Английский / Английский язык.2 курс

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2.He moved across the room to the box. He (pick) up a piece of paper that (lie) beside the box, (study) it carefully, (put) it down, (look) in the box, and then again at the paper. He (do) this for perhaps half an hour. He not (know) who (write) the paper.

3.Mary took his coat and (hang) it in the hall. They not (meet) for quite a long time. Then she (make) the drinks, the way he (teach) her, and soon he (tell) her the news which she not (hear) yet. Every day she took her grandchildren for walks. They (be) so beautiful! She (feed) them cakes, and (buy) them presents, and (tell) them charming stories. Those walks (become) a tradition with them.

4.I n the middle of the night Mary woke up. A heavy rain (start) falling again and the wind (blow) hard round the walls of the old house. Suddenly she (hear) the crying that she (hear) the night before. This time she decided to discover who it (be).

5.She (leave) her room and (go) to the other side of the house. At last she (find) the right room. She (push) the door open and (see) a big room with beautiful old furniture and pictures. A boy (lie) in a large bed. He (look) tired and cross. He stared at Mary. «Who you (be)? You (be) a dream?» he whispered.

6.«I (be) your second cousin, and your father (be) my uncle,» Mary explained. «I (hear) that you are ill. Your father often (come) and see you?» – «Not often. He not (like) to see me because it (make) him (remember) my mother. She (die) when I (bear), so he almost (hate) me, I think».

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A Night Accident

One night I (wake up) in the middle of the night as I (hear) a slight noise. I (feel) sure that someone (stand) outside my bedroom door. I was awfully sorry now that I not (lock) it before going to bed. As I (hurry) to lock it, I called «Who's there?» There was a strange sound, then I heard that someone (run) upstairs. My curiosity made me (open) the door, and I (find) the corridor full of smoke which (come) from Mr. Rochester's room. I understood that someone (set) lire to the house. I (forget) all my fears and (run) into the master's room. He (sleep). Everything around him was in flames and smoke. I (throw) some water to wake him up and to put out the flames. I explained what I (see). He (think) for a few seconds. «Jane, I (watch) you all this time, and I can't help admiring you!» he (say). «If we not (hurry) now, it (be) too late. I (call) the servants, sir?» I asked. «No, not (do) it», he answered. «If Adele (hear) something and (wake) up, she (frighten). I am glad that you are the only person who (know) about it. And thank you! You (save) my life a second time».

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Computer science

Computer science has roots in electrical engineering, mathematics, and linguistics. In the last third of the 20th century computer science emerged as a distinct discipline and developed its own methods and terminology. Most universities today have specific departments devoted to computer science, while some conjoin it with engineering. The fundamental question underlying all the computing is «What can be (efficiently) automated?»

The name «computer science» immediately gives the impression that the field is the study of computers, the everyday machines that run programs and perform computations. Nonetheless, the field (as noted above) is both wider and more abstract than this name would suggest. Alternate names such as «computation science» have been proposed but the traditional name remains the most common.

In French, the discipline is named informatique, in Spanish informatica, in German Informatik, in Polish informatika, in Russian информатика , and in Dutch informatica. However, informatics in English is not directly synonymous with computer science; it is actually more equivalent with information theory.

Computer

A computer is a device or machine for making calculations or controlling operations that are expressible in numerical or logical terms. Computers are made from components that perform simple well-defined functions. The complex interactions of these components endow computers with the ability to process information. If correctly configured (usually by programming) a computer can be made to represent some aspect of a problem or part of a system. If a computer configured in this way is given appropriate input data, then it can automatically solve the problem or predict the behavior of the system. The discipline which studies the theory, design, and application of computers is called computer science.

General-purpose computers

By definition a general-purpose computer can solve any problem that can be expressed as a program and executed within the practical limits set by: the storage capacity of the computer, the size of program, the speed of program execution, and the reliability of the machine. In 1934 Alan Turing proved that, given the right program, any general-purpose computer could emulate the behavior of any other computer. This mathematical proof was purely theoretical as no general-purpose computers existed at the time. The implications of this proof are profound; for example, any existing general-purpose computer is theoretically able to emulate, albeit slowly, any general-purpose computer that may be built in the future.

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Computers with general-purpose capabilities are called Turing-complete and this status is often used as the threshold capability that defines modern computers, however, this definition is problematic. Several computing devices with simplistic designs have been shown to be Turing-complete. The Z3, developed by Konrad Zuse in 1941 is the earliest working computer that has been shown to be Turing-complete, so far (the proof was developed in 1998). While the Z3 and possibly other early devices may be theoretically Turing-complete they are impractical as general-purpose computers. They lie in what is humorously known as the Turing Tar-Pit – «a place where anything is possible but nothing of interest is practical».

Robot programming

The setup or programming of motions and sequences for an industrial robot is typically taught by linking the robot controller via communication cable to the Ethernet, FireWire, USB or serial port of a laptop computer. The computer is installed with corresponding interface software. The use of a computer greatly simplifies the programming process. Robots can also be taught via teaching pendant, a handheld control and programming unit. The teaching pendant or PC is usually disconnected after programming and the robot then runs on the program that has been installed in its controller. In addition, machine operators often use «HMI» human-machine-interface devices, typically touch screen units, which serve as the operator control panel. The operator can switch from program to program, make adjustments within a program and also operate a host of peripheral devices that may be integrated within the same robotic system. These peripheral devices include robot end effectors which are devices that can grasp an object, usually by vacuum, electromechanical or pneumatic devices. Also emergency stop controls, machine vision systems, safety interlock systems, bar code printers and an almost infinite array of other industrial devices are accessed and controlled via the operator control panel.

Computer systems

Computer systems have been classed into 3 generations. The first generation consisted of vacuum-tube-based machines. They used magnetic drums for internal storage and magnetic tape for external storage. These computers were slow compared to modern machines and, owing to their bulk, they required data to be brought to them.

Second-generation computers using transistors began to appear in 1959. The internal storage used magnetic cores, with small doughnuts of magnetic material wired into frames that were stacked into large cores. This form of storage represented a tremendous increase in speed and reduction in bulk over previous storage methods. The external storage in second-generation computers used magnetic disks.

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Beginning in 1964, a third generation of computers began to emerge. These computers utilized integrated circuits to increase capability and decrease size, while integrated technology also provided improved internal storage capability.

Solid-state memory, being now totally electronic, greatly increased the speed and capacity of the internal memory. External memory continued to use magnetic disks, which became larger and faster.

The first electronic computer

The first fully electronic computer was developed at the University of Pennsylvania by Dr. John Mauchly and J. Presper Eckert, Jr. The computer used 18,000 electron tubes to make and store its calculations. Called the Electronic Numerical Integrator and Calculator (ENIAC), this device could, in 1946, multiply 300 numbers per second. As fast as ENIAC was, however, the lack of external control and the bulk and power consumption resulting from the use of vacuum tubes precluded large-scale production.

The direct-current machine

Electrical machines are divided into alternating current (a. c.) and directcurrent (d. c.) machines. The basic parts of a d. c. machine are the armature and electromagnets (or field coils). Coils would on the pole cores form the excitation field of the machine. The armature is the rotating part of the machine. In its insulated slots is placed a winding connected to the commutator. Carbon brushes are placed in brushholders and contact the rotating commutator.

There are 2 electric circuits in the d.c. machine, the armature circuits and the excitation circuit. A d. c. machine is reversible: if the machine is rotated and the magnetic field is excited the machine sends a direct current into the external circuit through the commutator and brushes: the machine operates as a generator.

If the armature and excitation winding are joined to a d. c. circuit the armature runs and the machine operates as a motor and converts electrical energy into mechanical energy.

Inspecting the electrical equipment

During installation, the machine must be reliably earthed and connected to general earthing system of the shop.

Before inspecting the electrical equipment, disconnect the machine from the power supply.

Clean the motors and other electrical devices from dust and durt. Never clean the motor windings with benzine or kerosene, for they corrode the insulation and reduce the service life of a motor. Once a year dismantle and clean the motors.

Wash the motor bearings in benzine and change their lubricant at least twice a year.

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Attending to the magnetic contacts clean their parts from dust and durt. Worn parts must be replaced without delay.

The contacts should not be greased as this reduces their service life.

Cement

The requirements to be fulfilled by concrete vary to a great extend. One of the essential properties of concrete is its compressive strength. From the time of its first production more than a century ago there was a steady and gradual improvement in the compressive strength of Portland cement until the beginning of the war. With the cements now available much higher strength can be obtained than some 30 or 40 years ago. The increase in strength is partly due to the increased fineness to which modern cements are ground.

Cement develops heat during hydration. This is of considerable important in certain types of concrete construction, particularly in structures of large volume, such as dams, massive retaining walls and the like. A very high rate of heat development is advantageous in work done in cold weather, so as to protect the fresh concrete from the effect of low temperatures.

Selection of the cement alone does not ensure concrete with the properties desired, which depends also on the choice of aggregates and mixes, the control of the quantity of water added to the mix, and on a series of other factors.

History of building materials

All the buildings erected nowadays are of two main types: they are intended either for housing or industrial purposes.

The main building materials are timber, stone, brick, concrete, steel, light metals, glass and plastics. Timber was one of the first materials to be used by man for constructional purposes. It is highly probable that it will be available when the earth’s capital deposits of iron, coal, clay and the rest have been consumed.

The buildings made of stone or brick are durable and fireproof, they have a poor heat conductivity.

Concrete made with natural hydraulic binders was used in antiquity, particularly by the Romans. After the decline of the Roman Empire the art of making concrete has been forgotten and the revival came much later.

Hydraulic cement

In the general sense, a cement (Latin caementum) is any material with adhesive properties. The term cement is also commonly used to refer more specifically to powdered materials which develop strong adhesive qualities when combined with water. These materials are more properly known as hydraulic cements. Gypsum plaster, common lime, hydraulic limes, natural pozzolana and

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Portland cements are the more common hydraulic cements, with Portland cement being the most important in construction.

Hydraulic cement was first invented by the Egyptians, and later reinvented by the Greeks and Babylonians, who made their mortar out of lime, much harder than the Roman mortars. Later, the Romans produced good cement from pozzolanic ash.

Portland cement

Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete and mortar. It consists of a mixture of oxides of calcium, silicon and aluminum. Portland cement and similar materials are made by heating limestone (as source of calcium) with clay or sand (as source of silicon) and grinding the product. The resulting powder, when mixed with water, will become a hydrated solid over time.

Manufacture of Portland cement requires the burning of large quantities of fuel, typically coal or natural gas, which along with impurities contained in the limestone can result in significant emissions of pollutants regulated in many countries, including greenhouse gases such as nitrogen oxides, sulfur dioxide, and carbon monoxide. Cement plants are known to emit substantial quantities of arsenic, lead and mercury.

Portland cement was first manufactured in Britain in the early part of the 19th century, and its name is derived from its similarity to Portland Stone, a type of building stone that was quarried on the Isle of Portland in Dorset, England. The patent for Portland cement was issued to Joseph Aspdin, a British bricklayer, in 1824.

Concrete

Concrete is a composite building material made from the combination of aggregate (composite) and a binder such as cement. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. It is commonly believed that concrete dries after mixing and placement. Actually, concrete does not solidify because water evaporates, but it is cement that hydrates, gluing the other components together and eventually creating a stone-like material. Concrete is used for building foundations, freeways, parking structures, bases for gates and fences, etc.

When used in the generic sense, this is the material referred to by the term concrete. As concrete has a rather low tensile strength, it is generally strengthened by using steel rods or bars (known as rebars). This strengthened concrete is then referred to as reinforced concrete. In order to minimize any air bubbles (that would weaken the structure), a vibrator is used to eliminate any air that has been entrained when the liquid concrete mix is poured around the ironwork.

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Mechanical engineering

Mechanical engineering is the application of physical principles to the creation of useful devices, objects and machines. Mechanical engineers use principles such as heat, force, and the conservation of mass and energy to analyze static and dynamic physical systems, in contributing to the design of things such as automobiles, aircraft, and other vehicles, heating and cooling systems, household appliances, industrial equipment and machinery, weapons systems, etc.

Fundamental subjects of mechanical engineering include: dynamics, statics, strength of materials, heat transfer, fluid dynamics, solid mechanics, control theory, pneumatics, hydraulics, kinematics, applied thermodynamics. Related disciplines include: electrical engineering, industrial engineering, systems engineering, civil engineering, nuclear engineering, aerospace engineering, and other engineering disciplines.

Mechanical engineers often create simulations of the operation of objects, as well as the manufacturing processes to be used, in order to optimize performance, cost effectiveness, and energy efficiencies, before settling on a particular design.

Machine tools

A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by the removal of metal. The term machine tool is usually reserved for tools that used a power source other than human movement. Machine tools can be powered from a variety of sources. Human and animal power are options, as is energy captured through the use of waterwheels. However, machine tools really began to develop after the development of the steam engine, leading to the Industrial Revolution. Today, most are powered by electricity.

Machine tools can be operated manually, or under automatic control. Early machines used flywheels to stabilize their motion and had complex systems of gears and levers to control the machine and the piece being worked on. Soon after World War II, the NC, or numerical control, machine was developed. NC machines used a series of numbers punched on paper tape or punch cards to control their motion. In the 1960s, computers were added to give even more flexibility to the process. Such machines became known as CNC, or computer numerical control, machines. NC and CNC machines could precisely repeat sequences over and over, and could produce much more complex pieces than even the most skilled tool operators.

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Tools

The machine can be employed for performing, drilling, tapping, milling and boring operations, and numerical control on the x, y, and z axes is provided by Bosch equipment. If required, a hydraulic horizontal-spindle indexing table can be mounted on the main table to enable machining operations to be performed on several workpiece surfaces at one set up. Indexing can be carried out under manual or numerical control, and provision can be made for obtaining fixed or variable positions.

A circular magazine for storing cutting tools vertically is mounted beneath the spindle head, and it can be indexed in either direction by a hydraulic motor. When the magazine is viewed from above, cutting tools are loaded at about the 3 o’clock position which is in line with the main spindle. Tools are selected for operation in the required sequence, by means of a coding system, and for the changing operation, the spindle is traversed downwards rapidly to bring the nose end into engagement with the short taper shank on the cutter.

Machine tools

Machine tools are stationary power-driven machines used to shape or form solid materials, especially metals. The shaping is made by removing material from a workpiece or by pressing it into the desired shape. Machine tools form the basis of modern industry and are used either directly or indirectly in the manufacture of machine and tool parts.

Machine tools may be classified under three main categories: conventional chip-making machine tools; presses; and unconventional machine tools. Conventional chip-making tools shape the workpiece by cutting away the unwanted portion in the form of chips. Presses employ a number of different shaping processes, including shearing, pressing, or drawing (elongating). Unconventional machine tools employ light, electrical and chemical energy; superheated gases; and high-energy particle beams to shape the exotic materials and alloys that have been developed to meet the needs of modern technology.

The machine is arranged with the spindle head traveling vertically on a column which in turn travels on a saddle in the direction of the spindle axis, and the third axis of movement is obtained by the saddle traveling on the bed. A particular feature of this machine is that the spindle housing can be swiveled under tape command to bring the spindle itself to the horizontal or vertical position as required. With this arrangement, machining can be carried out on the top as well as the side faces of the work at one cycle.

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Electric arc welding

This is a fusion-welding process in which surfaces to be joined are fused by the heat of an electric arc. By bringing the work and the electrode together as conductors, an electric circuit is established; then, by separating the conductors, an electric arc is created in which the electrical energy is converted into heat.

Electric are welding is widely used in the construction of many products, ranging from steamships, tanks, locomotives, and automobiles to small household appliances. Arc welding machines today are designed to join light and heavy gage metals of all kinds. The process of arc welding is not only simplifies the maintenance and manufacture of goods and machines, but it permits the skilled operator to perform welding operations quickly and easily.

Electrical terms

To understand the correct operation of an electric arc welding machine, you must know something about a few basic electrical terms and principles. The following are especially important:

Circuit. A circuit is the path along which electricity flows. It starts from the negative terminal of the generator, where the current is produced, moves along the wire or cable to the load or working source, and then returns to the positive terminal.

Amperes. Amperes (abbreviated amp. or amps.) refers to the amount or rate of current that flows in a circuit. The instrument that measures this rate is called an ammeter.

Voltage. The force that causes electrons to flow in a circuit is known as voltage. This force is similar to the pressure used to make water flow in pipes. In a water system, the pump provides the pressure, whereas in an electrical circuit the generator or transformer produced the force that pushes the current through the wires. This force is measured in volts and the instrument used to measure is called a voltmeter.

Direct and alternating current

There are two kinds of current used in arc-welding-direct and alternating. In direct current, called DC, the current flows constantly in one direction. With alternating current, known as AC, the current reverses its direction in the circuit a certain number of times per second. The rate of change is called frequency.

An arc-welding machine that furnishes AC current is known as an AC arc welder and one that furnishes DC current is called a DC welder.

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Importance of welding and types of welding processes

Welding is playing an important role in the expansion and production of our industries. Welding has become one of the principal means of fabricating and repairing metal products. It is almost impossible to name an industry, large or small, that does not employ some type of welding. Industry has found that welding is an efficient, dependable, and economical means of joining metal in practically all metal fabricating operations. If, today, all welding should cease, practically all industry dependent upon mechanical operation, production or maintenance, would come to a standstill within 90 days.

To-day, without exception, every metal fabricating industry uses welding. The more sophisticated, the more critical, the more difficult the joining problem – the more certain you may be that welding will be used. Modern industry increasingly demands the use of new vessels, new machines and new structures which cannot be produced economically except by welding.

Where welding is used

Many buildings, bridges, and ships are fabricated by welding; and where construction noise must be kept at a minimum, such as in the building of hospital additions, the value of welding as the chief means of joining steel sections is particularly significant.

Without welding, the aircraft industries would never be able to meet the enormous demands for planets, rockets, and missiles. Rapid progress in the exploration of outer space has been made possible by new methods and knowledge of welding metallurgy.

Welding processes are employed in the construction of television sets, refrigerators, kitchen cabinets, dishwashers and other similar products for house – hold use. As a means of fabrication welding has proved fast, dependable, and flexible. It lowers production costs by simplifying design and eliminates costly patterns and machining operations.

Welding is used extensively for the manufacture and repair of farm equipment, mining and oil machinery, machine tools, jigs and fixtures, and in the construction of boilers, furnace and railway cars.

Selection of the proper welding process

There are no had or fast rules which govern the type of welding that is to be used for a particular job. In general, the controlling factors are kind of metals to be joined, costs involved, nature of products to be fabricated, and production techniques. Some jobs are more easily accomplished by the oxyacetylene welding process whereas others are more easily done by means of arc welding.

Gas welding is used in all metal working industries and in the field as well as for plant maintenance. Because of its flexibility and mobility, it is widely