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Monday, 13 August 2012

Losses in transmission lines

There exist three types of losses during power transmission through copper cables. They are copper losses, dielectric losses and radiation (induction) losses. Copper losses are due to the resistance of the conductors. Here energy is dissipated in the form of heat. Loss may also occur due to skin effect where expanding and collapsing electric fields about each electron encircle other electrons. As a result of skin effect, encircled electrons suffer retardation leading to power loss. If there is a dielectric material between the conductors, it will result in dielectric loss. Polyethylene dielectric material is preferred in conductors which causes feeble dielectric loss. Induction losses arise when the electromagnetic field about a conductor cuts through any nearby metallic object and a current is induced in that object. This is a power dissipation loss. When some magnetic lines of force about a conductor fails to return to the conductor during cycle alternation, causes radiation losses.

Wednesday, 1 August 2012

Optical tweezers

Optical tweezer is an optical device where laser light is used for the fine manipulation of nanosized particles.  Here light is allowed to move around nanosized particles as well as single atoms. A sharply focused laser beam is allowed to pass through a lens. Lens focuses the light to a tiny spot in the specimen. This helps to create an optical trap which is capable of holding extremely small objects between 10nm and 100 nanometers in size. Movement and manipulation of these trapped nanoparticles can be done effectively. The main application of optical tweezers is in the study and characterization of DNA and proteins. Optical tweezers help scientists to see the nanoparticles and can be controlled by a computer. Computer controlled optical tweezers are capable of measuring fine displacements and forcing circular motion to the nanoparticles.