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Fourier series

Fourier series  

An expansion of a periodic function as a series of trigonometric functions. Thus,f(x) = a0+(a1cosx+b1sinx)+(a2cos2x+b2sin2x)+…, where a0, a1, b1, b2, etc., are constants, called Fourier coefficients. ...
Platonic hydrocarbons

Platonic hydrocarbons  

Hydrocarbons that have the same molecular geometry as the five Platonic solids, i.e. the tetrahedron, the cube, the octahedron, the dodecahedron and the icosahedron. These hydrocarbons have carbon ...
Laplace equation

Laplace equation  

The partial differential equation:∂2u/∂x2 + ∂2u/∂y2 + ∂2u/∂z2 = 0It may also be written in the form ∇2u = 0, where ∇2 is called the Laplace operator. It was formulated by the French mathematician P. ...
ultrasonics

ultrasonics   Quick reference

A Dictionary of Chemistry (8 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Chemistry
Length:
71 words

...The study and use of pressure waves that have a frequency in excess of 20 000 Hz and are therefore inaudible to the human ear. Ultrasonics are used in medical diagnosis, particularly in conditions such as pregnancy, in which X-rays could have a harmful effect. Ultrasonic techniques are also used industrially to test for flaws in metals, to clean surfaces, to test the thickness of parts, and to form...

mica

mica   Quick reference

A Dictionary of Chemistry (8 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Chemistry
Length:
127 words

...Any of a group of silicate minerals with a layered structure. Micas are composed of linked SiO 4 tetrahedra with cations and hydroxyl groupings between the layers. The cations between the layers link the layers. The general formula is X 2 Y 4–6 Z 8 O 20 (OH,F) 4 , where X = K,Na,Ca; Y = Al,Mg,Fe,Li; and Z = Si,Al. The three main mica minerals are: muscovite , KA1 2 (A1Si 3 )O 10 (OH) 2 ; biotite , K(Mg,Fe) 3 (AlSi 3 O 10 ) (OH) 2 ; lepidolite, KLi 2 Al (Si 4 O 10 ) (F,OH) 2 . Micas have perfect basal cleavage and the thin cleavage flakes are flexible and...

Platonic hydrocarbons

Platonic hydrocarbons   Quick reference

A Dictionary of Chemistry (8 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Chemistry
Length:
152 words

...the icosahedron. These hydrocarbons have carbon atoms at the vertices of the polyhedra and single bonds along the edges. In fact, there are only two known Platonic hydrocarbons: cubane (C 8 H 8 ) and dodecahedrane (C 20 H 20 ). The hydrocarbon based on a tetrahedron (C 4 H 4 ) does not exist because of angle strain, but substituted derivatives C 4 X 4 are known. Angle strain is also the reason for the nonexistence of octahedrane (C 6 H 6 ) and icosahedrane (C 12 H 12 ). A major difficulty that has prevented the synthesis of icosahedrane (C 12 H 12 ) is that it...

biochemistry

biochemistry   Quick reference

A Dictionary of Chemistry (8 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Chemistry
Length:
801 words

...The study of the chemistry of living organisms, especially the structure and function of their chemical components (principally proteins, carbohydrates, lipids, and nucleic acids). Biochemistry has advanced rapidly with the development, from the mid 20th century, of such techniques as chromatography, X-ray diffraction, radioisotopic labelling, and electron microscopy. Using these techniques to separate and analyse biologically important molecules, the steps of the metabolic pathways in which they are involved (e.g. glycolysis) have been determined. This...

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