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🔗 Physics 🔗 Systems 🔗 Systems/Dynamical systems

In mathematics and physics, the Poincaré recurrence theorem states that certain dynamical systems will, after a sufficiently long but finite time, return to a state arbitrarily close to (for continuous state systems), or exactly the same as (for discrete state systems), their initial state.

The Poincaré recurrence time is the length of time elapsed until the recurrence. This time may vary greatly depending on the exact initial state and required degree of closeness. The result applies to isolated mechanical systems subject to some constraints, e.g., all particles must be bound to a finite volume. The theorem is commonly discussed in the context of ergodic theory, dynamical systems and statistical mechanics. Systems to which the Poincaré recurrence theorem applies are called conservative systems.

The theorem is named after Henri Poincaré, who discussed it in 1890 and proved by Constantin Carathéodory using measure theory in 1919.

🔗 France 🔗 Languages

Verlan (French pronunciation: ​[vɛʁlɑ̃]), (verlan is the reverse of the expression "l'envers") is a type of argot in the French language, featuring inversion of syllables in a word, and is common in slang and youth language. It rests on a long French tradition of transposing syllables of individual words to create slang words. The name verlan itself is an example: it is derived from inverting the sounds of the syllables in l'envers ([lɑ̃vɛʁ], "the inverse", frequently used in the sense of "back-to-front").

🔗 Europe 🔗 Maps 🔗 Sociology

The Hajnal line is a border that links Saint Petersburg, Russia and Trieste, Italy. In 1965, John Hajnal discovered it divides Europe into two areas characterized by different levels of nuptiality. To the west of the line, marriage rates and thus fertility were comparatively low and a significant minority of women married late or remained single; to the east of the line and in the Mediterranean and select pockets of Northwestern Europe, early marriage was the norm and high fertility was countered by high mortality.

🔗 Energy 🔗 Engineering

A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.

At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquid, releasing the latent heat. The liquid then returns to the hot interface through capillary action, centrifugal force, or gravity and the cycle repeats.

Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The effective thermal conductivity varies with heat pipe length and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper.

Modern CPU heat pipes are typically made of copper and use water as the working fluid. They are common in many consumer electronics like desktops, laptops, tablets, and high-end smartphones.

🔗 Computing 🔗 Computing/Computer hardware 🔗 Computing/Early computers

In computer jargon, blinkenlights are diagnostic lights on front panels of old mainframe computers. More recently the term applies to status lights of modern network hardware (modems, network hubs, etc.). Blinkenlights disappeared from more recent computers for a number of reasons, the most important being the fact that with faster CPUs a human can no longer interpret the processes in the computer on the fly. Though more sophisticated UI mechanisms have since been developed, blinkenlights may still be present as additional status indicators and familiar skeuomorphs.

🔗 Computing

Wi-Fi over Coax is a technology for extending and distributing Wi-Fi signals via coaxial cables. As an in-building wireless solution, Wi-Fi over Coax can make use of existing or new cabling with native impedance of 50 ohms shared by a Wi-Fi access point, cabling run, and antenna. Coaxial cables with characteristic impedance of 75 ohms, such as RG-6 cables used for in-building television distribution, can also be used by incorporating impedance converters. As part of a distributed antenna system, Wi-Fi over Coax can connect multiple floors of a home or office via power dividers and zoned antennas either passively or via amplifiers, potentially eliminating the need for multiple access points.

🔗 Companies 🔗 Technology 🔗 Apple Inc. 🔗 Computing 🔗 Computing/Software 🔗 Computing/Free and open-source software 🔗 Linux

Eazel was an American software company operating from 1999 to 2001 in Palo Alto and then Mountain View, California. The company's flagship product is the Nautilus file manager for the GNOME desktop environment on Linux, which was immediately adopted and maintained by the free software movement. As the core of Eazel's business model, it is an early example of cloud storage services in the form of personal file storage, transparently and portably stored on the Internet. Renamed to Files, this application continues to be a centerpiece of some free Linux-based desktop environments.

🔗 Software 🔗 Software/Computing

Word2vec is a technique for natural language processing (NLP) published in 2013. The word2vec algorithm uses a neural network model to learn word associations from a large corpus of text. Once trained, such a model can detect synonymous words or suggest additional words for a partial sentence. As the name implies, word2vec represents each distinct word with a particular list of numbers called a vector. The vectors are chosen carefully such that they capture the semantic and syntactic qualities of words; as such, a simple mathematical function (cosine similarity) can indicate the level of semantic similarity between the words represented by those vectors.

🔗 Lists 🔗 Science Fiction 🔗 Transhumanism 🔗 Sociology 🔗 Futures studies 🔗 Science 🔗 Popular Culture

This is a list of fictional stories that, when written, were set in the future, but the future they predicted is now present or past. The list excludes works that were alternate histories, which were composed after the dates they depict, alternative futures, as depicted in time travel fiction, as well as any works that make no predictions of the future, such as those focusing solely on the future lives of specific fictional characters, or works which, despite their claimed dates, are contemporary in all but name. Entries referencing the current year may be added if their month and day were not specified or have already occurred.

🔗 Electronics

A plugtest or plugfest is an event based on a certain technical standard where the designers of electronic equipment or software test the interoperability of their products or designs with those of other manufacturers. It could be literally plugging company A's cable into company B's socket, or a more elaborate test resembling a realistic scenario.

The technical goal is twofold: check compliance with the standard, and test the effectiveness of the standard. The latter could be the case when the standard is ambiguous. A simplified example is: the width of a plug is prescribed, but vendors use different lengths.

Plugtests can be formal and have public test scores or informal and private. Besides helping vendors improve their interoperability, plugtests help create awareness about the standard and can improve transparency on compliance.