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🔗 Mathematics

In symbolic computation (or computer algebra), at the intersection of mathematics and computer science, the Risch algorithm is an algorithm for indefinite integration. It is used in some computer algebra systems to find antiderivatives. It is named after the American mathematician Robert Henry Risch, a specialist in computer algebra who developed it in 1968.

The algorithm transforms the problem of integration into a problem in algebra. It is based on the form of the function being integrated and on methods for integrating rational functions, radicals, logarithms, and exponential functions. Risch called it a decision procedure, because it is a method for deciding whether a function has an elementary function as an indefinite integral, and if it does, for determining that indefinite integral.

The complete description of the Risch algorithm takes over 100 pages. The Risch–Norman algorithm is a simpler, faster, but less powerful variant that was developed in 1976 by Arthur Norman.

🔗 Aviation 🔗 Aviation/Aviation accident 🔗 Africa/Angola 🔗 Africa

On 25 May 2003, a Boeing 727, registered N844AA, was stolen at Quatro de Fevereiro Airport, Luanda, Angola. Its disappearance prompted a worldwide search by the United States' Federal Bureau of Investigation (FBI) and Central Intelligence Agency (CIA). No trace of the aircraft has since been found.

🔗 Mathematics 🔗 Physics

An amplituhedron is a geometric structure introduced in 2013 by Nima Arkani-Hamed and Jaroslav Trnka. It enables simplified calculation of particle interactions in some quantum field theories. In planar N = 4 supersymmetric Yang–Mills theory, also equivalent to the perturbative topological B model string theory in twistor space, an amplituhedron is defined as a mathematical space known as the positive Grassmannian.

Amplituhedron theory challenges the notion that spacetime locality and unitarity are necessary components of a model of particle interactions. Instead, they are treated as properties that emerge from an underlying phenomenon.

The connection between the amplituhedron and scattering amplitudes is at present a conjecture that has passed many non-trivial checks, including an understanding of how locality and unitarity arise as consequences of positivity. Research has been led by Nima Arkani-Hamed. Edward Witten described the work as "very unexpected" and said that "it is difficult to guess what will happen or what the lessons will turn out to be".

🔗 Biography 🔗 Hungary 🔗 Women writers 🔗 Translation studies

Kató Lomb (Pécs, February 8, 1909 – Budapest, June 9, 2003) was a Hungarian interpreter, translator and one of the first simultaneous interpreters in the world. Originally she graduated in physics and chemistry, but her interest soon led her to languages. Native in Hungarian, she was able to interpret fluently in nine or ten languages (in four of them even without preparation), and she translated technical literature and read belles-lettres in six languages.She was able to understand journalism in further eleven languages. As she put it, altogether she earned money with sixteen languages (Bulgarian, Chinese, Danish, English, French, German, Hebrew, Italian, Japanese, Latin, Polish, Romanian, Russian, Slovak, Spanish, Ukrainian). She learned these languages mostly by self-effort, as an autodidact. Her aims to acquire these languages were most of all practical, to satisfy her interest.

According to her own account, her long life was highlighted not primarily by the command of languages but the actual study of them. Through her books, published in Hungarian in several editions as well as in some other languages, interviews (in print and on the air) and conversations, she tried to share this joy with generations. As an interpreter, she visited five continents, saw forty countries, and reported about her experiences and adventures in a separate book (Egy tolmács a világ körül, "An interpreter around the world").

🔗 Books 🔗 Women's History

Around the World in Seventy-Two Days is an 1890 book by journalist Elizabeth Jane Cochrane, writing under her pseudonym, Nellie Bly. The chronicle details her 72-day trip around the world, which was inspired by the book, Around the World in Eighty Days by Jules Verne. She carried out the journey for Joseph Pulitzer's tabloid newspaper, the New York World.

🔗 Aviation 🔗 New Zealand

On 22 December 1978, a small Cessna 188 aircraft, piloted by Jay Prochnow, became lost over the Pacific Ocean. The only other aircraft in the area that was able to assist was a commercial Air New Zealand flight. After several hours of searching, the crew of the Air New Zealand flight located the lost Cessna and led it to Norfolk Island, where the plane landed safely.

🔗 Computer science

In computer science, the shunting-yard algorithm is a method for parsing mathematical expressions specified in infix notation. It can produce either a postfix notation string, also known as Reverse Polish notation (RPN), or an abstract syntax tree (AST). The algorithm was invented by Edsger Dijkstra and named the "shunting yard" algorithm because its operation resembles that of a railroad shunting yard. Dijkstra first described the Shunting Yard Algorithm in the Mathematisch Centrum report MR 34/61.

Like the evaluation of RPN, the shunting yard algorithm is stack-based. Infix expressions are the form of mathematical notation most people are used to, for instance "3 + 4" or "3 + 4 × (2 − 1)". For the conversion there are two text variables (strings), the input and the output. There is also a stack that holds operators not yet added to the output queue. To convert, the program reads each symbol in order and does something based on that symbol. The result for the above examples would be (in Reverse Polish notation) "3 4 +" and "3 4 2 1 − × +", respectively.

The shunting-yard algorithm was later generalized into operator-precedence parsing.

🔗 Philosophy 🔗 Systems 🔗 Philosophy/Social and political philosophy 🔗 Sociology 🔗 Philosophy/Ethics 🔗 Philosophy/Metaphysics

In the social sciences, unintended consequences (sometimes unanticipated consequences or unforeseen consequences) are outcomes of a purposeful action that are not intended or foreseen. The term was popularised in the twentieth century by American sociologist Robert K. Merton.

Unintended consequences can be grouped into three types:

• Unexpected benefit: A positive unexpected benefit (also referred to as luck, serendipity or a windfall).
• Unexpected drawback: An unexpected detriment occurring in addition to the desired effect of the policy (e.g., while irrigation schemes provide people with water for agriculture, they can increase waterborne diseases that have devastating health effects, such as schistosomiasis).
• Perverse result: A perverse effect contrary to what was originally intended (when an intended solution makes a problem worse).

🔗 United States/U.S. Government 🔗 United States 🔗 Law 🔗 Lists

A national emergency is a situation in which a government is empowered to perform actions not normally permitted. The 1976 National Emergencies Act implemented various legal requirements regarding emergencies declared by the President of the United States.

Between the enactment of the National Emergencies Act in 1976 through March 13, 2020, 61 emergencies have been declared; 27 have expired while 34 are currently in effect, each having been renewed annually by the president.

🔗 Mathematics

Sexy primes are prime numbers that differ from each other by 6. For example, the numbers 5 and 11 are both sexy primes, because 11 - 5 = 6.

The term "sexy prime" is a pun stemming from the Latin word for six: sex.

If p + 2 or p + 4 (where p is the lower prime) is also prime, then the sexy prime is part of a prime triplet.