下载文档原格式
高三英语询问科学单选题50题1. Recent research has found that some bacteria can form a complex community structure called a biofilm. In a biofilm, bacteria are surrounded by a self - produced matrix. Which of the following is a major component of this matrix?A. DNAB. ProteinC. LipidD. Carbohydrate答案：D。
解析：在生物膜的基质中，碳水化合物是主要成分之一。
选项A，DNA虽然存在于细胞中，但不是生物膜基质的主要成分。
选项B，蛋白质是生物膜的组成部分，但不是基质的主要成分。
选项C，脂质主要参与细胞膜结构构建，而非生物膜基质的主要部分。
本题主要考查生物科学知识，语法上是一般现在时的陈述语句。
2. The mitochondria are known as the "powerhouses" of the cell. Which process mainly occurs in mitochondria?A. PhotosynthesisB. GlycolysisC. Cellular respirationD. Protein synthesis答案：C。
解析：线粒体中主要发生的过程是细胞呼吸，这是其重要功能。
选项A，光合作用主要发生在叶绿体中。
选项B，糖酵解发生在细胞质中。
选项D，蛋白质合成主要发生在核糖体上。
从语法来看，这是一个考查一般现在时和生物知识结合的题目。
3. In the process of evolution, some animals have developed unique adaptations. The giraffe's long neck is an example. Which theory best explains the evolution of the giraffe's long neck?A. Lamarck's theory of inheritance of acquired characteristicsB. Darwin's theory of natural selectionC. Mendel's law of inheritanceD. The theory of punctuated equilibrium答案：B。
The Formation of Volcanic IslandsEarth’s surface is not made up of a single sheet of rock that forms a crust but rather a number of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle. Some plates carry islands or continents, others form the seafloor. All are slowly moving because the plates float on a denser semiliquid mantle, the layer between the crust and Earth’s core. The plates have edges that are spreading ridges (where two plates are moving apart and new seafloor is being created), subduction zones(where two plates collide and one plunges beneath the other),or transform faults(where two plates neither converge nor diverge but merely move past one another).It is at the boundaries between plates that most of Earth’s volcanism and earthquake activity occur.Generally speaking, the interiors of plates are geologically uneventful. However, there are exceptions. A glance at a map of the Pacific Ocean reveals that there are many islands far out at sea that are actually volcanoes—many no longer active, some overgrown with coral—that originated from activity at points in the interior of the Pacific Plate that forms the Pacific seafloor.How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a very instructive answer. Like many other island groups, they from a chain. The Hawaiian Islands Chain extends northwest from the island of Hawaii. In the 1840s American geologist James Daly observed that the different Hawaii Islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probably older, toward the northwest. Then in 1963, in the early days of the development of the theory of plate tectonics, Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most northwest island would have been the first to form. Then, as the plate moved slowly northwest, new volcanic islands would have forms as the plate moved over the volcanic source. The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.Although this idea was not immediately accepted, the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently active volcano, just as Daly had suggested. Wilson’s analysis of these data is now a central part of plate tectonics. Most volcanoes that occur in the interiors of plates are believed to be produced by mantle plumes, columns of molten rock that rise from deep within the mantle. A volcano remains an active “hot spot” as long as it is over the plume. The plumes apparently originate at great depths, perhaps as deep as the boundary between the core and the mantle, and many have been active for a very long time. The oldest volcanoes in the Hawaii hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Islands in the Pacific, Reunion and Mauritius in the Indian Ocean, an indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes.The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologists because they record the past locations of the plate over a fixed source. They therefore permit the reconstruction of the process of seafloor spreading, and consequently of the geography of continents and of ocean basins in the past. For example, given the current position of the Pacific Plate, Hawaii is above the Pacific Ocean hot spot. So the position of the Pacific Plate 50 million years ago can be determined by moving it such that a 50-million-year-old volcano in the hot-spot trail sits at the location of Hawaii today. However, because the ocean basins really are short-lived features on geologic times scales, reconstructing the world’s geography by backtracking along thehot-spot trail works only for the last 5 percent or so of geologic time. (690 WORDS)****************************************************************************** Paragraph 1: Earth’s surface is not made up of a single sheet of rock that forms a crust butrather a number of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle. Someplates carry islands or continents, others form the seafloor. All are slowly moving because theplates float on a denser semiliquid mantle, the layer between the crust and Earth’s core. The plateshave edges that are spreading ridges (where two plates are moving apart and new seafloor is beingcreated), subduction zones(where two plates collide and one plunges beneath the other),ortransform faults(where two plates neither converge nor diverge but merely move past oneanother).It is at the boundaries between plates that most of Earth’s volcanism and earthquakeactivity occur.1. The author mentions "spreading ridges", "subduction zones", and "transform faults" in order to ○ illustrate that the boundaries of tectonic plates are neat, thin lines○ explain why some tectonic plates carry islands or continents while other form the seafloor○ explain the complex nature of the edges of tectonic plates○ provide examples of areas of tectonic plates where little geologic action occurs2. The word "converge" in the passage is closet in meaning to○ expand○ form○ rise○ move closerParagraph 2：Generally speaking, the interiors of plates are geologically uneventful.However, there are exceptions. A glance at a map of the Pacific Ocean reveals that there are manyislands far out at sea that are actually volcanoes—many no longer active, some overgrown withcoral—that originated from activity at points in the interior of the Pacific Plate that forms thePacific seafloor.3. Which of the sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important ways or leave outessential information○ Volcanic activity is responsible for the formation of the Pacific seafloor in the interior of thePacific Plate○ Many volcanoes in the Pacific Ocean are no longer active and have become islands that supportcoral○ There are many islands in the Pacific Ocean that originated as volcanoes in the interior of thePacific Plate○ The map of the Pacific Ocean reveals fewer volcanic islands than there truly are because manyare no longer active and some are completely overgrown with coralParagraph 3：How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a very instructive answer. ■Like many other island groups, they form a chain. ■The Hawaiian Islands Chain extends northwest from the island of Hawaii. ■In the 1840s American geologist James Daly observed that the different Hawaii Islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probably older, toward the northwest. ■Then in 1963, in the early days of the development of the theory of plate tectonics, Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most northwest island would have been the first to form. Then, as the plate moved slowly northwest, new volcanic islands would have forms as the plate moved over the volcanic source. The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.4.The word "instructive" in the passage is closet in meaning to○ clear○ detailed○ informative○ familiar5. The word "eroded" in the passage is closest in meaning to○ worm down○ scattered○ developed○ deserted6. In paragraph 3, what is the relationship between the scientific contribution of James Daly and Tuzo Wilson?○ Wilson provided an explanation for the observations made by Daly○ Wilson challenged the theory proposed by Daly○ Wilson found numerous examples of island chains that supported Daly’s theory○ Wilson popularized the explanation of volcanic island formation formulated by DalyParagraph 4：Although this idea was not immediately accepted, the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently active volcano, just as Daly had suggested. Wilson’s analysis of these data is now a central part of plate tectonics. Most volcanoes that occur in the interiors of plates are believed to be produced by mantle plumes, columns of molten rock that rise from deep within the mantle. A volcano remains an active “hot spot” as long as it is over the plume. The plumes apparently originate at great depths, perhaps as deep as the boundary between the core and the mantle, and many have been active for a very long time. The oldest volcanoes in the Hawaii hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Islands in the Pacific, Reunion and Mauritius in the IndianOcean, an indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes.7. Why does the author provide the information that "the dating of lavas in the Hawaii(and other) chains showed that their ages increase away from the presently active volcano"?○To point out differences between the Hawaii Island chain and other volcanic island chains○To question the idea that all the islands in an island chain have been formed by volcanic activity ○To explain why Wilson hypothesis was initially difficult to accept○To provide evidence in support of Daly’s and Wilson’s ideas about how the Hawaii Islands were formed8. According to paragraph 4, which of the following is true of mantel plumes○ They exist close to the surface of tectonic plates○ They cause most of the volcanic activity that occurs in the interiors of plates○ They are rarely active for long periods of time○ They get increasingly older away from the present hot spotsParagraph 5: The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologists because they record the past locations of the plate over a fixed source. They therefore permit the reconstruction of the process of seafloor spreading, and consequently of the geography of continents and of ocean basins in the past. For example, given the current position of the Pacific Plate, Hawaii is above the Pacific Ocean hot spot. So the position of the Pacific Plate 50 million years ago can be determined by moving it such that a 50-million-year-old volcano in the hot-spot trail (sits at the location of Hawaii today). However, because the ocean basins really are short-lived features on geologic times scales, reconstructing the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.9. According to paragraph 5, volcanic islands help geologists to○ reconstruct past geography○ detect changes in mantle plumes○ measure the rigidity of tectonic plates○ explain why the seafloor spreads10. What can be inferred about the Pacific Plate from paragraph 5?○ The hot spots on the Pacific plate are much older than the ones located on the other tectonic plates○ Most of the volcanic sources beneath the Pacific Plate have become extinct○ The Pacific Plate has moved a distance equal to the length of the Hawaiian Island chain in the past 80 million years○ The Pacific Plate is located above fewer mantle plumes than other plates are11. The word "current" in the passage is closest in meaning to○ original○ idea○ relative○ present12. According to paragraph 5, why are geologists unable to trace back the entire geologic of continents from hot-spot trails?○ Hot spots have existed for only about 5 percent of geologic time○ Hawaii did not exist 50 million years ago○ Oceanic basins that contained old hot-spot trails disappeared a long time ago○ Hot-spot trails can be reconstructed only for island chains13. Look at the four squares [ ■ ] that indicate where the following sentence could be added to the passage.This pattern remained unexplained for a long time.Where would the sentence best fit?Paragraph 3：How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a very instructive answer. ■Like many other island groups, they from a chain. ■The Hawaiian Islands Chain extends northwest from the island of Hawaii. ■In the 1840s American geologist James Daly observed that the different Hawaii Islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probably older, toward the northwest. ■Then in 1963, in the early days of the development of the theory of plate tectonics, Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most northwest island would have been the first to form. Then, as the plate moved slowly northwest, new volcanic islands would have forms as the plate moved over the volcanic source. The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.14. Directions: An introductory sentence for a brief summary of the passage is provided below.Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. This question is worth 2 points.Although volcanic activity is concentrated on the edges of tectonic plates, such activity can occur in the interiors of plates as well.●●●Answer Choices○Our understanding of volcanic islands comes from Daly’s and Wilson’s observations of the Hawaiian Islands, which was later confirmed by plate-tectonic theory.○ It has only recently been discovered that tectonic plates are closely fitting rather than loosely constructed, as geologists previously believed.○ The hot-spot trails formed by volcanic island chains indicate the positions of tectonic plates as far back as the present ocean basins have existed○ Volcanic island chains such as the Hawaiian Islands form in the interior of a tectonic plate as the plate moves over a fixed volcanic source in the mantle.○Whereas volcanic islands formed by mantle plumes are typically small, most of the world’s largest islands are formed at the edges of tectonic plates.○ The Pacific Plate has existed for as long as the Hawaiian Island have existed, namely for more than 80 million years.。
AP® Physics C1980 Free Response QuestionsThese materials were produced by Educational Testing Service® (ETS®), which develops and administers the examinations of the Advanced Placement Program for the College Board. The College Board and Educational Testing Service (ETS) are dedicated to the principle of equal opportunity, and their programs, services, and employment policies are guided by that principle.The College Board is a national nonprofit membership association dedicated to preparing, inspiring, and connecting students to college and opportunity. Founded in 1900, the association is composed of more than 4,200 schools, colleges, universities, and other educational organizations. Each year, the College Board serves over three million students and their parents, 22,000 high schools, and 3,500 colleges, through major programs and services in college admission, guidance, assessment, financial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT®, thePSAT/NMSQT®, and the Advanced Placement Program® (AP®). The College Board is committed to the principles of equity andexcellence, and that commitment is embodied in all of its programs, services, activities, and concerns.APIEL is a trademark owned by the College Entrance Examination Board. PSAT/NMSQT is a registered trademark jointly owned by the College Entrance Examination Board and the National Merit Scholarship Corporation. Educational Testing Service and ETS are registered trademarks of Educational Testing Service.1980M1. A small mass m1 rests on but is not attached to a large mass M2 that slides on its base without friction. The maximum frictional force between m1 and M2 is f. A spring of spring constant k is attached to thelarge mass M2 and to the wall as shown above.a. Determine the maximum horizontal acceleration that M2 may have without causing m1 to slip.b. Determine the maximum amplitude A for simple harmonic motion of the two masses if they are to movetogether, i.e., m1 must not slip on M2.c. The two-mass combination is pulled to the right the maximum amplitude A found in part (b) and released.Describe the frictional force on the small mass m1 during the first half cycle of oscillation.d. The two-mass combination is now pulled to the right a distance of A' greater than A and released.i. Determine the acceleration of m1 at the instant the masses are released.ii. Determine the acceleration of M2 at the instant the masses are released.1980M2. A block of mass m slides at velocity v o across a horizontal frictionless surface toward a large curved movable ramp of mass 3m as shown in Figure 1. The ramp, initially at rest, also can move without friction and has a smooth circular frictionless face up which the block can easily slide. When the blockslides up the ramp, it momentarily reaches a maximum height as shown in Figure II and then slides backdown the frictionless face to the horizontal surface as shown in Figure III.a. Find the velocity v1 of the moving ramp at the instant the block reaches its maximum height.b. To what maximum height h does the center of mass of the block rise above its original height?c. Determine the final speed v f of the ramp and the final speed v' of the block after the block returns to thelevel surface. State whether the block is moving to the right or to the left.1980M3. A billiard ball has mass M, radius R, and moment of inertia about the center of mass I c = 2MR²/5The ball is struck by a cue stick along a horizontal line through the ball's center of mass so that the ball initially slides with a velocity v o as shown above. As the ball moves across the rough billiard table (coefficient of sliding friction μk), its motion gradually changes from pure translation through rolling with slipping to rolling without slipping.a. Develop an expression for the linear velocity v of the center of the ball as a function of time while itis rolling with slipping.b. Develop an expression for the angular velocity ω of the ball as a function of time while it is rolling withslipping.c. Determine the time at which the ball begins to roll without slipping.d. When the ball is struck it acquires an angular momentum about the fixed point P on the surface of thetable. During the subsequent motion the angular momentum about point P remains constant despite the frictional force. Explain why this is so.1980E1. A thin plastic rod has uniform linear positive-charge density λ. The rod is bent into a semicircle of radius R as shown above.a. Determine the electric potential V o at point 0, the center of the semicircle.b. Indicate on the diagram above the direction of the electric field at point 0. Explain your reasoning.c. Calculate the magnitude E o of the electric field at point 0.d. Write an approximate expression, in terms of q, V o, and E o, for the work required to bring a positivepoint charge q from infinity to point P, located a small distance s from point O as shown in the diagram above.1980E2. A parallel-plate capacitor consists of two conducting plates separated by a distance D as shown above. The plates may be considered very large so that the effects of the edges may be ignored. The two plates have an equal but opposite surface charge per unit area, . The charge on either plate resides entirely on the inner surface facing the opposite plate.a. On the diagram below draw the electric field lines in the region between the plates.b. By applying Gauss's law to the rectangular box whose upper surface lies entirely within the topconducting plate, as shown in the following diagram, determine the magnitude of the electric field E in the region between the plates.c. A dielectric is inserted and fills the region between the plates. Is the electric field greater than, lessthan, or equal to the electric field when there is no dielectric? Describe the mechanism responsible for this effect. Recognize that the plates are not connected to a battery.1980E3. A spatially uniform magnetic field directed out of the page is confined to a cylindrical region of space of radius a as shown above. The strength of the magnetic field increases at a constant rate such that B = B o + Ct, where B o and C are constants and t is time. A circular conducting loop of radius r and resistance R is placed perpendicular to the magnetic field.a. Indicate on the diagram above the direction of the induced current in the loop. Explain your choice.b. Derive an expression for the induced current in the loop.c. Derive an expression for the magnitude of the induced electric field at any radius r < a.d. Derive an expression for the magnitude of the induced electric field at any radius r > a.。
小学上册英语第3单元期末试卷(有答案)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.We need to ________ the dishes.2.The Milky Way galaxy spins around its _______.3. A _____ is a group of stars that is visible in the night sky.4. A _______ can enhance indoor spaces.5.How many days are in a week?A. 5B. 6C. 7D. 8答案:C6.What is the capital of Italy?A. RomeB. FlorenceC. VeniceD. Milan答案:A7.Do you prefer __________ (玩具名) or __________ (玩具名)?8. A chemical reaction can be classified as endothermic or ______.9.I enjoy ______ with my friends. (talking)10.The squirrel collects _______ (松鼠收集_______).11.The chemical formula for ethyl alcohol is ______.12.The puppy loves to chase its ______ (尾巴). It looks very ______ (搞笑).13.The _____ (灌木) provide shelter for small animals.14.The freezing point of water is _______ degrees Fahrenheit.15.The __________ is a famous area known for its oasis.16.I saw a _______ (小鸟) perched on a fence.17.The chemical symbol for tellurium is _______.18.The street is _____ (busy/quiet).19.My aunt enjoys crafting ____ (scrapbooks).20.We have a ______ (有趣的) project on recycling.21.The hedgehog curls up into a ______ (球) when it feels ______ (害怕).22.What do we wear on our feet?A. ShoesB. HatC. ScarfD. Gloves答案:A Shoes23.The __________ (巴黎公社) was a radical socialist government that ruled Paris in 1871.24.I think art is a wonderful way to express emotions. I love visiting art exhibits and seeing different styles. My favorite artist is __________ because his/her work is amazing.25.写出所给字母的邻居。
吉林“PEP”2024年11版小学四年级下册英语第4单元期中试卷考试时间：90分钟（总分:140）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：The _____ (ball/balloon) is blue.2、选择题：What do we call a person who designs buildings?A. ArchitectB. EngineerC. ConstructorD. Developer3、填空题：My cousin is very . (我的表兄弟/表姐妹很。
)4、What is the name of our planet?A. MarsB. EarthC. VenusD. Jupiter5、听力题：In a redox reaction, one species is oxidized while another is reduced, involving a transfer of _____.6、填空题：The raccoon is often seen at _________. (夜晚)7、听力题：The color of bromothymol blue changes in acidic and basic solutions, indicating ______.8、听力题：A compound that has a high boiling point is likely to be ______.The ________ (teamwork) improves results.10、听力题：The chemical reaction between an acid and a base is called _____.11、听力题：The chemical formula for acetic acid is _______.12、How many wheels does a bicycle have?A. OneB. TwoC. ThreeD. Four答案: B. Two13、填空题：The teacher encourages _____ (批判性思维) in class discussions.14、metamorphic rock) changes due to heat and pressure. 填空题：The ____15、填空题：Every Sunday, I play board games with my _________ (家人).16、填空题：My dog has a _______ (特别的) collar.17、What is the most common color for a school bus?A. BlueB. GreenC. YellowD. Red答案:C18、填空题：The kitten likes to chase its own ______ (尾巴). It is very ______ (搞笑).19、填空题：My family has a tradition of having dinner together every ______ (星期日). It’s a time for us to catch up and enjoy each other’s company.20、听力题：The ______ is often seen in parks.My aunt loves __________ (进行活动策划).22、填空题：The phone is ringing ________ (响).23、填空题：The ______ (小鸟) sings a beautiful melody in the ______ (清晨).24、听力题：Reactants are the starting materials in a _____.25、选择题：What do we call the time when the sun rises?A. DawnB. NoonC. DuskD. Midnight26、What do we call a person who studies the structure and function of proteins?A. BiochemistB. Molecular BiologistC. GeneticistD. Microbiologist答案: A27、填空题：The __________ was a key moment in the history of the United States. (独立战争)28、听力题：A _______ solution contains the maximum amount of solute that can dissolve.29、填空题：My ________ (玩具名称) is a reminder of my childhood dreams.30、填空题：My dog gets excited when it's time for a _______ (散步).31、听力题：The children are ________ in the playground.32、听力题：The park is ______ (perfect) for picnics.We are going to the ___. (beach) this summer.34、What is the opposite of "happy"?A. SadB. AngryC. ExcitedD. Tired35、听力题：The chemical formula for table sugar is ______.36、填空题：My friend loves to watch ______ (鸟) fly in the sky.37、听力题：My brother is a ______. He enjoys participating in club activities.38、e of Gettysburg was fought during the _____ War. 填空题：The Batt39、听力题：A ____ is a tiny animal with whiskers that likes to explore.40、What is 10 + 10?A. 15B. 20C. 25D. 30答案: B41、听力题：The letter is ________ in the mailbox.42、听力题：The solid part of a solution that does not dissolve is called a _____.43、填空题：The first female pharaoh of Egypt was ______ (哈特谢普苏特).44、填空题：The famous singer I like is _______ (名字). 她的歌很 _______ (形容词).45、填空题：The octopus is known for its problem-solving ______ (能力).I enjoy _____ (旅行) with my family.47、What do we call a person who studies the effects of climate change on species?A. EcologistB. BiologistC. ConservationistD. Environmental Scientist答案: A48、填空题：The sky is _______ (晴朗的).49、听力题：Oxygen is necessary for ________.50、听力题：She is wearing a beautiful ___. (ring)51、ssance artist Michelangelo is famous for painting the _____. 填空题：The Rena52、填空题：In 1492, Columbus sailed the ocean blue to find a new __________. (航道)53、填空题：My uncle, ______ (我的叔叔), has a collection of coins.54、What is the capital of Canada?A. OttawaB. TorontoC. VancouverD. Montreal55、听力题：A __________ is the part of the earth that contains all living organisms.56、填空题：The bat uses echolocation to find its _________ (食物).57、填空题：My _______ (小鸟) chirps every morning.58、What do you call a baby hedgehog?A. HogletB. KidC. PupD. Kit59、听力题：The chemical formula for ethylene glycol is ______.60、听力题：Solubility is the ability of a substance to ______ in a solvent.61、填空题：The country known for its tea ceremonies is ________ (日本).62、填空题：A _____ (植物探索活动) can spark interest in botany.63、填空题：The fox is very _______ (狡猾) and clever.64、听力题：I need to _____ (buy/sell) groceries.65、What is 12 divided by 4?A. 1B. 2C. 3D. 4答案:C66、听力题：Granite is commonly used in construction because it is very ______.67、 (Protestant) Reformation changed the course of Christianity. 填空题：The ____68、What is the main ingredient in sushi?A. RiceB. BreadC. NoodlesD. Potatoes答案:A69、填空题：I enjoy making crafts for my toy ____. (玩具名称)The chemical symbol for indium is _____.71、听力题：An alloy is a mixture of two or more __________.72、Which sport is played with a bat and ball?A. SoccerB. BasketballC. BaseballD. Tennis73、填空题：Plants are vital for our _____ (生存).74、听力题：She likes to ________ pictures.75、填空题：Understanding the role of plants in the food chain is vital for ______. (了解植物在食物链中的作用对生态平衡至关重要。
郑州2024年04版小学三年级英语第3单元测验卷考试时间：100分钟（总分:110）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、填空题：I love going to the ______ (艺术展) to see incredible works. It inspires my creativity.2、What do you use to write on paper?A. PaintB. PencilC. WaterD. Glue答案:B3、填空题：My mom loves to ______.4、What do we call the study of cancer?A. OncologyB. PathologyC. HematologyD. Epidemiology5、听力题：Some _______ are used for decoration.6、填空题：I have a toy _____ that changes colors.7、听力题：Metallic elements tend to lose ______ when they react.8、填空题：The country with the kangaroo is __________. (澳大利亚)9、听力题：She is ___ her keys. (finding)10、What do you call the art of folding paper into shapes?A. DrawingB. OrigamiC. PaintingD. Sculpting答案: B11、ts can change colors with _____ (季节). 填空题：Some pla12、填空题：We visit the ______ (博物馆) to learn about history.13、What is the largest continent?A. AfricaB. AsiaC. EuropeD. North America答案: B14、填空题：The vulture eats ______ (腐肉).15、填空题：My _______ (兔子) is curious about everything.16、听力题：The _____ (sky/ground) is blue.17、听力题：We have a _____ (梦) of traveling.18、填空题：I have a big box of _____ (乐高).19、听力题：The chemical formula for sodium acetate is __________.20、填空题：Certain herbs are known for their ______ (美容效果).21、 Wall is a significant landmark in _____ (中国). 填空题：The Grea22、Which gas is essential for breathing?A. HeliumB. HydrogenC. OxygenD. Nitrogen答案：C23、ts are known for their _____ (香味). 填空题：Some pla24、填空题：A ________ (红树林) grows in coastal areas.25、听力题：My brother likes to watch ____ (cartoons) on weekends.26、听力题：The park is very ________.27、选择题：What is the favorite food of a panda?A. MeatB. BambooC. FruitsD. Vegetables28、填空题：The structure of a plant is designed to maximize ______ and growth. (植物的结构旨在最大化光合作用和生长。
α helixα螺旋A helical secondary structure in proteins. Pl. α helices. 蛋白质中一种螺旋形的二级结构。
复数：α helices 。
α-amanitinα鹅膏蕈碱 A toxin that inhibits the three eukaryotic RNApolymerases to different extents. Namederives from mushroom of genus Amanita inwhich toxin is found. 一种能不同程度地抑制三种真核生物RNA 聚合酶的毒素。
名称来自于产生此毒素的Amanita 属蘑菇。
β-galactosidaseβ-半乳糖苷酶 Enzyme that cleaves lactose into galactoseand glucose. Name origin: the bond cut by thisenzyme is called a β-galactosidic bond. 将乳糖分解为半乳糖和葡萄糖的酶。
名称来源：该酶切割的键称为β-半乳糖苷键。
β sheetβ折叠 A secondary structure in proteins, relativelyflat and formed hydrogen bonding between two parallel or anti-parallel stretches of polypeptide.蛋白质的一种二级结构，相对平坦，在两条平行的或反向平行的肽段之间形成氢键。
σ subunitσ亚基 Component of prokaryotic RNA polymeraseholoenzyme. Required for recognition ofpromoters. 原核生物RNA 聚合酶全酶的组成成分。
在启动子识别中需要。
小学上册英语上册试卷(有答案)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 like to share my ____ with my friends. (玩具名称)2.waste management) involves collecting and disposing of waste. The ____3.My favorite place to study is _______ (咖啡馆).4.The __________ (博物馆) displays fossils and artifacts.5.The _____ (狐狸) is a master of disguise.6.The chemical formula for lithium fluoride is _____.7.The __________ can change based on geological activity.8.The __________ can provide critical insights into the sustainability of natural systems.9.The _______ (The Great Society) aimed to reduce poverty and promote social welfare.10.The chemical process that breaks down food in our bodies is called ______.11.I eat cereal for ___ (breakfast).12.________ (生物多样性保护) is essential for ecosystems.13.The vulture cleans up ______ (尸体) in nature.14.I like to ______ (参与) in environmental projects.15.The chemical symbol for rubidium is ______.16.What do you call a young female whale?A. CalfB. PupC. KitD. Fawn答案: A17.What animal is known for its ability to fly?A. SnakeB. FishC. BirdD. Elephant答案: C. Bird18.The ______ (狼) howls at the moon.19.Which shape is round?A. SquareB. TriangleC. CircleD. Rectangle答案: C. Circle20. A chemical reaction that absorbs heat is called ______.21.The __________ can indicate areas of biodiversity and ecological significance.22. A __________ (反应) can be reversible or irreversible.23.I found a _______ (小蟋蟀) singing in the grass.24.The ________ (特殊植物) can be rare.25.What is 6 + 7?A. 12B. 13C. 14D. 15答案:B26.What fruit is typically associated with keeping the doctor away?A. BananaB. OrangeC. AppleD. Grape答案:C27.My brother is a _____ (学生) involved in student government.28.Which fruit is known for having seeds on the outside?A. AppleB. StrawberryC. GrapeD. Pear答案:B.Strawberry29.My favorite board game is _______ (大富翁).30.My dad is my strong _______ who lifts me up when I'm down.31. A saturated fat is typically found in ______ products.32.I believe that dreams are important. They motivate us to work towards our goals. I have a dream of __________, and I’m taking steps to make it happen.33.Christopher Columbus discovered America in _____ (1492).34.What do we call the part of the plant that absorbs water?A. LeafB. StemC. RootD. Flower答案: C. Root35.The chipmunk stores food in its _______.36.The _____ (road/path) is narrow.37.They are _____ (listening) to music.38.The _______ (蛇) sheds its skin.39.ocean floor) features ridges and valleys. The ____40.The weather is _____ (sunny/cloudy) today.41.The capital of Portugal is _____.42.The __________ of a substance tells how reactive it is.43.She enjoys ________ (cooking) for family.44. A bear can stand on its ________________ (后腿).45.The _______ (小小鸟) builds its nest high up in a tree.46.We are going to ________ a picnic.47.The bee buzzes around the ______ (花丛). It collects ______ (花蜜).48. A _____ (水生植物) can live in ponds and lakes.49.My cousin is a ______. She loves to lead group activities.50.I like to create stories about my ________ (玩具名). They have their own________ (名词) and adventures.51.My cousin has a beautiful ______ (小猫). Its fur is very ______ (柔软).52.I like to eat _____ for lunch. (sandwiches)53.I love to watch ________ (体育节目) on weekends.54.I saw a ________ at the zoo yesterday.55.The cake is ______ and delicious. (sweet)56.The _______ of sound can be influenced by the medium through which it travels.57. A chemical reaction that occurs when two substances combine is called a ______ reaction.58.We are making ________ (果汁) for breakfast.59.I want to learn to ________ (设计服装).60.Plants take in _____ (二氧化碳) during photosynthesis.61.In a photochemical reaction, light energy is used to drive a _____ change.62. A solution with a low concentration of solute is said to be _______.63.The _____ (电视) is on the shelf.64.The chemical formula for sodium bicarbonate is ______.65.I love to go ______ (滑冰) at the rink during winter.66.The discovery of America is credited to _______. (哥伦布)67.What do you call the sound a dog makes?A. MeowB. BarkC. RoarD. Hiss答案: B68.What do we use to write?A. EraserB. PaperC. PencilD. Book答案:C Pencil69. A _____ (小狐狸) is very cunning.70.My uncle is a ________ (医生).71.The __________ are beautiful in the spring garden. (花儿)72.The garden is full of ______ (昆虫) in summer.73.The _______ (Mayan calendar) predicted significant events in their culture.74.We take a _____ to school every day. (bus)75.The __________ was a major conflict in the history of the United States. (南北战争)76. A _______ (小蚕) spins silk in its cocoon.77.I want to be a _______ (teacher) when I grow up.78.The _____ (car/bike) is fast.79.I see a _____ (古董) at the fair.80.We have _____ (两) hands.81.The ancient Romans built roads to facilitate ________ (贸易).82.I want to _____ (learn) more about gardening.83.I like to read ________ (杂志) about animals.84.I always try to help my classmates when they need ________ (帮助) with their work.85.Gardeners often use ______ (肥料) to help plants grow.86.What is 9 - 4?A. 5B. 6C. 7D. 8答案:A 587.The rainbow has ______ colors. (seven)88.The dog barks at the _________. (邮递员)89.I want to _______ a great musician.90.My favorite animal is a _____ (lion/tiger).91.We will play ________ tomorrow.92. A _____ (社区花园) fosters cooperation and learning.93.What do you call the process of plants making their own food?A. PhotosynthesisB. RespirationC. GerminationD. Fertilization答案:A94.The _______ of a solution is how concentrated it is.95. A _______ is a chemical reaction that changes the physical state of a substance.96.What do you call the process of washing clothes?A. CleaningB. WashingC. DryingD. Folding答案: A97.We have a ________ (celebration) for birthdays.98.The ancient Romans spoke ________.99.The weather is _______ (非常凉爽).100.I love to watch the __________ change colors in the fall. (树叶)。
a r X i v :a s t r o -p h /9812058v 1 2 D e c 1998What Can the Accretion Induced Collapse of White Dwarfs Really Explain?Chris L.FryerLick Observatory,University of California at Santa Cruz,Santa Cruz,CA 95064Willy BenzPhysikalisches Institut,Universitaet Bern,Sidlerstrasse 5,CH-3012Bern SwitzerlandMarc Herant Washington University School of Medicine,Box 8107,660S.Euclid,St.Louis,MO 63110Stirling A.Colgate Theoretical Division,T-6,MS B288,Los Alamos National Laboratory,Los Alamos,NM 87545ABSTRACT The accretion induced collapse (AIC)of a white dwarf into a neutron star has been invoked to explain gamma-ray bursts,Type Ia supernovae,and a number of problematic neutron star populations and specific binary systems.The ejecta from this collapse has also been claimed as a source of r-process nucleosynthesis.So far,most AIC studies have focussed on determining the event rates from binary evolution models and less attention has been directed toward understanding the collapse itself.However,the collapse of a white dwarf into a neutron star is followed by the ejection of rare neutron-rich isotopes.The observed abundance of these chemical elements may set a more reliable limit on the rate at which AICs have taken place over the history of the galaxy.In this paper,we present a thorough study of the collapse of a massive white dwarf in 1-and 2-dimensions and determine the amount and composition of the ejected material.We discuss the importance of the input physics (equation of state,neutrino transport,rotation)in determining these quantities.These simulations affirm that AICs are too baryon rich to produce gamm-ray bursts and do not eject enough nickel to explain Type Ia supernovae (with the possible exception of a small subclass of extremely low-luminosity Type Ias).Although nucleosynthesis constraints limit the number of neutron stars formed via AICs to ∼<0.1%of thetotal galactic neutron star population,AICs remain a viable scenario for forming systems ofneutron stars which are difficult to explain with Type II core-collapse supernovae.Subject headings:stars:neutron –stars:white dwarfs –pulsars1.IntroductionWhite dwarfs accreting up to the Chandrasekhar limit follow one of two paths.Either the densities and temperatures become sufficiently high to ignite explosive nuclear burning,disrupting the white dwarf in what is now considered the favored Type Ia explosion mechanism (see Woosley &Weaver 1986for a summary),or electron capture reduces central temperatures and pressures and instead drives a collapse of the white dwarf.This collapse leads to the formation of a neutron star and is similar to the core collapse of massive stars,the mechanism behind Type II supernovae.Just as the core collapse of massive stars ejectsmaterial,one might also expect material to be ejected from the accretion induced collapse(AIC)of white dwarfs.Assuming some mass ejection occurs during collapse,AICs have been proposed as an alternate mechanism for Type Ia supernova(Colgate,Petschek,&Kriese1980)and as a source for gamma-ray bursts(Paczynski1986,Goodman1986;Goodman,Dar,&Nussinov1987;Paczynski1990;Dar et al. 1992).Neutron stars formed through AICs have been used to explain a variety of troublesome neutron star systems(see Canal,Isern,&Labay1990for a review).AICs have been proposed as an alternate channel to form neutron stars in globular clusters and in the galactic disk,the most common being millisecond pulsars (Bailyn&Grindlay1988;Bailyn&Grindlay1990;Kulkarni,Narayan,&Romani1990;Ray&Kluzniak 1990;Ruderman1991;Chen&Ruderman1993;Chen&Leonard1993).AICs have also been invokedin several X-ray binary formation scenarios(Canal et al.1990,van den Heuvel1984)and as a formation mechanism for specific cases of close neutron star binaries(Ergma1993).The role AICs play to produce these objects depends upon their rate.Super-soft X-ray sources are possible candidates of white dwarfs accreting up to the Chandrasekhar limit(Li&van den Heuvel1997). However,whether or not the white dwarf will form a Type Ia supernova in a thermonuclear explosion or collapse into a neutron star in an AIC depends sensitively upon the initial white dwarf mass,white dwarf composition,and the accretion rate onto the white dwarf(Nomoto1982,1984;Nomoto&Kondo1991). Although current observations verify that likely progenitors for AICs do exist,they do not place strong quantitative constraints on the event rate of these collapses.Similarly,uncertainties in binary evolution and white dwarf formation make it difficult to predict any definitive AIC event rate from population synthesis calculations(Yungelson&Livio1998).By simulating the collapse of white dwarfs,and their subsequent explosions,we can constrain the viability of AICs as gamma-ray bursts and Type Ia supernovae mechanisms.In addition,we can also use the nucleosynthetic yield from the ejecta of AICs to place limits on the event rate.The ejecta of AICs is neutron rich and leads to the production of many anomalous neutron-rich isotopes(e.g.62Ni,66Zn,68Zn, 87Rb,and88Sr)which pollute the interstellar medium.By comparing the observed abundance of these elements with the amount ejected per AIC event,we can place constraints on the allowable rate of AICs in the galaxy(Woosley&Baron1987,hereafter WB87).Previous work on AICs has identified three possible mass-ejection mechanisms:the prompt mechanism driven by the bounce of the collapsing white dwarf as the core reaches nuclear densities,the“delayed-neutrino”mechanism which occurs shortly after the bounce-shock stalls(20-200ms)and is driven by neutrino absorption,and the neutrino wind mechanism which is a relatively stable mass-loss occurring over the relatively long cooling timescales(1-2s)of the proto-neutron star.Baron et al.(1987),Mayle& Wilson(1988)and Woosley&Baron(1992)all found that the bounce shock stalls due to the energy losses from neutrino emission and dissociation and the prompt mechanism fails to drive an explosion.Mayle& Wilson’s simulations of the collapse of massive star(8−10M⊙)OMgNe cores,which have similar structures to most AIC progenitor models,led to explosions on short timescales(∼200ms)via the delayed-neutrino mechanism with0.042M⊙ejected.Simulations by Hillebrandt,Nomoto,&Wolff(1984)of the collapseof OMgNe white dwarfs ejected as much as∼0.1−0.2M⊙with explosions which developed even sooner (20-30ms).These explosions occur so quickly because the collapsing white dwarf does not have a huge infalling mantle that provides a ram pressure containing,at least temporarily,the explosion.WB92, however,found that no such explosion resulted from the collapse of a CO white dwarf.The only mass-loss (∼0.01M⊙)occurred at late times through the proto-neutron star’s neutrino-driven wind.In both the delayed-neutrino explosion mechanism and the neutrino-driven wind,the material ejected is likely to be neutron rich.Shortly after the inception of the neutrino-driven supernova mechanism,it was realized(Arnett&Truran1970)that the densities and temperatures near the neutrinosphere aresufficiently high to force this material to deleptonize via the emission of electron neutrinos.This material is ejected with extremely low electron fractions(0.35<Y e<0.45).In Type II supernovae simulations, the assumption is that either a longer delay in the supernova explosion(due to the ram-pressure of the infalling material)causes most of this material to remain part of the neutron star,or that the neutron-rich material falls back on the neutron star.The fallback is driven by the reverse shock that is created as the supernova shock wave traverses the envelope of the massive star.As we shall show in this paper,neither of these arguments can possibly hold for AICs and we can not easily explain away the low Y e ejecta from the delayed neutrino mechanism.Neutrino emission is not the only way to lower the electron fraction of matter.The electron fraction neutrino-wind driven ejecta is set by the relative absorption of electron neutrinos and anti-neutrinos(Qian et al.1993).Qian et al.(1993)have shown that since the neutrinosphere of the electron anti-neutrinos is deeper within the proto-neutron star crust,the anti-neutrinos are more energetic than the electron neutrinos.Since the neutrino cross-section is proportional to the square of the neutrino energy,given the sameflux of neutrino/anti-neutrinos,the wind driven material is likely to absorb more anti-neutrinos and it becomes neutron rich.In this paper,we give results from a series of AIC simulations using the CO white dwarf progenitor from the WB92model to determine the amount and composition of the ejecta.To measure the reliability of our results,we vary a number of parameters such as the details of the neutrino physics,the equation of state,and the initial rotation of the white dwarf.In particular,we are able to understand the difference between the WB92results and the other groups.We discuss the models in detail in§2.A summary of these results and their implications are given in§3.2.Models and ResultsTable1summarizes the entire set(60in total)of simulations we have performed.The different simulations were run to test the sensitivity of the results to changes in the neutrino physics(both source and transport columns3and4of Table1),the inclusion of relativistic effects,(runs6,11,and17),the choice of the equation of state(EOS)(column2),multi-dimensional effects(run2)and initial rotation rate of the white dwarf(run3).Except for changes in the equation of state for dense matter,most of these parameter variations lead to relatively small changes in the results(factors of2in the mass ejected).Changes in the equation of state explain the differences between the previous simulations(Hillebrandt,Nomoto&Wolff1984and Mayle& Wilson1988versus Woosley&Baron1992).We include calculations using both the equation of state of Swesty&Lattimer(1992)and that of Baron,Cooperstein,&Kahana(1985).The large differences can be appreciated by comparing the mass-point trajectories over the course of the simulation(Figs1,2).In this section we discuss the specific variations in our simulations and their effects on the results.To calculate the upper limit of the event rate of AICs,we must estimate the nucleosynthetic yieldof the neutron rich ejecta.Hartmann,Woosley,and El Eid(1985)estimate that there must be less than 10−5M⊙of Y e<0.4material ejected per supernova to avoid anomalous abundances of particular isotopes (e.g.62Ni,66Zn,68Zn,87Rb,and88Sr).Using the value of0.02M⊙of material with less than Y e<0.4ejected per AIC events(see Table1)and assuming a supernova rate of two per century for the Galaxy we find that the upper limit for rate of AICs must be(2/100y−1)(10−5M⊙)/(0.02M⊙)=10−5y−1.Note that we have assumed AICs to be the only source for material with such a low Y e.Should there be another source of these neutron rich isotopes,the allowed AIC rate will be correspondingly smaller.A similar constraint can be calculated by using the material ejected with0.45<Y e<0.40rather than with Y e<0.4. Following the method of WB92for0.02M⊙of ejected material,the upper limit for the rate of AICs becomes)(1/0.13)(2/100y−1)=4.5×10−5y−1.In table1,we list the upper limit of the (1M⊙/170,000)(1/0.02M−1⊙event rate for each simulation.In parentheses,we list the same upper limit if the electron fraction of the ejecta is30%higher than the predictions in our simulations.We note that much of the ejecta has a very low electron fraction(Y e<0.3)and large errors in the estimated electron fraction would be required to change the upper limit of the AIC event rate by more than an order of magnitude.2.1.Numerical MethodsThe internal structure of the initial white dwarf is taken from the progenitor used by WB92.This model is then mapped into our one-and/or two-dimensional codes and run for0.2s.The one-dimensional simulations were performed using the code developed and tested in previous work(Benz1991;Herantet al.1994;Fryer,Benz&Herant1996)with∼110zones where the highest resolution was constructed near the mass cut.This code does not include any form of convection modeling(mixing length or other). The two-dimensional simulations were performed using the Smooth Particle Hydrodynamics(SPH)code discussed in Herant et al.(1994)with typically∼8000particles.We model a180◦wedge assuming cylindrical symmetry about the angular momentum axis and also run these models for0.2s.As described in Herant et al.(1994),both codes use the same implementations of neutrino physics and transport,equations of state,etc.Thus,we can use the two dimensional simulations to compare the effects of convection and rotation.For some of the one-dimensional simulations,we include general relativistic effects using the formalism developed by van Riper(1997).For our late-time simulations,we have added a cell-splitting routine which allows us to follow the evolution of the explosion long after the collapse(we have run select simulations to0.5s).We only use the cell-splitting routine at late times,after the explosion has occurred.When the cell size becomes a sizable fraction(0.3)of its radius,we divide the cell in half and reduce the energy(and hence pressures)of the inner cell by5%to allow the forces at the boundaries to remain roughly equal.2.2.Effects of Neutrino PhysicsTo illustrate the importance of neutrinos on the composition of the ejecta,we compare the results of a simulation which includes the effects of neutrino physics(Fig.1-run1)and a simulation with no neutrino emission or absorption(Fig.3-run24).By comparing the mass-point trajectories between these two simulations,we note that without the cooling effects of neutrino emission,the bounce shock does not stall and an explosion develops(a“prompt”explosion).For the simulation which includes the effects of neutrino physics,neutrino emission from the shocked material(along with dissociation)stalls the shock.The neutrino emission from the shocked material and the new material falling onto the shocked region serves to deleptonize the ing the Swesty-Lattimer(1992)equation of state,wefind that neutrino heating is able to revive the explosion,ejecting∼0.1M⊙of material.The neutrino emission and later absorptionsets the electron fraction of the material.However,very quickly,the ejecta is thrown sufficiently far where adiabatic cooling causes recombination which lowers the free proton and free neutron fraction.The neutrino opacity of this material drops,and the electron fraction is effectively“frozen-out”.In all cases where the delayed-neutrino mechanism is the dominant mass ejector,we follow our simulations until this occurs.Including neutrino physics in the simulations involves two difficulties:the determination and numerical representation of the processes that emit or absorb neutrinos and the subsequent transport of these neutrinos through matter.Our neutrino processes are described in Herant et al.(1994)and include many of the possible emission and absorption rates for the standard three neutrino species(electron neutrino, electron antineutrino,and the entire set ofµandτneutrinos and antineutrinos).In many Type II supernova simulations,it is often assumed that the neutrinos are emitted from ultra-relativistic electrons(T≫12 F2(±η)β2±(2∆2−∆)F1(±η)β3+ 4∆2−12 F3(±η)β2± −3∆±12∆2−2∆38 F1(±η)β4± 2+3∆−4∆3k B T .F n are fermi integrals oforder n andηis the degeneracy parameter.Adopting the ultra-relativistic limit,WB92have simplified these equations,taking only thefirst term in each equation.To estimate the importance of this assumption,we have used both the limited and the full equations.In Table1,the runs using the full equations are identified by the letters TEH while those using the ultra-relativistic assumption are marked by WB.As can be seen from a careful comparison of these simulations,adopting the ultra-relativistic limit changes the amount of neutron rich ejecta(and the corresponding AIC event rate)by less than a factor of2.Despite the low cross-sections for neutrino interactions,the high densities involved in core-collapse scenarios place the neutrinos within the depths of the collapsing star in the diffusion regime.Thus, neutrino transport must include both the diffusion and free-streaming limits of the transport equations. The“standard”approximation to couple these two extremes calls upon the use of aflux-limiter(seefor example,Janka1991).We have incorporated several differentflux-limiters(Bowers&Wilson1982; Levermore&Pomraning(1981);Herant et al.1994)and the properties of their ejecta can be compared incolumn2of Table1.The Bowers-Wilson and Levermore-Pomraningflux limiters seem to bound the more accurate Monte-Carlo calculations by Janka(1991)and can be used to gauge the effect of theflux-limiter on the amount and composition of the ejecta.By comparing these twoflux limiters in otherwise identical simulations(e.g.run8and12),we see that the two approximations in the neutrino diffusion lead to only 10%differences in the mass ejected.The upper limit on the AIC rate with these twoflux limiters varies by factors of2.2.3.Impact of the Equation of StateUncertainties surrounding the equation of state for dense matter lead to the largest differences in the ejecta from AICs.We use two such equations of state:the one described in Herant et al.(1994)which couples the nuclear equation of state by Lattimer&Swesty(1991)to a low density equation of state (Blinnikov,Dunina-Barkovskaya&Nadyozhin1996)and a nuclear statistical equilibrium(NSE)scheme (Hix et al.1994)(hereafter called SL EOS);and the equation of state developed by Baron,Cooperstein,& Kahana(1985hereafter called BCK EOS)which covers both low and high density regimes.The BCK EOS is the equation of state used by WB92.For our progenitor,the effects of nuclear burning were minimal.We verified this by running a simulation(run7)in which we calculate the energy from nuclear burning with a14element nuclear network(Benz,Hills,&Thielemann1989)rather than assuming nuclear statistical equlibrium.As with the neutrino physics,nuclear burning varies the critical AIC rate by factors of2only.The main results of our simulations using one of the two equations of state are listed in Table1(see pare runs8and20).By using the BCK equation of state,we recover the resultsof WB92.The equation of state dramatically affects the amount and compositon of the ejecta in the simulations.Swesty,Lattimer,&Myra(1994),in a previous comparison between the two equations of state,report similarfindings(the softer BCK equation of state leads to denser,and hotter,cores after bounce).These differences have been discussed by Swesty,Lattimer,&Myra who argue that,given the standard equation of state parameters for the BCK EOS,the SL EOS is physically more accurate.We have run the SL EOS using two values for the incompressibility of bulk nuclear matter(K s=180,375MeV) and have run a grid of the faster BCK EOS varying the BCK gamma(1.5<γ<3.5),the bulk surface<375Mev), coefficient(25<W s<38),the symmetric bulk compressibility parameter(180MeV<K symand an asymmetry parameter(1.5<xkz<3.5).Table2gives the results for this grid of simulations in which we use the Levermore-Pomraningflux limiter.Despite the wide range in the physical parameters,the results from the BCK EOS never agree with those from the SL EOS.Clearly,the differences between the two equations of state goes beyond compressibility or asymmetry parameters.The ratio of the SL EOS pressure to the BCK EOS pressure along an S=2k B/nucleon adiabatis plotted in Figure4.Note that for densities less than1014g cm−3,the pressure of the BCK EOS is 10-20%greater than that of the SL EOS.Relatively small differences such as these mark the difference between a success or failure of the delayed-neutrino explosion mechanism,which then leads to greater than order-of-magnitude differences in the ejecta!We have also studied the effects of general relativity on the simulations using the SL equation of state. From Table1,we can compare the results of simulations with or without general relativity(runs1,6).The primary effect of general relativity is to cause the material to fall deeper into the potential well resulting in increased neutrino emission/absorption.Just as the equation of state strongly affects the amount and composition of the ejecta,the addition of general relativity leads to variations of over an order of magnitudein the upper limit of AIC event rate.2.4.Effects of Convection and RotationTwo-dimensional simulations of AICs can be used to test both the effects of convection and rotation. Since large entropy gradients do not develop in the one-dimensional simulations,we do not expect convection to cause large differences in the ejecta from AICs.Wefirst use our two-dimensional simulations to verify that convection does not play a major role in the collapse and ejecta of AICs.Although convection is indeed present in the simulations(Fig.5),the explosion occurs so rapidly(<100ms)that it has no time to alter the explosion results.The small differences between the one-and two-dimensional models(compare run1 and run2in Table1)are probably entirely due to the resolution differences between the two simulations.The progenitors to AICs accrete not only mass,but angular momentum,as the white dwarf approaches the Chandrasekhar limit.Typical rotation periods for cataclysmic variables range from200−1200s(Liebert 1980)although periods of∼30s exist(King&Lasota1991).A lower limit on the rotation period is set by the break-up spin period(∼0.5s for solar-mass white dwarfs).In our models,we assume solid-body rotation and conserve each individual particle’s angular momentum for the duration of the simulation.We take an extreme case of a white dwarf rotating with a20s period prior to collapse(Fig.5).For this short rotation period,the ratio of surface rotational velocity over the keplerian velocity of the outer material exceeds0.1as the white dwarf collapses.This will certainly alter theflow of the outer material.However,since white dwarfs are probably solid-body rotators,the bulk of the inner material is unaffected by rotation.For example,the ratio of rotational over keplerian velocity drops to0.01at the radius which encloses1.2M⊙(still87%of the white dwarf mass).Thus,while the collapse of the outer envelope of a white dwarf is affected by rotation,the core collapse itself is not(compare T=50,70ms in Fig.5).Since most of the material exterior to1.2M⊙is ejected,the net effect of rotation is negligible. Comparing runs2and3in Table1,we see that the amount and composition of the ejecta is not altered significantly by the effects of rotation.In addition,there is no preferential ejection of material along either axis.We do not follow the proto-neutron star as it cools and contracts and the spin period at the end of our simulation(where the hot proto-neutron star’s radius is30−50km)is still∼1s.Although much of the white dwarf’s angular momentum is ejected with the outer0.2M⊙,as the proto-neutron star continues to contract down to10km,unless further material is ejected,its spin period will decrease to10ms.This system is likely to continue to accrete from the same companion that caused it to collapse in thefirst place and this may speed up the neutron star’s spin even further,producing millisecond spin periods.2.5.Neutrino WindThe results in Table1do not include any mass loss from neutrino-driven winds.The amount of this ejecta is small when compared to that of our simulations using the SL equation of state(WB92predict ∼0.005M⊙s−1for thefirst two seconds).However,for the BCK EOS simulations,neutrino-driven winds dominate the mass ing a cell-adding routine,we follow the fate of an AIC model beyond the delayed neutrino-induced explosion to obtain the wind driven mass loss(run1).Because we are also modeling the core,we are limited to very small timesteps and are able to follow this phase for only0.5s after bounce.Wefind that during this period of time,an additional∼0.002M⊙peels offthe neutron star.Thus,in this limited way,we confirm the results obtained by WB92that further neutrino driven mass loss is to be expected.Independent of the equation of state or other input physics,it is likely that a neutrino-wind phase exists and that∼0.01M⊙is ejected during this phase.However,the electron fraction of such a wind is very sensitive to theflux and energy of the electron neutrino/anti-neutrinos.We do not list the upper limits for the AIC event rate placed by“wind”ejecta,but prefer to rely upon the ejecta from the delayed-neutrino mechanism which we are better able to test with our simulations.3.So What Are AIC Good For?Table1summarizes the results of our suite of accretion-induced collapse simulations varying the input physics within the range of current uncertainties.Wefind that the differences in past work were primarily due to differences in the equations of state.Even with these uncertainties,the study of explosions resulting from the collapse of white dwarfs,can help determine the viability of AICs as models for Type Ia supernovae and gamma-ray bursts.In addition,by calculating the nucleosynthetic yields of the neutron rich ejecta from AICs,we can limit the event rate(following the procedure described in§2).The upper limit of the AIC rate is given in Table1and,if we use the possibly more reliable Lattimer&Swesty(1991)equation of state,is roughly10−7−10−5yr−1.To change these timescales appreciably,there must be large changes in the electron fraction of the ejecta which,although unlikely,can not be excluded at this time.3.1.Neutron Star PopulationsOur upper limit on the event rate somewhat constrains the role AICs play in producing neutron stars. The Type II supernova rate(∼10−2yr−1:Cappellaro et al.1998)is3-4orders of magnitude higher than our upper limit of the AIC rate,so neutron stars formed from AICs will not make up a large fraction of the total population of galactic neutron stars.However,neutron stars formed via accretion induced collapse may not receive the same large kicks observed in neutron stars formed in Type II supernovae,and hence may be prime candidates for globular cluster neutron star populations.Bailyn&Grindlay(1990)estimate that the AIC rate must be∼10−5−10−5yr−1to explain the globular cluster neutron star population, barely consistent with our upper limit on the AIC event rate.In addition,the event rate does not preclude AICs explaining any peculiar neutron star systems.3.2.NucleosynthesisBecause of their neutron rich ejecta,AICs are prime sites for r-process nucleosynthesis(Wheeler,Cowan, &Hillebrandt1998).However,although we can constrain the AIC event rate from the nucleosynthetic yield with our current models,predicting yields of specific isotopes remains beyond our grasp.To predict precisely the nucleosynthetic yields from AICs,the physical processes that cause the largest variationsin the results(in particular,the equation of state and the effects of general relativity,and possibly,the characteristics of the progenitor)must be precisely known.3.3.Gamma-Ray BurstsTo achieve the high Lorentz factors required to drive a gamma-ray burst,a viable mechanism must have both large explosion energies(∼1051ergs for isotropic explosions)and eject very little mass(∼<10−5M⊙). For our most-likely models,AICs eject4orders of magnitude too much mass with an order of magnitude too little energy.In agreement with Woosley&Baron(1992),this clearly rules out those gamma-ray burst models relying upon neutrino/anti-neutrino annihilation(Paczynski1986;Goodman1986;Goodman,Dar, &Nussinov1987;Paczynski1990;Dar et al.1992).It also rules out all magnetically beamed models of AICs(Shaviv&Dar1995;Yi&Blackman1997,1998;Dai&Lu1998).In beamed models,the actual ejecta that effects the gamma-ray burst is limited to the ejecta swept up in the beam.In order for these beamed models to avoid ejecting too much mass,the beaming fraction must be smaller than0.01%of the sky(hence sweeping up only0.01%of the mass).However,with such a small beaming fraction,the AIC event rate must be greater than10−3yr−1for this mechanism to make up the majority of the observed gamma-ray bursts.This is an order of magnitude above our upper limit for the AIC event rate and it appears that AICs are simply unable to meet the observed requirements of gamma-ray bursts.3.4.Type Ia SupernovaeOn the other hand,AICs do not eject enough nickel to match most Type Ia supernova light curves. The amount of nickel ejecta is tantalizingly close to the properties of some peculiar Type Ia supernovae with very low nickel masses(e.g.SN1991bg:Filippenko et al.1992).AICs may be able to explain some peculiar Ias,a possibility that could be confirmed by either neutrino detections or the discovery of a neutron star formed in these Ias.This paper has benefitted from the contributions of many people.We are grateful to R.Hix for making available his nuclear statistical equilibrium code,to D.Swesty for his nuclear equation of state,to D. Nadyozhin for his equation of state,to C.Wingate for his graphics software,and to S.Woosley for the progenitor star and many useful discussions.We would especially like to thank Edward Baron for providing access to his equation of state,insightful advice,and encouragement.The work of C.F.and W.B.was partially supported by NSF grant AST9206738and from the Swiss National Science Foundation.The work of M.H.was supported by a director funded post-doctoral fellowship at Los Alamos National Laboratory.REFERENCESArnett,W.D.,&Truran,J.W.,1970,ApJ,160,959Bailyn,C.D.&Grindlay,J.E.1988,Nature,336,48Bailyn,C.D.&Grindlay,J.E.1990,ApJ,353,159Baron,E.,Cooperstein,J.,&Kahana,S.,1985,Phys.Rev.Lett.,55,126Baron,E.,Cooperstein,J.,Kahana,S.,&Nomoto1987,ApJ,320,304Benz,W.,Hills,J.G,&Thielemann,F.-K.,1989,ApJ,342,986。
