Have a deep view into what people are curious about.

🔗 Aviation 🔗 Aviation/aircraft

The Airbus Beluga XL (Airbus A330-743L) is a large transport aircraft based on the Airbus A330 airliner. The aircraft entered service with Airbus Transport on 9 January 2020 to replace the Airbus Beluga in the movement of oversized aircraft components, for example wings. The Beluga XL made its first flight on 19 July 2018, and received its type certification on 13 November 2019.

It made its first operational flight on January 9, 2020, and by January 20, had entered full-time service.

🔗 Visual arts 🔗 Morocco

Zellige (Arabic: [zˈliʑ]; Arabic: الزليج‎; also zelige or zellij or zileej) is mosaic tilework made from individually chiseled geometric tiles set into a plaster base. This form of Islamic art is one of the main characteristics of Moroccan architecture. It consists of geometrically patterned mosaics, used to ornament walls, ceilings, fountains, floors, pools and tables. The Moroccan traditional patterns and styles are found inside famous buildings such as Al-Qarawiyyin Mosque in Fez, the Alhambra in Granada, Spain, the Great Mosque of Cordoba, the Ben Youssef Madrasa in Marrakech, and the Hassan II mosque in Casablanca, which adds a new color palette with traditional designs.

🔗 Statistics

Nelson rules are a method in process control of determining if some measured variable is out of control (unpredictable versus consistent). Rules, for detecting "out-of-control" or non-random conditions were first postulated by Walter A. Shewhart in the 1920s. The Nelson rules were first published in the October 1984 issue of the Journal of Quality Technology in an article by Lloyd S Nelson.

The rules are applied to a control chart on which the magnitude of some variable is plotted against time. The rules are based on the mean value and the standard deviation of the samples.

The above eight rules apply to a chart of a variable value.

A second chart, the moving range chart, can also be used but only with rules 1, 2, 3 and 4. Such a chart plots a graph of the maximum value - minimum value of N adjacent points against the time sample of the range.

An example moving range: if N = 3 and values are 1, 3, 5, 3, 3, 2, 4, 5 then the sets of adjacent points are (1,3,5) (3,5,3) (5,3,3) (3,3,2) (3,2,4) (2,4,5) resulting in moving range values of (5-1) (5-3) (5-3) (3-2) (4-2) (5-2) = 4, 2, 2, 1, 2, 3.

Applying these rules indicates when a potential "out of control" situation has arisen. However, there will always be some false alerts and the more rules applied the more will occur. For some processes, it may be beneficial to omit one or more rules. Equally there may be some missing alerts where some specific "out of control" situation is not detected. Empirically, the detection accuracy is good.

🔗 Physics

Isaac Newton's rotating bucket argument (also known as Newton's bucket) was designed to demonstrate that true rotational motion cannot be defined as the relative rotation of the body with respect to the immediately surrounding bodies. It is one of five arguments from the "properties, causes, and effects" of "true motion and rest" that support his contention that, in general, true motion and rest cannot be defined as special instances of motion or rest relative to other bodies, but instead can be defined only by reference to absolute space. Alternatively, these experiments provide an operational definition of what is meant by "absolute rotation", and do not pretend to address the question of "rotation relative to what?" General relativity dispenses with absolute space and with physics whose cause is external to the system, with the concept of geodesics of spacetime.

🔗 Mathematics 🔗 Ancient Egypt 🔗 British Museum

The Rhind Mathematical Papyrus (RMP; also designated as papyrus British Museum 10057 and pBM 10058) is one of the best known examples of ancient Egyptian mathematics. It is named after Alexander Henry Rhind, a Scottish antiquarian, who purchased the papyrus in 1858 in Luxor, Egypt; it was apparently found during illegal excavations in or near the Ramesseum. It dates to around 1550 BC. The British Museum, where the majority of the papyrus is now kept, acquired it in 1865 along with the Egyptian Mathematical Leather Roll, also owned by Henry Rhind. There are a few small fragments held by the Brooklyn Museum in New York City and an 18 cm (7.1 in) central section is missing. It is one of the two well-known Mathematical Papyri along with the Moscow Mathematical Papyrus. The Rhind Papyrus is larger than the Moscow Mathematical Papyrus, while the latter is older.

The Rhind Mathematical Papyrus dates to the Second Intermediate Period of Egypt. It was copied by the scribe Ahmes (i.e., Ahmose; Ahmes is an older transcription favoured by historians of mathematics), from a now-lost text from the reign of king Amenemhat III (12th dynasty). Written in the hieratic script, this Egyptian manuscript is 33 cm (13 in) tall and consists of multiple parts which in total make it over 5 m (16 ft) long. The papyrus began to be transliterated and mathematically translated in the late 19th century. The mathematical translation aspect remains incomplete in several respects. The document is dated to Year 33 of the Hyksos king Apophis and also contains a separate later historical note on its verso likely dating from the period ("Year 11") of his successor, Khamudi.

In the opening paragraphs of the papyrus, Ahmes presents the papyrus as giving "Accurate reckoning for inquiring into things, and the knowledge of all things, mysteries ... all secrets". He continues with:

This book was copied in regnal year 33, month 4 of Akhet, under the majesty of the King of Upper and Lower Egypt, Awserre, given life, from an ancient copy made in the time of the King of Upper and Lower Egypt Nimaatre. The scribe Ahmose writes this copy.

Several books and articles about the Rhind Mathematical Papyrus have been published, and a handful of these stand out. The Rhind Papyrus was published in 1923 by Peet and contains a discussion of the text that followed Griffith's Book I, II and III outline. Chace published a compendium in 1927–29 which included photographs of the text. A more recent overview of the Rhind Papyrus was published in 1987 by Robins and Shute.

🔗 Russia 🔗 Mathematics 🔗 Statistics 🔗 Russia/science and education in Russia

In statistics, the Gauss–Markov theorem states that the ordinary least squares (OLS) estimator has the lowest sampling variance within the class of linear unbiased estimators, if the errors in the linear regression model are uncorrelated, have equal variances and expectation value of zero. The errors do not need to be normal, nor do they need to be independent and identically distributed (only uncorrelated with mean zero and homoscedastic with finite variance). The requirement that the estimator be unbiased cannot be dropped, since biased estimators exist with lower variance. See, for example, the James–Stein estimator (which also drops linearity) or ridge regression.

The theorem was named after Carl Friedrich Gauss and Andrey Markov, although Gauss' work significantly predates Markov's. But while Gauss derived the result under the assumption of independence and normality, Markov reduced the assumptions to the form stated above. A further generalization to non-spherical errors was given by Alexander Aitken.

🔗 Economics 🔗 Sociology

The Lindy effect is a theory that the future life expectancy of some non-perishable things like a technology or an idea is proportional to their current age, so that every additional period of survival implies a longer remaining life expectancy. Where the Lindy effect applies, mortality rate decreases with time.

🔗 California 🔗 Law

The Mulford Act was a 1967 California bill that repealed a law allowing public carrying of loaded firearms. Named after Republican assemblyman Don Mulford, and signed into law by governor of California Ronald Reagan, the bill was crafted with the goal of disarming members of the Black Panther Party who were conducting armed patrols of Oakland neighborhoods, in what would later be termed copwatching. They garnered national attention after Black Panthers members, bearing arms, marched upon the California State Capitol to protest the bill.

Assembly Bill 1591 was introduced by Don Mulford (R) from Oakland on April 5, 1967, and subsequently co-sponsored by John T. Knox (D) from Richmond, Walter J. Karabian (D) from Monterey Park, Frank Murphy Jr. (R) from Santa Cruz, Alan Sieroty (D) from Los Angeles, and William M. Ketchum (R) from Bakersfield. AB-1591 was made an “urgency statute” under Article IV, §8(d) of the Constitution of California after “an organized band of men armed with loaded firearms [...] entered the Capitol” on May 2, 1967; as such, it required a 2/3 majority in each house. It passed the Assembly (controlled by Democrats, 42:38) at subsequent readings, passed the Senate (controlled by Democrats, 20:19) on July 26 by 29 votes to 7, and was signed by Governor Ronald Reagan on July 28, 1967. The law banned the carrying of loaded weapons in public.

Both Republicans and Democrats in California supported increased gun control, as did the National Rifle Association of America. Governor Ronald Reagan, who was coincidentally present on the capitol lawn when the protesters arrived, later commented that he saw "no reason why on the street today a citizen should be carrying loaded weapons" and that guns were a "ridiculous way to solve problems that have to be solved among people of good will." In a later press conference, Reagan added that the Mulford Act "would work no hardship on the honest citizen."

The bill was signed by Reagan and became California penal code 25850 and 171c.

🔗 California 🔗 Companies 🔗 Technology 🔗 Private Equity 🔗 California/San Francisco Bay Area

Y Combinator is an American seed accelerator launched in March 2005 and has been used to launch over 2,000 companies including Stripe, Airbnb, Cruise Automation, DoorDash, Coinbase, Instacart, and Dropbox. The combined valuation of the top YC companies was over $155 billion as of October, 2019.

🔗 Mathematics 🔗 Germany 🔗 Germany/Prussia

The Seven Bridges of Königsberg is a historically notable problem in mathematics. Its negative resolution by Leonhard Euler in 1736 laid the foundations of graph theory and prefigured the idea of topology.

The city of Königsberg in Prussia (now Kaliningrad, Russia) was set on both sides of the Pregel River, and included two large islands—Kneiphof and Lomse—which were connected to each other, or to the two mainland portions of the city, by seven bridges. The problem was to devise a walk through the city that would cross each of those bridges once and only once.

By way of specifying the logical task unambiguously, solutions involving either

1. reaching an island or mainland bank other than via one of the bridges, or
2. accessing any bridge without crossing to its other end

are explicitly unacceptable.

Euler proved that the problem has no solution. The difficulty he faced was the development of a suitable technique of analysis, and of subsequent tests that established this assertion with mathematical rigor.