Implements for Growing Crops
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Many types of implements have been developed for the activities involved in growing crops. These activities include breaking ground, planting, weeding, fertilizing, and combating pests.
Ground is broken by ploughs to prepare the seed-bed. A plough consists of a blade-like ploughshare that cuts under, then lifts, turns, and pulverizes the soil. Modern tractor ploughs are usually equipped with two or more ploughshares so that a wide area of ground can be broken at a single sweep. Harrows are used to smooth the ploughed land and sometimes to cover seeds and fertilizer with earth. The disc harrow, which has curved, sharp-edged steel discs, is used mainly to cut up crop residues before ploughing and to bury weeds during seedbed preparation. Rollers with V-shaped wheels break up clods of soil to improve the aeration of the soil and its capacity for taking in water.
Some cereal crops are still planted by broadcasting seeds — that is, by scattering the seeds over a wide area. Machines for broadcasting usually consist of a long seed-box mounted on wheels and equipped with an agitator to distribute the seeds. Broadcast seeds are not always covered by a uniform or sufficient depth of soil, so seeding is more often done with drills, which produce continuous furrows of uniform depth. Specialized implements called planters are necessary for sowing crops that are planted in rows, such as maize. Maize planters and other similar machines have a special feed wheel that picks up small quantities of grain or separate kernels and places them in the ground.
Fertilizer can be distributed during the winter or shortly before seeding time. Commercial fertilizers are commonly distributed, along with seeds, by drills and planters. Manure is distributed most efficiently by a manure spreader, which is a wagon equipped with a bottom conveyor to carry the fertilizer back to a beater attachment, which disintegrates it and then scatters it on the ground.
After crops have begun to grow, a cultivatoris used to destroy weeds and loosen and aeratethe soil. A flame weeder, which produces a hot-air blast, can be used to destroy weeds growing around crops, such as cotton,thathave stems of tough bark. The weeds are vulnerable to thehot air, but the tough stems protect the crops from damage. Chemical herbicides applied in the form of a spray or as granules are used extensively for weed control.
Insecticides for pest control arc applied to soil andcrops in the form of granules, dust, or liquid sprays. A variety of mechanical spraying and dusting equipment is used to spread chemicals on crops and fields; the machinery may be self-powered,or drawn and powered by atractor. In areas where large crops of vegetables andgrain are grown, aircraft are sometimes used to dust or spray pesticides.
Chemical pesticides are used in nearly all farming operations undertaken in developed countries. However, increasing concern over the harmful effects that pesticides may have on the environment has led to the use of alternative forms of pest control. For example, farmers use crop rotation to prevent pests that feed on a certain crop. Also, certain pests are controlled by introducing an organism that damages or kills the pests, but leaves the crops unharmed. Finally, some crops are being genetically engineered to be more resistant to pests.
ELECTRICAL AND ELECTRONICS ENGINEERING
Electrical and electronics engineering is the largest and most diverse field of engineering. Among the most important subjects in the field are electric power and machinery, electronic circuits, control systems, computer design, superconductors, solid-state electronics, medical imaging systems, robotics, lasers, radar, consumer electronics, and fibre optics. Despite its diversity, electrical engineering can be divided into four main branches: electric power and machinery, electronics, communications and control, and computers.
Electric Power and Machinery
The field of electric power is concerned with the design and operation of systems for generating, transmitting, and distributing electric power Engineers in this field have brought about several important developments since the late 1970s. One of these is the ability to transmit power at extremely high voltages in both the direct current (DC) and alternating current (AC) modes, reducing power losses proportionately. Another is the real-time control of power generation, transmission, and distribution, using computers to analyse the data fed back from the power system to a central station and thereby optimizing the efficiency of the system while it is in operation.
A significant advance in the engineering of electric machinery has been the introduction of electronic controls that enable AC motors to run at variable speeds by adjusting the frequency of the current fed into them. DC motors have also been made to run more efficiently this way.
Electronic engineering deals with the research, design, integration, and application of circuits and devices used in the transmission and processing of information. Information is now generated, transmitted, received, and stored electronically on a scale unprecedented in history, and there is every indication that the explosive rate of growth in this field will continue unabated.
Electronic engineers design circuits to perform specific tasks, such as amplifying electronic signals, adding binary numbers, and demodulating radio signals to recover the information they carry. Circuits are also used to generate waveforms useful for synchronization and timing, as in television, and for correcting errors in digital information, as in telecommunications.
Prior to the 1960s, circuits consisted of separate electronic devices — resistors, capacitors, inductors, and vacuum tubes — assembled on a chassis and connected by wires to form a bulky package. The electronics revolution of the 1970s and 1980s set the trend towards integrating electronic devices on a single tiny chip of silicon or some other semiconductive material. The complex task of manufacturing these chips uses the most advanced technology, including computers, electron-beam lithography, micro-manipulators, ion-beam implantation, and ultraclean environments.
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