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🔗 Germany 🔗 Time 🔗 Archaeology 🔗 Visual arts 🔗 Fashion

Golden hats (or Gold hats) (German: Goldhüte, singular: Goldhut) are a very specific and rare type of archaeological artifact from Bronze Age Europe. So far, four such objects ("cone-shaped gold hats of the Schifferstadt type") are known. The objects are made of thin sheet gold and were attached externally to long conical and brimmed headdresses which were probably made of some organic material and served to stabilise the external gold leaf. The following Golden Hats are known as of 2012:

• Golden Hat of Schifferstadt, found in 1835 at Schifferstadt near Speyer, c. 1400–1300 BC.
• Avanton Gold Cone, incomplete, found at Avanton near Poitiers in 1844, c. 1000–900 BC.
• Golden Cone of Ezelsdorf-Buch, found near Ezelsdorf near Nuremberg in 1953, c. 1000–900 BC; the tallest known specimen at c. 90 cm.
• Berlin Gold Hat, found probably in Swabia or Switzerland, c. 1000–800 BC; acquired by the Museum für Vor- und Frühgeschichte, Berlin, in 1996.

🔗 Physics 🔗 Physics/relativity

The Gödel metric is an exact solution of the Einstein field equations in which the stress–energy tensor contains two terms, the first representing the matter density of a homogeneous distribution of swirling dust particles (dust solution), and the second associated with a negative cosmological constant (see lambdavacuum solution). It is also known as the Gödel solution or Gödel universe.

This solution has many unusual properties—in particular, the existence of closed timelike curves that would allow time travel in a universe described by the solution. Its definition is somewhat artificial in that the value of the cosmological constant must be carefully chosen to match the density of the dust grains, but this spacetime is an important pedagogical example.

This solution was found in 1949 by Kurt Gödel.

🔗 Computer science 🔗 Mathematics

In computer science and graph theory, the Canadian traveller problem (CTP) is a generalization of the shortest path problem to graphs that are partially observable. In other words, the graph is revealed while it is being explored, and explorative edges are charged even if they do not contribute to the final path.

This optimization problem was introduced by Christos Papadimitriou and Mihalis Yannakakis in 1989 and a number of variants of the problem have been studied since. The name supposedly originates from conversations of the authors who learned of a difficulty Canadian drivers had: traveling a network of cities with snowfall randomly blocking roads. The stochastic version, where each edge is associated with a probability of independently being in the graph, has been given considerable attention in operations research under the name "the Stochastic Shortest Path Problem with Recourse" (SSPPR).

🔗 Numismatics

The EURion constellation (also known as Omron rings or doughnuts) is a pattern of symbols incorporated into a number of banknote designs worldwide since about 1996. It is added to help imaging software detect the presence of a banknote in a digital image. Such software can then block the user from reproducing banknotes to prevent counterfeiting using colour photocopiers. According to research from 2004, the EURion constellation is used for colour photocopiers but probably not used in computer software. It has been reported that Adobe Photoshop will not allow editing of an image of a banknote, but in some versions this is believed to be due to a different, unknown digital watermark rather than the EURion constellation.

🔗 Cognitive science

The Sussman anomaly is a problem in artificial intelligence, first described by Gerald Sussman, that illustrates a weakness of noninterleaved planning algorithms, which were prominent in the early 1970s. In the problem, three blocks (labeled A, B, and C) rest on a table. The agent must stack the blocks such that A is atop B, which in turn is atop C. However, it may only move one block at a time. The problem starts with B on the table, C atop A, and A on the table:

However, noninterleaved planners typically separate the goal (stack A atop B atop C) into subgoals, such as:

1. get A atop B
2. get B atop C

Suppose the planner starts by pursuing Goal 1. The straightforward solution is to move C out of the way, then move A atop B. But while this sequence accomplishes Goal 1, the agent cannot now pursue Goal 2 without undoing Goal 1, since both A and B must be moved atop C:

If instead the planner starts with Goal 2, the most efficient solution is to move B. But again, the planner cannot pursue Goal 1 without undoing Goal 2:

The problem was first identified by Sussman as a part of his PhD research. Sussman (and his supervisor, Marvin Minsky) believed that intelligence requires a list of exceptions or tricks, and developed a modular planning system for "debugging" plans. Most modern planning systems can handle this anomaly, but it is still useful for explaining why planning is non-trivial.

🔗 Companies 🔗 Lists 🔗 Disney

The following is a list of assets owned and operated by The Walt Disney Company, unless otherwise indicated.

🔗 Brazil 🔗 Plants

The Cashew of Pirangi (Cajueiro de Pirangi), also called the world's largest cashew tree (maior cajueiro do mundo), is a cashew tree in Pirangi do Norte, Rio Grande do Norte, Brazil. In 1994, the tree entered the Guinness Book of Records. It covers an area between 7,300 square metres (1.8 acres) and 8,400 square metres (2.1 acres). Having the size of 70 normally sized cashew trees, it has a circumference of 500 m (1,600 ft). The vicinity of the World's Largest Cashew Tree in North Pirangi is also a main place for the sale of lace and embroidery in Rio Grande do Norte state.

The spread over a hectare of land was, unlike other trees, created by the tree's outward growth. When bent towards the ground (because of their weight), the branches tend to take new roots where they touch the ground. This may be seen in the images of the interior. It is now difficult to distinguish the initial trunk from the rest of the tree.

The tree is said to have been planted in 1888. However, based on its growth nature, "the tree is estimated to be more than a thousand years old." The tree produces over 60,000 fruits each year.

Flávio Nogueira, Jr., the state secretary of tourism for Piauí, has claimed that the Cashew of Pirangi in Piauí is, in fact, the largest tree, covering an area of 8,800 square metres (2.2 acres). That tree was studied by a laboratory from the State University of Piauí.

🔗 Biology 🔗 Palaeontology 🔗 Geology

The Boring Billion, otherwise known as the Mid Proterozoic and Earth's Middle Ages, is the time period between 1.8 and 0.8 billion years ago (Ga) spanning the middle Proterozoic eon, characterized by more or less tectonic stability, climatic stasis, and slow biological evolution. It is bordered by two different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.

The oceans may have been oxygen- and nutrient-poor and sulfidic (euxinia), populated by mainly anoxygenic purple bacteria, a type of chlorophyll-based photosynthetic bacteria which uses hydrogen sulfide (H₂S) instead of water and produces sulfur instead of oxygen. This is known as a Canfield ocean. Such composition may have caused the oceans to be black- and milky-turquoise instead of blue. (By contrast, during the much earlier Purple Earth phase the photosynthesis was retinal-based.)

Despite such adverse conditions, eukaryotes may have evolved around the beginning of the Boring Billion, and adopted several novel adaptations, such as various organelles, multicellularity, and possibly sexual reproduction, and diversified into plants, animals, and fungi at the end of this time interval. Such advances may have been important precursors to the evolution of large, complex life later in the Ediacaran and Phanerozoic. Nonetheless, prokaryotic cyanobacteria were the dominant lifeforms during this time, and likely supported an energy-poor food-web with a small number of protists at the apex level. The land was likely inhabited by prokaryotic cyanobacteria and eukaryotic proto-lichens, the latter more successful here probably due to the greater availability of nutrients than in offshore ocean waters.

🔗 Indigenous peoples of the Americas 🔗 Peru

Quipu (also spelled khipu) are recording devices fashioned from strings historically used by a number of cultures in the region of Andean South America. Knotted strings were used by many other cultures such as the ancient Chinese and native Hawaiians, but such practices should not be confused with the quipu, which refers only to the Andean device.

A quipu usually consisted of cotton or camelid fiber strings. The Inca people used them for collecting data and keeping records, monitoring tax obligations, properly collecting census records, calendrical information, and for military organization. The cords stored numeric and other values encoded as knots, often in a base ten positional system. A quipu could have only a few or thousands of cords. The configuration of the quipus has been "compared to string mops." Archaeological evidence has also shown the use of finely carved wood as a supplemental, and perhaps more sturdy, base to which the color-coded cords would be attached. A relatively small number have survived.

Objects that can be identified unambiguously as quipus first appear in the archaeological record in the first millennium AD. They subsequently played a key part in the administration of the Kingdom of Cusco and later Tawantinsuyu, the empire controlled by the Inca ethnic group, flourishing across the Andes from c. 1100 to 1532 AD. As the region was subsumed under the invading Spanish Empire, the quipu faded from use, to be replaced by European writing and numeral systems. However, in several villages, quipu continued to be important items for the local community, albeit for ritual rather than practical use. It is unclear as to where and how many intact quipus still exist, as many have been stored away in mausoleums.

Quipu is the Spanish spelling and the most common spelling in English. Khipu (pronounced [ˈkʰɪpʊ], plural: khipukuna) is the word for "knot" in Cusco Quechua. In most Quechua varieties, the term is kipu.