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.