Computer networks

Computer networks are now common in educational institutions, offices and even in homes. Companies which have large number of computers prefer a network between these computers to access data from one another. By the effective resource sharing, management can reduce the manpower as well as time. This also reduces the peripherals such as printer. Thus in an office a high volume networked printer can perform the work of many individual printers. This reduces cost as well as maintenance complexity. Servers are used in big offices which can store enormous amount of data. Thus client-server model is used for large network-huge data systems. World Wide Web uses this model. Electronic mail or e-mail is used for communication. Videoconferencing is a latest tool by which employees at different locations can interact with each other just like in a meeting. For doing business including buy and sell, electronic commerce is used. Internet is a network now used by individuals sitting at home. Mobile phones and laptops opened the door for accessing internet while travelling too.

History of LASER

LASER is the short form of light amplification by stimulated emission of radiation. LASER is a highly coherent, highly monochromatic, high intensity unidirectional source of light. Ruby laser was the first fabricated laser. Maiman operated it for the first time. Later Sorokin and Stevenson fabricated Uranium-calcium fluoride laser. In 1961, Neodymium: glass laser was fabricated by Snitzer and Neodymium: CaWO4 laser by Johnson. After 4 years, Johnson and team succeeded in the fabrication of Neodymium:YAG laser and Holmium: YAG laser. The working of Holmium laser is based on the cascade energy transfer phenomena. This enhances lasing efficiency. Later GaAs lasers were fabricated which are quite economical, efficient, compact and portable. Now many types of laser exist in the market that cover a wide range of wavelength from ultraviolet to infrared and with wide variety of output power. The main components of a laser system are active medium, pumping unit, cavity resonator and a cooling system.

Street lighting

Street lighting is an important thing to be implemented with utmost care and vision since this affects both motorists and pedestrians. The main reason for accident during night is poor street lighting. The major varieties of street lamps used are tungsten filament lamps, tubular fluorescent lamps, sodium vapour discharge lamps and mercury high pressure discharge lamps. Tungsten filament lamps are suitable for minor residential streets and pedestrian walk-ways. Tubular fluorescent lamps are best for shopping streets. Sodium vapour discharge lamps and mercury vapour discharge lamps are widely used nowadays in the streets of India. These lamps are highly efficient and have longer life span. Different treatments and skilled method has to be employed while designing lighting at bends or curves, bridges and tunnels.