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Simulation (Fifth Edition) Sheldon M. Ross [論壇首發第五版] attachment 计量经济学与统计软件 Toyotomi 2013-2-9 31 15656 Xvideo 2017-1-23 18:05:55
two excellent business law textbooks attach_img 经管相关法律法规 carrick13 2013-8-24 10 1835 ┏_木市孓℡ 2013-9-29 17:18:05
IP Network-based Multi-agent Systems for Industrial Automation Information Manag attach_img 管理信息系统 Toyotomi 2013-1-27 1 1956 olderp 2013-9-18 07:50:34
经典10步骤教你怎样减少英文拼写错误 外语学习 reduce_fat 2013-8-15 29 4238 功夫之王 2013-9-14 10:57:44
悬赏 Factors for implementing end-of-life computer recycling - [!reward_solved!] attachment 求助成功区 下雨就打伞 2013-7-3 2 663 jmb321 2013-7-3 09:00:56
悬赏 The development of computer science research in the People’s Republic of China - [!reward_solved!] attachment 求助成功区 limeiwangxin 2013-6-26 1 747 jmb321 2013-6-26 22:04:31
Textbook Seeking - "Multivariate Analysis" (Chatfield & Collins) 计量经济学与统计软件 karinadu 2013-1-17 3 2802 kkwei 2013-6-6 08:20:42
50 Top Sources Of Free eLearning Courses 人力资源管理 lxblxb1985 2013-2-15 4 2340 generator 2013-4-23 18:17:30
DemProj. Version 4. A computer program for making population projections. attachment 公共经济学 tyn 2009-7-10 1 1886 hht19900707 2013-2-28 12:29:59
比较以下四种行业的固定成本和可变成本。→有福利 attachment 微观经济学 BeAllYouCanBe 2013-2-27 2 5855 remlus 2013-2-27 21:29:29
(求助!)Bookshelf无法运行 CFA、CVA、FRM等金融考证论坛 窒息 2013-2-3 0 2156 窒息 2013-2-3 20:41:07
[下载]台湾computer行业分析 attachment 商学院 MEI眼泪 2007-5-8 0 1610 MEI眼泪 2011-11-24 15:26:49
哈佛商学院Dell computer case attachment 版权审核区(不对外开放) oldfive 2006-1-9 0 2189 oldfive 2011-10-13 11:32:07
哈佛商学院Apple computer case attachment 金融学(理论版) oldfive 2006-1-9 0 2828 oldfive 2011-10-13 11:29:12
悬赏 求OBHDP文献1篇 - [悬赏 10 个论坛币] attachment 求助成功区 xbcd79 2013-2-21 2 2034 平凡的平凡 2011-2-23 20:37:40
[感谢]英文文献一篇(Journal of Computer Information Systems ) attachment 文献求助专区 yj1891 2009-10-1 1 1440 sam_ben 2009-10-2 13:59:42
Learning SAS: A Computer Handbook for Econometrics (SAS PROGRAM) attachment 数据分析与数据科学 pertain 2009-7-27 3 1961 mrzhao82468246 2009-7-27 14:07:32
[公告]Call for papers: Computer Science&Software Engineering Conference S SAS专版 shirley2 2008-4-30 0 1562 shirley2 2008-4-30 14:48:00
Computer Science&Software Engineering Conference[公告] slm 经管在职研 shirley2 2008-4-24 0 1751 shirley2 2008-4-24 15:58:00


分享 'Military-Style' Raid on California Power Station
insight 2015-4-11 10:34
'Military-Style' Raid on California Power Station 'Military-Style' Raid on California Power Station Spooks U.S. When U.S. officials warn about "attacks" on electric power facilities these days, the first thing that comes to mind is probably a computer hacker trying to shut the lights off in a city with malware. But a more traditional attack on a power station in California has U.S. officials puzzled and worried about the physical security of the the electrical grid--from attackers who come in with guns blazing. Around 1:00 AM on April 16, at least one individual (possibly two) entered two different manholes at the PGE Metcalf power substation, southeast of San Jose, and cut fiber cables in the area around the substation. That knocked out some local 911 services, landline service to the substation, and cell phone service in the area, a senior U.S. intelligence official told Foreign Policy. The intruder(s) then fired more than 100 rounds from what two officials described as a high-powered rifle at several transformers in the facility. Ten transformers were damaged in one area of the facility, and three transformer banks -- or groups of transformers -- were hit in another, according to a PGE spokesman. Cooling oil then leaked from a transformer bank, causing the transformers to overheat and shut down. State regulators urged customers in the area to conserve energy over the following days, but there was no long-term damage reported at the facility and there were no major power outages. There were no injuries reported. That was the good news. The bad news is that officials don't know who the shooter(s) were, and most importantly, whether further attacks are planned. "Initially, the attack was being treated as vandalism and handled by local law enforcement," the senior intelligence official said. "However, investigators have been quoted in the press expressing opinions that there are indications that the timing of the attacks and target selection indicate a higher level of planning and sophistication." The FBI has taken over the case. There appears to have been some initial concern, or at least interest, in the fact that the shooting happened one day after the Boston Marathon bombing. But the FBI has no evidence that the attack is related to terrorism, and it appears to be an isolated incident, said Peter Lee, a spokesman for the FBI field office in San Francisco, which is leading the investigation. Lee said the FBI has "a couple of leads we're still following up on," which he wouldn't discuss in detail. There has not been any published motive or intent for the attack, the intelligence official said, and no one has claimed credit. Local investigators seemed to hit a dead end in June, so they released surveillance footage of the shooting. But that apparently produced no new information. The FBI says there have been no tips from the public about who the shooter might be and what he was doing there. The incident might have stayed a local news story, but this month, Rep. Henry Waxman, the California Democrat and ranking member of the Energy and Commerce Committee, mentioned it at a hearing on regulatory issues. "It is clear that the electric grid is not adequately protected from physical or cyber attacks," Waxman said. He called the shooting at the the San Jose facility "an unprecedented and sophisticated attack on an electric grid substation with military-style weapons. Communications were disrupted. The attack inflicted substantial damage. It took weeks to replace the damaged parts. Under slightly different conditions, there could have been serious power outages or worse." The U.S. official said the incident "did not involve a cyber attack," but that's about all investigators seem to know right now. ATT, which operates the phone network that was affected, has offered a $250,000 reward for information leading to the arrest and conviction of the perpetrator or perpetrators. "These were not amateurs taking potshots," Mark Johnson, a former vice president for transmission operations at PGE, said last month at a conference on grid security held in Philadelphia. "My personal view is that this was a dress rehearsal" for future attacks. At the very least, the attack points to an arguably overlooked physical threat to power facilities at a time when much of the U.S. intelligence community, Congress, and the electrical power industry is focused on the risk of cyber attacks. There has never been a confirmed power outage caused by a cyber attack in the United States. But the Obama administration has sought to promulgate cyber security standards that power facilities could use to minimize the risk of one. At least one senior official thinks the government is focusing too heavily on cyber attacks. Jon Wellinghoff, the chairman of the Federal Energy Regulatory Commission, said last month that an attack by intruders with guns and rifles could be just as devastating as a cyber attack. A shooter "could get 200 yards away with a .22 rifle and take the whole thing out," Wellinghoff said last month at a conference sponsored by Bloomberg . His proposed defense: A metal sheet that would block the transformer from view. "If you can't see through the fence, you can't figure out where to shoot anymore," Wellinghoff said. Price tag? A "couple hundred bucks." A lot cheaper than the billions the administration has spent in the past four years beefing up cyber security of critical infrastructure in the United States and on government computer networks. "There are ways that a very few number of actors with very rudimentary equipment could take down large portions of our grid," Wellinghoff said. "I don't think we have the level of physical security we need." __________________
个人分类: war|2 次阅读|0 个评论
分享 Mathematics for Computer Graphics
uohuo 2013-4-25 18:35
Mathematics for Computer Graphics Greg Turk, August 1997 "What math should I learn in order to study computer graphics?" This is perhaps the most common general question that students ask me about computer graphics. The answer depends on how deeply you wish to go into the field. If you wish to begin to use off-the-shelf graphics programs then the answer is that you probably do not need to know very much math at all. If you wish to take an introductory course in computer graphics, then you should read the first two sections below for my recommendations (algebra, trigonometry and linear algebra). If you want some day to be a researcher in graphics then I believe that you should consider your mathematics education to be an ongoing process throughout your career. If you do not particularly care for mathematics, is there still a chance of working in the field? Yes, a few areas within computer graphics are not much concerned with mathematical ideas. You should not give up on graphics just because you are not a math wizard. It is likely, however, that you will have more freedom in choosing research topics if you have a willingness to learn about new mathematical ideas. There is no absolute answer to what mathematics is important in computer graphics. Different areas within the field require different mathematical techniques, and your own interests will likely lead you towards some topics and may never touch others. Below are descriptions of a number of areas in mathematics that I believe are useful in computer graphics. Do not feel that you need to be an expert in each of these areas to become a graphics researcher! I deliberately included many areas below to give a fairly broad view of the mathematical ideas used in graphics. Many researchers, however, will never find the need to look at some of the topics that I mention below. Finally, although it should be clear from reading this, the opinions given within this document are entirely my own. It is likely that you would get a different list of topics or at least different emphases from other people who work in computer graphics. Now on to the list of topics. Algebra and TrigonometryHigh-school level algebra and trigonometry are probably the most important areas to know in order to begin to learn about computer graphics. Just about every day I need to determine one or more unknowns from a simple set of equations. Almost as often I need to perform simple trigonometry such as finding the length of the edge of some geometric figure based on other lengths and angles. Algebra and trigonometry are the subjects that will solve such day-to-day tasks in computer graphics. What about the geometry that we learn in high school? It may come as a surprise, but our high school geometry is not very often needed for most tasks in computer graphics. The reason for this is that geometry as it is taught in many schools actually is a course in how to construct mathematical proofs. While proof construction is definitely a valuable intellectual tool, the actual theorems and proofs from your geometry class are not often used in computer graphics. If you go to graduate school in a mathematics related field (including computer graphics) then you may well find yourself proving theorems, but this is not necessary in order to start out in graphics. If you have a good understanding of algebra and trigonometry then you are quite prepared to begin reading an introductory book in computer graphics. Most such books contain at least an abbreviated introduction to the next important area of mathematics for computer graphics, namely linear algebra. Book recommendation: Computer Graphics: Principles and Practice James Foley, Andries van Dam, Steven Feiner, John Hughes Addison-Wesley Linear AlgebraThe ideas of linear algebra are used throughout computer graphics. In fact, any area that concerns itself with numerical representations of geometry often will collect together numbers such as x,y,z positions into mathematical objects called vectors. Vectors and a related mathematical object called a matrix are used all the time in graphics. The language of vectors and matrices is an elegant way to describe (among other things) the way in which an object may be rotated, shifted (translated), or made larger or smaller (scaled). Linear algebra is usually offered either in an advanced high school class or in college. Anyone who wishes to work in computer graphics should eventually get a solid grounding in this subject. As I mentioned before, however, many textbooks in graphics give a reasonable introduction to this topic-- often enough to get you through a first course in graphics. Book recommendation: Linear Algebra and Its Applications Gilbert Strang Academic Press CalculusKnowledge of calculus is an important part of advanced computer graphics. If you plan to do research in graphics, I strongly recommend getting a basic grounding in calculus. This is true not just because it is a collection of tools that are often used in the field, but also because many researchers describe their problems and solutions in the language of calculus. In addition, a number of important mathematical areas require calculus as a prerequisite. This is the one area in mathematics in addition to basic algebra that can open the most doors for you in computer graphics in terms of your future mathematical understanding. Calculus is the last of the topics that I will mention that is often introduced in high school. The topics to follow are almost always found in college courses. Differential GeometryThis area of mathematics studies equations that govern the geometry of smooth curves and surfaces. If you are trying to figure out what direction is perpendicular to (points directly away from) a smooth surface (the "normal vector") then you are using differential geometry. Making a vehicle travel at a particular speed along a curved path is also differential geometry. There is a common technique in graphics for making a smooth surface appear rough known as "bump mapping", and this method draws on differential geometry. If you plan to do work with curves and surfaces for shape creation (called "modeling" in the graphics field) then you should learn at least the basics of differential geometry. Multivariable calculus is the prerequisite for this area. Book recommendation: Elementary Differential Geometry Barrett O'Neill Academic Press Numerical MethodsAlmost every time we represent and manipulate numbers in the computer we use approximate instead of exact values, and because of this there is always the possibility for errors to creep in. Moreover, there are often many different approaches to solving a given numerical problem, and some methods will be faster, more accurate or require less memory than others. The study of these issues goes by a number of names including "numerical methods" and "scientific computing". This is a very broad area, and several of the other areas of mathematics that I will mention can be considered sub-areas underneath this umbrella. These sub-areas include sampling theory, matrix equations, numerical solution of differential equations, and optimization. Book recommendation: Numerical Recipes in C: The Art of Scientific Computing William Press, Saul Teukolsky, William Vetterling and Brian Flannery Cambridge University Press Sampling Theory and Signal ProcessingOver and over in computer graphics we represent some object such as an image or a surface as a collection of numbers that are stored in a regular two-dimensional array. Whenever we do this we are creating a "sampled" representation of the object. A good understanding of sampling theory is important if we are to use and to control the quality of such representations. A common issue in sampling as it applies to graphics is the jagged edges that can appear on the silhouette of an object when it is drawn on a computer screen. The appearance of such jagged edges (one form of a phenomenon known as "aliasing") is very distracting, and this can be minimized by using well-understood techniques from sampling theory. At the heart of sampling theory are concepts such as convolution, the Fourier transform, and spatial and frequency representations of functions. These ideas are also important in the fields of image and audio processing. Book recommendation: The Fourier Transform and Its Applications Ronald N. Bracewell McGraw Hill Matrix EquationsThere are a wide variety of problems that come up in computer graphics that require the numerical solution of matrix equations. Some problems that need matrix techniques include: finding the best position and orientation to match one object to another (one example of a "least squares" problem), creating a surface that drapes over a given collection of points with minimal creases (thin-plate splines), and simulation of materials such as water or cloth. Matrix formulations of problems come up often enough in graphics that I rank this area very high on my list of topics to know. Book recommendation: Matrix Computations Gene Golub and Charles Van Loan Johns Hopkins University Press PhysicsPhysics is obviously a field of study in its own right and not a sub-category of mathematics. Nevertheless, physics and mathematics are closely tied to one another in several areas within computer graphics. Examples of graphics problems that involve physics include how light interacts with the surfaces of objects, how light bounces around in a complex environment, the way people and animals move, and the motion of water and wind. Knowledge of physics is important for simulating all of these phenomena. This is closely tied to solving differential equations, which I shall discuss next. Numerical Solutions of Differential EquationsIt is my belief that techniques for solving differential equations are extremely important to computer graphics. As we just discussed, much of computer graphics is devoted to simulating physical systems from the real world. How waves form in water and how an animal walks across the ground are two examples of physical simulation. Simulation of physical systems very often leads to numerical solutions of differential equations. Note that this is actually very different than symbolic solutions to differential equations. Symbolic solutions are exact answers, and usually can be found only for extremely simple sets of equations. Sometimes a college course called "Differential Equations" will only examine symbolic solutions, and this will not help much for most computer graphics problems. In physical simulation, one breaks the world down into little pieces that are represented as large vectors. Then the relations between the parts of the world are captured in the entries in matrices. Solving the matrix equations that arise is not usually done exactly, but is instead performed by carrying out a long series of calculations that yields an approximate solution as a list of numbers. This is what numerical solutions of differential equations are about. Note that the solution of matrix equations is an intimate part of numerical solutions to differential equations. OptimizationQuite often in computer graphics we are looking for a description of an object or a collection of objects that satisfies some desired goal. Examples include looking for the positions of lights that give a certain "feeling" to how a room is lit, figuring out how an animated character can move its limbs to carry out a particular action, and positioning shapes and text on a page so that the result does not look cluttered. Each of these examples can be stated as an optimization problem. Ten years ago there was little in the graphics literature that made use of optimization techniques, but the field is using optimization more and more in recent work. I think that optimization will continue to play an increasingly important role in computer graphics. Probability and StatisticsThere are a number of areas within computer graphics that make use of probability and/or statistics. Certainly when researchers carry out studies using human subject, they require statistical methods in order to perform the analysis of the data. Graphics related areas that often make use of human subjects include Virtual Reality and Human-Computer Interaction (HCI). In addition, many computer descriptions of the real world involve using various probabilities that a given action will occur. The probability that a tree limb will branch during growth or that a synthetic animal will decide to walk in a particular direction are two examples of this. Finally, some techniques for solving difficult equations make use of random numbers to estimate their solutions. An important example of this is a class of techniques known as Monte Carlo methods that are often used to determine how light propagates in an environment. These are just a few of the ways that probability and statistics are used in computer graphics. Computational GeometryComputational geometry is the study of efficient ways to represent and manipulate geometry within the computer. Typical problems include testing whether two objects collide, deciding how to break up a polygon into triangles, and finding the nearest point in a group to a given location. This area is a blend of algorithms, data structures and mathematics. Researchers in graphics who work on creating shapes (modeling) draw heavily upon this area. Book recommendations: Computational Geometry in C Joseph O'Rourke Cambridge University Press Computational Geometry: An Introduction Franco Preparata and Michael Shamos Springer-Verlag Concluding Words: Applied and Pure MathematicsOne common thread to many of the mathematical topics that are associate with graphics is that they are from the applied side instead of the theoretical side of mathematics. This should not come as a surprise. Many of the problems in computer graphics are closely tied to problems that physicists and engineers have studied, and the mathematical tools of the physicist and of the engineer are overwhelmingly the tools that graphics researchers use. Most of the topics that make up theoretical ("pure") mathematics are seldom put to use in computer graphics. This should not be taken as an absolute truth, however. We should pay attention to examples from other fields: molecular biology is now drawing upon knot theory for the study of DNA dynamics, and subatomic physics makes use of abstract group theory. Who can tell when a "pure" mathematics topic will be put to use in computer graphics? There are a few areas of mathematics that seem as though they ought to be important and yet never really play a large part in computer graphics. Perhaps the most interesting of these areas is topology. The usual one-sentence description of topology is the study of why a doughnut and a coffee cup are the same. The answer is that they are both surfaces with one hole. Here we are talking about ideas from topology. Aren't surfaces a big part of computer graphics? Yes, but it turns out that most of the ideas in topology that are useful to graphics can be learned in a first course in differential geometry. Differential geometry studies the *shapes* of surfaces, whereas topology studies things such as which parts of a surface are next to which other parts. I have seen very little topology that is put to use in graphics, and I believe that this is because much of topology is concerned with rather abstract sets, and that much of topology is far removed from the concepts in three dimensional Euclidean space that is so central to most of graphics. There are times when the formalism of topology (the symbolic notation) is a convenient way to express ideas in graphics, but the actual tools from abstract topology so seldom play a role in graphics. Study this beautiful subject for its own sake, but don't expect an immediate payoff for graphics! I have been asked a few times whether either abstract algebra (group theory, rings, etc.) or number theory play a role in computer graphics. Not much that I have seen. These subjects, like topology, are areas that are full of beautiful ideas. Unfortunately these ideas seldom find their way into computer graphics.
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