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Moment of truth
The word 'nanotechnology' is first coined by University of Tokyo researcher Norio Taniguchi back in 1974.


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LD50 Tox.
Lethal dose 50. It is the amount of a solid or liquid substance that it takes to kill 50% of test animals such as mice or rats in one dose. It is often quoted in milligrams per kilogram of body weight. A substance is considered to be highly toxic if LD50 is less than 50 mg/kg.

leaching Chem., Geol.
Removal of substances trapped within a solid by diffusing into the solvent running over the solid. For instance, removal of minerals and humus from the soil by the water.

lead-chamber process Chem.
An obsolete method of producing sulfuric acid by the oxidation of sulfur dioxide in moist air using nitrogen oxide or potassium nitrate as catalysts. The process was carried out in a series of lead-lined containers. The process was expensive and only produced dilute acid of up to 78%. Originally introduced by John Roebuck in 1746, the lead-chamber process was used in large-scale industrial production of sulfuric acid, until it was replaced by the contact process in 1876.

Lense-Thirring effect Phys.
A relativistic effect predicted by Austrian physicist Joseph Lense and Hans Thirring in 1918. They predicted that if an object spins (like a planet), the space-time will be twisted accordingly, in addition to the wrapping distortion of space-time due to the mass of the object, as predicted by Einstein relativity theorem. Such spin-twisting effect should slow other objects around it. Hence, the effect is also called frame dragging. Such effect was confirmed in October 2004, where two Earth-orbiting satellites, LAGEOS and LAGEOS 2, were found to drag by about 2 meters every year.

LEP Phys.
Abbreviation for the Large Electron Collider. It is a large circular particle accelerator that housed in 27 km circular tunnel outside Geneva and straddle the Franco-Swiss border. It was built by the Organisation Européene pour la Recherche Nucléaire (CERN) and operated from 1989 to 2000. The accelerator contributed to several significant discoveries in particle physics. For example, the proof of three generations of neutrinos and precise measurements of electroweak and strong forces.

lepton Phys.
Group of fundamental particles with half integral spin and do not have any internal structure. When similar leptons approach very close to each other, the electromagnetic force dominates and repel each other. Examples of leptons are electron, muon, tauon and their associated neutrinos.

lepton number Phys.
A number which can be either +1, -1 or 0 for a particle. It is used to determine the validity of a process in particle physics by making use the law of the conservation of lepton number. For a given type of lepton (either electrons, muons or tauons) will have the lepton number, Lx, of +1, where x is either e (electron), m (muon) or t (tauon) and the antileptons will have a lepton number of -1. Non-lepton particles will have a number of 0. For example, the lepton numbers for both electron and electron-neutrino are +1, while the lepton number for anti-electron (e+) is -1.

Lepton conservation Phys.
See Conservation of lepton number.

Lewis acid Chem.
A molecule or ion that forms a dative bond (coordinate bond) by accepting a lone pair of electrons. The definition forms one of the basis of defining an acid. For instance, proton (H+) is a Lewis acid. See also Lewis base.

Lewis base Chem.
A molecule or ion that forms a dative bond (coordinate bond) by donating a lone pair of electrons. It is named after Gilbert Lewis, an American chemist. This also forms of the basis of defining a base which can accept a proton (H+). For instance, the lone pair of electrons on the oxygen atom of a water molecule donate to a proton (a Lewis acid) to form an oxonium ion (H3O+).

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