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Moment of truth
The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms.

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escape velocity Astron., Space
The minimum speed necessary for an object to escape, in a parabolic orbit, the gravitational pull of another larger (primary) object. Any object with equal or greater than the escape velocity will move away from the primary object and never return. The escape velocity of an object is related to the size of the primary object as follows:

escape velocity

where R is the radius of the primary object and g is the acceleration due to the gravitaional pull. For the surface of the Earth, V = 11.2 km/s and for the Moon, 2.4 km/s.

Escherichia coli Biol.
See E. coli.

essential oil Bot., Chem.
A volatile, natural occurring aromatic oil extracted from plants, flowers and citrus peels. Different plants or even different parts (seeds, flowers, leaves) of a plant can have distinct aromatic smells. Terpenes are the main constituents. Essential oils can be extracted from plants by cold pressing, steam distillation or organic solvents such as alcohol. Essential oils are used in perfumes, flavourings and medicine. Examples of essential oils are citrus oils, oil of cloves etc.

esterification Chem.
The reactions between carboxylic acids and alcohols to produce esters. The process is used extensively in fragrance and flavor industry. Esterification is a reversible process that usually use concentrated sulfuric acid as a catalyst. Depending on the type of reactants, the ester can either be filtered off or water be removed to ensure reaction is moving towards a more favorable direction of producing more esters.

esters Chem.
Organic compounds formed by reaction between alcohols and acids (such as carboxylic acid: RCOOH) and have the general formula RCOOR'. For example, ethyl ethanoate is made by ethanol (ethyl alcohol) and ethanoic acid (acetic acid). Esters are usually volatile fragrant compounds and can be found in fruits. They are used as flavorings (usually in small concentrations) in the food industry. For example, amyl acetate smells like banana.

etiology Med.
The study or theory of the factors that cause disease. This includes the method of their introduction to the host and the origin and cause of a disease or condition. Named after the Greek aitia, meaning cause. It is also called aetiology.

eukaryote Biol.
A higher form of organism (animals, plants and fungi etc.) with membrane-bound nuclei in its cells. The nuclear DNA contain complex chromosomes and many other organelles. Opposite to prokaryote.

eutrophication Ecol.
An ecological process whereby an increase in concentration of nutrients in an ecosystem results in excessive growth of one species and reduction of living quality for other species. For example, release of sewage effluent or run-off excess fertilizers result in excessive nutrient feeds. This promotes excessive growth of aquatic vegetation and restrict oxygen supply to other aquatic species like shellfish and fish.

evaporation Phys.
A physical conversion of a liquid into a vapor (gaseous form), at temperatures below the boiling point. It is a technique used to concentrate a solution.

even function Math.
A function f(x) is said to be even if f(x) = f(-x). For instance, f(x) = x2 is an even function since the value is the same for both x or -x. An even function, hence, is symmetrical about an axis.

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