17)Submersibles

A submersible is a small vehicle designed to operate underwater. The term submersible is often used to differentiate from other underwater vehicles known as submarines, in that a submarine is a fully autonomous craft, capable of renewing its own power and breathing air, whereas a submersible is usually supported by a surface vessel, platform, shore team or sometimes a larger submarine. In common usage by the general public, however, the word submarine may be used to describe a craft that is by the technical definition actually a submersible. There are many types of submersibles, including both crewed and uncrewed craft, otherwise known as remotely operated vehicles or ROVs. Submersibles have many uses worldwide, such as oceanography, underwater archaeology, ocean exploration, adventure, equipment maintenance/recovery or underwater videography

Apart from size, the main technical difference between a "submersible" and a "submarine" is that submersibles are not fully autonomous and may rely on a support facility or vessel for replenishment of power and breathing gases. Submersibles typically have shorter range, and operate primarily underwater, as most have little function at the surface

There are three basic technologies used in the design of submersibles. Single atmosphere submersibles (one atmosphere subs) have a pressurized hull and the occupants are at standard atmospheric pressure. This requires the hull to be capable of withstanding the high pressure from the water outside that is many times greater than the internal pressure.

Another technology called ambient pressure maintains the same pressure both inside and outside the vessel. This reduces the pressure that the hull has to withstand.

A third technology is the "Wet Sub", which refers to a vehicle that may or may not be enclosed, but in either case water floods the interior so SCUBA equipment is used to facilitate breathing. In both single atmosphere and ambient pressure subs, there is no need to use SCUBA equipment and occupants can breath normally without wearing any equipment.

18)Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term “laser” originated as an acronym for “light amplification by stimulated emission of radiation”.

There are a lot of types of laser: gas (He-Ne, CO₂), chemical (hydrogen fluoride, deuterium fluoride), excimer, solid-state (ruby, neodymium), fiber, photonic crystal, semiconductor, dye, free-electron.

Laser have become so much a part of daily life that many people may not realize how ubiquitous they are. Every home with a CD-player has a laser; hardware stores are now selling a wide variety of laser levels; many, if not most, computers, printers and copiers are using laser technology. Laser application are so numerous that it would be fruitless to try to list them all.

So, laser are used in the three-dimensional stereolithography, in the photolithography, to make a noncontact measurement (scatter measurement, polarimetry, ellipsometry, interferometric measurement), in the scientific laboratory for a wide variety of spectroscopic and analytic tasks. One of the earliest applications of laser in medicine was photocoagulation, using an argon-ion laser to seal off ruptured blood vessels on the retina of the eye. Today, lasers are used extensively in analytical instrumentation, ophthalmology, cellular sorting, and of course, to correct vision.

The laser's most important potential may be its use in commu­nications. The intensity of a laser can be rapidly changed to encode very complex signals. In principle, one laser beam, vibrating a bil­lion times faster than ordinary radio waves, could carry the radio, TV and telephone messages of the world simultaneously. In just a fraction of a second, for example, one laser beam could transmit the entire text of the Encyclopaedia Britannica.

Besides, there are projects to use lasers for long distance com­munication and for transmission of energy to space stations, to the surface of the Moon or to planets in the Solar system. Projects have also been suggested to place lasers aboard Earth satellites nearer to the Sun in order to transform the solar radiation into laser beams, with this transformed energy subsequently transmitted to the Earth or to other space bodies. These projects have not yet been put into effect, because of the great technological difficulties to be over­come and, therefore, the great cost involved. But there is no doubt that in time6 these projects will be realized and the laser beam will begin operating in outer space as well.