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An animated image showing the definition of pi. A number line is marked off by a circle of unit diameter. Starting from zero, the circle "unrolls" its circumference. At one full turn, the unrolled circumference has extended to the point we call π. This number is real but irrational, transcendental, and cannot be constructed with compass and straightedge.

Animation credit: John Reid
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🔗 Internet 🔗 Computing 🔗 Computing/Software

The Gopher protocol is a communications protocol designed for distributing, searching, and retrieving documents in Internet Protocol networks. The design of the Gopher protocol and user interface is menu-driven, and presented an alternative to the World Wide Web in its early stages, but ultimately fell into disfavor, yielding to the Hypertext Transfer Protocol (HTTP). The Gopher ecosystem is often regarded as the effective predecessor of the World Wide Web.

The protocol was invented by a team led by Mark P. McCahill at the University of Minnesota. It offers some features not natively supported by the Web and imposes a much stronger hierarchy on the documents it stores. Its text menu interface is well-suited to computing environments that rely heavily on remote text-oriented computer terminals, which were still common at the time of its creation in 1991, and the simplicity of its protocol facilitated a wide variety of client implementations. More recent Gopher revisions and graphical clients added support for multimedia. Gopher was preferred by many network administrators for using fewer network resources than Web services.

Gopher's hierarchical structure provided a platform for the first large-scale electronic library connections. The Gopher protocol is still in use by enthusiasts, and although it has been almost entirely supplanted by the Web, a small population of actively-maintained servers remains.

🔗 Computing 🔗 Computing/Software 🔗 Computing/Free and open-source software

netcat (often abbreviated to nc) is a computer networking utility for reading from and writing to network connections using TCP or UDP. The command is designed to be a dependable back-end that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and investigation tool, since it can produce almost any kind of connection its user could need and has a number of built-in capabilities.

Its list of features includes port scanning, transferring files, and port listening, and it can be used as a backdoor.

🔗 Biography 🔗 Physics 🔗 Biography/science and academia 🔗 Astronomy 🔗 Physics/Biographies 🔗 Biophysics

Thomas Gold (also known as Tommy Gold), (May 22, 1920 – June 22, 2004) was an Austrian-born astrophysicist, a professor of astronomy at Cornell University, a member of the U.S. National Academy of Sciences, and a Fellow of the Royal Society (London). Gold was one of three young Cambridge scientists who in 1948 proposed the now mostly abandoned "steady state" hypothesis of the universe. Gold's work crossed academic and scientific boundaries, into biophysics, astronomy, aerospace engineering, and geophysics.

🔗 Economics 🔗 Literature 🔗 Astronomy

The Theory of Interstellar Trade is a paper written in 1978 by the economist Paul Krugman. The paper was first published in March 2010 in the journal Economic Inquiry. He described the paper as something he wrote to cheer himself up when he was an "oppressed assistant professor" caught up in the academic rat race.

Krugman analyzed the question of

How should interest rates on goods in transit be computed when the goods travel at close to the speed of light? This is a problem because the time taken in transit will appear less to an observer traveling with the goods than to a stationary observer.

Krugman emphasized that in spite of its farcical subject matter, the economic analysis in the paper is correctly done. In his own words,

while the subject of this paper is silly, the analysis actually does make sense. This paper, then, is a serious analysis of a ridiculous subject, which is of course the opposite of what is usual in economics.

🔗 Databases 🔗 Databases/Computer science

Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) proposed by Edgar F. Codd, a pioneer of the relational model for databases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS). They are sometimes jokingly referred to as "Codd's Twelve Commandments".

🔗 Mathematics

In number theory, the Pólya conjecture stated that "most" (i.e., 50% or more) of the natural numbers less than any given number have an odd number of prime factors. The conjecture was posited by the Hungarian mathematician George Pólya in 1919, and proved false in 1958 by C. Brian Haselgrove.

The size of the smallest counterexample is often used to show how a conjecture can be true for many cases, and still be false, providing an illustration for the strong law of small numbers.

🔗 Astronomy 🔗 Geology 🔗 Geology/Meteorites 🔗 Solar System

The Perseids are a prolific meteor shower associated with the comet Swift–Tuttle. The meteors are called the Perseids because the point from which they appear to hail (called the radiant) lies in the constellation Perseus.

🔗 Philately 🔗 Czech Republic

The Prague pneumatic post (Czech: Pražská potrubní pošta) is the world's last preserved municipal pneumatic post system. It is an underground system of metal tubes under the wider centre of Prague, totaling about 55 kilometres (34 mi) in length. The system started service in 1889 and remained in use by the government, banks and the media until it was rendered inoperative by the August 2002 European floods.

Sold on by former owner Telefónica O2 Czech Republic after some limited attempts to make repairs, the system now belongs to businessman Zdeněk Dražil, who has announced plans to repair and reopen it as a working tourist attraction. As of 2012, however, it remains closed.