Английский язык. Учебное пособие по развитию навыков устной речи и чтения для магистрантов технических специальностей
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2. Work in pairs or small groups. Read the text again and say whether the author is optimistic or sceptical about modern robots. Find the facts to prove your idea, then report the general idea of the group to the class. Text 8 AUTOMATED PRODUCTION LINES (ASSEMBLY LINE) 1. Read the text and answer the question. 1.What does an automated production lines consist of? How is it controlled? Where is it utilized? 2. What is a flexible manufacturing system? Name its components. 3. What is the difference between an FMS and an automated production line? An automated production line consists of a series of workstations connected by a transfer system to move parts between the stations. This is an example of fixed automation, since these lines are typically set up for long production runs, perhaps making millions of product units and running for several years between changeovers. Each station is designed to perform a specific processing operation, so that the part or product is constructed stepwise as it progresses along the line. A raw work part enters at one end of the line, proceeds through each workstation, and emerges at the other end as a completed product. In the normal operation of the line, there is a work part being processed at each station, so that many parts are being processed simultaneously and a finished part is produced with each cycle of the line. The various operations, part transfers, and other activities taking place on an automated transfer line must all be sequenced and coordinated properly for the line to operate efficiently. Modern automated lines are controlled by programmable logic controllers, which are special computers that facilitate connections with industrial equipment (such as automated production lines) and can perform the kinds of timing and sequencing functions required to operate such equipment. Automated production lines are utilized in many industries, most notably automotive industry, where they are used for processes such as machining and pressworking. Machining is a manufacturing process in which metal is removed by a cutting or shaping tool, so that the remaining work part is the desired shape. Machinery and motor components are usually made by this process. In many cases, multiple operations are required to completely shape the part. If the part is mass-produced, an automated transfer line is often the most economical method of production. The many separate operations are divided among the workstations. Transfer lines date back to about 1924. Pressworking operations involve the cutting and forming of parts from sheet metal. Examples of such parts include automobile body panels, outer shells of major appliances (e.g., laundry machines and ranges), and metal furniture (e.g., desks and file cabinets). More than one processing step is often required to complete a complicated part. Several presses are connected together in sequence by handling mechanisms that transfer the partially completed parts from one press to the next, thus creating an automated pressworking line. Flexible manufacturing systems A flexible manufacturing system (FMS) is a form of flexible automation in which several machine tools are linked together by a material-handling system, and all aspects of the system are controlled by a central computer. An FMS is distinguished from an automated production line by its ability to process more than one product style simultaneously. At any moment, each machine in the system may be processing a different part type. An FMS can also cope with changes in product mix and production schedule as demand patterns for the different products made on the system change over time. New product styles can be introduced into production with an FMS, so long as they fall within the range of products that the system is designed to process. This kind of system is therefore ideal when demand for the products is low to medium and there are likely to be changes in demand. The components of an FMS are (1) processing machines, which are usually CNC machine tools that perform machining operations, although other types of automated workstations such as inspection stations are also possible, (2) a material-handling system, such as a conveyor system, which is capable of delivering work parts to any machine in the FMS, and (3) a central computer system that is responsible for communicating NC part programs to each machine and for coordinating the activities of the machines and the material-handling system. In addition, a fourth component of an FMS is human labour. Although the flexible manufacturing system represents a high level of production automation, people are still needed to manage the system, load and unload parts, change tools, and maintain and repair the equipment. Text 9 STATISTICAL MECHANICS 1. Answer the following questions on the text. 1) Can you explain what statistical mechanics deals with? 2) How was it developed? 3) Describe the difference in the nature of particles from a position of quantum theory and classical physics. 4) Why do we need two formulations of quantum statistical mechanics? Statistical Mechanics, in physics, field that seeks to predict the average properties of systems that consist of a very large number of particles. Statistical mechanics employs principles of statistics to predict and describe particle motion. Statistical mechanics was developed in the 19th century, largely by British physicist James Clerk Maxwell, Austrian physicist Ludwig Boltzmann, and American mathematical physicist J. Willard Gibbs. These scientists believed that matter is composed of many tiny particles (atoms and molecules) in constant motion. These scientists knew that determining the motions of the particles by assuming each particle individually obeys Newtonian mechanics is unworkable, because any sample of matter contains an enormous number of particles. For example, a cubic foot of air contains about a trillion trillion (1 followed by 24 zeroes) particles. Rather than dealing with all of these microscopic particles individually, Maxwell, Boltzmann, and Gibbs developed statistical techniques to average the microscopic dynamics of individual particles and obtain their macroscopic (large-scale) thermodynamic features. Through their calculations they discovered that temperature is a measure of the average kinetic energy of microscopic particles. They also found that entropy is proportional to the logarithm of the number of ways a given macroscopic system can be microscopically arranged. Statistical mechanics had to be extended in the 1920s to incorporate the new principles of quantum theory. The nature of particles is regarded differently in quantum theory than in classical physics, which is based on Newton's laws of motion. In particular, two classical particles are in principle distinguishable; just as two cue balls can be distinguished by placing an identifying mark on one, so in principle can classical particles. In contrast, two identical quantum particles are indistinguishable, even in principle, requiring new formulations of statistical mechanics. Furthermore, there are two quantum mechanical formulations of statistical mechanics corresponding to the two types of quantum particles—fermions and bosons. The formulation of statistical mechanics designed to describe the behavior of a group of classical particles is called Maxwell-Boltzmann (MB) statistics. The two formulations of statistical mechanics used to describe quantum particles are Fermi-Dirac (FD) statistics, which applies to fermions, and Bose-Einstein (BE) statistics, which applies to bosons. Two formulations of quantum statistical mechanics are needed because fermions and bosons have significantly different properties. Fermions – particles that have odd half-integer spin – obey the Pauli exclusion principle, which states that two fermions cannot be in the same quantum mechanical state. Some examples of fermions are electrons, protons, and helium-3. On the other hand, bosons – particles that have integer spin – do not obey the Pauli exclusion principle. Some examples of bosons are photons and helium-4. While only one fermion at a time can be in a particular quantum mechanical state, it is possible for multiple bosons to be in a single state. The phenomenon of superconductivity dramatically illustrates the differences between systems of quantum mechanical particles that obey Bose-Einstein statistics instead of Fermi-Dirac statistics. At room temperature, electrons, which have spin , are distributed among their possible energy states according to FD statistics. At very low temperatures, the electrons pair up to form spin-0 Cooper electron pairs, named after the American physicist Leon Cooper. Since these electron pairs have zero spin, they behave as bosons, and promptly condense into the same ground state. A large energy gap between this ground state and the first excited state ensures that any current is «frozen in». This causes the current to flow through without resistance, which is one of the defining properties of superconducting materials. Text 10 FRICTION 1. Answer the following questions on the text. 1) Why does friction occur? 2) Give some examples of friction from your everyday life. 3) When is it necessary to use friction effect? 4) When is it necessary to reduce it? Introduction Friction, force that opposes the motion of an object when the object is in contact with another object or surface. Friction results from two surfaces rubbing against each other or moving relative to one another. It can hinder the motion of an object or prevent an object from moving at all. The strength of frictional force depends on the nature of the surfaces that are in contact and the force pushing them together. This force is usually related to the weight of the object or objects. In cases involving fluid friction, the force depends upon the shape and speed of an object as it moves through air, water, or other fluid. Friction occurs to some degree in almost all situations involving physical objects. In many cases, such as in a running automobile engine, it hinders a process. For example, friction between the moving parts of an engine resists the engine’s motion and turns energy into heat, reducing the engine’s efficiency. Friction also makes it difficult to slide a heavy object, such as a refrigerator or bookcase, along the ground. In other cases, friction is helpful. Friction between people’s shoes and the ground allows people to walk by pushing off the ground without slipping. On a slick surface, such as ice, shoes slip and slide instead of gripping because of the lack of friction, making walking difficult. Friction allows car tires to grip and roll along the road without skidding. Friction between nails and beams prevents the nails from sliding out and keeps buildings standing. When friction affects a moving object, it turns the object’s kinetic energy, or energy of motion, into heat. People welcome the heat caused by friction when rubbing their hands together to stay warm. Frictional heat is not so welcome when it damages machine parts, such as car brakes. Causes of friction Friction occurs in part because rough surfaces tend to catch on one another as they slide past each other. Even surfaces that are apparently smooth can be rough at the microscopic level. They have many ridges and grooves. The ridges of each surface can get stuck in the grooves of the other, effectively creating a type of mechanical bond, or glue, between the surfaces. Two surfaces in contact also tend to attract one another at the molecular level, forming chemical bonds. These bonds can prevent an object from moving, even when it is pushed. If an object is in motion, these bonds form and release. Making and breaking the bonds takes energy away from the motion of the object. Scientists do not yet fully understand the details of how friction works, but through experiments they have found a way to describe frictional forces in a wide variety of situations. The force of friction between an object and a surface is equal to a constant number times the force the object exerts directly on the surface. The constant number is called the coefficient of friction for the two materials and is abbreviated µ. The force the object exerts directly on the surface is called the normal force and is abbreviated N. Friction depends on this force because increasing the amount of force increases the amount of contact that the object has with the surface at the microscopic level. The force of friction between an object and a surface can be calculated from the following formula: F = µ × N In this equation, F is the force of friction, µ is the coefficient of friction between the object and the surface, and N is the normal force. Scientists have measured the coefficient of friction for many combinations of materials. Coefficients of friction depend on whether the objects are initially moving or stationary and on the types of material involved. The coefficient of friction for rubber sliding on concrete is 0.8 (relatively high), while the coefficient for Teflon sliding on steel is 0.04 (relatively low). The normal force is the force the object exerts perpendicular to the surface. In the case of a level surface, the normal force is equal to the weight of the object. If the surface is inclined, only a fraction of the object’s weight pushes directly into the surface, so the normal force is less than the object’s weight. Effects of friction Friction helps people convert one form of motion into another. For example, when people walk, friction allows them to convert a push backward along the ground into forward motion. Similarly, when car or bicycle tires push backward along the ground, friction with the ground makes the tires roll forward. Friction allows us to push and slide objects along the ground without our shoes slipping along the ground in the opposite direction. While friction allows us to convert one form of motion to another, it also converts some energy into heat, noise, and wear and tear on material. Losing energy to these effects often reduces the efficiency of a machine. For example, a cyclist uses friction between shoes and pedals, the chain and gears, and the bicycle’s tires and the road to make the bicycle move forward. At the same time, friction between the chain and gears, between the tires and the road, and between the cyclist and the air all resist the cyclist’s motion. As the cyclist pedals, friction converts some of the cyclist’s energy into heat, noise, and wear and tear on the bicycle. This energy loss reduces the efficiency of the bicycle. In automobiles and airplanes, friction converts some of the energy in the fuel into heat, noise, and wear and tear on the engine’s parts. Excess frictional heat can damage an engine and braking system. The wearing away of material in engines makes it necessary to periodically replace some parts. Sometimes the heat that friction produces is useful. When a person strikes a match against a rough surface, friction produces a large amount of heat on the head of the match and triggers the chemical process of burning. Static friction, which prevents motion, does not create heat. Reducing friction Reducing the amount of friction in a machine increases the machine’s efficiency. Less friction means less energy lost to heat, noise, and wearing down of material. People normally use two methods to reduce friction. The first method involves reducing the roughness of the surfaces in contact. For example, sanding two pieces of wood lessens the amount of friction that occurs between them when they slide against one another. Teflon creates very little friction because it is so smooth. Applying a lubricant to a surface can also reduce friction. Common examples of lubricants are oil and grease. They reduce friction by minimizing the contact between rough surfaces. The lubricant’s particles slide easily against each other and cause far less friction than would occur between the surfaces. Lubricants such as machine oil reduce the amount of energy lost to frictional heating and reduce the wear damage to the machine surfaces caused by friction. Text 11 COMPUTER CACHES 1. Answer the following questions on the text. 1) What is the fastest and the slowest thing in your computer? Why is it so? 2) How can you explain the notion «cache»? Read the text and check your ideas. A computer is a machine in which we measure time in very small increments. When the microprocessor accesses the main memory (RAM), it does it in about 60 nanoseconds (60 billionths of a second). That's pretty fast, but it is much slower than the typical microprocessor. Microprocessors can have cycle times as short as 2 nanoseconds, so to a microprocessor 60 nanoseconds seems like an eternity. What if we build a special memory bank, small but very fast (around 30 nanoseconds)? That's already two times faster than the main memory access. That's called a level 2 cache or an L2 cache. What if we build an even smaller but faster memory system directly into the microprocessor's chip? That way, this memory will be accessed at the speed of the microprocessor and not the speed of the memory bus. That's an L1 cache, which on a 233-megahertz (MHz) Pentium is 3.5 times faster than the L2 cache, which is two times faster than the access to main memory. There are a lot of subsystems in a computer; you can put cache between many of them to improve performance. Here's an example. We have the microprocessor (the fastest thing in the computer). Then there's the L1 cache that caches the L2 cache that caches the main memory which can be used (and is often used) as a cache for even slower peripherals like hard disks and CD-ROMs. The hard disks are also used to cache an even slower medium – your Internet connection. Your Internet connection is the slowest link in your computer. So your browser (Internet Explorer, Netscape, Opera, etc.) uses the hard disk to store HTML pages, putting them into a special folder on your disk. The first time you ask for an HTML page, your browser renders it and a copy of it is also stored on your disk. The next time you request access to this page, your browser checks if the date of the file on the Internet is newer than the one cached. If the date is the same, your browser uses the one on your hard disk instead of downloading it from Internet. In this case, the smaller but faster memory system is your hard disk and the larger and slower one is the Internet. Cache can also be built directly on peripherals. Modern hard disks come with fast memory, around 512 kilobytes, hardwired to the hard disk. The computer doesn't directly use this memory – the hard-disk controller does. For the computer, these memory chips are the disk itself. When the computer asks for data from the hard disk, the hard-disk controller checks into this memory before moving the mechanical parts of the hard disk (which is very slow compared to memory). If it finds the data that the computer asked for in the cache, it will return the data stored in the cache without actually accessing data on the disk itself, saving a lot of time. Here's an experiment you can try. Your computer caches your floppy drive with main memory, and you can actually see it happening. Access a large file from your floppy – for example, open a 300-kilobyte text file in a text editor. The first time, you will see the light on your floppy turning on, and you will wait. The floppy disk is extremely slow, so it will take 20 seconds to load the file. Now, close the editor and open the same file again. The second time (don't wait 30 minutes or do a lot of disk access between the two tries) you won't see the light turning on, and you won't wait. The operating system checked into its memory cache for the floppy disk and found what it was looking for. So instead of waiting 20 seconds, the data was found in a memory subsystem much faster than when you first tried it (one access to the floppy disk takes 120 milliseconds, while one access to the main memory takes around 60 nanoseconds – that's a lot faster). You could have run the same test on your hard disk, but it's more evident on the floppy drive because it's so slow. To give you the big picture of it all, here's a list of a normal caching system: 1) L1 cache – Memory accesses at full microprocessor speed (10 nanoseconds, 4 kilobytes to 16 kilobytes in size) 2) L2 cache – Memory access of type SRAM (around 20 to 30 nanoseconds, 128 kilobytes to 512 kilobytes in size) 3) Main memory – Memory access of type RAM (around 60 nanoseconds, 32 megabytes to 128 megabytes in size) 4) Hard disk – Mechanical, slow (around 12 milliseconds, 1 gigabyte to 10 gigabytes in size) 5) Internet - Incredibly slow (between 1 second and 3 days, unlimited size) As you can see, the L1 cache caches the L2 cache, which caches the main memory, which can be used to cache the disk subsystems, and so on. |