abundance range and,2 A.D´ıaz&E.Hardymoreover,that much better physical calibrations were needed.It was also recognized that complete sets of stellar models for a wide range of metallicities and masses,including mass loss and rotation,should be computed.The importance of performing“truth tests”,that is of confronting the results of population synthesis models based on the spectral properties of the integrated light of galaxies with the observa-tions of globular clusters(GC)and Local Group(LG)dwarf galaxies was stressed,as it was the need for compiling good quality multi-wavelength observations of selected objects.The latter would become the basis of a reference library.The former would show the limitation of spectral synthesis,by nature an“inverse problem”,when confronted with the age-metallicity results issued from the presumably more re-liable deep color-magnitude diagrams of the same object.Quantifying internal errors both in the theoretical models and in the observational data was also deemed essential.At the end of the Crete meeting expectations ran high for new stud-ies based on the unprecedented resolution and depth provided by both Hubble Space Telescope(HST)and the new generation of ground based telescopes:color-magnitude diagrams(CMD)for galaxy populations, Wolf-Rayet content,upper mass of the Initial Mass Function(IMF), etc.The then new HST images of Eta Carina,NGC2403,and IZw18 became the“stars of the show”,and many of us were impressed by the identification of young(1to5Myr)bursts of star formation in the latter object,one of the all-time favorite astronomical playgrounds.Following this lead we suggested the audience at the Granada con-ference an outline for the discussion session based on the following very general and loose scheme as ordered by category and by subject:− A.Population Synthesis(partial accent on tools)•Unicity of models•Sensitivity to input(IMF,stellar libraries,evolutionary tracks)•Is the age-metallicity degeneracy still with us?If so,can it be beaten?− B.Stellar Systems(partial accent on astrophysical ques-tions)•“Truth Tests”.Globular clusters,nearby galaxies,the galactic bulge:how well can we date GCs via integrated light;how wellcan we solve the age-metallicity degeneracy via integratedlight?•Giant Ellipticals:are there“young”stars there;if so,how metal–rich are they?Stellar Populations3•Dwarf Irr,Blue Compact Galaxies(BCD’s),starbursts‘`a la IZw18:are there“old”stars there;if so,how metal-poor arethey?The ensuing discussion was quite lively and a large number of people took part in it.We are aware that we have probably not done justice to all that was said,nor to all who participated.Then not all of the subjects proposed were discussed,nor all of them were discussed in the same depth,nor recorded by us with the same degree of detail.Refer-ences to the many posters related to our session were interspaced within the text where appropiate,and the reader willfind a full description of each of them in this volume.2.Population Synthesis2.1.Models:libraries,evolutionary tracks,errors,IMFG.Bruzual,who had given the conference’s review paper on models, insisted upon the fact that spectral libraries of intermediate resolution (∼10˚A)providing a better coverage of the metallicity and metallicity ratios were required and not yet satisfactory.He reminded us that in the UV we are still using old data for about40stars taken by IUE. More,better and more modern data are required,and not only in the UV but also in the IR.These libraries can be supplemented by or be a complement to existing cluster libraries such as those of Bica and Alloin (Bica&Alloin,1987).Along the same lines,A.Vazdekis commented that the spectral resolution of the Lick system,for which an extensive library exists,is adequate for the velocity dispersion of most galaxies, but pointed out that there is a lack in that library of hot stars and of low-metallicity stars.In addition he feels a betterflux calibration is needed.The difficulties in using evolutionary models for Red Giant Branch (RGB)and Asympthotic Giant Branch(AGB)stars were stressed by D.Schaerer who questioned the existence of an adequate observational sample for these stars.Indeed,is there a proper modeling of AGB stars in Single Stellar Populations(SSP)(A.Bressan)?How reliably can we use Wolf Rayet features in galaxies to date ionizing stellar populations (A.Maeder,D.Schaerer,D.Kunth)?Again,is the effect of binaries properly taken into account(M.Cervi˜n o)?The issue of unicity of the models was raised,but did not unduly stirred the audience.D.Alloin,a practitioner of the art,did not re-gard this as a major drawback when some astrophysical assumptions were introduced,such as reasonable tracks in the age-metallicity plane:4 A.D´ıaz&E.Hardyold populations should be more metal-poor than young ones,etc.M. Tosi stressed the need for studies of good Color Magnitude Diagramas (CMDs)of galaxies to test the models.Are we happy with stellar evolutionary tracks computed only,or mainly,with solar abundance ratios?It would seem that scaling schemes to apply solar-ratio tracks to complex situations are well in hand,and this was also not regarded as a major drawback.G.Stasi´n ska raised the issue of the impact of binaries in synthe-sis models.R.Schulte-Ladbeck estimates at about30%the fraction of binaries needed to synthesize open clusters.As far as quantifying theoretical uncertainties is concerned,nothing was proposed beyond recommending the use of different evolutionary tracks for comparison purposes.The issue of the universality of the IMF was raised,but no consensus was reached.J.Melnick,who had presented a theoretical approach to the IMF formation in an earlier talk,specified during the present dis-cussion that his work is restricted to starbursts,and will not necessarily apply,for example,to the Magellanic Clouds(MCs)where P.Massey finds IMF shapes which are at variance with the classical function.Some but not much evolution is detectable in this area since Crete.2.2.Models:Age vs Metallicity Degeneracy:an oldproblem.New solutions?How to break the age-metallicity degeneracy that has been with us for so long?Two general approaches were proposed,one based on the study of the CMD,the other based on the study of spectral indices.C.Gallart builds CMDs reaching the old Main Sequence(MS)turnoffs and with good statistics in all phases of evolution.She insists that in this way detailed information on the age distribution of the stars is gained from their distribution along the MS and subgiant branch.Once this distribution is determined,the possible metallicity distributions obtained from a modelfit to the detailed distribution of stars in the CMD are strongly constrained and are relatively unique.A lively discussion about methods and results took place among some of the main practitioners of CMD synthesis including C.Gallart, E.Grebel and M.Tosi.E.Grebel suggested using deep(HST)CMDs of open clusters as input for synthesis models.In this way open clus-ters of known age and metallicity are used as building blocks for the CMD diagram of complex systems.Something similar is in fact done in spectral synthesis(e.g.Bica&Alloin,1987).A number of participants,including A.Bressan,C.Maraston and A.Vazdekis,discussed the use of spectral indices to break the age-Stellar Populations5 metallicity degeneracy.One of the most intriguing recent results in this area is the unacceptably old age of20Gyr for47Tuc obtained using the high-resolution Balmer index HγHR(Gibson et al.,1999).How are we to interpret this result?C.Maraston proposed an answer(Maraston &Thomas,2000)which has important consequences for the dating of elliptical galaxies:Hβ(and presumably other Balmer indices)increases steeply for metal-poor globular clusters in such a way that a population containing even a small fraction of old metal-poor stars will produce strong Balmer ing their calibration of Hβbased on new SSP models theyfind an age of15Gyr for47Tuc consistent with most CMD studies.Furthermore,they argue that there’s no need for young stars in elliptical galaxies.In the end,the question is whether a“smoking gun”index,essen-tially a Balmer line(thus sensitive to main sequence turn-offposition), versus a(mostly)metallicity index such as those proposed by Worthey (1994)or the CaT as calibrated by Moll´a&Garc´ıa–Vargas(2000)for example(see also the poster contribution by J.Gorgas et al.),will break the degeneracy.D.Alloin proposes the alternative use of a large number of indices which are individually sensitive to both parameters but which together can provide the required degeneracy breaking.Is the problem solved,or not solved at all?Stay tuned.3.Stellar Systems3.1.“Truth tests”One of the outstanding issues,which has only seen partial progress since Crete,is that of testing spectral synthesis on objects for which the age-metallicity distribution is known a priori.Astronomers tend to believe color-magnitude diagrams better than they believe spectral synthesis: will the twain ever meet?The obvious objects in which to start this enterprise are globular clusters as they are single-age,single-metallicity objects.We have seen above that conflicting results have been obtained for the classical test-bench,47Tuc.But at least in this latter case it seems that proper calibration of the spectral indices may give consistent results.The situation for the more interesting(and needed!)composite populations of galaxies is still uncertain.E.Hardy advocated(as he did in Crete)the study of nearby resolved populations such as the galactic bulge,and the Magellanic Clouds.Observations of the MCs are underway in collaboration with C.Gallart,D.Alloin and others.In this respect the last few years have witnessed a certain loss of innocence in dealing with the CMDs of composite systems.The question is what6 A.D´ıaz&E.Hardya priori means in thefirst sentence of this section.CMDs of composite system do not unveil their secrets just by visual inspection.CMD syn-thesis work by C.Gallart,E.Tolstoy,E.Grebel and others has shown how difficult it is to disentangle ages from metallicity in the CMD of these systems(see above),and has shown that a proper analysis of a CMD requires careful modeling.This points towards a limitation of the proposed“truth tests”in that the CMD itself does not yield an answer which is model-independent.Both synthesis methods are indeed model-dependent.It is the consistency between their results,and the way in which they might complement each other that is now the real issue to be resolved before spectral synthesis can confidently jump beyond the Local Group.3.2.On the existence of old populations in all dwarfirregulars and Blue Compact GalaxiesFor some in the audience,if there has been something new and exciting since Crete it is probably the convincing observational evidence for the presence of an old stellar population in the strongest candidate to be a primeval galaxy:IZw18.In fact,given the leading role of this particular galaxy during the whole session,it was generally felt that a conference devoted solely to IZw18,the most metal poor blue compact(HII) galaxy known,would be welcome.The evidence comes from separate analyses of HST data(WFPC2(Alloisi et al.,1999)and NICMOS (Ostlin,2000))showing the presence of AGB stars corresponding to a stellar population of at least1Gyr,a result which is not seriously compromised even if the distance to the object is significantly larger than assumed.Moreover,IZw18does not seem to be unique amongst its class.There seems to be general agreement that there is evidence for the presence of an old(several Gyr)population in BCGs,as shown by U.Hopp from HST/NICMOS data of a sample of these objects(see also the poster contribution by R.Schulte-Ladbeck et al.).However,a similar consensus has not yet been reached regarding the way in which star formation proceeds in these galaxies.Is it going on in short bursts separated by long periods of laziness as generally accepted?Or there is a continuous,albeit low,star formation rate on top of which star bursts occur as proposed by F.Legrand?Another related question is whether BCG can in some way be iden-tified with the high redshift dwarfs which would be experiencing their first star formation episodes.Can this hypothesis be tested?The anal-ysis of the rest UV spectrum of MS1512-cB58(z=2.73),conveniently amplified by a gravitational lens,by Sally Heap et al.points to a constant SFR for this galaxy,otherwise a starburst-like galaxy.On theStellar Populations7 other hand,the local star forming galaxies(UCM sample)do not seem to be composed of very spectacular objects,but rather by objects with masses around5×1010M⊙undergoing a starburst involving about2% of their mass(see the poster contribution by A.Gil de Paz et al.). 3.3.New windows for the study of stellar populationsDue to fast progress in observing and analyzing high redshifts objects we will be obtaining a large amount of data in the IR(near to far). This means observing in the IR the UV rest frame spectra of the high z objects.On the other hand,recent advances in instrumentation make possible the observation of spectral properties of stellar populations in the IR.These IR studies are already yielding very interesting results, as can be appreciated by looking at the numerous poster contributions on this topic:the underlying populations of BCG(mentioned above); stellar populations in AGN(through the H window);composite stellar systems(CaT)kinematics;edge-on galaxies;inner Milky Way Galaxy (MWG)and so on and so forth.As a result,we need to study in the UV rest frame stellar populations of galaxies which will be observed in the near IR for objects at z=3.Not much seems to have been done in this direction(but see Gonz´a lez Delgado et al.,1997a and Gonz´a lez Delgado et al.,1997b).In a related way,but moving this time towards the mm and sub-mm spectral range,the fast approaching ALMA era will create unheard of opportunities and challenges for the study of the early Universe. Preparatory work on nearby objects at“shorter”wavelengths will also be required,and it was gratifying that some in the audience showed an appreciation for this opportunity.The multiwavelength approach is undoubtedly the most complete way of studying stellar populations as well as to test population synthe-sis models.An example of this approach was presented by R.Gonz´a lez Delgado for the giant HII region NGC604.Multivawelength observa-tions,on the other hand,introduce extra observational difficulties and, as A.D´ıaz pointed out,it might be worth to have some representative objects with complete wavelength coverage,at least from the UV to the far IR.In some cases this would involve completing and extending existing data libraries.Hopefully we could all work together to generate a database that could serve to test our stellar population synthesis models.8 A.D´ıaz&E.Hardy4.Conclusion and desiderata:on the way to the nextEuroconferenceLet us take again,for the purpose of summarizing this discussion and preparing the list of problems we would like to see solved in the near future,the discussion scheme proposed in the Introduction:− A.Population Synthesis•Unicity of models:not much emphasis was placed on this and for some it simply is a non-issue.It may however bea dormant problem which may raise its head as we comecloser to testing the consistency of models based on spectralsynthesis and color magnitude diagrams.•Sensitivity to input(IMF,stellar libraries,evolutionary tracks).The universality of the IMF remains an open funda-mental question especially for evolutionary synthesis where itis one of the fundamental input parameters.Also,we certainlyneed to improve on the present spectral libraries,not onlyfor stars,but also for key reference objects.The improve-ment should come from better physical calibrations,a morecomplete coverage of the metallicity range,and the extensionof the wavelength coverage.Improvement in the quality andscope of stellar evolutionary tracks,and the required atmo-spheres,is likely to come in the near future.We hope to see,atleast,a better agreement between theory and observations inthe all-important red giant branch as well as a more detailedtreatment of non-solar abundance ratios•Is the age-metallicity degeneracy still with us?If so, can it be beaten?The answer to both question is a qualifiedyes.On the one hand some of the spectral tools used on simplesystems,such as globular clusters,give contradictory results,but on the other hand more realistic SSP models are possi-ble and they seem to lead towards consistency with the agesdetermined via the color magnitude diagram.For compositesystems containing a range of ages and metallicities,the samespectral tools,once properly calibrated,may lift the degener-acy.Synthetic CMD for complex systems are coming of ageand they are likely to present their own set of new problems.Stellar Populations9− B.Stellar Systems(partial accent on astrophysical ques-tions)•‘‘Truth Tests”.Globular clusters,nearby galaxies,the galac-tic bulge:how well can we date GCs via integrated light;how well can we solve the age-metallicity degeneracy via in-tegrated light?Little has been done on this subject,but ob-servations of key LG members are on the way.Equally impor-tantly,we now have a better idea of how to interpret CMDof complex non-coeval systems.•Giant Ellipticals:are there“young”stars there;if so,how metal–rich are they?The jury is still out.Conventional wis-dom used to dictate that ellipticals were old,metal-rich,basi-cally single-burst objects.Then conventional wisdom evolvedand intermediate-age stars appeared more likely.Now,com-ing full circle,we are told that we can reproduce the strongBalmer lines in ellipticals with even a small contribution fromold metal-poor stars.Are we reaching a climax here?•Dwarf Irr,BCD’s,starbursts`a la IZw18:are there“old”stars there;if so,how metal-poor are they?Old stars seem tobe everywhere,unless wefind a true primordial galaxy.ButIZw18does not seem to be the one.In any case the history ofstar formation in these galaxies is largely unknown.In all ofthis ALMA is likely to tell us much,and we can hardly wait.Let’s hope that by the end of this series of Euroconferences many of the questions raised here will have found an answer.Many more new questions are waiting for us.AcknowledgementsWe would like to thank Elena Terlevich who faithfully took note of what was said during the discussion session thus providing the basis for this written contribution.ReferencesAloisi,A.,Tosi,M.and Greggio,L.,1999,AJ118,302Bica,E.,and Alloin,D.,1987,A&A186,49Gibson,B.K.,Madgwick,D.S.,Jones,L.A.,Da Costa,G.S.,and Norris,J.E., 1999,AJ118,126810 A.D´ıaz&E.HardyGonz´a lez Delgado,R.M.,Leitherer,C.and Heckman,T.,1997,ApJ489,601 Gonz´a lez Delgado,R.M.,Leitherer,C.,Heckman,T.and Cervi˜n o,M.,1997,ApJ 483,705Leitherer,C.,Fritze-von Alvensleben,U.,and Huchra,J..1996,From Stars To Galaxies:The Impact Of Stellar Physics On Galaxy Evolution.ASP Conference 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