Semiconductor injection laser

A source of light which produce light radiations by stimulated emission when it is placed between two mirrors (optical cavity) is known as semiconductor injection laser. Here photons are produced by stimulated emission which is due to the recombination of injected carriers. On proper amplification, semiconductor injection laser gives high radiance in terms of mill watts of laser power.  Line width of laser is very narrow and hence semiconductor injection laser is highly monochromatic. Line width is always less than 10 Å. Provision for increasing modulation bandwidth, high degree of temporal coherence, moderate spatial coherence and high focusing power are the other characteristics of this type of laser. A modified version of injection laser, called stripe geometry double heterostructure laser provides high degree of carrier and optical confinement in active region. In a gain guided injection laser, optical mode distribution along the junction plane is determined from optical gain.

Ergonomics

Meaning of ‘Ergons’ is ‘work’ and meaning of ‘Nomos’ is ‘natural laws’. Thus Ergonomics is the study of the relationship between man and his working environments.  An Ergonomist should have the knowledge of an engineer, psychologist, biometrician, anatomist, physiologist and anthropologist. The main objective of ergonomics study is optimizing the integration of man and machine and thus increasing the work rate, efficiency and accuracy. Here first stage involves the design of working environment suited to various requirements of the worker. In the second stage, equipments, machinery and controls are designed in such a way that the mental and physical strains of workers are decreased.  The third stage involves the design of a conductive environment for the smooth execution of tasks. Ergonomics is applied in the design of working environments, work place and some other areas. In the design of working environments and workplace, different factors which are worth taking care of are lighting, temperature, humidity, fresh air circulation, noise, bad odor, smokes, fumes, furniture placement, machine tools placement etc. Ergonomics is also applied in studies related to fatigue.

Highway engineering

Highways gained importance recent days due to the great advancement in vehicle manufacturing technology which helps to achieve very high speeds. But to maintain very high speeds, highways should be wide and damage free. Aggregate crushing value which gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load should be less for better results. A quantity which gives a measure of resistance to sudden impact or shock is termed as aggregate impact value which is very significant in the design of highways. Los Angeles test machine is a machine which measures resistance to abrasion of aggregate. For the determination of the abrasion value of road aggregates, we use Deval’s machine. For the determination of the strength of the subgrade soil for design of pavement thickness, California bearing ratio has to be calculated. For any Bituminous material, consistency test has to be carried out by a penetrometer and viscosity by a viscometer. A ring and ball apparatus can be used to determine softening point of Bituminous material.

Heat treatment in metallurgy

In metallurgy, heat treatment is defined as the combination of heating and cooling operations carried out on a metal or alloy in the solid state. Heat treatment helps to achieve desired microstructure and properties. For steel, a wide range of mechanical properties can be accomplished by proper heat treatments. Heat treatment helps to improve mechanical properties such as tensile strength, impact resistance and ductility. It also improves magnetic and electrical properties. By heat treatment we can increase wear resistance, abrasion etc. Heat treatment also helps in improving machinability and refining grains. By suitable heat treatment, we can produce hard surfaces and soft interior portions. There are two types of heat treatment processes. They are full heat treatment and surface heat treatment. Recrystallization annealing, full annealing, partial annealing, process annealing, spheroidising annealing, normalizing, hardening, austempering and mastempering comes in the category of full heat treatment. Surface heat treatment includes pack carburizing, liquid carburizing, gas carburizing, cyaniding, nitriding, carbo-nitriding, flame hardening and induction hardening. Some advanced techniques of heat treatment are ion nitriding, plasma carburizing, electron beam hardening and laser hardening.

Aeroplane component parts

Aeroplane is slowly becoming a common mode of transportation after the global economic reforms. The main components of an aeroplane are engine, propeller, fuselage, wings, three controls, flaps and tricycle under-carriage. Engine provides proper propelling force. There exist four types of engines. They are piston engine, rocket, turbojet and turbofan. A piston engine is powered by gasoline fed reciprocating engine which is driven by propeller. Propeller consists of two or more blades which are driven round in a circular path. Fuselage is the main part of the aircraft where power plant, fuel, cockpit, passenger space, cargo etc. are accommodated. Wings are used to support the machine in the air when the engine has given it the necessary forward speed. Three controls namely elevator, rudder and aileron are required for the fine controlling of the aeroplane. Elevator and rudder are also known as empennagewhich are located at the tail end of the fuselage. Aileron is a binged flap which is fixed in the trailing edge of the wing near the wing tip. Pilot can easily operate these control units from his cabin. Flaps are used to increase the lift on aerofoils. Tricycle under carriage supports the aircraft whenever it is in contact with the ground.

Commonly used printers

Printers are common in use in all the offices and organizations. Mainly there are three types of printers. They are dot matrix printers, inkjet printers and laser printers. Dot matrix printer is an impact printer (a printer which works by physically striking an ink ribbon that is placed on the paper) while inkjet printers and laser printers are non-impact printers. In a dot matrix printer, a hammer print head which consists of pins represents the character or the image. Dot matrix printers are bi-directional printers. The speed of the dot matrix printer is measured in characters per second and normally it ranges from 60 to 600 cps. Some other impact printers which are rarely used are line printer and band printer. In an inkjet printer, characters and images are sprayed in small drops of ink on the paper. Inkjet print quality is high and up to 30 pages can be printed in a minute. Laser technology is used in laser printer which is a high speed high quality printer. The major components of a laser printer are mirror, laser scanning unit, toner, photoreceptor drum, fuser and a paper tray.

3G Networks

The year 1980 observed the first commercial mobile networks. This was based on analog communication in the radio path and was termed as first generation network (1G). 1G network were confined to national boundaries. In 1990, second generation (2G) networks came with the replacement of analog networks with the digital second generation networks. The most popular 2G technology is GSM- Global System for Mobile communication. The specification of GSM was developed in the year 1989 by the European Telecommunication Standards Institute (ETSI). The 2G technology employed by Japan was PDC- Personal Digital Communication. The main limitation of 2G networks are low transfer rates, low efficiency for packet-switched services and multiple standards. Modification of 2G resulted in 2.5 Generation networks which include High Speed Circuit-Switched Data (HSCSD), General Packet Radio Services (GPRS) and Enhanced Data rates for Global Evolution (EDGE). Third generation partnership program (3GPP) emerged in the year 1998. Here a mobile competence centre has been established to ensure day-to-day running of the 3GPP. Both frequency division duplex (FDD) mode and time division duplex (TDD) mode are employed in the access network which is based on Universal Terrestrial Radio Access (UTRA) radio interface.

Radio wave propagation

There exist two ways of radio wave propagation. They are ground wave propagation and ionospheric propagation. If the electromagnetic waves are propagating near the surface of the earth, it is called ground wave propagation. This includes propagation of radio waves through troposphere too. Electromagnetic waves can travel in different ways (multiple paths) between transmitter and receiver antenna. A direct path can be established by fixing transmitter and receiver antenna in the line of sight of each other.  A wave which propagates along this path is called direct wave. The different mechanisms for electromagnetic energy transfer are direct, reflection, scattering and diffraction. The direct, reflected, scattered and diffracted waves are collectively known as space wave. When an electromagnetic wave reaches an interface between two dissimilar media, a part of the energy flows along the interface. This is known as surface wave. For a vertically polarized electromagnetic radiation, surface wave is predominant at low and medium frequencies.