Opal

Opal is a hydrated amorphous form of silica (SiO₂·nH₂O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.

The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semitransparent.

Precious opal

Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice. It was shown by J. V. Sanders in the mid-1960s, that these ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of the opal. The regularity of the sizes and the packing of these spheres determines the quality of precious opal. Where the distance between the regularly packed planes of spheres is around half the wavelength of a component of visible light, the light of that wavelength may be subject to diffraction from the grating created by the stacked planes. The colors that are observed are determined by the spacing between the planes and the orientation of planes with respect to the incident light. The process can be described by Bragg's law of diffraction.

Opal (armoured personnel carrier)

The Opal-I is a multi-purpose fully amphibious armoured personnel carrier developed and produced by HSW S.A.. APC is a development of MT-LB that was produced in HSW on licence. Major changes are with reworked nose section and propellers for better in water speed and manoeuvrability, new turret with 12.7 mm NSVT machine-gun instead of old with 7.62 PKT and powered-up engine. Opal-II is a stretched variant with longer chassis with 7 road wheels on each side, like the 2S1 and MT-LBu and 300 hp (220 kW) SW680T engine.

Variants

WPT Mors

(WPT for Wóz Pogotowia Technicznego - lit Technical Support Vehicle) - technical support vehicle with light crane, hydraulic dozerblade, welding equipment and an NBC detection system. The vehicle is a basic support vehicle of mechanized battalions equipped with BMP-1 IFV in Polish Land Forces.

TRI Hors

(TRI for Transporter Rozpoznania Inżynieryjnego - lit. Engineering Reconnaissance Vehicle) - engineering vehicle with basic equipment. In use with Polish Land Forces.

List of recurring The Simpsons characters

The Simpsons includes a large array of supporting characters: co-workers, teachers, family friends, extended relatives, townspeople, local celebrities, fictional characters within the show, and even animals. The writers originally intended many of these characters as one-time jokes or for fulfilling needed functions in the town. A number of them have gained expanded roles and have subsequently starred in their own episodes. According to the creator of The Simpsons, Matt Groening, the show adopted the concept of a large supporting cast from the Canadian sketch comedy show Second City Television.

Agnes Skinner

Agnes Skinner (voiced by Tress MacNeille) is the mother of Principal Skinner and first appeared in the first season episode "The Crepes of Wrath" as an old woman who embarrassingly calls her son "Spanky". However, as episodes progressed, the character turned bitter. She is very controlling of her son and often treats him as if he is a child. She hates Edna Krabappel due to her son's feelings for the other woman. Agnes has married four times. Several Springfield residents (including the Simpsons) are afraid of her. When "the real Seymour Skinner" arrives in Springfield, Agnes ends up rejecting him in part because he stands up to her, but also because unlike Skinner/Tamzarian, her biological son is independent and doesn't need her anymore, while Skinner immediately reverts to a good-for-nothing without her.