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🔗 Horse racing

Potoooooooo or variations of Pot-8-Os (1773 – November 1800) was an 18th-century thoroughbred racehorse who won over 30 races and defeated some of the greatest racehorses of the time. He went on to be a sire. He is now best known for the unusual spelling of his name, pronounced 'Potatoes'.

🔗 Norway

The Norwegian butter crisis began in late 2011 with an acute shortage of butter and inflation of its price across markets in Norway. The shortage caused soaring prices and stores' stocks of butter ran out within minutes of deliveries. According to the Danish tabloid B.T., Norway was gripped by smør-panik ("butter panic") as a result of the butter shortage.

🔗 Netherlands 🔗 Speed Skating 🔗 Frisia

The Elfstedentocht (Dutch pronunciation: [ɛlf'steːdə(n)tɔxt]; West Frisian: Alvestêdetocht [ɔlvəˈstɛːdətɔχt], English: Eleven cities tour) is a long-distance tour skating event on natural ice, almost 200 kilometres (120 mi) long, which is held both as a speed skating competition (with 300 contestants) and a leisure tour (with 16,000 skaters). It is held in the province of Friesland in the north of the Netherlands, leading past all eleven historical cities of the province. The tour is held at most once a year, only when the natural ice along the entire course is at least 15 centimetres (6 in) thick; sometimes on consecutive years, other times with gaps that may exceed 20 years. When the ice is suitable, the tour is announced and starts within 48 hours.

🔗 United States 🔗 Biography 🔗 Internet 🔗 Computing 🔗 Internet culture 🔗 New York City 🔗 Biography/science and academia 🔗 Biography/arts and entertainment 🔗 United States/Massachusetts 🔗 Chicago 🔗 Open 🔗 United States/Massachusetts - Boston 🔗 Open Access

Aaron Hillel Swartz (November 8, 1986 – January 11, 2013) was an American computer programmer, entrepreneur, writer, political organizer, and Internet hacktivist. He was involved in the development of the web feed format RSS, the Markdown publishing format, the organization Creative Commons, and the website framework web.py, and joined the social news site Reddit six months after its founding. He was given the title of co-founder of Reddit by Y Combinator owner Paul Graham after the formation of Not a Bug, Inc. (a merger of Swartz's project Infogami and Redbrick Solutions, a company run by Alexis Ohanian and Steve Huffman). Swartz's work also focused on civic awareness and activism. He helped launch the Progressive Change Campaign Committee in 2009 to learn more about effective online activism. In 2010, he became a research fellow at Harvard University's Safra Research Lab on Institutional Corruption, directed by Lawrence Lessig. He founded the online group Demand Progress, known for its campaign against the Stop Online Piracy Act.

In 2011, Swartz was arrested by Massachusetts Institute of Technology (MIT) police on state breaking-and-entering charges, after connecting a computer to the MIT network in an unmarked and unlocked closet, and setting it to download academic journal articles systematically from JSTOR using a guest user account issued to him by MIT. Federal prosecutors, led by Carmen Ortiz, later charged him with two counts of wire fraud and eleven violations of the Computer Fraud and Abuse Act, carrying a cumulative maximum penalty of $1 million in fines, 35 years in prison, asset forfeiture, restitution, and supervised release. Swartz declined a plea bargain under which he would have served six months in federal prison. Two days after the prosecution rejected a counter-offer by Swartz, he was found dead by suicide in his Brooklyn apartment. In 2013, Swartz was inducted posthumously into the Internet Hall of Fame.

🔗 Mathematics

The Ulam spiral or prime spiral is a graphical depiction of the set of prime numbers, devised by mathematician Stanisław Ulam in 1963 and popularized in Martin Gardner's Mathematical Games column in Scientific American a short time later. It is constructed by writing the positive integers in a square spiral and specially marking the prime numbers.

Ulam and Gardner emphasized the striking appearance in the spiral of prominent diagonal, horizontal, and vertical lines containing large numbers of primes. Both Ulam and Gardner noted that the existence of such prominent lines is not unexpected, as lines in the spiral correspond to quadratic polynomials, and certain such polynomials, such as Euler's prime-generating polynomial x² − x + 41, are believed to produce a high density of prime numbers. Nevertheless, the Ulam spiral is connected with major unsolved problems in number theory such as Landau's problems. In particular, no quadratic polynomial has ever been proved to generate infinitely many primes, much less to have a high asymptotic density of them, although there is a well-supported conjecture as to what that asymptotic density should be.

In 1932, more than thirty years prior to Ulam's discovery, the herpetologist Laurence Klauber constructed a triangular, non-spiral array containing vertical and diagonal lines exhibiting a similar concentration of prime numbers. Like Ulam, Klauber noted the connection with prime-generating polynomials, such as Euler's.

🔗 Electronics

The two capacitor paradox or capacitor paradox is a paradox, or counterintuitive thought experiment, in electric circuit theory. The thought experiment is usually described as follows: Two identical capacitors are connected in parallel with an open switch between them. One of the capacitors is charged with a voltage of ${\displaystyle V_{i}}$, the other is uncharged. When the switch is closed, some of the charge ${\displaystyle Q=CV_{i}}$ on the first capacitor flows into the second, reducing the voltage on the first and increasing the voltage on the second. When a steady state is reached and the current goes to zero, the voltage on the two capacitors must be equal since they are connected together. Since they both have the same capacitance ${\displaystyle C}$ the charge will be divided equally between the capacitors so each capacitor will have a charge of ${\displaystyle {Q \over 2}}$ and a voltage of ${\displaystyle V_{f}={Q \over 2C}={V_{i} \over 2}}$. At the beginning of the experiment the total initial energy ${\displaystyle W_{i}}$ in the circuit is the energy stored in the charged capacitor:

${\displaystyle W_{i}={1 \over 2}CV_{i}^{2}}$.

At the end of the experiment the final energy ${\displaystyle W_{f}}$ is equal to the sum of the energy in the two capacitors

${\displaystyle W_{f}={1 \over 2}CV_{f}^{2}+{1 \over 2}CV_{f}^{2}=CV_{f}^{2}=C({V_{i} \over 2})^{2}={1 \over 4}CV_{i}^{2}={1 \over 2}W_{i}}$

Thus the final energy ${\displaystyle W_{f}}$ is equal to half of the initial energy ${\displaystyle W_{i}}$. Where did the other half of the initial energy go?

🔗 Mathematics

A tautochrone or isochrone curve (from Greek prefixes tauto- meaning same or iso- equal, and chrono time) is the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point on the curve. The curve is a cycloid, and the time is equal to π times the square root of the radius (of the circle which generates the cycloid) over the acceleration of gravity. The tautochrone curve is related to the brachistochrone curve, which is also a cycloid.

🔗 China 🔗 Maps

Due to national security concerns, the use of geographic information in the People's Republic of China is restricted to entities that obtain a special authorization from the administrative department for surveying and mapping under the State Council. Consequences of the restriction include fines for unauthorized surveys, lack of geotagging information on many cameras when the GPS chip detects a location within China, incorrect alignment of street maps with satellite maps in various applications, and seeming unlawfulness of crowdsourced mapping efforts such as OpenStreetMap.

🔗 Computer science

TLA⁺ is a formal specification language developed by Leslie Lamport. It is used to design, model, document, and verify programs, especially concurrent systems and distributed systems. TLA⁺ has been described as exhaustively-testable pseudocode, and its use likened to drawing blueprints for software systems; TLA is an acronym for Temporal Logic of Actions.

For design and documentation, TLA⁺ fulfills the same purpose as informal technical specifications. However, TLA⁺ specifications are written in a formal language of logic and mathematics, and the precision of specifications written in this language is intended to uncover design flaws before system implementation is underway.

Since TLA⁺ specifications are written in a formal language, they are amenable to finite model checking. The model checker finds all possible system behaviours up to some number of execution steps, and examines them for violations of desired invariance properties such as safety and liveness. TLA⁺ specifications use basic set theory to define safety (bad things won't happen) and temporal logic to define liveness (good things eventually happen).

TLA⁺ is also used to write machine-checked proofs of correctness both for algorithms and mathematical theorems. The proofs are written in a declarative, hierarchical style independent of any single theorem prover backend. Both formal and informal structured mathematical proofs can be written in TLA⁺; the language is similar to LaTeX, and tools exist to translate TLA⁺ specifications to LaTeX documents.

TLA⁺ was introduced in 1999, following several decades of research into a verification method for concurrent systems. A toolchain has since developed, including an IDE and distributed model checker. The pseudocode-like language PlusCal was created in 2009; it transpiles to TLA⁺ and is useful for specifying sequential algorithms. TLA⁺² was announced in 2014, expanding language support for proof constructs. The current TLA⁺ reference is The TLA⁺ Hyperbook by Leslie Lamport.