Wave

a mechanism of energy transfer through a medium. The origin of the wave is vibrating particles, which store and release energy while their mean position remains constant as it is only the wave that travels. Waves can be classified as being either LONGITUDINAL WAVES, e.g. sound, or TRANSVERSE WAVES, e.g., light, depending on the direction of their vibrations. There is a basic wave equation that related the wavelength (λ), frequency(f), and speed (c) of the wave as c = fλ. All forms of waves have the following properties: diffraction; interference; reflection and refraction. ELECTROMAGNETIC WAVES have all of these properties but differ from ordinary waves, such as water waves, in that they can travel through a vacuum, e.g. outer space.

Taken from Dictionary of Science

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A wave is a disturbance that propagates through space and time, usually with transference of energy. A mechanical wave is a wave that propagates or travels through a medium due to the restoring forces it produces upon deformation. There also exist waves capable of traveling through a vacuum, including electromagnetic radiation and probably gravitational radiation. Waves travel and transfer energy from one point to another, often with no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); they consist instead of oscillations or vibrations around almost fixed locations.

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Valency Electrons

the electrons present in the outermost shell of an atom of an element and therefore the ones involved in forming bonds with other atoms when they are shared, lost or gained in the formation of a compound or ION. Some elements always have the same number of valence electrons, e.g., hydrogen has one, ordinary oxygen has two, and calcium has two.

Taken from Dictionary of Science

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In chemistry, valence electrons are the outermost electrons of an atom, which are important in determining how the atom reacts chemically with other atoms. Atoms with a complete shell of valence electrons (corresponding to an electron configuration s²p⁶) tend to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions. Atoms with one or two valence electrons less than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions, or to share electrons and form covalent bonds.

Valence electrons have the ability, like electrons in inner shells, to absorb or release energy in the form of photons. This gain or loss of energy can trigger an electron to move (jump) to another shell or even break free from the atom and its valence shell. When an electron absorbs energy in the form of one or more photons, then it moves to a more outer shell depending on the amount of energy gained. (See also : electrons in an excited state). When an electron loses energy (photons), then it moves to a more inner shell.

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Umbra

a region of complete shadow, which is usually applied to eclipses. The area of half or partial shadow is termed the penumbra.

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The umbra, penumbra and antumbra are the names given to three distinct parts of a shadow, created by any light source. For a point source only the umbra is cast.

These names are usually used when referring to the shadows cast by celestial bodies.

The umbra (Latin for "shadow") is the darkest part of the shadow. From within the umbra, the light source is completely occluded. In astronomy, an observer in the umbra is said to be in the shadows experiencing total eclipse.

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Taxonomy

the study, identification and organization of organisms according to their similarities and differences. Taxonomy is concerned with the classification of all organisms, whether plant or animal, dead or alive and so fossils are also important. Modern taxonomy provides a convenient method of identification and classification of organisms, which expresses the evolutionary relationships to one another. There are different levels of classification with five kingdoms, beneath which are the phyla, classes, right down to the level of species.

Taken from Dictionary of Science

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Taxonomy is the practice and science of classification. The word finds its roots in the Greek τάξις, taxis (meaning 'order', 'arrangement') and νόμος, nomos ('law' or 'science'). Taxonomy uses taxonomic units, known as taxa (singular taxon).

In addition, the word is also used as a count noun: a taxonomy, or taxonomic scheme, is a particular classification ("the taxonomy of ..."), arranged in a hierarchical structure. Typically this is organized by supertype-subtype relationships, also called generalization-specialization relationships, or less formally, parent-child relationships. In such an inheritance relationship, the subtype by definition has the same properties, behaviors, and constraints as the supertype plus one or more additional properties, behaviors, or constraints. For example, car is a subtype of vehicle. So any car is also a vehicle, but not every vehicle is a car. Therefore, a type needs to satisfy more constraints to be a car than to be a vehicle.

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Sandstone

a SEDIMENTARY ROCK made up of sand grains with sizes between 0.06 mm and 1 mm, and a variety of other minerals and materials cementing the grains together. CALCITE is a common cement, and silica (as QUARTZ) cements sands to produce a hard sandstone often referred to as an orthoquartzite (to tell it apart from the metamorphic rock, quartzite). Brown and red sandstones usually have an iron-rich cement such as LIMONITE or haematite. Other minerals which may be present include FELDSPAR and MICA.

Taken from Dictionary of Science

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Sandstone (sometimes known as arenite) is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material. However, some that have been used in the past, such as the Collyhurst sandstone used in North West England, have been found less resistant, necessitating repair and replacement in older buildings. Because of the hardness of the individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone.

Rock formations that are primarily composed of sandstone usually allow percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

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