Chaos in Black holes Surrounded by Electromagnetic Fields
介绍黑洞的引言英文作文
介绍黑洞的引言英文作文Introduction to Black Holes。
Black holes, one of the most fascinating objects in the universe, have been a subject of scientific research for decades. These mysterious objects are formed when a massive star collapses under its own gravity, creating a region in space where the gravitational pull is so strong that nothing, not even light, can escape. The concept of black holes was first proposed by the physicist John Michell in 1783 and was later refined by Albert Einstein's theory of general relativity in 1915.Black holes are invisible to the naked eye, as they do not emit any light or radiation. However, their presence can be detected by observing the effects of their immense gravitational pull on nearby stars and gas. The area surrounding a black hole is known as the event horizon, which marks the point of no return. Anything that crosses the event horizon is pulled into the black hole and is lostOne of the most intriguing aspects of black holes is their ability to distort time and space. The intensegravity near a black hole causes time to slow down, and space to be warped and stretched. This phenomenon, known as gravitational time dilation, has been confirmed by observations of stars orbiting black holes.Black holes come in different sizes, ranging from a few times the mass of the sun to billions of times the mass of the sun. Supermassive black holes, found at the centers of galaxies, are thought to play a crucial role in the evolution of galaxies, as they can influence the motion of stars and gas.Despite their mysterious nature, black holes have become a topic of intense research in astrophysics and cosmology. Scientists are using a variety of techniques, such as gravitational wave detection and observations of the effects of black holes on nearby objects, to study these enigmatic objects and unlock the secrets of theIn conclusion, black holes are one of the most intriguing and mysterious objects in the universe. They are formed by the collapse of massive stars and have a gravitational pull so strong that nothing can escape. Their ability to distort time and space and influence the motion of nearby objects makes them a subject of intense research in astrophysics and cosmology.。
Extremality conditions for isolated and dynamical horizons
∗ E-mail: † E-mail:
ibooth@math.mun.ca Stephen.Fairhurst@
these are the ADM mass and angular momentum as measured at spatial infinity. By contrast Petroff and Ansorg [4, 5, 6] have recently generated numerical examples of black holes surrounded by rotating rings of matter for which the Komar mass and angular momentum violate 2 the bound JKomar ≤ MKomar . Clearly in considering these issues one needs to be careful about how the physical quantities are defined. In particular, in formulating a bound one would like to distinguish between the mass and angular momentum directly associated with the black hole versus any matter or gravitational waves surrounding it. This is, of course, easier said than done. Mass and energy are notoriously ambiguous quantities in general relativity. They are well-defined for entire asymptotically flat spacetimes but in general it is not possible to assign mass and energy to more localized regions of spacetime (see, for example, the discussion in [7]). Similar problems arise for angular momentum and away from axi-symmetry it is not at all clear that angular momentum can be described by a single number. Distinguishing between local and global properties of black holes is one of the main motivations for the recent interest in quasilocal characterizations of horizons, including trapping [8, 9, 10, 11], isolated [12, 13, 14, 15, 16], and dynamical [17, 18] horizons. In this paper we apply the machinery developed in the study of quasilocal horizons to investigate local characterizations of extremality. We will argue that the ambiguities in defining mass and angular momentum mean that, in general, the usual Kerr extremality bound is not well formulated for quasilocal horizons. Thus we will examine alternative characterizations of extremality and show that they do apply. For isolated horizons these arise from 1) the non-negativity of the surface gravity and 2) the idea that there should be trapped surfaces just inside the horizon. For dynamical horizons only the second these characterizations is applicable since the surface gravity is only meaningful for slowly evolving dynamical horizons (in the sense of [19, 20, 21]). Both the surface gravity and trapped surface characterizations of extremality give rise to an alternative, local
太阳黑洞英文短文
太阳黑洞英文短文A black hole is an astronomical phenomenon that occurs when a massive star collapses under its own gravity, creating a region in space where gravity is so strong that nothing, not even light, can escape its gravitational pull. The concept of a black hole was first theorized by Albert Einstein's theory of general relativity.Solar black holes, also known as stellar black holes, are formed from the remnants of massive stars that have exhausted their nuclear fuel and undergone a supernova explosion. These black holes have a mass ranging from a few times that of our Sun to several tens of times greater. When a solar black hole forms, it creates a gravitational well that is incredibly deep and powerful.Due to their intense gravitational pull, objects that venture too close to a solar black hole will be stretched and torn apart by a process called spaghettification. The powerful tidal forces near the event horizon of a black hole are responsible for this phenomenon. Beyond the event horizon, which is the point of no return, nothing can escape the gravitational grip of the black hole.Despite their reputation for devouring everything intheir path, black holes themselves do not emit any light or radiation. They can only be detected indirectly through their effects on surrounding matter or by observing the high-energy particles and radiation emitted by the matter falling into them, known as an accretion disk.The study of black holes has greatly contributed to our understanding of the universe, including the nature of gravity and the behavior of matter under extreme conditions. Scientists continue to explore and unravel the mysteries surrounding black holes, seeking answers to questions about their formation, growth, and eventual fate.In conclusion, solar black holes are fascinating cosmic objects formed from the remnants of massive stars. They possess immense gravitational power and have significantly contributed to our knowledge of the universe.。
Chaos and Rotating Black Holes with Halos
ห้องสมุดไป่ตู้
elements of the previous two is the “vesture method”, all these methods are closely related [10]. The general metric that represents the nonlinear superposition of a Kerr solution with a Weyl solution, in particular, with a multipolar expansion can be found by using the “inverse scattering method” [11]. We find
gtϕ = 2pqe−2Dp(u+v+1)[e−4Dpu(e−4Dpv(p + 1)(u − v)(u + 1) +e−4Dp(p − 1)(u + v)(u − 1))(v + 1))
−e−4Dpv(p + 1)(u + v)(u + 1)(v − 1) − e−4Dp(p − 1)(u − v)(u − 1)(v − 1)]/F, gϕϕ = [(gtϕ)2 − (mr)2]/gtt, f = m2e−4Dp((v+1)u−v+1)[e−4Dpuv(p − 1)2(u − 1)2 + e−4Dp((v+1)u+v−1)(v + 1)2q2]
In this Letter we study the effects of rotation in the motion of a particle orbitating around a slowly rotating black hole surrounded by a dipolar halo. The non rotating case is chaotic, so we shall study mainly the change in the chaotic behavior due to the rotation of the center of attraction. A typical situation is represented by a galaxy with a rapid rotating center surrounded by a distant massive halo, ring or other shell-like distributions of matter. We study the motion of particles moving between the center and the halo whose first contribution is dipolar. This contribution is always present whenever the halo does not possess reflection symmetry with respect to the black hole equatorial plane.
英语关于黑洞的作文
英语关于黑洞的作文The Mysterious and Fascinating Black Holes.In the vast and enigmatic universe, black holes standas one of the most intriguing and perplexing phenomena. These regions of space, characterized by their intense gravity and complete absence of light, have captivated the imagination of scientists and laypeople alike for centuries. Despite their otherworldly nature, black holes play acrucial role in understanding the evolution and structureof our universe.The concept of black holes emerged in the late 18th century, with the pioneering work of scientists like John Michell and Pierre-Simon Laplace. They theorized the existence of objects so massive that not even light could escape their intense gravitational pull. However, it wasnot until the 20th century that astronomers began to gather evidence that supported the existence of these mysterious objects.One of the most significant milestones in the study of black holes was the work of Albert Einstein. His theory of general relativity provided a mathematical framework to describe the behavior of gravity and its interaction with matter. This theory laid the foundation for understanding the properties of black holes, including their formation, evolution, and interaction with their environment.Black holes are formed when a massive star collapses under its own weight at the end of its life cycle. This collapse compresses the star's matter into a tiny, ultra-dense region known as a singularity. The gravity around this singularity is so intense that nothing, including light, can escape its pull. The boundary of this region, known as the event horizon, marks the point where the escape velocity exceeds the speed of light.There are two main types of black holes: stellar-mass black holes and supermassive black holes. Stellar-mass black holes are formed when a star of about 10 to 30 times the mass of the Sun collapses. These black holes have adiameter of only a few kilometers but possess a mass comparable to that of a small star. On the other hand, supermassive black holes have masses ranging from millionsto billions of times the mass of the Sun. They are believed to reside at the centers of most galaxies, including ourown Milky Way.The study of black holes has revealed much about the structure and dynamics of the universe. For instance, black holes play a crucial role in the evolution of galaxies. By accreting matter and emitting radiation, they can significantly impact the star formation and gas dynamics of their host galaxies. Additionally, the merging of black holes, a common occurrence in the universe, can emit gravitational waves, ripples in the fabric of spacetimethat can be detected by advanced telescopes like the Laser Interferometer Gravitational-Wave Observatory (LIGO).Despite their otherworldly nature, black holes are not entirely devoid of life. In fact, there are theories that suggest the existence of accretion disks around black holes. These disks are formed when matter from a nearby star orgas cloud is attracted to the black hole and begins toorbit it. As the matter spirals inward, it heats up and emits radiation, creating a bright and energetic environment.The study of black holes also holds the key to understanding some of the most fundamental questions about our universe. For instance, black holes provide a unique laboratory to test the limits of Einstein's theory of general relativity. By studying the behavior of matter and light near the event horizon, scientists can gain insights into the nature of gravity and its interaction with quantum mechanics.In conclusion, black holes are one of the most mysterious and fascinating phenomena in the universe. They challenge our understanding of gravity, matter, and the structure of the cosmos. As we continue to explore and study these enigmatic objects, we may unlock the secrets of the universe and gain a deeper understanding of our placein the cosmos.。
《哈利波特与阿兹卡班囚徒》第4章《破釜酒吧》中英文对照学习版
中英文对照学习版Harry Potter and the Prisoner of Azkaban《哈利波特与阿兹卡班囚徒》Chapter FourThe Leaky Cauldron第4章破釜酒吧It took Harry several days to get used to his strange new freed om. Never before had he been abl e to get up whenever he want or eat whatever he fancied. He coul d even go wherever he liked, as l ong as it was in Diagon All ey, and as this l ong cobbl ed street was packed with the most fascinating wizarding shops in the worl d, Harry felt no d esire to break his word to Fudge and stray back into the Muggl e worl d.过了几天，哈利才习惯了这种从未体验过的奇特的自由。
以前，他从来不能想什么时候起床就什么时候起床，喜欢吃什么就吃什么。
现在，他甚至可以想去哪儿就去哪儿，只要是在对角巷内，而这条长长的卵石街道上布满了世界上最诱人的巫师商店。
哈利一点儿也不想违反他对福吉的承诺，重新回到麻瓜世界里去。
Harry ate breakfast each morning in the Leaky Caul dron, where he liked watching the other guests: funny little witches from the country, up for a day's shopping; venerabl e-l ooking wizards arguing over the latest article in Transfiguration Today; wild-l ooking warlocks, raucous dwarfs and, once, what l ooked suspiciously like a hag, who ord ered a plate of raw liver from behind a thick wooll en balaclava.哈利每天早晨在破釜酒吧吃早饭，他喜欢打量其他的顾客：从乡下来的怪模怪样的小个子女巫，大清早出来买东西；看上去弱不禁风的男巫，为《今日变形术》上的最新文章展开辩论；不修边幅的巫师；吵吵闹闹的小矮人……一次，还有一个活像老巫婆的人，裹在一件厚厚的带巴拉克拉瓦盔式帽的羊毛大衣里，要了一盘生肝。
关于黑洞的英文想象作文
关于黑洞的英文想象作文英文：As a space enthusiast, I have always been fascinated by the concept of black holes. The idea of a region in space where the gravitational pull is so strong that nothing, not even light, can escape is both terrifying and awe-inspiring. 。
Black holes are formed when a massive star collapses under its own gravity at the end of its life cycle. This creates a singularity, a point of infinite density, surrounded by an event horizon, the boundary beyond which nothing can escape. 。
One of the most interesting things about black holes is their impact on time and space. According to Einstein's theory of general relativity, time near a black hole passes more slowly than it does farther away. This means that if you were to approach a black hole, time for you wouldappear to pass more slowly than it does for someone watching from a safe distance. This phenomenon, known as time dilation, is mind-boggling and demonstrates just how bizarre and mysterious black holes truly are.Another fascinating aspect of black holes is their ability to warp space. The intense gravitational pull of a black hole can bend and distort the fabric of space-time, creating mind-bending visual effects. For example, if you were to observe a spacecraft approaching a black hole from a safe distance, you would see the spacecraft's image become stretched and distorted as it nears the event horizon. This gravitational lensing effect is a direct result of the warping of space by the black hole's immense gravity.In addition to their mind-bending effects on time and space, black holes also have a voracious appetite. When an object, such as a star or a planet, comes too close to a black hole, it is torn apart by the immense gravitational forces at play. This process, known as spaghettification, is a gruesome yet fascinating consequence of a black hole'sextreme gravity.Overall, black holes are some of the most enigmatic and captivating objects in the universe. Their ability to warp time and space, their voracious appetite, and their mysterious nature make them a topic of endless fascination for scientists and space enthusiasts alike.中文：作为一个对太空的热爱者，我一直对黑洞的概念充满着兴趣。
理解黑洞需要一定的想象力和科学知识 英语
理解黑洞需要一定的想象力和科学知识英语Understanding Black Holes Requires a Certain Degree of Imagination and Scientific KnowledgeThe vastness of the universe is a constant source of fascination and wonder for human beings. As we gaze up at the night sky, our eyes are drawn to the twinkling stars, the enigmatic planets, and the mysterious celestial bodies that lie beyond our immediate reach. Among these cosmic enigmas, perhaps none have captured the public's imagination more than the phenomenon known as the black hole.Black holes are regions of space-time where the gravitational pull is so immense that nothing, not even light, can escape their grasp. These cosmic behemoths are the result of the collapse of massive stars at the end of their life cycle. When a star runs out of fuel, its core can no longer support the outward pressure that counteracts the inward pull of gravity, causing it to implode and form a singularity – a point in space-time where the laws of physics as we know them break down.Understanding the true nature of black holes requires a certaindegree of imagination and scientific knowledge. On the surface, the concept of a region of space-time where nothing can escape may seem straightforward, but the deeper one delves into the intricacies of black hole physics, the more complex and mind-bending the subject becomes.One of the key aspects of black holes that challenges our intuitive understanding is the concept of the event horizon. The event horizon is the point of no return – the boundary beyond which nothing, not even light, can escape the gravitational pull of the black hole. Visualizing this invisible barrier and comprehending its significance is a task that requires a significant amount of abstract reasoning.Imagine a person standing on the edge of a cliff, gazing out at the vast expanse of the ocean. As they look down, they can see the waves crashing against the rocks below, but they know that if they were to step over the edge, they would be unable to return. The event horizon of a black hole is analogous to this – it is the point at which the gravitational forces become so overwhelming that even the fastest-moving particles in the universe, photons of light, cannot escape.But the event horizon is just the tip of the iceberg when it comes to the complexities of black hole physics. As one delves deeper into the subject, the challenges to our understanding only grow moreprofound.Consider, for example, the concept of time dilation. According to Einstein's theory of general relativity, the passage of time is affected by the presence of strong gravitational fields. As an object approaches the event horizon of a black hole, the rate at which time passes for that object becomes increasingly slowed down relative to an observer outside the black hole. This means that from the perspective of an external observer, the object appears to be frozen in time, gradually becoming fainter and fainter as it crosses the event horizon.Visualizing this phenomenon requires a significant amount of imagination and a deep understanding of the principles of relativity. It challenges our everyday experience of time and forces us to consider the universe from a radically different perspective – one where the familiar laws of physics no longer apply in the same way.Another aspect of black holes that pushes the limits of our imagination is the nature of the singularity itself. At the center of a black hole, where all the matter and energy of the collapsed star is concentrated, the laws of physics as we know them break down completely. This point of infinite density and infinite curvature of space-time is known as the singularity, and it represents the ultimate limit of our current scientific understanding.Trying to comprehend the singularity, a region where the very fabric of space-time is torn apart, is a task that requires a leap of imagination that few can truly make. It forces us to confront the limitations of our own understanding and to grapple with the fundamental mysteries of the universe.Despite these challenges, the study of black holes has been a cornerstone of modern astrophysics and has led to numerous groundbreaking discoveries. Through the use of sophisticated telescopes and advanced mathematical models, scientists have been able to observe the behavior of black holes in unprecedented detail, shedding light on the most extreme and enigmatic phenomena in the cosmos.From the detection of gravitational waves, the ripples in the fabric of space-time caused by the collision of black holes, to the stunning images of the supermassive black hole at the center of the Milky Way, the study of black holes has pushed the boundaries of our scientific knowledge and our understanding of the universe.But perhaps the greatest contribution of the study of black holes is the way it has challenged our fundamental assumptions about the nature of reality. By confronting us with the limits of our own understanding, black holes have forced us to reckon with thepossibility that there are aspects of the universe that may forever remain beyond our grasp.In this sense, the study of black holes is not just a scientific endeavor, but a philosophical one as well. It reminds us that the universe is a vast and mysterious place, and that our knowledge, no matter how extensive, is always a work in progress. It challenges us to remain humble in the face of the unknown and to continue to explore the limits of our understanding with curiosity, wonder, and a willingness to adapt our perspectives as new evidence emerges.Ultimately, the study of black holes is a testament to the power of the human mind to grapple with the most complex and enigmatic phenomena in the universe. It requires a unique blend of imagination, scientific knowledge, and a willingness to embrace the unknown – qualities that have defined the pursuit of scientific discovery since the dawn of human civilization.。
国王的恩赐黑暗面 英文原版
国王的恩赐黑暗面英文原版Title: The Dark Side of the King"s Bounty: The Original English EditionIntroduction:"The King"s Bounty" is a renowned video game series that combines strategy, role-playing, and adventure elements.One of its most popular installments is "The Dark Side," which offers players a fascinating journey through a mystical world filled with challenges and moral dilemmas.This document aims to explore the original English edition of "The King"s Bounty: The Dark Side," providing a detailed and immersive experience for readers.I.Background Story"The King"s Bounty: The Dark Side" is set in a world where the balance between light and darkness is at stake.Players assume the role of a hero who must navigate through the treacherous lands of Endoria, facing the consequences of their actions and the choices they make.The game"s story revolves around the struggle between two factions: the forces of light, led by the king, and the dark forces that threaten to engulf the world in chaos.II.Game MechanicsThe original English edition of "The King"s Bounty: The Dark Side"offers a unique blend of turn-based strategy and role-playing elements.Players can explore a vast, open world, complete quests, and engage in thrilling battles.Here are some key features of the game:1.Hero Development: Players can choose from various classes, such as Warrior, Paladin, and Mage, and customize their hero"s skills and abilities as they progress through the game.2.Army Management: Building and managing an army is crucial for success in "The Dark Side." Players can recruit various units, including infantry, cavalry, and flying creatures, and upgrade their abilities and equipment.3.Tactical Battles: The game"s combat system requires strategic thinking and careful planning.Players must consider factors such as terrain, unit placement, and magic spells to emerge victorious from battles.4.Exploration and Quests: The world of Endoria is filled with secrets and dangers.Players can explore diverse locations, interact with non-playable characters (NPCs), and complete numerous side quests and main story missions.III.The Dark SideWhat sets "The King"s Bounty: The Dark Side" apart from other installments in the series is its focus on moral ambiguity and the consequences of the player"s choices.Here are some key aspects of thegame"s dark side:1.Alignments: Players can choose to align themselves with either the forces of light or darkness.This decision affects the hero"s abilities, available units, and the course of the story.2.Corruption: As players make darker choices, their hero becomes more corrupt, unlocking new skills and abilities.However, excessive corruption may lead to negative consequences and affect the hero"s relationships with NPCs.3.Dark Creatures: The game introduces a variety of dark creatures, such as vampires, werewolves, and demons, which can be recruited into the player"s army.These units have unique abilities and playstyles, offering new strategic possibilities.IV.Conclusion"The King"s Bounty: The Dark Side" is a captivating game that allows players to explore the complexities of good and evil in a fantasy world.The original English edition provides a rich and immersive experience, challenging players to make difficult decisions and face the consequences of their actions.With its engaging gameplay, compelling story, and stunning visuals, "The Dark Side" is a must-play for fans of strategy and role-playing games.ote: This document aims to provide an informative and immersive experience for readers interested in the original English edition of "TheKing"s Bounty: The Dark Side." It does not contain any copyrighted material or promotional content.。
Massive Charged Scalar Quasinormal Modes of Reissner-Nordstrom Black Hole Surrounded by Qui
with M and Q mass and charge of the black hole. ǫ is the quintessential state c 3ǫ parameter and c is the normalization factor which depends on ρq = − ,the density 2 r 3(1−ǫ) of quintessence. The Klein-Gordon equation describing the evolution of massive charged scalar perturbation field outside a charged black hole is given by[19] Φ;µν g µν − ieAµ g µν (2Φ;ν − ieAν Φ) − ieAµ;ν g µν Φ = m2 Φ, (2)
black hole作文
black hole作文英文回答：Black holes have always fascinated me. The concept of a region in space where gravity is so strong that nothing, not even light, can escape is mind-boggling. It's like a cosmic vacuum cleaner that sucks in everything around it. But what exactly is a black hole?A black hole is formed when a massive star collapses under its own gravity. The core of the star becomes so dense that it creates a gravitational pull that is incredibly strong. This gravitational pull is what makes a black hole so fascinating and terrifying at the same time.Imagine you are standing on the edge of a black hole. If you were to fall into it, the gravitational pull would be so strong that you would be stretched like a piece of spaghetti. This is known as spaghettification, a term coined by scientists to describe the extreme tidal forcesexperienced near a black hole.But what happens once you cross the event horizon, the point of no return? Well, according to the theory of general relativity, you would be sucked into the blackhole's singularity, a point of infinite density. Time and space become warped near the singularity, and our understanding of physics breaks down. It's like entering a whole new realm of the unknown.Black holes also have an event called the "black hole information paradox." According to quantum mechanics, information cannot be destroyed. However, if something were to fall into a black hole, it would seemingly disappear forever. This contradiction has puzzled scientists for years and is still a topic of active research.中文回答：黑洞一直以来都让我着迷。
黑洞 作文 英文
黑洞作文英文英文：Black holes have always been a fascinating topic for me. The idea of a region in space where the gravitational pullis so strong that nothing, not even light, can escape, is mind-boggling. It's like a cosmic vacuum cleaner that sucks in everything that comes too close. 。
One of the most interesting things about black holes is their formation. They are formed when a massive star runs out of fuel and collapses under its own gravity. This collapse causes the star to become extremely dense, with a gravitational pull so strong that it creates a black hole.It's like the ultimate cosmic implosion.The concept of black holes has been a source of inspiration for many science fiction stories and movies. From "Interstellar" to "Star Trek," black holes have been depicted as mysterious and dangerous phenomena. In reality,we are still learning a lot about black holes and their behavior. They challenge our understanding of the laws of physics and the nature of the universe.One of the most intriguing aspects of black holes is the event horizon, which is the point of no return. Once something crosses the event horizon, it is destined to be pulled into the black hole's singularity, where the laws of physics as we know them break down. It's like falling into a bottomless pit with no way out.Despite their mysterious nature, black holes play a crucial role in the universe. They are thought to be responsible for the formation of galaxies and the distribution of matter in the cosmos. They also have a significant impact on the space-time fabric, warping it in ways that are still not fully understood.In conclusion, black holes are one of the most enigmatic and awe-inspiring phenomena in the universe. They challenge our understanding of the cosmos and open up new possibilities for scientific exploration.中文：黑洞一直是我感到着迷的话题。
古希腊神话之奥德修斯(下)
Notes to the Story of Odysseus (下):00:10 Blocking his way are bloodthirsty monsters,00:13 enchanting seductresses,00:15 treacherous seas and angry gods.阻碍奥德修斯归家的有嗜血的怪兽、迷人的海妖、暗藏危险的大海，还有那愤怒的神灵。
00:29 To us it is myth,00:31 but to the ancients it was reality00:34 and perhaps even a blueprint for one of the Christian gospels.对于我们这是一个神话，而对于古人这却是现实，也许甚至还是基督教福音书的源泉。
01:38 As Odysseus battles danger on the high seas,01:41 his wife, Penelope, anxiously awaits his return01:44 and wonders if she has become a sailor's widow.01:48 Meanwhile, a rogue's gallery of suitors is knocking at her door,01:52 pressuring her to forget her husband and marry again.就在奥德修斯与大海上的种种危险搏斗的时候，他的妻子，珀涅罗珀，焦急的等待着他的归来，她很想知道自己是否已经成了寡妇。
与此同时，一群无耻的求婚者正在骚扰她的家门，他们企图让她忘记她的丈夫，择人另嫁。
04:46 Poseidon, one of the most powerful gods,04:49 has this personal antipathy to Odysseus.波塞冬，最强大的神祇之一，对奥德修斯十分反感。
00015自考英语二教程电子版
大学英语自学教程（下）01-A. What Is a Decision?A decision is a choice made from among alternative courses of action that are available. The purpose of making a decision is to establish and achieve organizational goals and objectives. The reason for making a decision is that a problem exists, goals or objectives are wrong, or something is standing in the way of accomplishing them.Thus the decision-making process is fundamental to management. Almost everything a manager does involves decisions, indeed, some suggest that the management process is decision making. Although managers cannot predict the future, many of their decisions require that they consider possible future events. Often managers must make a best guess at what the future will be and try to leave as little as possible to chance, hut since uncertainty is always there, risk accompanies decisions. Sometimes the consequences of a poor decision are slight; at other times they are serious.Choice is the opportunity to select among alternatives. If there is no choice, there is no decision to be made. Decision making is the process of choosing, and many decisions have a broad range of choice. For example, a student may be able to choose among a number of different courses in order to implement the decision to obtain a college degree. For managers, every decision has constraints based on policies, procedures, laws, precedents, and the like. These constraints exist at all levels of the organization.Alternatives are the possible courses of action from which choices can be made. If there are no alternatives, there is no choice and, therefore, no decision. If no alternatives are seen, often it means that a thorough job of examining the problems has not been done. For example, managers sometimes treat problems in an either/or fashion; this is their way of simplifying complex problems. But the tendency to simplify blinds them to other alternatives.At the managerial level, decision making includes limiting alternatives as well as identifying them, and the range is from highly limited to practically unlimited.Decision makers must have some way of determining which of several alternatives is best -- that is, which contributes the most to the achievement of organizational goals. An organizational goal is an end or a state of affairs the organization seeks to reach. Because individuals (and organizations) frequently have different ideas about how to attain the goals, the best choice may depend on who makes the decision. Frequently, departments or units within an organization make decisions that are good for them individually but that are less than optimal for the larger organization. Called suboptimization, this is a trade-off that increases the advantages to one unit or function but decreases the advantages to another unit or function. For example, the marketing manager may argue effectively for an increased advertising budget. In the larger scheme of things, however, increased funding for research to improve the products might be more beneficial to the organization.These trade-offs occur because there are many objectives that organizations wish to attainsimultaneously. Some of these objectives are more important than others, but the order and degree of importance often vary from person to person and from department to department. Different managers define the same problem in different terms. When presented with a common case, sales managers tend to see sales problems, production managers see production problems, and so on.The ordering and importance of multiple objectives is also based, in part, on the values of the decision maker. Such values are personal; they are hard to understand, even by the individual, because they are so dynamic and complex. In many business situations different people's values about acceptable degrees of risk and profitability cause disagreement about the correctness of decisions.People often assume that a decision is an isolated phenomenon. But from a systems point of view, problems have multiple causes, and decisions have intended and unintended consequences. An organization is an ongoing entity, and a decision made today may have consequences far into the future. Thus the skilled manager looks toward the future consequences of current decisions. 01-B. Secrets of Success at an InterviewThe subject of today's talk is interviews.The key words here are preparation and confidence, which will carry you far.Do your homework first.Find out all you can about the job you are applying for and the organization you hope to work for.Many of the employers I interviewed made the same criticism of candidates. "They have no idea what the day to day work of the job brings about. They have vague notions of "furthering the company's prospects’ or of 'serving the community', but have never taken the trouble to find out the actual tasks they will be required to do.”Do not let this be said of you. It shows an unattractive indifference to your employer and to your job.Take the time to put yourself into the interviewer's place. He wants somebody who is hard-working with a pleasant personality and a real interest in the job.Anything that you find out about the prospective employer can be used to your advantage during the interview to show that you have bothered to master some facts about the people who you hope to work for.Write down (and remember) the questions you want to ask the interviewer(s) so that you are not speechless when they invite your questions. Make sure that holidays and pay are not the first things you ask about. If all your questions have been answered during the interview, reply: "In fact, I did have several questions, but you have already answered them all.”Do not be afraid to ask for clarification of something that has been said during the interview if you want to be sure what was implied, but do be polite.Just before you go to the interview, look again at the original advertisement that you answered,any correspondence from your prospective employer, photocopies of your letter of application or application form and your resume.Then you will remember what you said and what they want. This is very important if you have applied for many jobs in a short time as it is easy to become confused and give an impression of inefficiency.Make sure you know where and when you have to report for the interview. Go to the building (but not inside the office) a day or two before, if necessary, to find out how long the journey takes and where exactly the place is.Aim to arrive five or ten minutes early for the actual interview, then you will have a little time in hand and you will not panic if you are delayed. You start at a disadvantage if you arrive worried and ten minutes late.Dress in clean, neat, conservative clothes. Now is NOT the time to experiment with the punk look or (girls) to wear low-cut dresses with miniskirts. Make sure that your shoes, hands and hair (and teeth) are clean and neat.Have the letter inviting you for an interview ready to show in case there is any difficulty in communication.You may find yourself facing one interviewer or a panel. The latter is far more intimidating, but do not let it worry you too much. The interviewer will probably have a table in front of him/her. Do not put your things or arms on it.If you have a bag or a case, put it on the floor beside your chair. Do not clutch it nervously or, worse still, drop it, spilling everything.Shake hands if the interviewer offers his hand first. There is little likelihood that a panel of five wants to go though the process of all shaking hands with you in turn. So you do not be upset if no one offers.Shake hands firmly -- a weak hand suggests a weak personality, and a crushing grip is obviously painful. Do not drop the hand as soon as yours has touched it as this will seem to show you do not like the other person.Speak politely and naturally even if you are feeling shy. Think before you answer any questions. If you cannot understand, ask: "Would you mind rephrasing the question, please?" The question will then be repeated in different words.If you are not definitely accepted or turned down on the spot, ask: "When may I expect to hear the results of this interview?"If you do receive a letter offering you the job, you must reply by letter (keep a photocopy) as soon as possible.Good luck!02-A. Black HolesWhat is a black hole? Well, it's difficult to answer this question, since the terms we would normally use to describe a scientific phenomenon are inadequate here. Astronomers andscientists think that a black hole is a region of space (not a thing ) into which matter has fallen and from which nothing can escape ?not even light. So we can't see a black hole. A black hole exerts a strong gravitational pull and yet it has no matter. It is only space -- or so we think. How can this happen?The theory is that some stars explode when their density increases to a particular point; they collapse and sometimes a supernova occurs. From earth, a supernova looks like a very bright light in the sky which shines even in the daytime. Supernovae were reported by astronomers in the seventeenth and eighteenth centuries. Some people think that the Star of Bethlehem could have been a supernova. The collapse of a star may produce a White Dwarf or a neutron star -- a star, whose matter is so dense that it continually shrinks by the force of its own gravity. But if the star is very large (much bigger than our sun) this process of shrinking may be so intense that a black hole results. Imagine the earth reduced to the size of a marble, but still having the same mass and a stronger gravitational pull, and you have some idea of the force of a black hole. Any matter near the black hole is sucked in. It is impossible to say what happens inside a black hole. Scientists have called the boundary area around the hole the "event horizon." We know nothing about events which happen once objects pass this boundary. But in theory, matter must behave very differently inside the hole.For example, if a man fell into a black hole, he would think that he reached the center of it very quickly. However an observer at the event horizon would think that the man never reached the center at all. Our space and time laws don't seem to apply to objects in the area of a black hole. Einstein's relativity theory is the only one which can explain such phenomena. Einstein claimed that matter and energy are interchangeable, so that there is no "absolute" time and space. There are no constants at all, and measurements of time and space depend on the position of the observer. They are relative. We do not yet fully understand the implications of the relativity theory; but it is interesting that Einstein's theory provided a basis for the idea of black holes before astronomers started to find some evidence for their existence. It is only recently that astronomers have begun specific research into black holes. In August 1977, a satellite was launched to gather data about the 10 million black holes which are thought to be in the Milky Way. And astronomers are planning a new observatory to study the individual exploding stars believed to be black holes,The most convincing evidence of black holes comes frown research into binary star systems. Binary stars, as their name suggests, are twin stars whose position in space affects each other. In some binary systems, astronomers have shown that there is an invisible companion star, a "partner" to the one which we can see in the sky. Matter from the one which we can see is being pulled towards the companion star. Could this invisible star, which exerts such a great force, be a black hole? Astronomers have evidence of a few other stars too, which might have black holes as companions.The story of black holes is just beginning. Speculations about them. are endless. There might bea massive black hole at the center of our galaxy swallowing up stars at a very rapid rate. Mankind may one day meet this fate. On the other hand, scientists have suggested that very advanced technology could one day make use of the energy of black holes for mankind. These speculations sound like science fiction. But the theory of black holes in space is accepted by many serious scientists and astronomers. They show us a world which operates in a totally different way from our own and they question our most basic experience of space and time.02-B. Worlds within WorldsFirst of all let us consider the earth (that is to say, the world) as a planet revolving round the sun. The earth is one of nine planets which move in orbit round the sun. These nine planets, together with the sun, make up what is called our solar system. How this wonderful system started and what kept it working with such wonderful accuracy is largely a mystery but astronomers tell us that it is only one of millions of similar systems in space, and one of the smallest.The stars which we see glittering in the sky on a dark and cloudless night are almost certainly the suns of other solar systems more or less like our own, but they are so far away in space that it is unlikely that we shall ever get to know very much about them. About our own solar system, however, we are learning more every day.Before the American and Russian astronauts made their thrilling journeys into outer space it was difficult for us to realise what our earth looked like from hundreds of thousands of miles away, but the photographs which the astronauts were able to take show us the earth in space looking not very different from what the moon looks like when we look at it from the earth. The earth is, however, very different from the moon, which the American astronauts have found to be without life or vegetation, whereas our earth is very much alive in every respect. The moon, by the way, is called a satellite because it goes round our earth as well as round the sun. In other words, it goes round the sun with our earth.The surface of our earth is covered by masses of land and larger areas of water. Let us consider the water areas first. The total water area is about three times as large as the land area. The very large separate areas of water are called "oceans” and the lesser areas are called "seas.”In most of the oceans and seas some of the water is found to be flowing in a particular direction -- that is to say, from one part towards another part of the ocean or sea concerned. The water which is flowing in this manner is said to be moving as a "current." There are many thousands of currents in the waters of the oceans and seas, but only certain of the stronger and better marked currents are specially named and of great importance. These currents are important because they affect the climate of the land areas close to where they flow and also because they carry large quantities of microscopic animal and vegetable life which forms a large part of the food for fishes.The nature and characteristics of the surface of the land areas of the earth vary a great deal from area to area and from place to place. The surface of some areas consists largely of high mountains and deep valleys whilst, in other areas, most of the surface consists of plains. If onemade a journey over the Continents one would find every kind of surface including mountain ranges, plains, plateaux, deserts, tropical forestlands and empty areas covered permanently by ice and snow.When thinking and learning about the world we should not forget that our world is the home of a very great many different people -- peoples with different coloured skins, living very different lives and having very different ideas about a great many important things such as religion, government, education and social behaviour.The circumstances under which different people live make a great difference between the way in which they live and the way in which we live, and it ought to be our business to try to understand those different circumstances so that we can better understand people of other lands. Above all, we should avoid deciding what we think about people different from ourselves without first having learned a great deal about them and the kind of lives they have to live. It is true to say that the more we learn about other people, the better we understand their ideas and, as a rule, the better we like those people themselves.03-A. Euthanasia: For and Against"We mustn't delay any longer ... swallowing is difficult ... and breathing, that's also difficult. Those muscles are weakening too ... we mustn't delay any longer.”These were the words of Dutchman Cees van Wendel de Joode asking his doctor to help him die. Affected with a serious disease, van Wendel was no longer able to speak clearly and he knew there was no hope of recovery and that his condition was rapidly deteriorating.Van Wendel's last three months of life before being given a final, lethal injection by his doctor were filmed and first shown on television last year in the Netherlands. The programme has since been bought by 20 countries and each time it is shown, it starts a nationwide debate on the subject.The Netherlands is the only country in Europe which permits euthanasia, although it is not technically legal there. However, doctors who carry out euthanasia under strict guidelines introduced by the Dutch Parliament two years ago are usually not prosecuted. The guidelines demand that the patient is experiencing extreme suffering, that there is no chance of a cure, and that the patient has made repeated requests for euthanasia. In addition to this, a second doctor must confirm that these criteria have been met and the death must be reported to the police department.Should doctors be allowed to take the lives of others? Dr. Wilfred van Oijen, Cees van Wendel's doctor, explains how he looks at the question:"Well, it's not as if I'm planning to murder a crowd of people with a machine gun. In that case, killing is the worst thing I can imagine. But that's entirely different from my work as a doctor. I care for people and I try to ensure that they don't suffer too much. Th at's a very different thing.”Many people, though, are totally against the practice of euthanasia. Dr. Andrew Ferguson, Chairman of the organisation Healthcare Opposed to Euthanasia, says that "in the vast majorityof euthanasia cases, what the patient is actually asking for is something else. They may want a health professional to open up communication for them with their loved ones or family -- there's nearly always another question behind the question.”Britain also has a strong tradition of hospices -- special hospitals which care only for the dying and their special needs. Cicely Saunders, President of the National Hospice Council and a founder member of the hospice movement, argues that euthanasia doesn't take into account that there are ways of caring for the dying. She is also concerned that allowing euthanasia would undermine the need for care and consideration of a wide range of people: "It's very easy in society now for the elderly, the disabled and the dependent to feel that they are burdens, and therefore that they ought to opt out. I think that anything that legally allows the shortening of life does make those people more vulnerable.”Many find this prohibition of an individual's right to die paternalistic. Although they agree that life is important and should be respected, they feel that the quality of life should not be ignored. Dr. van Oijen believes that people have the fundamental right to choose for themselves if they want to die: "What those people who oppose euthanasia are telling me is that dying people haven't the right. And that when people are very ill, we are all afraid of their death. But there are situations where death is a friend. And in those cases, why not?But "why not?" is a question which might cause strong emotion. The film showing Cees van Wendel's death was both moving and sensitive. His doctor was clearly a family friend; his wife had only her husband's interests at heart. Some, however, would argue that it would be dangerous to use this particular example to support the case for euthanasia. Not all patients would receive such a high level of individual care and attention.03-B. Advantage UnfairAccording to the writer Walter Ellis, author of a book called the Oxbridge Conspiracy, Britain is still dominated by the old-boy network: it isn't what you know that matters, but who you know. He claims that at Oxford and Cambridge Universities (Oxbridge for short) a few select people start on an escalator ride which, over the years, carries them to the tops of British privilege and power. His research revealed that the top professions all continue to be dominated, if not 90 per cent, then 60 or 65 per cent, by Oxbridge graduates.And yet, says Ellis, Oxbridge graduates make up only two per cent of the total number of students who graduate from Britain's universities. Other researches also seem to support his belief that Oxbridge graduates start with an unfair advantage in the employment market. In the law, a recently published report showed that out of 26 senior judges appointed to the High Court last year, all of them went to private schools and 21 of them went to Oxbridge.But can this be said to amount to a conspiracy? Not according to Dr. John Rae, a former headmaster of one of Britain's leading private schools, Westminster:"I would accept that there was a bias in some key areas of British life, but that bias has now gone. Some time ago -- in the 60s and before ?entry to Oxford and Cambridge was not entirely onmerit. Now, there's absolutely no question in any objective observer's mind that, entry to Oxford and Cambridge is fiercely competitive."However, many would disagree with this. For, although over three-quarters of British pupils are educated in state schools, over half the students that go to Oxbridge have been to private, or "public" schools. Is this because pupils from Britain's private schools are more intelligent than those from state schools, or are they simply better prepared?On average, about $ 5,000 a year is spent on each private school pupil, more than twice the amount spent on state school pupils. So how can the state schools be expected to compete with the private schools when they have far fewer resources? And how can they prepare their pupils for the special entrance exam to Oxford University, which requires extra preparation, and for which many public school pupils traditionally stay at school and do an additional term?Until recently, many blamed Oxford for this bias because of the university's special entrance exam (Cambridge abolished its entrance exam in 1986). But last February, Oxford University decided to abolish the exam to encourage more state school applicants. From autumn 1996, Oxford University applicants, like applicants to other universities, will be judged only on their A level results and on their performance at interviews, although some departments might still set special tests.However, some argue that there's nothing wrong in having elite places of learning, and that by their very nature, these places should not be easily accessible. Most countries are run by an elite and have centres of academic excellence from which the elite are recruited. Walter Ellis accepts that this is true:"But in France, for example, there are something like 40 equivalents of university, which provide this elite through a much broader base. In America you've got the Ivy League, centred on Harvard and Yale, with Princeton and Stanford and others. But again, those universities together -- the elite universities -- are about ten or fifteen in number, and are being pushed along from behind by other great universities like, for example, Chicago and Berkeley. So you don't have just this narrow concentration of two universities providing a constantly replicating elite.”When it comes to Oxford and Cambridge being elitist because of the number of private school pupils they accept, Professor Stone of Oxford University argues that there is a simple fact he and his associates cannot ignore:"If certain schools do better than others then we just have to accept it. We cannot be a place for remedial education. It's not what Oxford is there to do.”However, since academic excellence does appear to be related to the amount of money spent per pupil, this does seem to imply that Prime Minister John Major's vision of Britain as a classless society is still a long way off. And it may be worth remembering that while John Major didn't himself go to Oxbridge, most of his ministers did.04-A. Slavery on Our DoorstepThere are estimated to be more than 20,000 overseas domestic servants working in Britain (theexact figure is not known because the Home Office, the Government department that deals with this, does not keep statistics). Usually, they have been brought over by foreign businessmen, diplomats or Britons returning from abroad. Of these 20,000, just under 2,000 are being exploited and abused by their employers, according to a London-based campaigning group which helps overseas servants working in Britain.The abuse can take several forms. Often the domestics are not allowed to go out, and they do not receive any payment. They can be physically, sexually and psychologically abused. And they can have their passports removed, making leaving or "escaping" virtually impossible.The sad condition of women working as domestics around the world received much media attention earlier this year in several highly publicised cases. In one of them, a Filipino maid was executed in Singapore after being convicted of murder, despite protests from various quarters that her guilt had not been adequately established. Groups like Anti-Slavery International say other, less dramatic, cases are equally deserving of attention, such as that of Lydia Garcia, a Filipino maid working in London:"I was hired by a Saudi diplomat directly from the Philippines to work in London in 1989. I was supposed to be paid $ 120 but I never received that amount. They always threatened that they would send me back to my country.”Then there is the case of Kumari from Sri Lanka. The main breadwinner in her family, she used to work for a very low wage at a tea factory in Sri Lanka. Because she found it difficult to feed her four children, she accepted a job working as a domestic in London. She says she felt like a prisoner at the London house where she worked:"No days off -- ever, no breaks at all, no proper food. I didn't have my own room; I slept on a shelf with a spad0 of only three feet above me. I wasn't allowed to talk to anybody. I wasn't even allowed to open the window. My employers always threatened to report me to the Home Office or the police.”At the end of 1994 the British Government introduced new measures to help protect domestic workers from abuse by their employers. This included increasing the minimum age of employees to 18, getting employees to read and, understand an advice leaflet, getting employers to agree to provide adequate maintenance and conditions, and to put in writing the main terms and conditions of the job (of which the employees should see a copy).However, many people doubt whether this will successfully reduce the incidence of abuse. For the main problem facing overseas maids and domestics who try to complain about cruel living and working conditions is that they do not have independent immigrant status and so cannot change employer. (They are allowed in the United Kingdom under a special concession in the immigration rules which allows foreigners to bring domestic staff with them.) So if they do complain, they risk being deported.Allowing domestic workers the freedom to seek the same type of work but with a different employer, if they so choose, is what groups like Anti-Slavery International are campaigning the。
关于黑洞的作文400字
关于黑洞的作文400字英文回答：Black holes are one of the most fascinating and mysterious phenomena in the universe. These celestial objects have such immense gravitational force that nothing, not even light, can escape their grasp. Scientists believe that black holes are formed from the remnants of massive stars that have collapsed under their own gravity.The concept of a black hole can be quite mind-boggling. Imagine a point in space where gravity is so strong that it creates a "hole" in the fabric of space-time. Anything that gets too close to this hole will be pulled in, never to be seen again. It's like a cosmic vacuum cleaner!Black holes come in different sizes, ranging from stellar black holes that are a few times more massive than our sun, to supermassive black holes that can be millions or even billions of times more massive. These supermassiveblack holes are thought to exist at the center of most galaxies, including our own Milky Way.The study of black holes has revolutionized our understanding of the universe. It has led to the discovery of many other intriguing phenomena, such as wormholes, which are hypothetical tunnels that could potentially connect different parts of the universe. Black holes also play a crucial role in the formation of galaxies and the evolution of the universe itself.中文回答：黑洞是宇宙中最迷人和神秘的现象之一。
关于黑洞的英文作文
关于黑洞的英文作文Black holes are one of the most mysterious and fascinating objects in the universe. They are regions in space where the gravitational pull is so strong that nothing, not even light, can escape from them.Scientists believe that black holes are formed when massive stars collapse at the end of their life cycle. The core of the star collapses under its own gravity, creating a black hole with an incredibly dense center known as a singularity.The boundary surrounding a black hole is called the event horizon. Once anything crosses the event horizon, it is pulled into the black hole and can never escape. This is why black holes are often described as cosmic vacuum cleaners.Despite their name, black holes are not actually black. As they pull in surrounding matter, they emit powerfulradiation and can be detected by the telescopes on Earth and in space.The study of black holes has revolutionized our understanding of the universe and has led to many groundbreaking discoveries in the field of astrophysics. They continue to be a source of wonder and intrigue for scientists and space enthusiasts alike.。
描写黑洞的英文作文
描写黑洞的英文作文Black holes are like the ultimate vacuum cleaners of the universe. They suck in everything in their path, including light, and nothing can escape their gravitational pull. It's like a bottomless pit in space, where everything gets swallowed up and never seen again.The concept of a black hole is mind-boggling. It's a place where the laws of physics as we know them break down, and the very fabric of space and time is warped beyond recognition. It's like a cosmic anomaly that defies all our understanding of the universe.The sheer power of a black hole is terrifying. It can tear apart stars, planets, and even entire galaxies withits intense gravitational forces. It's like a cosmic monster that devours everything in its path, leaving nothing but emptiness and darkness in its wake.The event horizon of a black hole is like a point of noreturn. Once something crosses this boundary, it's doomed to be pulled into the black hole's abyss, never to escape. It's like a cosmic trap that ensnares anything that comes too close.The idea of a black hole has captured the imagination of scientists and science fiction writers alike. It's like a mysterious enigma that continues to fascinate andintrigue us, even as we struggle to comprehend its true nature.In the end, black holes remain one of the most enigmatic and awe-inspiring phenomena in the universe. They challenge our understanding of the cosmos and force us to confront the limits of our knowledge. It's like a cosmic riddle that continues to elude our grasp, leaving us to wonder and speculate about its secrets.。
小学上册第二次英语第六单元测验卷
小学上册英语第六单元测验卷英语试题一、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.What do we use to write on paper?A. PaintB. PencilC. BrushD. MarkerB2.The process of rusting is a type of ______ reaction.3.The dog is ___ (digging/sitting).4.It is _____ (sunny/rainy) today.5.Gardeners often use ______ to help their plants grow strong. (园艺师常常使用肥料来帮助植物健康成长。
)6.The _____ (细胞) of plants are specialized for different functions.7.My sister has a pet _____ that likes to cuddle.8.What do we call the area of land that is home to a specific community of living organisms?A. EcosystemB. HabitatC. BiomeD. NicheB Habitat9.What do you call a person who teaches others?A. EducatorB. InstructorC. MentorD. All of the aboveD10.The clock ticks _____ (slowly/quickly).11.What do we call the process of making bread?A. BakingB. CookingC. BoilingD. RoastingA12.__________ are known to migrate long distances during winter.13.I love to ______ (与家人一起) travel.14.The stars are ___ (twinkling) at night.15.I saw a ______ (蝴蝶) in the garden today, it was beautiful.16.Frogs have ______ to catch insects.17.The __________ can reveal the history of ancient geological formations.18.He has a collection of _____ (火车模型).19.What is the boiling point of water in Fahrenheit?A. 32°FB. 100°FC. 212°FD. 300°FC20.I have a special place for my toy ____. (玩具名称)21.__________ (反应条件) must be controlled to achieve desired outcomes in experiments.22.The turtle is a symbol of _______ (长寿).23.The Earth's surface is made up of various ______ ecosystems.24.What is the opposite of "fast"?A. SlowB. QuickC. SpeedyD. Swift25.What do we call the time when the sun sets?A. SunriseB. SunsetC. DuskD. DawnB26.The flowers are ________ in the garden.27.I enjoy watching the _______ (小动物) in the park.28.We learn to ______ (计算) numbers.29.I often _______ (参加) community events on weekends.30.I often visit my grandparents at their ________.31.They are friends and like to ___ (play/talk).32.The stars are ___ (fading/shining) brightly.33.She is a ________ student.34.I like to play with my ____.35.My sister is a _____ (演员) who participates in community theater.36.What is the hottest planet in our solar system?A. VenusB. MarsC. MercuryD. Jupiter37.What sport uses a bat and ball?A. SoccerB. TennisC. BaseballD. BasketballC38.The plant needs more ___ (water).39.Which vegetable is long and green?A. CarrotB. TomatoC. CucumberD. Potato40.The __________ is a region known for its cultural diversity.41. A ________ (岛) is surrounded by water.42.My best friend's name is ______.43.The _______ (猫) has keen senses.44.My favorite toy is a soft _______ that I cuddle at night.45.What do we call a person who studies the effects of space on human behavior?A. Space PsychologistB. SociologistC. AnthropologistD. BiologistA46.ts can ______ (适应变化) in their environment. Some pla47.What do we call a person who studies the relationship between humans and technology?A. TechnologistB. SociologistC. AnthropologistD. Environmental ScientistA48.The chemical formula for carbon dioxide is ______.49.________ (植物多样性保护研究) is crucial for health.50.In spring, flowers like ________ bloom everywhere.51.The __________ (世界的变化) reflects the impact of human actions.52.The ________ was a famous treaty that ended World War II.53.We have a ______ (精彩的) event planned for this weekend.54.The process of _______ separates mixtures based on different boiling points. (蒸馏)55.Which of these is a type of weather?A. SunshineB. SandwichC. HomeworkD. Running56.What do you call a baby chicken?A. DucklingB. GoslingC. ChickD. Puppy57.Which gas do we breathe in?A. Carbon dioxideB. OxygenC. NitrogenD. Helium答案:B58. A __________ is a mixture that consists of two or more substances that retain their properties.59.The sun is shining ________ today.60.The __________ (历史的探寻) uncovers truths.61.The school bell ________ at PM.62.I want to _______ (了解) more about space.63. A ________ (河流) can change its course over time.64.The bear hibernates in the winter to conserve ____.65.My ________ (邻居) shares their delicious cookies with us.66.The ancient city of Rome is known for its _______.67.The ____ has big, floppy ears and enjoys nibbling on carrots.68.Which of these is a dairy product?A. BreadB. CheeseC. RiceD. Pasta69.My sister has a lovely _______ (我妹妹有一个可爱的_______).70. A parakeet's diet consists of seeds, fruits, and ________________ (蔬菜).71.My ________ (玩具名称) helps me learn about different places.72.The _____ (sand/gravel) is warm.73.Which sport is played with a hoop and a ball?A. SoccerB. BasketballC. TennisD. BaseballB74.How many legs does a spider have?A. 6B.8C.10D.12答案:B75.________ (植物保护倡导者) raise awareness.76.What is 3 + 5?A. 7B. 8C. 9D. 10B77.What is the first letter of the English alphabet?A. AB. BC. CD. DA78. A puppy loves to play and ________________ (探索).79.What do we call a person who studies the stars?A. GeologistB. MeteorologistC. AstronomerD. BiologistC80.The __________ (种植计划) should be well thought out.81.She is a journalist, ______ (她是一名记者), traveling to report stories.82. A ______ (社区花园) promotes social interaction.83.What is the name of the famous dinosaur known for its long neck?A. T-RexB. StegosaurusC. BrachiosaurusD. Triceratops84.My aunt loves to paint ____ (murals).85.The __________ (历史的展示手法) can enhance understanding.86.I love to decorate my toy ____ with stickers. (玩具名称)87.The ______ helps us learn about important events.88.The __________ (历史的记忆) shapes identity.89. A ________ (湿地) helps filter water.90.Certain plants can ______ (创造) jobs in agriculture.91.I have a pet _____ that loves to run.92.In art class, we use crayons, markers, and ________ (水彩) to create beautiful pictures. I love expressing my ________ (创造力).93.The chemical formula for propanol is ______.94.What is the currency used in the USA?A. EuroB. DollarC. PoundD. YenB95.The _______ (蝴蝶) flaps its wings.96.Bacteria can be helpful or ______ to humans.97.The chocolate cake is ______ (so) good.98.I want to _______ (学习) gardening.99.What is the capital of Australia?A. SydneyB. MelbourneC. CanberraD. Brisbane100.She is _____ (cooking/eating) dinner.。
The mysteries of the universe Black holes
The mysteries of the universe BlackholesBlack holes have long been a source of fascination and mystery for scientists and the general public alike. These enigmatic cosmic entities possess such intense gravitational pull that not even light can escape their grasp, making them invisible and seemingly impenetrable to our current technology and understanding. Despite their elusive nature, researchers have been able to gather some insights into the workings of black holes through theoretical models and observations of their effects on surrounding matter. One of the most intriguing aspects of black holes is their formation. It is believed that black holes are created when massive stars exhaust their nuclear fuel and collapse under their own gravity, leading to the formation of a singularity - a point of infinite density where the laws of physics as we know them break down. This singularity is surrounded by an event horizon, beyond which nothing can escape the black hole's gravitational pull. The concept of a singularity is mind-boggling, as it challenges our understanding of the universe and the fundamental laws that govern it. The study of black holes has also shed light on the concept of spacetime curvature. According to Einstein's theory of general relativity, massive objects like black holes warp the fabric of spacetime, causing it to bend and curve around them. This curvature is what gives rise to the gravitational pull of black holes, sucking in anything that comes too close. The idea of spacetime being malleable and influenced by the presence of matter is a profound concept that has revolutionized our understanding of the cosmos. Another fascinating aspect of black holes is their role in the cosmic ecosystem. While they may seem like cosmic vacuum cleaners, devouring everything in their path, black holes also play a crucial role in the formation and evolution of galaxies. It is believed that supermassive black holes reside at the centers of most galaxies, including our own Milky Way, and their gravitational influence shapes the movement of stars and gas within the galaxy. In some cases, black holes can also trigger the formation of new stars by compressing and heating surrounding gas clouds. Despite the wealth of knowledge we have gained about black holes, there are still many unanswered questions and mysteries surrounding these cosmicenigmas. One of the biggest puzzles is the information paradox, which arises from the conflict between quantum mechanics and general relativity in the context of black hole evaporation. According to quantum mechanics, information cannot be destroyed, yet when a black hole evaporates through Hawking radiation, it seems to lose all the information it has swallowed over its lifetime. This paradox challenges our understanding of the fundamental laws of physics and has yet to be resolved. The study of black holes also raises philosophical questions about the nature of reality and our place in the universe. The sheer scale and power of black holes serve as a humbling reminder of the vastness and complexity of the cosmos, prompting us to question our place in the grand scheme of things. Black holes force us to confront the limits of our knowledge and the mysteries thatstill elude our understanding, inspiring a sense of wonder and awe at the beauty and complexity of the universe. In conclusion, black holes are truly one of the most fascinating and mysterious phenomena in the cosmos. From their formation and spacetime curvature to their role in galaxy evolution and the information paradox, black holes continue to captivate and challenge scientists and laypeople alike. As we strive to unravel the secrets of these cosmic enigmas, we are reminded of the boundless wonders of the universe and the endless possibilities for discovery and exploration that lie ahead.。
爱德华和难以置信黑洞英文原文及汉语翻译
Edward and His Incredible Black HoleEdward had a marvelous plan. He was going to create a genuine mini Black Hole, right here on earth.Edward lived alone in the suburban sprawl of a large city. His father had experimented with inventions in his large steel garage. Because of this, his mother had left home four years ago. He missed his father who had died of a heart attack two summers ago.Edward worked during the day as an attendant at the City Library where he taught himself technology so that he could understand his father’s notebooks. At home he stumbled around in track-pants and a T-shirt and busily modified his father’s equipment.Edward put coils of copper tube, large permanent magnets, sheets of aluminum foil, old iron tubes full of silicone sealant together to construct a two and a half meters high intricate apparatus, putting a copper vertical horn on top. The horn, like the front of a large trumpet, was pointed towards the ceiling.Today was Edward’s twenty-second birthday, remembered only by the lovely Fiona, the Circulation Librarian. At lunchtime, Fiona had kissed him on the cheek in front of everybody in the tearoom. Edward had flushed crimsonwith embarrassment.But now was the moment. He climbed the stepladderand peered into the trumpet. The curved mirror at its base magnified his reflected image and he admired his golden curly hair and his green eyes, but loathed his big ears.Edward sipped on a glass of cheap soda and whisper ed, “Black holes are the mysteries of our universe. Everything that enters them never leaves——even light.” He had a collection of hardware items arranged near him so that he could throw them into the Black Hole and watch them disappear. Edward sat at the computer controls for the Black Hole Generator.“That’s one small step for a man…” Edward intonedand double-clicked on the start icon. There was a loud vibrating noise and a strange glaring effect in the horn. Edward didn’t realize that a simple software mistake had reversed the polarityof his black hold generator. Yes, he could see that the interior of the horn was indeed the deepest, blackest thing that he had ever seen, but within the blackness he could soon make out sparkling points of every color imaginable.“Stars?” he thought just before he died. Within a few seconds, around a hundred million colorful ballpoint pens shot out of the horn, bounced off the roof and filled up the garage, spearing poor Edward to death. As every lost ballpoint pen in the world poured out of the black hole, the pressure blew the top off the garage and the mountain of pens continued to grow.Soon every lost sock in the world flew into the air from the trumpet, and covered the mountain of pens. Then a great number of shopping lists fluttered into the air, followed by an emission of lottery tickets, and train, tram, bus and concert tickets. This was followed by every letter, telegram and E-mail that had never arrived.Edward’s garage then collapsed as millions of metal keys shot o ut of the horn and rained down---lost front door keys, car keys and locker keys. The overflow continued as sewing needles, cufflinks, pencil sharpeners, razors and lost passports, followed by countless of pins.Can openers, bottle openers and corkscrewswere followed by sink plugs and remote controls. As these flooded over the local community, they were covered by clothes pegs, the caps of toothpaste tubes and a flow of overdue library books.A veritablemountain of lost-receipts needed by the taxman was followed by every lost screw nut from a world of car engines, household appliances and technical instruments.As the city saggedbeneath the weight of all these lost things, millions of credit cards fluttered into the air and rained down.Edward would have been amazed, except that he was long dead.Finally, just before the black hole generator disappeared in a puff of smoke, every lost love in the history of the world was expelled into the air and rained down in an overflow of desolation.爱德华和他那难以置信的黑洞爱德华有一个不可思议的计划，他将要在地球上创造一个名副其实的迷你黑洞。
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Chaos in Black Holes Surrounded by Electromagnetic Fields
Manuele Santoprete∗ and Giampaolo Cicogna†
Abstract In this paper we study the occurrence of chaos for charged particles moving around a Schwarzschild black hole, perturbed by uniform electric and magnetic fields. The appearance of chaos is analyzed resorting to the Poincar´ e-Melnikov method.
Chaos in Black Holes Surrounded by Electromagnetic Fields
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but we deal more in general with the full three dimensional problem, i.e. with perturbations which may change the plane of the orbit. Let us also remark that we will consider time-independent perturbations, and show that they produce chaos; this happens even when only the rotational invariance is broken. The problem we study in this paper can be related to the astrophysical reality, since it is well known that magnetic fields can be associated with black holes. We will consider Schwarzschild black holes, i.e. non rotating ones, and we reserve to tackle the more interesting, but more complex problem of rotating black holes in a forthcoming paper. Isolated black holes cannot possess any properties other than mass, electric charge and angular momentum, but the medium surrounding the hole can be responsible for the magnetic field. For example, super massive black holes can acquire surrounding matter either by gravitationally pulling interstellar gas into its vicinity, or by the disruption of passing stars. The surrounded matter will be shaped in an accretion disk in a state of plasma, that produces a magnetic field. Electric fields are less likely to be found near a black hole, although the Blandford-Znajek mechanism [8] is a process that can develop a potential difference (i.e. an electric field) between the poles and the equator of a black hole spinning in a magnetic field pointing along the axis of rotation. On the other hand, it is not easy to account for the presence of charged particles since the ionized gas, that is shaped in an accretion disk surrounding a black hole, is in a state of plasma, and a plasma is electrically neutral. One way to account for the presence of charged particles is to consider again the Blandford-Znajek mechanism, that, if the field strength is large enough, can separate charges and accelerate them to relativistic velocities. Otherwise, we can model the motion of electromagnetic currents in a macroscopic piece of plasma considering the equivalent problem of the motion of a charged particle moving around a black hole surrounded by a magnetic field. This can be done since the magnetic field has the same effect on an electric current in a macroscopic piece of plasma as on a single charge. As said before, we will deal in this paper only with uniform fields. Although the fields which can be found in the astrophysical reality, e.g. the Blanford-Znajek ones, are not uniform, some authors (see [9] and references therein) pointed out that models with uniform external fields are a fairly good approximation in order to explain the qualitative features of a black hole in a magnetic field, indeed qualitative arguments indicate the existence of a quasi-uniform field.
PACS numbers: 04.20.-q, 05.45.-a, 95.10.Fh, 95.30.Sf
Dept. of Mathematics and Statistics, University of Victoria, P.O. Box 3045, Victoria B.C., Canada, V8W 3P4. Email: msantopr@math.uvic.ca. † Dip. di Fisica “E.Fermi” and I.N.F.N., Sez. di Pisa, Via Buonarroti 2, Ed. B, I-56127, Pisa, Italy. Email: cicogna@df.unipi.it
∗
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Chaos in Black Holes Surrounded by Electromagnetic Fields
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1
Introduction
In the last decade chaotic behaviour in general relativity started to be the subject of many interesting papers. Two main lines of research can be recognized. The first deals with chaoticity associated with inhomogeneous cosmological models, the second line assumes a given metric and looks for chaotic behaviour of geodesic motion in this background. An interesting selection of references can be found in [1]. In particular many papers devoted to the study of chaotic dynamics in general relativity resort to the Poincar´ e-Melnikov method (see e.g. [2, 3] for the general theory). The Melnikov method is an analytical criterion to determine the occurrence of chaos in integrable systems in which homoclinic (or heteroclinic) manifolds biasymptotic to unstable critical points or to periodic orbits (more generally to invariant tori) are subjected to small perturbations. Such perturbations may lead to the phenomenon of transversal intersections of the stable and unstable manifolds. This kind of dynamics can be then detected by the Melnikov functions, since they describe the transversal distance between the stable and the unstable manifolds of the critical point or periodic orbit. The Melnikov method has been applied in many branches of physics and applied mathematics, so that it is impossible to give here even a partial account of the vast literature, and we will quote only some of the applications to general relativity that are more strictly related to the present paper (for a more completeபைடு நூலகம்list of references see e.g. [3, 4, 5]). Examples of applications of the Melnikov method in general relativity concern the study of the orbits around a black hole perturbed either by an external quadrupolar shell [4, 6] or gravitational radiation [1, 7]. In this work we take a slightly different approach, compared with the previous literature. Firstly, we do not analyze perturbations of the metric, but perturbations due to the interactions produced by uniform electric or magnetic fields. We consider these as perturbations to the Hamiltonian of a charged test particle in free fall in a Schwarzschild black hole. Secondly, we do not restrict ourselves to perturbations lying in the plane of the orbit,