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🔗 Physics 🔗 Telecommunications 🔗 Astronomy 🔗 Electrical engineering 🔗 Glass

A photon sieve is a device for focusing light using diffraction and interference. It consists of a flat sheet of material full of pinholes that are arranged in a pattern which is similar to the rings in a Fresnel zone plate, but a sieve brings light to much sharper focus than a zone plate. The sieve concept, first developed in 2001, is versatile because the characteristics of the focusing behaviour can be altered to suit the application by manufacturing a sieve containing holes of several different sizes and different arrangement of the pattern of holes.

Photon sieves have applications to photolithography. and are an alternative to lenses or mirrors in telescopes and terahertz lenses and antennas.

When the size of sieves is smaller than one wavelength of operating light, the traditional method mentioned above to describe the diffraction patterns is not valid. The vectorial theory must be used to approximate the diffraction of light from nanosieves. In this theory, the combination of coupled-mode theory and multiple expansion method is used to give an analytical model, which can facilitate the demonstration of traditional devices such as lenses and holograms.

🔗 United States 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 United States/Military history - U.S. military history 🔗 Military history/Military science, technology, and theory 🔗 Physics 🔗 Women's History 🔗 History of Science 🔗 Tennessee 🔗 Military history/World War II 🔗 Physics/History 🔗 Science

The Calutron Girls were a group of young women, mostly high school graduates who joined the World War II efforts in Oak Ridge, Tennessee in 1945.

Although they were not allowed to know at the time, they were monitoring dials and watching meters for a calutron, a mass spectrometer that separates uranium isotopes. The enriched uranium was used to make the first atomic bomb.

Calutron Girls were trained and employed at the Y-12 National Security Complex. Wartime labor shortages forced the Tennessee Eastman Corporation to hire women to work at the Y-12 plant.

According to Gladys Owens, one of the few Calutron Girls, a manager at the facility once told them: "We can train you how to do what is needed, but cannot tell you what you are doing. I can only tell you that if our enemies beat us to it, God have mercy on us!"

🔗 Vietnam

The Đông Yên Châu inscription is an Old Cham inscription written in Pallava script, found in 1936 at Đông Yên Châu, northwest of Trà Kiệu, which used to be the old Champa capital known as Simhapura, in central Vietnam. The inscription was written in prose, is the oldest document of Cham (and indeed of any Austronesian language), and testifies to the existence of indigenous beliefs among the ancient Cham people of the Champa kingdom. Though not itself dated, the phrasing of the inscription is identical to those of dated Sanskrit inscriptions of Bhadravarman I of the second dynasty, who ruled Champa at the end of the 4th century CE. It contains an imprecatory formula ordering respect for the "naga of the king", undoubtedly a reference to the protective divinity of a spring or well. This vernacular text shows that in the 4th century, the land that now constitutes modern-day central Vietnam was inhabited by an Austronesian-speaking population. The evidence, both monumental and palaeographic, also suggests that Hinduism was the predominant religious system.

The fact that the language in the inscription shares some basic grammar and vocabulary with Malay has led some scholars to argue that the inscription contains the oldest specimen of Malay words in the form of Old Malay, older by three centuries than the earliest Srivijayan inscriptions from southeastern Sumatra. However, most scholars consider it established that this inscription was written in Old Cham instead. The shared basic grammar and vocabulary comes as no surprise, since Chamic and Malayic languages are closely related; both are the two subgroups of a Malayic–Chamic group within the Malayo-Polynesian branch of the Austronesian family.

🔗 Africa 🔗 Writing systems 🔗 Igbo 🔗 Africa/Nigeria

Nsibidi (also known as nsibiri, nchibiddi or nchibiddy) is a system of symbols indigenous to what is now southeastern Nigeria that are apparently pictograms, though there have been suggestions that some are logograms or syllabograms. The symbols are at least over 4,000 years old. Early forms appeared on excavated pottery as well as what are most likely ceramic stools and headrests from the Calabar region with a range of dates from at least 400 AD (and possibly earlier), to 1400 AD. Nsibidi was used to decorate the skin, calabashes, sculptures, and clothing items, as well as to communicate messages on houses.“ There are thousands of nsibidi symbols, of which over 500 have been recorded. They were once taught in a school to children. Many of the signs deal with love affairs; those that deal with warfare and the sacred are kept secret. Nsibidi is used on wall designs, calabashes, metals (such as bronze), leaves, swords, and tattoos. It is primarily used by the Ekpe leopard society (also known as Ngbe or Egbo), a secret society that is found across Cross River State among the Ekoi, Efik, Igbo people, and other nearby peoples.

Outside knowledge of nsibidi came in 1904 when T. D. Maxwell noticed the symbols. Before the British colonisation of the area, nsibidi was divided into a sacred version and a public, more decorative version which could be used by women. Aspects of colonisation such as Western education and Christian doctrine drastically reduced the number of nsibidi-literate people, leaving the secret society members as some of the last literate in the symbols. Nsibidi was and is still a means of transmitting Ekpe symbolism. Nsibidi was transported to Cuba and Haiti via the Atlantic slave trade, where it developed into the anaforuana and veve symbols.

🔗 Computing

SETL (SET Language) is a very high-level programming language based on the mathematical theory of sets. It was originally developed at the New York University (NYU) Courant Institute of Mathematical Sciences in the late 1960s, by a group including (Jack) Jacob T. Schwartz, R.B.K. Dewar, and E. Schonberg. Schwartz is credited with designing the language.

🔗 Architecture

Atlantropa, also referred to as Panropa, was a gigantic engineering and colonisation idea devised by the German architect Herman Sörgel in the 1920s and promoted by him until his death in 1952. Its central feature was a hydroelectric dam to be built across the Strait of Gibraltar, which would have provided enormous amounts of hydroelectricity and would have led to the lowering of the surface of the Mediterranean Sea by up to 200 metres (660 ft), opening up large new lands for settlement, for example in the Adriatic Sea. The project proposed four additional major dams as well:

• Across the Dardanelles to hold back the Black Sea
• Between Sicily and Tunisia to provide a roadway and further lower the inner Mediterranean
• On the Congo River below its Kwah River tributary to refill the Mega-Chad basin around Lake Chad providing fresh water to irrigate the Sahara and creating a shipping lane to the interior of Africa
• Suez Canal extension and locks to maintain Red Sea connection

Sörgel saw his scheme, projected to take over a century, as a peaceful European-wide alternative to the Lebensraum concepts that later became one of the stated reasons for Nazi Germany's conquest of new territories. Atlantropa would provide land and food, employment, electric power, and most of all, a new vision for Europe and neighbouring Africa.

The Atlantropa movement, through its several decades, was characterised by four constants:

• Pacifism, in its promises of using technology in a peaceful way;
• Pan-European sentiment, seeing the project as a way to unite a war-torn Europe;
• Eurocentric attitudes to Africa (which was to become united with Europe into "Atlantropa" or Eurafrica), and
• Neo-colonial geopolitics, which saw the world divided into three blocs—America, Asia, and Atlantropa.

Active support was limited to architects and planners from Germany and a number of other primarily northern European countries. Critics derided it for various faults, ranging from lack of any cooperation of Mediterranean countries in the planning to the impacts it would have had on the historic coastal communities left stranded inland when the sea receded. The project reached great popularity in the late 1920s to the early 1930s, and for a short period again, in the late 1940s to the early 1950s, but soon disappeared from general discourse again after Sörgel's death.

🔗 Mathematics

Pentagramma mirificum (Latin for miraculous pentagram) is a star polygon on a sphere, composed of five great circle arcs, all of whose internal angles are right angles. This shape was described by John Napier in his 1614 book Mirifici logarithmorum canonis descriptio (Description of the wonderful rule of logarithms) along with rules that link the values of trigonometric functions of five parts of a right spherical triangle (two angles and three sides). The properties of pentagramma mirificum were studied, among others, by Carl Friedrich Gauss.

🔗 Wiltshire

The Salisbury cathedral clock is a large iron-framed tower clock without a dial, in Salisbury Cathedral, England. Supposedly dating from about 1386, it is a well-preserved example of the earliest type of mechanical clock, called verge and foliot clocks, and is said to be the oldest working clock in the world, although similar claims are made for other clocks. Previously in a bell-tower which was demolished in 1790, the clock was restored to working condition in 1956 and is on display in the North nave aisle of the cathedral, close to the West front.

🔗 Military history 🔗 Military history/Early Modern warfare 🔗 Military history/Medieval warfare 🔗 Former countries 🔗 Czech Republic 🔗 Former countries/Holy Roman Empire

The Defenestrations of Prague (Czech: Pražská defenestrace, German: Prager Fenstersturz, Latin: Defenestratio Pragensis) were three incidents in the history of Bohemia in which people were defenestrated (thrown out of a window). Though already existing in Middle French, the word defenestrate ("out of the window") is believed to have first been used in English in reference to the episodes in Prague in 1618 when the disgruntled Protestant estates threw two royal governors and their secretary out of a window of the Hradčany Castle and wrote an extensive apologia explaining their action. In the Middle Ages and early modern times, defenestration was not uncommon—the act carried elements of lynching and mob violence in the form of murder committed together.

The first governmental defenestration occurred in 1419, the second in 1483 and the third in 1618, although the term "Defenestration of Prague" more commonly refers to the third. Often, however, the 1483 event is not recognized as a "significant defenestration", which leads to some ambiguity when the 1618 defenestration is referred to as the "second Prague defenestration". The first and third defenestrations helped to trigger a prolonged religious conflict inside Bohemia (the Hussite Wars, 1st defenestration) or beyond (Thirty Years' War, 3rd defenestration), while the second helped establish a religious peace in the country for 31 years (Peace of Kutná Hora, 2nd defenestration).

🔗 Economics 🔗 Sociology

Commons-based peer production (CBPP) is a term coined by Harvard Law School professor Yochai Benkler. It describes a model of socio-economic production in which large numbers of people work cooperatively; usually over the Internet. Commons-based projects generally have less rigid hierarchical structures than those under more traditional business models. Often—but not always—commons-based projects are designed without a need for financial compensation for contributors. For example, sharing of STL (file format) design files for objects freely on the internet enables anyone with a 3-D printer to digitally replicate the object saving the prosumer significant money.

The term is often used interchangeably with the term social production.