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🔗 Palaeontology 🔗 Marine life 🔗 Indigenous peoples of the Americas 🔗 Bivalves

Spondylus is a genus of bivalve molluscs, the only genus in the family Spondylidae. They are known in English as spiny oysters or thorny oysters (though they are not, in fact, true oysters).

🔗 Computing 🔗 Computing/Software 🔗 Computing/Computer science 🔗 Cryptography 🔗 Cryptography/Computer science

In cryptography and computer science, a hash tree or Merkle tree is a tree in which every leaf node is labelled with the cryptographic hash of a data block, and every non-leaf node is labelled with the cryptographic hash of the labels of its child nodes. Hash trees allow efficient and secure verification of the contents of large data structures. Hash trees are a generalization of hash lists and hash chains.

Demonstrating that a leaf node is a part of a given binary hash tree requires computing a number of hashes proportional to the logarithm of the number of leaf nodes of the tree; this contrasts with hash lists, where the number is proportional to the number of leaf nodes itself.

The concept of hash trees is named after Ralph Merkle, who patented it in 1979.

🔗 Plants

A floral formula is a notation for representing the structure of particular types of flowers. Such notations use numbers, letters and various symbols to convey significant information in a compact form. They may represent the floral form of a particular species, or may be generalized to characterize higher taxa, usually giving ranges of numbers of organs. Floral formulae are one of the two ways of describing flower structure developed during the 19th century, the other being floral diagrams. The format of floral formulae differs according to the tastes of particular authors and periods, yet they tend to convey the same information.

A floral formula is often used along with a floral diagram.

🔗 Chess

Zugzwang (German for "compulsion to move", pronounced [ˈtsuːktsvaŋ]) is a situation found in chess and other turn-based games wherein one player is put at a disadvantage because they must make a move when they would prefer to pass and not move. The fact that the player is compelled to move means that their position will become significantly weaker. A player is said to be "in zugzwang" when any possible move will worsen their position.

Although the term is used less precisely in games such as chess, it is used specifically in combinatorial game theory to denote a move that directly changes the outcome of the game from a win to a loss. Putting the opponent in zugzwang is a common way to help the superior side win a game, and in some cases it is necessary in order to make the win possible.

The term zugzwang was used in German chess literature in 1858 or earlier, and the first known use of the term in English was by World Champion Emanuel Lasker in 1905. The concept of zugzwang was known to chess players many centuries before the term was coined, appearing in an endgame study published in 1604 by Alessandro Salvio, one of the first writers on the game, and in shatranj studies dating back to the early 9th century, over 1000 years before the first known use of the term.

Positions with zugzwang occur fairly often in chess endgames, especially in king and pawn endgames. According to John Nunn, positions of reciprocal zugzwang are surprisingly important in the analysis of endgames.

🔗 Chemistry

Aqua regia (; from Latin, lit. "regal water" or "king's water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange (sometimes red) fuming liquid, so named by alchemists because it can dissolve the noble metals, gold and platinum, though not all metals.

🔗 Mathematics

In number theory, a weird number is a natural number that is abundant but not semiperfect.

In other words, the sum of the proper divisors (divisors including 1 but not itself) of the number is greater than the number, but no subset of those divisors sums to the number itself.

🔗 Computing 🔗 Systems 🔗 Business 🔗 Computing/Software 🔗 Computing/Computer science 🔗 Engineering 🔗 Systems/Systems engineering

Hofstadter's law is a self-referential adage, coined by Douglas Hofstadter in his book Gödel, Escher, Bach: An Eternal Golden Braid (1979) to describe the widely experienced difficulty of accurately estimating the time it will take to complete tasks of substantial complexity:

Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

The law is often cited by programmers in discussions of techniques to improve productivity, such as The Mythical Man-Month or extreme programming.

🔗 Computing/Free and open-source software

🔗 Video games

Tibia is a 1997 massively multiplayer online role-playing game (MMORPG) developed and published by CipSoft. It is one of the earliest and longest-running MMORPGs, with a popularity that peaked in 2007. It is a free game to download and play, though players may pay to upgrade to a premium account, granting substantial in-game benefits. Tibia is a two-dimensional tile-based game set in a fantasy world with pixel art graphics and a top-down perspective.

🔗 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.