SUMMARY / RELATED TOPICS

Transparency and translucency

In the field of optics, transparency is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale, the photons can be said to follow Snell's Law. Translucency allows light to pass through, but does not follow Snell's law. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction. Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color; the opposite property of translucency is opacity. When light encounters a material, it can interact with it in several different ways; these interactions depend on the nature of the material. Photons interact with an object by some combination of reflection and transmission; some materials, such as plate glass and clean water, transmit much of the light that falls on them and reflect little of it.

Many liquids and aqueous solutions are transparent. Absence of structural defects and molecular structure of most liquids are responsible for excellent optical transmission. Materials which do not transmit light are called opaque. Many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of white light frequencies, they absorb certain portions of the visible spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation; this is. The attenuation of light of all frequencies and wavelengths is due to the combined mechanisms of absorption and scattering. Transparency can provide perfect camouflage for animals able to achieve it; this is easier in turbid seawater than in good illumination. Many marine animals such as jellyfish are transparent. With regard to the absorption of light, primary material considerations include: At the electronic level, absorption in the ultraviolet and visible portions of the spectrum depends on whether the electron orbitals are spaced such that they can absorb a quantum of light of a specific frequency, does not violate selection rules.

For example, in most glasses, electrons have no available energy levels above them in range of that associated with visible light, or if they do, they violate selection rules, meaning there is no appreciable absorption in pure glasses, making them ideal transparent materials for windows in buildings. At the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, on selection rules. Nitrogen and oxygen are not greenhouse gases. With regard to the scattering of light, the most critical factor is the length scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include: Crystalline structure: whether or not the atoms or molecules exhibit the'long-range order' evidenced in crystalline solids. Glassy structure: scattering centers include fluctuations in density or composition. Microstructure: scattering centers include internal surfaces such as grain boundaries, crystallographic defects and microscopic pores.

Organic materials: scattering centers include fiber and cell structures and boundaries. Diffuse reflection - Generally, when light strikes the surface of a solid material, it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material, by its surface, if it is rough. Diffuse reflection is characterized by omni-directional reflection angles. Most of the objects visible to the naked eye are identified via diffuse reflection. Another term used for this type of reflection is "light scattering". Light scattering from the surfaces of objects is our primary mechanism of physical observation. Light scattering in liquids and solids depends on the wavelength of the light being scattered. Limits to spatial scales of visibility therefore arise, depending on the frequency of the light wave and the physical dimension of the scattering center. Visible light has a wavelength scale on the order of a half a micrometer. Scattering centers as small. Optical transparency in polycrystalline materials is limited by the amount of light, scattered by their microstructural features.

Light scattering depends on the wavelength of the light. Limits to spatial scales of visibility therefore arise, depending on the frequency of the light wave and the physical dimension of the scattering center. For example, since visible light has a wavelength scale on the order of a micrometer, scattering centers will have dimensions on a similar spatial scale. Primary scattering centers in polycrystalline materials include microstructural defec

Doug Rickard

Doug Rickard was an Australian-born space engineer. He is known for his stories of engineering while at the Woomera Deep Space Station, he died in 2002 from myelofibrosis caused by contact with cobalt-60 while working at the Maralinga nuclear test facility. Some of his stories have been collected by the Australian Broadcasting Corporation, whose logo he inspired, under the title Memoirs of a space engineer. Additional humorous engineering stories include hand-decoding images from Mariner 4 onto a sheet of graph paper since NASA JPL had only built a single display system, running a magnetic tape recorder 25 times over its rated speed to have enough bandwidth to record Ranger 9 video of its impact on the moon, an impromptu excavation of Pompeii's plumbing systems. Rickard worked for some time for the Australian subsidiary of Digital Equipment Corporation. During that time he was seconded to Project Athena, the Campuswide Computing environment developed at MIT, with the specific responsibility of developing "Bones" a version of the Kerberos Authentication System, that did not relying on strong encryption, as such would not require US Government approval for export

Tiger Palpatja

Tiger Palpatja was an Australian Aboriginal artist from the Aṉangu Pitjantjatjara Yankunytjatjara Lands. Tiger was born around 1920, he was born in the bush, at a rockhole called Piltati, close to what is now Nyapaṟi in north-west South Australia. His family were Pitjantjatjara, they lived a traditional, nomadic life in the bushland around Piltati; when he was a teenager, Tiger's family settled at Ernabella, which at the time was a Presbyterian mission and a sheep station. Tiger grew up on the mission, learned to speak a little English in school there, he married Nyalapanytja, they lived in Ernabella for many years. Tiger worked on the station, shearing building fences. In the 1970s, Tiger and his family moved to Amaṯa, closer to his homeland; when he aged, Tiger became a ngangkaṟi, an important and respected role in traditional Pitjantjatjara communities. In 1997, the women at Amaṯa began a community art centre called Minymaku Arts; the word minymaku means "women's", they called it this because, at the time, Pitjantjatjara men did not like to paint.

After several men began painting in the early 2000s, the centre's name was changed to Tjala Arts. Tiger started painting less than eight years before his death, he had never painted before this, was better known for woodworking making spears. Although he only began painting in his final years, his work became recognised by critics. In 2005, Tiger was a finalist for the National Torres Strait Islander Art Award, he became a finalist three more time before his death, in 2006, 2010, 2011, but he never won. He was a finalist in the Western Australian Indigenous Art Awards in 2009, again in 2011. Tiger painted for Tjala Arts, but from 2009 he began working for Tjungu Palya in nearby Nyapaṟi. Tiger's painted sacred stories from his Dreaming to do with Piltati, where he was born; this place is associated with a creation story involving two sisters and their husbands, who change themselves into Wanampi. According to Tiger's Dreaming, the Wanampi are his family's ancestors who created the country around Piltati.

The snake's form can be seen in many of Tiger's paintings painted several different colours. His paintings were known for their bright colours, as opposed to the traditional natural ochre colours used by many other artists of the Western Desert. Tiger died on 16 April 2012, over the age of 90. While he was alive, his paintings were exhibited in several major cities, including Sydney, Adelaide and Perth, his work is now held in permanent galleries in most of these cities. He had work exhitied overseas: at the University of Virginia in 2006, in Singapore in 2008, his paintings are held in the National Gallery of Victoria, the National Gallery of Australia, the Australian National University, Charles Darwin University, Flinders University, the Art Gallery of New South Wales. Tiger Palpatja at Design & Art Australia Online