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Техника нижней прямой подачи мяча.
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Agronomical classification of crop plants.
From the agronomical standpoint, crop plants are classified according to the way or ways in which they are used. On this principle, the following classification is often used.
Cereals or Grain Crops1. It is known that a cereal may be defined as any grass grown for its edible grain. ”Grain” is a collective term for the fruit of cereals. Wheat, rye, barley, corn, oats and rice are considered to be the great cereals of the world. One should know that wheat, barley, and oats occupy by far the greatest part of the cultivated area occupied by cereals.
Legumes2 for Seed. The term ”legumes’’ may be defined as a plant of the natural family Leguminoseae. It is field beans, field peas, peanuts, cowpeas and soybeans that are the principle legumes raised for their seeds.
Forage Crops3. The term ’’forage’’ may be defined as vegetable matter utilized as feed for animals in the form of harvested hay, soilage, silage, or a pasture. Forage crops include all grasses cut for hay, legumes cut for forage, sorghum, and corn fodder.
Root Crops4. A root crop is one grown for its edible roots. In this group are found such plants as turnips, rutabagas, and various form of the beet. The sweet potato is a true root crop, whereas the potatoes is not. Many root crops such as turnips, rutabagas, mangels5 and carrots are grown far less in the United States than Canada and Europe.
1cereals or grain –зерновые культуры
3forage crops-фуражные культуры
4root crops- корнеплоды
5turnips, rutabagas, mangels- турнепс, брюква, кормовая свекла
Scab begins when tubers start forming. Initially the spots may be so small that they are not noticed. As the tuber continues to grow, the areas of these reddish brown spots also enlarge. An older tuber has too thick a protective layer on its surface to be invaded readily. In any thimbleful1of soil there may occur thousands, or even millions, of individuals belonging to the genus Streptomyces. These are actinomycetes2 which have characteristics placing them between bacteria and fungi. Not all of the Streptomyces organisms recovered from the soil can cause scab on potatoes, but many of them can. Collectively these usually are grouped under the name Streptomyces scabies. Streptomyces scabies can live on decomposing material in the soil and does not require a potato or root crop to remain alive. However, it does become more aggressive on any given crop, such as potatoes, if the same crop is grown year after year without rotation. The organism infects the tuber by means of a tiny thread that pushes directly through the tender skin of the forming potato. It slowly continues to grow until the crop is harvested. The infected areas on the potato respond at once by laying down a corky layer. As each layer is invaded by the scab organism, new cork formation takes place until a mature scab spot is produced. Scab does not develop further after the potatoes are dug, but the organism remains alive all winter in storage.
Thimbleful-небольшое количество, щепотка
The tomato is one of the most widely planted of all home garden vegetable crops. The seed should be sown in the hot-bed during February and the plants later transplanted to the field when all danger of frost has passed. A few plants of at least two varieties should be grown, one of the early sorts, such as Barliana, and the other of the later type. Where only a few plants are to be set out and space is scarce, it is best to stake and prune1 them to a single stem.
If not staked, the plants should be mulched with straw so as to keep the fruit off the soil and conserve moisture.
Young tomato plants should be kept free of weeds and grass by hosing and shallow cultivation. Deep cultivation is discouraged at all times because of the resulting root pruning and breaking of the plants. Where available without much expense, irrigation will serve to increase the yields and occasionally prolong the picking season until frost.
1stake and prune-подпирать колышком и удалять боковые веточки
Agriculture is an important branch of economy of any state. It deals with plant growing and animal breeding.
Modern agriculture in all leading countries of the world is highly equipped with machinery. Such processes as plowing, sowing and harvesting are carried out by machines. Electricity is widely used in agriculture, especially in animal husbandry. We cannot imagine modern agriculture without applying commercial fertilizers, without using herbicides against pests, without means of control diseases of plants and animals. Thus, mechanization, electrification and chemization are the most important factors of rapid development of highly productive agriculture.
Land areas used in agriculture are called agricultural lands. Not all agricultural lands are absolutely fit ones. People turn unsuitable lands into suitable by rooting up trees and bushes, by draining swamps and irrigating deserts. Land reclamation or land improvement is called melioration. Drainage and irrigation are the main components of melioration.
The need for seed testing.
A knowledge of the quality of the seed to be planted is of the highest importance to the farmer.
It is the purpose of the seed test to disclose any undesirable conditions of crop seeds that might result in failure of crops, an excessive cost of the actually good seed, or the introduction and spread of troublesome and noxious weeds. The usual laboratory test of a seed sample consists of a purity test and a germination test. In the purity test the seed is examined to determine the actual proportion of the crop seed in the sample: the quantity and kinds of other crop seeds that may be present; the quantity and kinds of weed seed; and the quantity and character of the inert matter present. The germination test shows the proportion of the pure crop seeds that may be expected to produce plants.
Symptoms: A common tuber disease2 that occurs wherever potatoes are grown, potato scab appears as superficial, dark brown, pithy patches that may be raised and "warty." These lesions may affect just a small portion of the tuber surface, or may completely cover it. Sometimes the ridged portions are in broken concentric rings.
Potato scab is caused by the bacteria-like organism Streptomyces scabies that overwinters in fallen leaves and in the soil. The organism can survive indefinitely in slightly alkaline soil but is relatively scarce in highly acid soils. It is transmitted to plants by infected seed tubers, wind and water. The organism is also spread in fresh manure, since it can survive passage through the digestive tract of animals.
S. scabies enters through pores (lenticels) in stems, through wounds, and directly through the skin of young tubers. In addition to potato, other crops infected include beets, radish, turnip, carrot, rutabaga, and parsnips. This should be kept in mind when considering a crop rotation schedule.
Note: S. scabies can survive in the soil for many years in the absence of potato.
1potato scab-парша на картофеле
2tuber disease-заболевание клубней
Lettuce is the most popular of the salad crops. It is grown on many kinds of soils from clay loams to sandy loams. Lettuce reaches its highest development on sandy loams and silt loams well supplied with organic matter and on a good well-drained muck or peat soil. Where earliness is important sandy loam is preferred because it warms up earlier than other soils.
Lettuce does not grow well on mineral soils that are strongly acid, but it is not desirable to completely neutralize the acidity by liming.
The soil for lettuce should be well drained but retentive of moisture. Thorough preparation to obtain a good seedbed is important.
The lettuce plant has a small root system, therefore the surface soil should be well supplied with nutrients. The soil should have a good supply of organic matter also. When lettuce is grown on mineral soils, manure or soil-improving crops should be used to maintain the soil in good physical conditions.
Shallow cultivation2 to control weeds is very important for lettuce as the plants cannot compete successfully with weeds. The root system is small and many of the roots are near the surface, therefore cultivation should be shallow.
1 lettuce-cалат- латук
2 shallow cultivation-неглубокое возделывание
Wheat is one of the leading crops of the eastern United States. This region is made up of eastern Texas, eastern Oklahoma, eastern Kansas, southeastern Nebraska, Iowa, southern Wisconsin, and all States to the east, and produces about one-fifth of the country’s wheat.
More than 75 distinct varieties of wheat are grown on a commercial scale in this region. Soft red winter varieties predominate, but white winter wheat is grown extensively in New York and Michigan, and hard red winter varieties are grown in Iowa, northern Illinois, northwestern Indiana, and southern Wisconsin, primarily because of their greater winter hardiness.
This wheat is grown largely as a supplement to other crops. It fits well into rotations and serves as an important cover crop to prevent soil erosion and leaching in the late fall, winter, and early spring, when the land would otherwise be bare. It is often grown because it can immediately be converted into cash.
A weed may be defined as ’’a plant out of place’’ or ’’a plant growing where it is not desired’’. It follows that a plant may be a weed in some places and not in others. For example, Bermuda grass, which is considered one of the most noxious weeds in places, where it is not desired in certain parts of the South is the most valuable pasture grass. Some plants are considered weeds wherever they grow, as they do not seem to serve a useful purpose anywhere. Some of our most useful plants, however, have been considered worthless weeds in the past. As late as 1893, laws were passed in Wisconsin (US) to prevent the spread of sweat clover, which was classed as a weed pest.
A weed has other characteristics that classify it than the place where it is growing. In the first place, a weed has no economical use. This does not imply that an economic use may not some day be discovered, but until it is the plant should continue to be called a weed.
The cost of weeds to the farmers is enormous as weeds (1) reduce crop yields, (2) increase the expense (cost) of cultivation and harvest, (3) reduce the market value of crops, (4) harbor fungi and insect pests that attack adjacent crops, (5) poison or injure man, livestock, or livestock products.
The science of building is Architecture. Any engineer cannot take a form of the building without consideration of structural principles, materials, social and economic requirements. So a building cannot be considered as a work of architecture. From the very beginning architecture of many skills, systems and theories have been used for the construction of the buildings that men have housed in all their essential activities. The coexistence of change and survival1 is evident in all phases of the human story. This change and repetition is clearly illustrated in any architectural style. The historical background of architecture is the value of our cultural heritage. The heritage2 of the past cannot be ignored. Such recognition of continuity does not imply repetition or imitation. It must be expressed in contemporary terminology.
Writing on architecture is almost as old as writing itself. There are a lot of books on the theory of architecture, on the art of a building and on the aesthetic appearance3 of buildings. The oldest book is a work of Marcus Vitruvius Pollio, written in the first century B.C. Nearly two thousand years ago the Roman architect Vitruvius set the principles upon which buildings should be designed and aims to guide the architect. He was the first who listed three basic factors in architecture — "convenience, strength and beauty". The sequence of these three basic aims — "convenience, strength and beauty" — has its own significance. These three factors are always present and are always interrelated in the best structures. It is impossible for a true architect to think of one of them without considering the other two as well. Thus architectural design entails a consideration of the constant interaction of these factors. At last we can say that every element in a building has a triple implication. At the same time its contemporary expression4 must be creative and consequently new.
Architecture is an art. The triple nature of architectural design is one of the reasons why architecture is a difficult art. The architect does not first plan a building from the point of view of convenience, then designs around his plan a strong construction to shelter it, and finally adjusts and decorates the whole to make it pretty. It takes him a special type of imagination as well as long years of training and experience to produce a designer capable of making the requisite in the light of these three factors — "use, construction, aesthetic effect" — simultaneously. First of all, the designer must have sufficient knowledge of engineering, building materials to enable him to create economically. I see any building is built because of some definite human need. The use problem — "convenience" — is therefore primary5. In addition, the designer must possess the creative imagination which will enable him to integrate the plan and the construction into one harmonious whole. The architect's feeling of satisfaction in achieving such as integration is one of his greatest rewards.
We can not ignore the heritage1 of the past. There are different styles and kinds of architecture in the past around the world. It is not a secret, that various cultures have left their imprint on history through their great monuments and buildings, great castles and cathedrals. The oldest monuments which are met within architecture are great structures such as Egyptian pyramids, the Parthenon in Athens, the Roman Pantheon, and Hagia Sophia in the "New Rome", Constantinople, great castles and cathedrals of the Middle Ages, the palaces of the Renaissance2 and the civil engineering infrastructure of the industrial revolution. Great architects and engineers followed an integrated process of conception, design and construction. This integrated construction process persisted through the end of the nineteenth century, when the Roebling family (John, Washington, and Emily) designed and built the Brooklyn Bridge.
It is necessary to select materials, a type, a size and a configuration to carry loads in a safe and serviceable fashion. The architects and engineers mobilize the resources needed to realize the final structure. This classical approach is used to build. In general, structural design implies engineering of stationary objects such as buildings and bridges, objects that may be mobile but have a rigid shape such as ship hulls and aircraft frames. But it is an area of mechanical design, to which devices are generally assigned. These are devices with parts planned to move with relation to each other.
First of all, the value of true architecture lies in the direct effect of the structure itself. It depends on many reasons. One of them is a drawing1. Drawings are works of architecture. An architect uses drawings to achieve his objective. In fact, drawings can represent buildings only on paper. It is called "paper architecture". We mean the result of architect's thinking of drawings. But, there is a danger of "paper architecture". The architect mustn't forget that many elements which look well on a drawing may be either completely ineffective or definitely harmful2in the actual building.
For example, it is electric architecture. Electric buildings are full of decorative elements which look well on the drawing. Perhaps even seem necessary on the drawing. But in the actual buildings they are completely meaningless3. An architect is able to see variations of a plan, of color and a shade. Each of these variations is due to the effects of light on the building materials employed. The architect must always study each detail from the viewpoints of both use and appearance4 as well as from that of construction. He must not see it as an isolated detail but as an individual note in a great composition. A work of an architect exists only when it stands a complete, concrete object for all to see or to use.
The architect must project an integration of the whole in order to create a work of architecture. He must remember about the architect's alphabet. Knowledge of this alphabet is as essential to him as knowledge of words to the writer or of notes to the musician. The letters of the architect's alphabet are such elements as walls and openings, supports and ceilings, enclosed areas or rooms. We enter the building and our attention meets the same complexity of elements. They are doors to allow ingress and egress5; windows to admit light and air; walls for shelter or support; roofs to keep out the rain, snow, cold, and sometimes sun. A partition separates space from space. There may be stairs, escalators, or elevators to allow progress from level to level and halls or corridors to permit easy circulators from part to part Finally there may be all sorts of interior spaces for definite human activities — rooms both public and private — to take care of the varying functions of human living. No building can exist without some of them.
Any true architectural design is no mere fantasy, no unreal dream. It contemplates an actual building. There must be adequate structure for a building to exist. Then we observe the physical structure of a building outside. Next, "strength" becomes the second necessity for the construction. A true construction must stand up solidly.
Finally, mankind has always realized that buildings to be complete must have not only "convenience" and "strength", but also "beauty". Some people think that architecture is not a fine art at all. For such people the world of fine arts is something entirely set apart from ordinary living and that its single purpose should be satisfying of physical necessities. At the same time architecture is a matter of pictures or sculpture, poems or music. The architect has the task of being an artist as well as an inventive engineer. The expression of the purpose of buildings would seem to call for additional thought on this point. The emotions are evoked by beauty. It may be theaters, churches, dwellings and buildings, which always differ from one another. Yet a separate consideration of an individual building is a very real artificial sense.
We have mentioned that architecture is a science of building. On one hand, coming of a building science also marked a major change in the role of an architect. The response of the architect was to develop a new role of licensed professional on the model of licensed professions such as law1 and medicine. It meant a bewildering range of new building types. On the other hand, with coming of a building science, there was a farther division of labor in the design process. Some new disciplines appeared to teach engineers and architects. One of them was structural engineering2 as a separate discipline specializing in the application.
We know that for building an architect and an engineer are needed. One of the first buildings for which an architect and an engineer were separate persons was the Granary (1811) in Paris. The building design professions were founded, including the Institute of Civil Engineers (1818) and the Royal Institute of British Architects (1834), both in London, and the American Institute of Architects (1857). Official government licensing of architects and engineers was not realized until beginning with the Illinois Architects Act of 1897. With the rise of professionalism was the development of government regulation, which took the form of detailed municipal and nation a building codes3 specifying both prescriptive and performance requirements for buildings.
Engineering1 is a complex discipline, including a lot of fields2. One of them is an architectural engineering. It is a discipline that deals with the technological aspects of buildings. They are the properties and behavior of building materials and their components, foundation design, structural analysis and design, construction management, and building operation. Besides architectural engineering deals with environmental system analysis3 and design. Every engineer knows an environmental system, which may account for 45—70% of a building's cost, includes heating, ventilating and air conditioning, illumination, building power system, plumbing4 and piping, storm drainage, building communications, acoustic, vertical and horizontal transportation, fire protection, alternate energy sources, heat recovery, and energy conservation. In addition, it is necessary to help protect everybody from unnecessary risk. That's why architectural engineers must know and be familiar with the various building codes, plumbing, electrical and mechanical codes, and the Life Safety Code. The latter code is designed to require planning and construction techniques in buildings which will minimize possible hazards to the occupants.
One of the ancient1 human activities is building construction. It began with a purely functional need for a controlled environment to moderate the effects of climate. Human shelters2 were constructed to adapt human beings to a wide variety of climates and become a global species. But temporary structures were used only a few days or months. Over time were they evolved into such a highly refined form as the igloo. After adventing agriculture, people began to stay in one place for long periods. That's why more durable3 structures began to appear. The first human shelters were very simple. The first shelters were dwellings. But later they were used for other functions, such as food storage and ceremony. Some structures began to have symbolic as well as functional value, marking the beginning of the distinction between architecture and building.
Building construction has its own history, which is marked by a number of trends. Let's describe some of them. One of these trends is increasing durability of the materials. The first building materials were perishable. We mention leaves, branches and animal hides. Later people began to use more durable natural materials such as clay, stone, timber. Finally, synthetic materials such as bricks, concrete, metals, plastics were used in building. Another trend is quest for buildings of greater height and span. It was possible by the development of stronger building materials and by knowledge of how materials behave and how to exploit them to greater advantage. The third trend involves the degree of control exercised over the interior environment of buildings: increasingly precise regulation of air temperature, light and sound levels, humidity, air speed. All factors that affect human comfort become possible. A modern trend is change in energy of the construction progress, starting with human muscle power and developing toward the powerful machinery.
The present state of building construction is complex. There is a wide range of products and systems which are aimed primarily at groups of building types. We know about a great role of the design process for buildings. It draws upon research establishments that study material properties and performance, code officials. Last ones adopt and enforce safety standards and design professionals who determine user's needs and design a building to meet those needs. It proves that the design process for buildings is highly organized. The construction progress is also highly organized. It includes the manufacturers of building products and systems. On the building site craftsmen assemble themselves. A work of the craftsmen is employed and coordinated by contractors. There are also consultants who specialize in such aspects as construction management, quality control and insurance. We must mention about complexity and measure of mastery of natural forces, which can produce a widely varied built environment to serve the needs of society. In conclusion, modern building construction is a significant part of an industrial culture.
We have mentioned about some problems connected with building. One of them is a foundation. Architects and engineers are aware of the problems involved in laying building's foundations. They do not always realize to what extent the earth can be pressed down by the weight of a building. Too little allowance has sometimes been made for the possibility of a heavy structure's sinking unevenly. There are a lot of examples of foundations' problems. One of them is the Leaning Tower of Pisa1. Why did the Leaning Tower of Pisa lean? The answer is that its foundations were not soundly laid. Though the Leaning Tower is 14 feet out of the perpendicular, it has never toppled. But there is a way out. As the building began to lean over, the builders altered the design of the tipper stories to balance it. At the same time as one side of it sank into the ground, the earth beneath was compressed until it became dense enough to prevent further movement.
That's why a foundation engineer has a lot of work. But in a tall modern structure the load may be very heavy indeed. In this way the foundation engineer has an extremely important job to do. To begin with, he must have thorough understanding of soil mechanics, which entails a scientific study of the ground to see what load it can be without dangerous movement. We know that trial pits, holes can be. So the engineer must collect undisturbed samples of earth from various depths. By examining this, the engineer can forecast the probable shifts in the earth during and after building, according to the sort of the foundation he designs. Thus he comes to the most important decision of all in the building's construction. He decides whether the earth is a type that can best support each column on a separate solid block, or whether he must aim at lightness.
It is important for the foundation engineer to know about different types of the ground. If it is a firm ground at great depth, the foundation engineer may use piles. These are solid shafts made either by driving reinforced, concrete deep into the ground, or by boring holes in the earth and pouring in the concrete. Each pile supports its load in one, or two ways. It may serve as a column with its foot driven into solid еаrth. At the same time it may stand firm because friction along its sides "grips" the column and prevents it from sinking.
But it may be a question of building's floating. In this way the foundations take the form of a vast, hollow concrete box. This box is divided into chambers. These ones will be house heating and ventilating plants as well as provide garage and storage space for the building.
The situations may be different. There are no problems at all or few of them. It can be if the earth is stable. Buildings stand on hard rock like granite or ironstone. For them neither piles nor need flotation be used. It is the best time for those foundation engineers whose buildings stand on the foundations possessing few problems.
A very important part of any structure is a wall. Walls may be constructed in different forms. The walls include windows and doors, heads1 and sills2, stanchion casings3 and inner lining panels4. The doors and windows provide for controlled passage of environmental factors and people through the, wall line. The aluminium heads, sills and windows are fixed from inside the building. After this, the 900 mm and 1.800 mm wide exterior doors are installed. These doors are aluminum framed and pre-glazed or hardwood framed and glazing5 is done on site. All walls are also designed to provide resistance to passage of fire for some defined period of time, such as a one-hour wall. The function of resisting fire fulfills stanchions. The stanchions are enclosed in casings.
That's why any engineer most knows all methods of constructing walls for buildings. Of cause walls are made of various materials to serve several functions. Тhе walls are divided into interior and exterior walls. The exterior walls protect the building interior from external environmental effects such as heat and cold, sunlight, ultraviolet radiation, rain, sound, while containing desirable interior environmental conditions. The exterior walls are made up of brick cladding, wall planks. The wall planks are designed to be weatherproof and to support the outer cladding. The wall planks and floor units are fixed only while the steel frame is being erected. The concrete floor units are capable of carrying a load of up to 5 kn/sq m. Finally, the internal sills and lining panels are installed. The lining panels are capable of being removed to give access to the services. The lining panels and the internal sills are cavity for heating and electrical services.
Finally, the internal sills and lining panels are installed. The lining panels are capable of being removed to give access to the services. The lining panels and the internal sills are cavity for heating and electrical services.
ВАРИАНТ № 4.
We have mentioned about some methods of constructing walls for buildings. All walls are made of different materials. For example, walls are made of brick1. The brick walls are laid up with a space between separate vertical parallel walls and connected with occasional cross bricks or metal ties. This method provides «cavity walls».
In areas of possible earthquake damage2 the «cavity» in brick work and the open cells in concrete units is reinforced with standard reinforcing rods and fully grouted with a soupy mixture of concrete. Normal spacing for vertical reinforcement3 is #4 at 24" with #4 at 48" horizontal fully, encased in grout up to 10" high. Reinforcement requirements should be shown on the drawings for other situations.
But it is a special part of building called masonry. Masonry is installed with cement mortar at bed and end joints, usually 3/8" or 1/2" thick. The masonry includes a stone or brick work and concrete units. The concrete units are laid in a similar manner, but obviously there is no open space between inner and outer shells. Each unit has an open core. The concrete units are used primarily as foundation, exterior or fire-separation walls. The brick and concrete units are manufactured in standard sizes. Though a stone may be any size, thickness4, quality or color.
Besides masonry1, a brick work, any engineer must know about heating and ventilation. They are two branches of engineering which are very closely connected. Both they are treated as a dual subject. Heating is to prevent too rapid loss of heat from the body. The rate of heat lost from the body is controlled. Some old concepts of heating have been gradually changed since engineers obtained more precise knowledge2 about how the body loses heat. Insufficient attention was paid formerly to loss by radiation, which is the transmission of energy in the form of waves from a body to surrounding bodies at a temperature. The human being also loses heat by conduction (through his clothes) and convection, the latter by air currents not only past his skin or outside clothing surface but also by evaporation of moisture3 from his skin (respiration).
The determination of the capacity or size of the various components of the heating system is based on the fundamental concept that heat supplied to a space equals heat lost from the space. The most widely used system of heating is the central heating4.
There are two most common systems of heating: hot water and steam. There the fuel is burned in one place, from which steam, hot water or warm air is distributed to adjacent and remote spaces to be heated. Both systems are widely used nowadays. A hot-water system consists of the boilers and a system of pipes connected to radiators suitably located in the rooms. The steel or copper pipes give hot water to radiators or convectors which give up their heat to the rooms. Then cooled water is returned to the boiler for reheating. As for steam systems, steam is usually generated. The steam is led to the radiators through or, by means of steel or copper pipes. The steam gives up its heat to the radiators and the radiators to the room. After this cooling of the steam condenses to water. The condensate is returned to the boiler by gravity or by a pump. The air valve on each radiator is necessary for air to escape. Otherwise it would prevent steam from entering the radiator.
Recent efforts have resulted to completely conceal heating equipment in an arrangement. Hot water, steam, air, or electricity are circulated through distribution units embedded in the building construction. Panel heating is a method of introducing heat to rooms in which emitting surfaces are usually completely concealed in the floor, walls or ceiling. The heat is disseminated from such panels partly by radiation and partly by convection. Ceiling panels release the largest proportion of heat by radiation and floor panels release the smallest one. The proportion of heat disseminated by radiation and convection is also dependent to some extent upon panel-surface temperatures. Other factors must be considered by an engineer. They are a type of occupancy, furniture or equipment location, large glass areas, heat-storing capacity of building construction, room height, and possible change of wall partitions, climate, exposure5, cost. Sometimes fuel is used for heating. They include coal, oil, manufactured and natural gas, wood. Nowadays gas fuel is being used on an increasing level.
But to do comfortable atmosphere is to use heating and ventilation together, Heating and ventilation are concerned with providing a required atmospheric environment within a space to produce a desired temperature for maintaining comfort, health or efficiency of the beings. Nowadays air-conditioning is closely related to both heating and ventilation.
One of the building materials used in a construction is a brick. The production of a brick was industrialized in the 19th century. Earlier it was a process of hand-molding. Later it was superseded1 by «pressed» bricks. It was a mass production by a mechanical extrusion process. In this way clay was squeezed by "pressed" through a rectangular die as a continuous column and sliced to size by a wire cutter2. Periodically fired kilns3 were used. Bricks were moved slowly on a conveyor belt. New methods considerably reduced the cost of a brick. That's why it became one of the constituent building materials of the age.
Rapid development of timber technology was in the 19th century in North America. It was explained large softwood fir's forests and pine trees. There they were used as industrial methods. Steam- and water-powered sawmills began producing standard-dimension timbers4 in the 1820s. The production of cheap machine made nails in the 1830s. It provided other necessary ingredient — a balloon frame5. That made possible a major innovation in building construction. The first example was a warehouse erected in Chicago in 1832 by George W. Snow. There was a great demand for small buildings of all types settled on North American continent. Light timber frame provided a quick, flexible, inexpensive solution6 to this problem. Heavy timbers and complex joinery were abandoned in the balloon frame system. The building walls were framed with 5 x 10-centimetre (2 x4-inch) vertical members. They were placed at 40 centimeters (16 inches) from the centre. This supplied a roof and floor joists, usually 5x25 centimeters (2x10 inches) and placed 40 centimeters (16 inches) apart and were capable of spanning up to six meters (20 feet).
Among the oldest and newest of structural materials are composite materials1. It was discovered many years ago that two or more materials could be used together as one. Later it was proved that such a combination often behaved better than each material alone. Following this principle, clay and straw were combined to make bricks. For centuries composite materials remained virtually untapped. Only then monolithic materials, such as iron, copper were served for needs of an advancing technology. Recently it was a development of technology with coming of reinforced concrete, linoleum, plasterboard and plywood panels2. During the 1930`s and 1940`s light-weight honeycomb structures, machine parts made from compressed metal powders and plastic reinforced with glass fibers became commercial realities. These developments marked the beginning of the modern era of composite engineering materials. It was mentioned growing and using composite materials. The consumption3 of the fiber reinforced plastics4, for example, has been increasing at the phenomenal rate of 25 per cent annually. Nevertheless, the emergence of a strict discipline and technology of composite materials is barely 20 years old.
There are two major reasons for the current interest in composite materials. The first is the demand for materials that will outperform the traditional monolithic materials. The second and more important in the long run, is that composites offer engineers the opportunity to design totally new materials, with the precise combination of properties needed for a specific task. Although new composites are usually more costly than conventional materials, they can be used more sparingly, because of their superior qualities.
All cultures have their own traditions and customs. That's why it is important to know about them. Of cause, architecture has its own history. There are a lot of different kinds of architectural styles, describing some features1 of every country. For example red brick buildings of old Petersburg factories, grey Ferro-concrete cases of industrial giants tell us about Soviet epoch. But, today they look old-fashioned. Besides external unattractiveness2, the constructions of the last centuries have lacks3. They are internal narrowness4, conditions of communications in these buildings. In particular, because of these lacks it is impossible to organize modern competitive manufacture. The majority of the companies do not prefer building of new constructions, using the тоя perspective materials and technologies, including an easy metallic construction (LMC).
Let's tell some words about a basic fast construction for building» It is a metal skeleton. There metal vertical racks5 and horizontal crossbar6 with the help bolt connections gather in cross-section frames. The cross-section frames are a system of extensions communications, giving to design settlement durability fastens. There it is established roofing, wall runs, frames under windows, doors. Any engineer may say that a bearing skeleton is ready. Further it is possible to use any facing. It can be Ferro-concrete, bricklaying, special panels such as "sandwich" any combinations of the specified designs. It is necessary to tell some words about panels such as "sandwich". Every panel consists of two sheets of the zinced iron between which a special heater is placed. The design has no internal skeleton. Its durability is reached due to the certain orientation of fibers.
It is very important for a future skilled engineer7 to remember about a distinctive feature such as "fast". It is a high degree of a factory's readiness to complete the building. In practice it is carried out as follows. All details, delivered to a building site, are made at a factory with their obligatory8, test characteristics of strong. On a building site all elements of a design are gathered with the help bolt connections. With the purpose, excepting possible problems during installation, all details are adjusted to each other on the factory-manufacturer control assembly of each design.
The scope9 of fast metallic construction is very wide. For example, metallic construction is not used at construction of buildings in which nuclear reactors will place, or bank storehouses. There walls' and roofing designs should possess raised isolation properties10. It is not accepted to use them. Practically, fast metallic constructions are used at the construction of any industrial targets, warehouses, sports complexes. Recently fast construction designs are used in the market. This process does .metallic construction attractive in the field of trading constructions.
Every construction has its own advantages and disadvantages. Advantages of a fast metallic construction are obvious. A cost of a building from a metallic construction is 30-40 % less, than on construction of a similar building, using traditional materials. Naturally, the given statement is correct only under condition of the certain identity of quality of external and internal furnishing11. For example, the building constructed from the cheapest brick without additional external furnishing, will be cheaper than a construction from a fast metallic construction with a facade trimmed with dark glass12. The essential economy, while using a metallic construction, is reached to decrease in expenses of a zero cycle approximately on 50%. Today a fast metallic construction is a leader among all building designs, first of all, because of its low price. On the other hand, it has the shortest terms of erection. The economy of time can become very significant and essentially important for any customer13. Besides the price and terms of assembly, fast metallic constructions have more important advantage. The matter is that a metallic construction is not only quickly gathered, but also can be disassembled14 fast and without special financial expenses.
Вариант № 1.
Thermostat Selection. In addition to consideration of types, initial cost, type of enclosure, and usage, several other factors are important when ordering a thermostat. The desired temperature range and the allowable variations in temperature must be specified. The range of a thermostat must include the temperature for which it is to be used and the temperature variation should be consistent with the application. Usually the thermostat allowing variations of 5° is satisfactory. A 5° variation (differential) means that the thermostat would operate 2.5 above the temperature setting and would operate again 21/2° below the setting. (Set at 85° F, contacts open at 87.5° and close at 82.5°.) Closer control is available if desired.
A second important factor is the switch contacts. The ampere rating of the contacts, the type of contact material (silver is best), whether single- or double-pole, and single-or double-throw, must all be specified when placing an order. The decision relative to these items is made after considering certain operating characteristics of the controlled appliance, such as surge current, normal current, input voltage (230 volts double-pole contacts), and the need for operating auxiliary equipment with the same thermostat.
Time Switch. A time switch1 is an electric clock that automatically operates switch contacts at definite time intervals. The general-purpose time switch is designed automatically to close the switch contacts two times and open them two times during any 24-hr period. By adjusting the trip levers the timer can be set to provide only one on and one off operation during the 24-hr period. Various appliances can be controlled by the contacts of the switch. The clock motor is connected to the source of power independent of the switch contacts so that the clock runs continuously, but the appliance is on only when the switch contacts are closed.
On the farm, time switches are used more for poultry-house lighting than for any other application. In addition, they are frequently used for controlling home-yard lighting, automatic feeders, greenhouse lighting, cooling systems, hay curing, grain drying, and heating systems.
Two models of time switches along with typical wiring diagrams are shown in Fig. 15. For simplicity single wires are used in the wiring diagrams. One of the diagrams illustrates the use of a d i m circuit which provides a 15- or 20-min period of dim lights before all lights are extinguished. The actual dimming is not incorporated in the switch but must be provided by connecting an external resistance into the dimming circuit or by placing a low value of lamp wattage on this circuit. Double-pole switch2 contacts are available for the 230-volt-circuit application such as a three-wire poultry-house wiring system and for single appliances requiring large wattages.
The automatic operation is performed by metal trip levers or r i d e r s 3which are fastened4to the rotating dial5 and trip the switch mechanism as they pass by. The riders can be removed or adjusted in position in order to regulate the timing intervals. Clocks performing two on — off opera-lions in 24 hr require four riders. If more on — off operations are desired, additional riders are necessary. However, there is a practical limit to the number of switching operations possible with a single timer. The actual switching is a mechanical feature and the dial must rotate some distance (and therefore some time elapses) before one rider can trip the switch contacts and move past, thereby allowing the next rider to function.
In selecting a time switch, consideration should be given to the voltage rating of the clock motor, the rating of the contacts, and the number of operations and the interval between operations, as well as to the type of enclosure. The energy for operating the timer is negligible, and the clock are self starting and should last indefinitely.
Float Switch. A float switch is an automatic control that operates according to some predetermined liquid level. The float is usually a hollow copper ball or cylinder and is connected to the float switch by a rod or chain. The principle of operation is based on the up and down motion о the float as the liquid level rises and falls.
The float switch is used mostly for controlling water levels in a non-pressure tank or trough, but is also readily adapted for use with fuel-oil containers. The switch contact are sometimes connected directly into the circuit of the con, trolled appliance, such as a small motor, or they may be connected to control the relay coil of a magnetic starter which operates larger motors or appliances. In other instances the contacts are used for controlling the operation of a solenoid valve which in turn controls the flow of water or similar liquid through a pipe. It is also possible to employ a float switch to control the operation of a sump pump. For this latter application the operating-lever position or the relative position of the float and the counterweight must be sue' as to cause closed-switch contacts in the up position of the float and open-switch contacts in the down position.
The counterweight is heavy enough to operate the switch contacts when the float is supported by the proper level о liquid. When the liquid level decreases, the float is not adequately supported and its unsupported weight is sufficient to overcome the counterweight and to operate the switch contacts. The larger the diameter of the float, the more sensitive it is to changes in the level of the liquid. The switch contacts are so mounted mechanically, as to provide the snap-action feature necessary for long life.
When placing an order for a float switch, the usual items of information to be listed are the current rating of the switch contacts, type of enclosure, rod or chain length, and number of poles required in the switch.
1time switch – временный включатель, таймер, часы
2double-pole switch – двухполюсный выключатель
3rider – подвижный контакт
4to fasten – пристегивать, застегивать
5rotating dial – вращающийся диск, циферблат
Вариант № 2.
A pressure switch is an automatic control having switch contacts which are operated according to variations in liquid or gas pressure. The gas, vapour, or liquid passes through the control, and the pressure of the eras or liquid expands a metal bellows against the force of a spring. The motion of the expanding and contracting bellows operates a snap-action switch mechanism. '' On the farm the pressure switch serves as the control for pressure-type water systems and air compressors. It starts and stops the electric motor which drives the water pump or thecompressor. The switch contacts of the control are generally used directly in the motor circuit, but they could be .used to control the input to the coil of a magnetic starter. The latter case is the usual connection for motors larger than2 hp.
When considering the application2 of a pressure switch, particular attention must be given to the differential (difference in pressure between cut-in and cut-out) and to the pressure range (upper and lower limits of desired pressure settings). The user can adjust these values, within specified limits, by increasing and decreasing the tension of springs. For instance, the pressure range of the average water-pump Pressure control is from 20 to 80 psi, while the pressure differential is from 10 to 40 lb. If the range setting is adjusted" то 35 lb and the differential is set for 10 lb, the switch would cut on and start the motor at 25 lb and would open, thereby stopping the motor when the pressure reached 45 lb. The 'manufacturer varies the range limits and the differential by •combining different springs with different sizes of bellows. Other items of importance in making a final selection of this type of control are voltage, motor horsepower, pipe sizes, safety release valve, and type of enclosure.
Limit Switch.A limit switch is an electric switch which «s operated mechanically by the movement of some other piece of material or machine. The switch mechanism is frequently tripped by a knot in a rope, a metal stop fastened to ft chain, a cam, or some similar specially rigged arrangement. One switch contacts are usually returned to their normal position by the action of a spring. There is also a maintained contact type which must be manually reset. The contacts may be of either slow-action or snap-action type. The latter type trips instantly, once the mechanical tripping device has traveled the required distance to trip the limit switch. The switch having snap-action contacts is suggested for general-purpose use around the farm.
Limit switches are useful in farm applications where it is desired to limit the travel of a rope, chain, or carriage.
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