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🔗 Computing 🔗 Computer science

In theoretical computer science, the π-calculus (or pi-calculus) is a process calculus. The π-calculus allows channel names to be communicated along the channels themselves, and in this way it is able to describe concurrent computations whose network configuration may change during the computation.

The π-calculus is simple, it has few terms and so is a small, yet expressive language (see #Syntax). Functional programs can be encoded into the π-calculus, and the encoding emphasises the dialogue nature of computation, drawing connections with game semantics. Extensions of the π-calculus, such as the spi calculus and applied π, have been successful in reasoning about cryptographic protocols. Beside the original use in describing concurrent systems, the π-calculus has also been used to reason about business processes and molecular biology.

🔗 United States 🔗 Law 🔗 Linux

In a series of legal disputes between SCO Group and Linux vendors and users, SCO alleged that its license agreements with IBM meant that source code IBM wrote and donated to be incorporated into Linux was added in violation of SCO's contractual rights. Members of the Linux community disagreed with SCO's claims; IBM, Novell, and Red Hat filed claims against SCO.

On August 10, 2007, a federal district court judge in SCO v. Novell ruled on summary judgment that Novell, not the SCO Group, was the rightful owner of the copyrights covering the Unix operating system. The court also ruled that "SCO is obligated to recognize Novell's waiver of SCO's claims against IBM and Sequent". After the ruling, Novell announced they had no interest in suing people over Unix and stated "We don't believe there is Unix in Linux". The final district court ruling, on November 20, 2008, affirmed the summary judgment, and added interest payments and a constructive trust.

On August 24, 2009, the U.S. Court of Appeals for the Tenth Circuit partially reversed the district court judgment. The appeals court remanded back to trial on the issues of copyright ownership and Novell's contractual waiver rights. The court upheld the $2,547,817 award granted to Novell for the 2003 Sun agreement.

On March 30, 2010, following a jury trial, Novell, and not The SCO Group, was unanimously found to be the owner of the UNIX and UnixWare copyrights. The SCO Group, through bankruptcy trustee Edward Cahn, decided to continue the lawsuit against IBM for causing a decline in SCO revenues.

On March 1, 2016, SCO's lawsuit against IBM was dismissed with prejudice; SCO filed an appeal later that month.

🔗 Mathematics

Pentagramma mirificum (Latin for miraculous pentagram) is a star polygon on a sphere, composed of five great circle arcs, all of whose internal angles are right angles. This shape was described by John Napier in his 1614 book Mirifici logarithmorum canonis descriptio (Description of the wonderful rule of logarithms) along with rules that link the values of trigonometric functions of five parts of a right spherical triangle (two angles and three sides). The properties of pentagramma mirificum were studied, among others, by Carl Friedrich Gauss.

🔗 Computer science

The limits of computation are governed by a number of different factors. In particular, there are several physical and practical limits to the amount of computation or data storage that can be performed with a given amount of mass, volume, or energy.

🔗 Science

The Salmon Protocol is a message exchange protocol running over HTTP designed to decentralize commentary and annotations made against newsfeed articles such as blog posts. It allows a single discussion thread to be established between the article's origin and any feed reader or "aggregator" which is subscribing to the content. Put simply, that if an article appeared on 3 sites: A (the source), B and C (the aggregates), that members of all 3 sites could see and contribute to a single thread of conversation regardless of site they were viewing from.

🔗 Psychology 🔗 Gender Studies

Wife acceptance factor, wife approval factor, or wife appeal factor (WAF) is an assessment of design elements that either increase or diminish the likelihood a wife will approve the purchase of expensive consumer electronics products such as high-fidelity loudspeakers, home theater systems and personal computers. Stylish, compact forms and appealing colors are commonly considered to have a high WAF. The term is a tongue-in-cheek play on electronics jargon such as "form factor" and "power factor" and derives from the idea that men are predisposed to appreciate gadgetry and performance criteria whereas women must be wooed by visual and aesthetic factors.

🔗 Internet 🔗 Computing 🔗 Psychology 🔗 Marketing & Advertising

Banner blindness is a phenomenon in web usability where visitors to a website consciously or unconsciously ignore banner-like information. A broader term covering all forms of advertising is ad blindness, and the mass of banners that people ignore is called banner noise.

The term banner blindness was coined in 1998 as a result of website usability tests where a majority of the test subjects either consciously or unconsciously ignored information that was presented in banners. The information that was overlooked included both external advertisement banners and internal navigational banners, often called "quick links".

This does not, however, mean that banner ads do not influence viewers. Website viewers may not be consciously aware of an ad, but it does have an unconscious influence on their behavior. A banner's content affects both businesses and visitors of the site. Native advertising and social media are used to avoid banner blindness.

🔗 United States 🔗 Law 🔗 Politics 🔗 United States Constitution 🔗 Politics/American politics 🔗 U.S. Congress

The Twenty-fifth Amendment (Amendment XXV) to the United States Constitution addresses issues related to presidential succession and disability.

It clarifies that the vice president becomes president if the president dies, resigns, or is removed from office by impeachment. It also establishes the procedure for filling a vacancy in the office of the vice president.

The amendment provides for the temporary transfer of the president's powers and duties to the vice president, either on the president's initiative alone or on the initiative of the vice president, together with a majority of the president's cabinet. In either case, the vice president becomes the acting president until the president's powers and duties are restored.

The amendment was submitted to the states on July 6, 1965, by the 89th Congress, and was adopted on February 10, 1967, the day the requisite number of states (38) ratified it.

🔗 Trains 🔗 Trains/Operations

Signalling block systems enable the safe and efficient operation of railways by preventing collisions between trains. The basic principle is that a route is broken up into a series of sections or "blocks". Only one train may occupy a block at a time, and the blocks are sized to allow a train to stop within them. That ensures that a train always has time to stop before getting dangerously close to another train on the same line. The block system is referred to in the UK as the method of working, in the US as the method of operation, and in Australia as safeworking.

In most situations, a system of signals is used to control the passage of trains between the blocks. When a train enters a block, signals at both ends change to indicate that the block is occupied, typically using red lamps or indicator flags. When a train first enters a block, the rear of the same train has not yet left the previous block, so both blocks are marked as occupied. That ensures there is slightly less than one block length on either end of the train that is marked as occupied, so any other train approaching that section will have enough room to stop in time, even if the first train has stopped dead on the tracks. The previously-occupied block will only be marked unoccupied when the end of the train has entirely left it, leaving the entire block clear.

Block systems have the disadvantage that they limit the number of trains on a particular route to something fewer than the number of blocks. Since the route has a fixed length, increasing the number of trains requires the creation of more blocks, which means the blocks are shorter and trains have to operate at lower speeds in order to stop safely. As a result, the number and size of blocks are closely related to the overall route capacity, and cannot be changed easily because expensive alterations to the signals along the line would be required.

Block systems are used to control trains between stations and yards, but not normally within the yards, where some other method is used. Any block system is defined by its associated physical equipment and by the application of a relevant set of rules. Some systems involve the use of signals while others do not. Some systems are specifically designed for single track railways, on which there is a danger of both head-on and rear-end collision, as opposed to double track, on which the main danger is rear-end collisions.

🔗 Physics 🔗 Astronomy

A helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low mass stars (between 0.8 solar masses (M_☉) and 2.0 M_☉) during their red giant phase. The Sun is predicted to experience a flash 1.2 billion years after it leaves the main sequence. A much rarer runaway helium fusion process can also occur on the surface of accreting white dwarf stars.

Low-mass stars do not produce enough gravitational pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into degenerate matter, supported against gravitational collapse by quantum mechanical pressure rather than thermal pressure. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million kelvin, which is hot enough to initiate helium fusion (or "helium burning") in the core.

However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, thermal expansion regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes, but during that time, produces energy at a rate comparable to the entire Milky Way galaxy.

In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash, and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.