Regulation of metabolism by the mediation of enzyme

A good coordination of anabolic and catabolic processes is required for the growth and maintenance of a cell. The working of metabolic machinery is dependent on enzyme catalyzed reactions. Thus a fine control of enzyme catalyzed reactions is essential in the regulation of metabolism. For the study of these reactions, we can make use of both prokaryotic and eukaryotic organisms. There exist four major steps in metabolic regulation. They are compartmentation of enzymes, differentiating pathways for catabolism and anabolism of a key substrate, interaction of substrates with change in kinetic factors and control of enzyme activity and enzyme concentration. The factors which control the actual functioning concentration of the enzymes in a cell are the rates of enzyme synthesis and degradation. A prokaryotic cell is a cell with a plasma membrane. The plasma membrane acts as a substrate for organic enzymes. In a eukaryotic cell, compartmentation of metabolic machineries occurs for very specific purposes. A plasma membrane is associated with this cell too which serves the purpose of selective transportation of important cations, anions and neutral compounds. Metabolic reactions are always reversible which makes use of two types of enzymes. One enzyme is used for forward reaction and the other one for backward reaction. These reactions are called opposing unidirectional reactions or substrate cycles.

Irrigation

Irrigation is defined as the artificial application of water to land for agricultural purposes. Irrigation is required when there is a deficiency in rainfall, non-uniform rainfall and augmentation of crop yields. It is also required in cash crops cultivation, orchards and gardens. Irrigation increases the food output, prevents damage through drought and floods and lowers production risks. Irrigation also increases the employment, value of land property, ground water storage etc. In a direct irrigation project, water is directly diverted from the river into the canal. Water is stored in a reservoir with the construction of a dam across the river in an indirect irrigation project. In the initial days, single purpose irrigation projects were announced and implemented by the various governments which were meant for a particular purpose. Now multipurpose irrigation projects are running which serves purposes like irrigation, navigation, power generation, flood control, domestic water supply, industrial water supply and tourism. Based on the financial return, irrigation projects are classified into three. They are productive, unproductive and protective. Irrigation potential is the aggregate area that can be irrigated in a year by the amount of water available at the field. India’s irrigation potential was only 19.5 M ha in 1947 which now crossed 120 M ha. The various systems of irrigation are gravity irrigation, lift irrigation, infiltrating irrigation, sewage irrigation and supplemental irrigation.

Designing dams

Dam is a water reservoir which is constructed across a river. It can be used for irrigation and power production. Water can be stored during the days of excess rainfall and can be released during other days to achieve continuous hydro power generation and irrigation. Dams are also effective in the protection from flood. Dams also serve some other purposes like navigation, fishing and recreation. Dams are also effective in improving climatic conditions and lowering river pollution. But dams can also harm in many ways. It may lead to the submergence of fertile lands, migration of population and disturbance in wildlife. The different requirements while choosing the dam site are there should be good runoff from the catchment area with minimum percolation losses, soil should be free from harmful soluble salts and minerals, runoff should be free from excessive slit load, there should be high and steep side hills, rock and soil erosion should be minimum, rock formation should have dip in the upstream direction, submergence of forest and cultivated lands should be minimum, site should be away from seismic zone and there should not be any vegetation and marshy land.

General purpose simulation system (GPSS)

General purpose simulation system is a process-oriented language originally designed by Geoffrey Gordon in 1961 which is used for discrete event modeling. GPSS, which was developed by IBM Corporation, is a very dynamic language. Modifications were being done on this language many times and hence exist many versions of this language now. Now GPSS become a multi-vendor language. GPSS is a very popular simulation language and it started with the advent of mainframe computers. GPSS is a superior language with in-built mechanism for the collection of data, analysis, production of tabulated output data and execution. In 1977, Henriksen developed a new language which is known as GPSS/H. This language is reported to be five times faster in execution time. GPSS/H offers some unique features like a real value clock for recording the simulation time, ability to read and write external files, enhanced control statements, increased number of mathematical functions, capability of generating unlimited number of independent random number series and capability of generating random variants from different probability distributions. A block-by-block construction model is used in GPSS. Block time is an integer which gives an idea about the number of units required to execute the action represented by the block.

Luminescence

Luminescence is the phenomenon in which a crystal absorbs energy and emits the energy back in the visible range. There are two varieties here-florescence and phosphorescence. Fluorescence is an instantaneous re-emission. Phosphorescence which is also known as afterglow takes a longer time to glow. Luminescence is greatly influenced by the presence of impurities and imperfections in the material. These impurities are called activators and introduce additional energy states in the bandgap of the material. These energy states are called recombination centers and traps. If the discrete energy states are located near the center of the bandgap, they are referred as recombination centers. All the other energy states in the bandgap are called traps. Thus a trap is an imperfection which is capable of capturing an electron or a hole. The existence of recombination centers and traps introduces a number of newer possible transitions in the semiconducting material. Luminescence finds applications in electroluminescent lamps, fluorescent tubes, cathode ray oscilloscopes and television displays. The phenomenon of luminescence may be classified into photoluminescence, cathodoluminescence, electroluminescence, chemiluminescence, thermoluminescence, triboluminescence and injection luminescence. Photoluminescence is produced by photons. Cathodoluminescence by high energy electrons, electroluminescence due to ac electric fields, chemiluminescence due to some chemical reactions, thermoluminescence by simulation at low temperatures, triboluminescence is due to mechanical energy and injection luminescence is due to forward biased p-n junction.

Manometers

Manometers are used for the measurement of pressure. In a single-tube manometer, a piezometer is connected to a pipe at the point where the static pressure of the fluid is to be measured. Piezometers are suitable for fluids under measurement. In a twin-tube manometer, two tubes of equal cross-section are connected together to form a U-tube. Both gas pressure and liquid pressure can be measured by using twin-tube manometers but care should be taken for not to mix or react chemically the liquid/gas under measurement with the manometric liquid. For low gauge pressures, water is taken as manometric liquid and in all other cases mercury is advisable. We can also employ a sealing liquid as a buffer to avoid reaction. The cistern type manometer requires only one reading while measurement. For the measurement of low differential pressures arising in gas-flow metering, ring-balance manometers are used. An electric displacement transducer is used in Bell-type manometers. Some other commonly used manometric liquids are transformer oil, dibutylphthalate, carbon tetrachloride and tetraboromethane. 

Welding processes

Various welding processes that can be used for joining the metal parts are solid phase welding, arc welding, resistance welding, thermit welding, ultrasonic welding, electron beam welding, laser beam welding and explosive welding. Solid state phase welding can be further classified into five categories- forge welding, butt welding, oxyacetylene pressure welding, flash butt welding and friction welding. In forge welding, the parts to be welded are heated in a furnace and then hammered together to form the weld. Electric current is used in Butt welding. An Oxyacetylene ring burner is used in oxyacetylene pressure welding. In flash butt welding, the parts are brought in contact with a light pressure and followed by the passage of an electric current. Heat due to friction is employed in friction welding.

Concrete sleepers used in railway lines

Economic considerations and changing traffic patterns forced railway industry to introduce concrete sleepers. The problem with wooden sleepers was shortage in material and expensive. In the initial stages RCC sleepers were used. After some time, block-type RCC sleepers connected by a steel tie bar were introduced. Latest in this category are prestressed concrete blocks and steel or an articulated concrete tie bar. The advantages of concrete sleepers are strength, stability, resistance to the buckling of the track, better packing, better alignment, improved cross leveling, better gauging, easy maintenance, less electrical conductivity, non-flammable, less damage, longer lifespan and can be produced in bulk. The main disadvantages are handling and transportation difficulties due to large weights, less scrap value, difficulty in beater packing etc. While designing a concrete sleeper, we have to consider the following factors: forces acting on sleeper, effects of geometric form, provision of failure on a damage and effect of the characteristics of fastenings used. The different varieties of concrete sleeper used by Indian railways are BG monoblock sleeper, BG twin block sleeper and MG twin block sleeper.

Turbomachines

Turbomachines are rotary type machines where the transfer of energy is brought about by dynamic action. Here impervious boundary containing the fluid does not exist. In a  turbomachine, energy exchange is brought about by hydrodynamic forces that appear between a moving fluid and the rotating and stationary elements of the machine. Here a dynamic energy exchange is taking place between one or several rotating elements and a rapidly moving fluid. The main components of a turbomachine are a vane carrying rotating element which operates in a fluid stream, some stationary elements acting as guide vanes for the proper control of flow direction and the energy conversion process, two shafts and housing. A turbomachine creates thermodynamic and dynamic action between a slow moving surface and a static fluid. This action involves a change in either volume or displacement of the fluid. Some characteristics of turbomachine are high rotational speed, simple design, less weight and almost vibration free.

Overhead power lines

Two mechanisms exist for electric power transmission-underground cable transmission and overhead line transmission. Underground cable transmission is not commonly used because it is very expensive and it is very difficult there to provide proper insulation. The main components of overhead lines are conductors, line supports, insulators, cross arms, phase plates, danger plates, lightning arresters and anticlimbing wires. Conductor material should have high electrical conductivity, high tensile strength, highly economical and low specific gravity. Some commonly used conductor materials are copper, aluminium, steel cored aluminium (aluminium conductor steel reinforced), galvanized steel and cadmium copper. Line supports should have high mechanical strength, less weight, cheap, longer life span and accessibility. Commonly used line supports are wooden poles, steel poles, RCC poles and steel towers. Insulators are used to insulate line conductors from line supports. Commonly used insulators are pin type insulators, suspension type insulators, strain insulators and shackle insulators. These insulators should have high mechanical strength, high electrical resistance, high relative permittivity, non-porous and high ratio of puncture strength to flashover.

Gas welding

Welding is an important industrial tool to join cuts. Gas welding is an important welding process which is actually a fusion welding process. Here heat is developed by the combustion of oxygen or air with a fuel like acetylene, hydrogen butane etc. The commonly used combination is oxygen-acetylene which can reach up to 3000 degree Celsius temperature and is most preferred for welding metals and metal alloys. Oxygen is filled in a steel cylinder at a pressure of 150 kg per square cm. Colour code used for oxygen cylinder is black. Acetylene is also filled in a cylinder at a pressure of 16 kg per square cm. Here acetylene is dissolved in a cylinder containing porous silicate filler. For directing the flow, a welding torch is used. This torch also helps to mix up the gases and control the volume of the gases. Here flame is produced by ignition technique. Pressure regulators are also required here to regulate the cylinder gas pressure. Green colour hose is used for oxygen gas and red colour hose for acetylene. For the protection of eyes from heat, ultraviolet rays and infrared rays, goggles are used while gloves are used to protect hands from heat and the metal splashes. To clean the surfaces of joints before and after welding, a wire brush is used.

Reciprocating engines

Aircraft engines, marine engines, automotive engines and stationary engines are examples of reciprocating engines. Engine can be designed on the basis of the otto cycle where fuel is mixed with air before compression. In otto engine, combustion takes place with no excess air. In diesel engines, fuel is injected near the end of the compression and combustion takes place with much excess air. Spark ignition is employed in otto engines where volatile fuels are used. Low volatile fuels are used for its operation in diesel engines where ignition is by compression. Depending upon the number of piston strokes required for the complete combustion cycle, there exist two varieties in the engine- two stroke and four stroke. In two stroke engines, piston uncovers exhaust ports in the cylinder wall near the end of the expansion stoke and permits the exhaust gases to flow out. The various events that occur in four stroke engine are stroke, exhaust, suction and compression. According to the arrangement of cylinders with each other and the crankshaft, there exist three types of engines. They are three-cylinder in-line engine, five-cylinder in-line engine and V-type engines. V-type engine has two banks of in-line cylinders connected to a single crankshaft.

Protecting a transformer

Mainly there are two faults that can occur in transformers. They are internal faults and external faults. Internal faults are of three types. They are incipient faults, winding faults and terminal faults. The main incipient faults are fault due to the breakdown of core lamination, breakdown of bolts and clamps, earthing fault, coolant failure, oil flow fault etc. Terminal faults are associated with high voltage or low voltage terminals and winding faults are associated with windings. External faults include the appearance of overcurrent for short duration, short circuit outside the transformer and overloading. Different methods employed for the protection of transformers are electromagnetic protection, differential protection, percentage biased differential protection, tank leakage protection, restricted earth fault protection and digital protection.

Protecting a generator

The major faults that can happen in a generator are overloading, winding faults such as stator winding insulation failure, rotor winding insulation failure, field winding failure, unbalanced loading, overvoltage, overspeeding, overheating, prime mover failure, loss of synchronism and underfrequency. The various protective schemes employed are differential protection, inter-turn fault protection, stator earth fault protection, rotor earth fault protection, pole slipping protection, overload protection, overvoltage protection, over current earth fault protection, underfrequency protection, negative phase sequence protection, field failure protection, reverse power protection and back-up impedance protection. There are three classes of protection schemes for synchronous generators. They are class A, class B and class C schemes.

Circuit-breakers

During overloading and short circuits, we require circuit-breakers to safeguard electric circuits. Circuit-breakers are automatic devices capable of making and breaking of electric circuits. Insulating fluids are used here to extinguish the arc produced due to the fault current interruption and to provide total insulation between the contacts and from each contact to earth. Some examples of insulating fluids are air, compressed air, hydrogen producing oil and sulphur hexafluoride gas. Insulating materials used in circuit-breakers should have high dielectric strength, thermal and chemical stability, high thermal conductivity, low dissociation temperature, should be non-flammable, should not produce carbon during arcing and should be commercially available. The arc between the circuit-breaker consists of ionized gas particles. By deionizing, we can execute arc interruption. This can be done by high pressure development, arc splitting or forced convention and turbulence. Switchgear can be used to execute current interruption.