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🔗 Psychology 🔗 Sociology

The Ringelmann effect is the tendency for individual members of a group to become increasingly less productive as the size of their group increases. This effect, discovered by French agricultural engineer Maximilien Ringelmann (1861–1931), illustrates the inverse relationship that exists between the size of a group and the magnitude of group members’ individual contribution to the completion of a task. While studying the relationship between process loss (i.e., reductions in performance effectiveness or efficiency) and group productivity, Ringelmann (1913) found that having group members work together on a task (e.g., pulling a rope) actually results in significantly less effort than when individual members are acting alone. Ringelmann discovered that as more and more people are added to a group, the group often becomes increasingly inefficient, ultimately violating the notion that group effort and team participation reliably leads to increased effort on behalf of the members.

🔗 Computing 🔗 Computer science

In computer science, the five-minute rule is a rule of thumb for deciding whether a data item should be kept in memory, or stored on disk and read back into memory when required. It was first formulated by Jim Gray and Gianfranco Putzolu in 1985, and then subsequently revised in 1997 and 2007 to reflect changes in the relative cost and performance of memory and persistent storage.

The rule is as follows:

The 5-minute random rule: cache randomly accessed disk pages that are re-used every 5 minutes or less.

Gray also issued a counterpart one-minute rule for sequential access:

The 1-minute rule: cache sequentially accessed disk pages that are re-used every 1 minute or less.

Although the 5-minute rule was invented in the realm of databases, it has also been applied elsewhere, for example, in Network File System cache capacity planning.

The original 5-minute rule was derived from the following cost-benefit computation:

BreakEvenIntervalinSeconds = (PagesPerMBofRAM / AccessesPerSecondPerDisk) × (PricePerDiskDrive / PricePerMBofRAM)

Applying it to 2007 data yields approximately a 90-minutes interval for magnetic-disk-to-DRAM caching, 15 minutes for SSD-to-DRAM caching and 2​¹⁄₄ hours for disk-to-SSD caching. The disk-to-DRAM interval was thus a bit short of what Gray and Putzolu anticipated in 1987 as the "five-hour rule" was going to be in 2007 for RAM and disks.

According to calculations by NetApp engineer David Dale as reported in The Register, the figures for disc-to-DRAM caching in 2008 were as follows: "The 50KB page break-even was five minutes, the 4KB one was one hour and the 1KB one was five hours. There needed to be a 50-fold increase in page size to cache for break-even at five minutes." Regarding disk-to-SSD caching in 2010, the same source reported that "A 250KB page break even with SLC was five minutes, but five hours with a 4KB page size. It was five minutes with a 625KB page size with MLC flash and 13 hours with a 4KB MLC page size."

In 2000, Gray and Shenoy applied a similar calculation for web page caching and concluded that a browser should "cache web pages if there is any chance they will be re-referenced within their lifetime."

🔗 Chess

The mutilated chessboard problem is a tiling puzzle proposed by philosopher Max Black in his book Critical Thinking (1946). It was later discussed by Solomon W. Golomb (1954), Gamow & Stern (1958) and by Martin Gardner in his Scientific American column "Mathematical Games". The problem is as follows:

Suppose a standard 8×8 chessboard has two diagonally opposite corners removed, leaving 62 squares. Is it possible to place 31 dominoes of size 2×1 so as to cover all of these squares?

Most considerations of this problem in literature provide solutions "in the conceptual sense" without proofs. John McCarthy proposed it as a hard problem for automated proof systems. In fact, its solution using the resolution system of inference is exponentially hard.

🔗 Board and table games

Uckers is a two- or four-player board game traditionally played in the Royal Navy and has spread to many of the other arms of the UK Armed Forces as well as to, mainly Commonwealth Forces. It can now be found also in the Royal Marines, Army Air Corps, Royal Canadian Navy, Royal New Zealand Navy, Royal Australian Navy, Royal Australian Air Force (RAAF), Royal Dutch Navy, and the Royal Air Force (RAF). It is believed to originate in the 18th/19th centuries from the Indian game Pachisi, although the first reference to it in print does not appear until 1946. It is mentioned in a diary by EJF Records (served 1928-1950) in 1937 as Huckers. Uckers is generally played using the rules stated below, but these will vary from one branch of the Royal Navy to another, most famously with the WAFU Rules of the Fleet Air Arm. Where those branches of the RN have worked with the other Armed Forces usually has dictated what rules the new playing Service use; why fellow aviators tend to play under WAFU Rules for example.

It is also played in units of the Army Air Corps (United Kingdom) where it was introduced by aircraft technicians on loan from the Fleet Air Arm in the late 1950s/early 1960s. Uckers boards can now also be found in most RAF Squadron crewroom, where the game has caught on, especially with the Aircraft Technicians. Most RAAF crew rooms feature uckers boards also. In addition to the units services, units mentioned, uckers was also played by units in the Royal Artillery, particularly meteorologists and LifeFlight Toowoomba Rescue Helicopter crews aka Rescue 588. The current and now 7-time world champion is Queenslander Mark Arthur. In the UK the Pusser's Rum World 'Uckers championships have been played for the last 5 years at various ROYAL NAVAL MUSEUMS, the most being notable being 2017 when the final was played on Nelson's Flagship HMS VICTORY and was won by the'timber shifters' Wally Blagden and David Clark both ex RN. The next Pusser's Rum WORLD 'uckers' championships are being played in the Explosion Museum Gosport 26 October 2019. Wally andDavid are also current HMS GANGES Champions won in April 2019 Update Wally Blagden and Dave Clark the 'Timbershifters' have won the 2019 Championships. Knock knock. The chicken

It is similar to the board game Ludo and is based on the same principles; getting four player pieces around the board before the opposition. The whole point of Uckers is to get all player pieces home before the opponent does. However, greater glory is attached to achieving all pieces home without the opponent getting any home at all—this is known as an 8 piecer. The ultimate win is when the player gets all their pieces home and the opponent has all their pieces still in the base—this is called an 8 piece in harbour, or an eight-piece dicking and merits the unfortunate player's name to be recorded on the reverse of the board.

🔗 Aviation 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/Military science, technology, and theory 🔗 Aviation/aircraft

In aerobatics the Cobra maneuver, also known as just the Cobra, is a dramatic and demanding maneuver in which an airplane flying at a moderate speed suddenly raises the nose momentarily to the vertical position and slightly beyond, before dropping it back to normal, effectively making the plane a full body air brake.

The maneuver relies on the ability of the plane to be able to quickly change alpha which momentarily stalls the plane without overloading the airframe and powerful engine thrust to maintain approximately constant altitude through the entire move. It is an impressive maneuver to demonstrate an aircraft's pitch control authority, high alpha stability and engine-versus-inlet compatibility, as well as the pilot's skill.

Although the maneuver is mainly performed at air shows it has use in close range air combat as a last ditch maneuver to make a pursuing plane overshoot. There is currently no widely spread or readily available evidence of the Cobra being used in real combat, although, there are records of it being used during mockup-dogfights and during border protection.

🔗 Computing 🔗 Microsoft Windows 🔗 Microsoft Windows/Computing

The AARD code was a segment of code in a beta release of Microsoft Windows 3.1 that would determine whether Windows was running on MS-DOS or PC DOS, rather than a competing workalike such as DR-DOS, and would result in a cryptic error message in the latter case. This XOR-encrypted, self-modifying, and deliberately obfuscated machine code used a variety of undocumented DOS structures and functions to perform its work, and appeared in the installer, WIN.COM, and several other executables in the OS.

The AARD code was originally discovered by Geoff Chappell on 17 April 1992 and then further analyzed and documented in a joint effort with Andrew Schulman. The name was derived from Microsoft programmer Aaron R. Reynolds (1955–2008), who used "AARD" to sign his work; "AARD" was found in the machine code of the installer. Microsoft disabled the AARD code for the final release of Windows 3.1, but did not remove it, so that it could have become reactivated later by the change of a single byte in an installed system, thereby constituting a "smoking gun".

DR-DOS publisher Digital Research released a patch named "business update" in 1992 to enable the AARD tests to pass on its operating system.

The rationale for the AARD code came to light when internal memos were released during the United States v. Microsoft Corp. antitrust case in 1999. Internal memos released by Microsoft revealed that the specific focus of these tests was DR-DOS. At one point, Microsoft CEO Bill Gates sent a memo to a number of employees, reading "You never sent me a response on the question of what things an app would do that would make it run with MS-DOS and not run with DR-DOS. Is there [sic] feature they have that might get in our way?" Microsoft Senior Vice President Brad Silverberg later sent another memo, stating: "What the [user] is supposed to do is feel uncomfortable, and when he has bugs, suspect that the problem is DR-DOS and then go out to buy MS-DOS."

Following the purchase of DR-DOS by Novell and its renaming to "Novell DOS", Microsoft Co-President Jim Allchin stated in a memo, "If you're going to kill someone there isn't much reason to get all worked up about it and angry. Any discussions beforehand are a waste of time. We need to smile at Novell while we pull the trigger."

What had been DR-DOS changed hands again. The new owner, Caldera, Inc., began a lawsuit against Microsoft over the AARD code, Caldera v. Microsoft, which was later settled. It was believed that the settlement ran in the order of $150 million, but was revealed in November 2009 with the release of the Settlement Agreement to be $280 million.

🔗 Biography 🔗 Computing

Francesco Vianello (30 August 1952 – 3 May 2009), better known by his nickname Fravia (sometimes +Fravia or Fravia+), was a software reverse engineer, and hacker, known for his web archive of reverse engineering techniques and papers. He is also known for his work on steganography. He had taught on subjects such as data mining, anonymity, stalking, klebing, advertisement reversing and ad-busting.

Fravia spoke six languages (including Latin) and had a degree in the history of the early Middle Ages. He was an expert in linguistics-related informatics. For five years he made available a large quantity of material related to reverse engineering through his website, which also hosted the advice of reverse engineering experts, known as reversers, who provided tutorials and essays on how to hack software code as well as advice related to the assembly and disassembly of applications, and software protection reversing.

Fravia was a professor at the High Cracking University (+HCU), founded by Old Red Cracker (+ORC), a legendary figure in reverse engineering, to conduct research into Reverse Code Engineering. The addition of the "+" sign in front of the nickname of a reverser signified membership in the +HCU. His website was known as "+Fravia's Pages of Reverse Engineering" and he used it to challenge programmers as well as the wider society to "reverse engineer" the "brainwashing of a corrupt and rampant materialism". In its heyday, his website was receiving millions of visitors per year and its influence was "widespread".

His web presence dates from 1995 when he first got involved in research related to reverse code engineering (RCE). In 2000 he changed his focus and concentrated on advanced internet search methods and the reverse engineering of search engine code.

His websites "www.fravia.com" and "www.searchlores.org" contained a large amount of specialised information related to data mining. His website "www.searchlores.org" has been called a "very useful instrument for searching the web", and his "www.fravia.com" site has been described as "required reading for any spy wanting to go beyond simple Google searches."

🔗 Lists 🔗 History of Science 🔗 Science

Historians and sociologists have remarked the occurrence, in science, of "multiple independent discovery". Robert K. Merton defined such "multiples" as instances in which similar discoveries are made by scientists working independently of each other. "Sometimes," writes Merton, "the discoveries are simultaneous or almost so; sometimes a scientist will make a new discovery which, unknown to him, somebody else has made years before."

Commonly cited examples of multiple independent discovery are the 17th-century independent formulation of calculus by Isaac Newton, Gottfried Wilhelm Leibniz and others, described by A. Rupert Hall; the 18th-century discovery of oxygen by Carl Wilhelm Scheele, Joseph Priestley, Antoine Lavoisier and others; and the theory of the evolution of species, independently advanced in the 19th century by Charles Darwin and Alfred Russel Wallace.

Multiple independent discovery, however, is not limited to such famous historic instances. Merton believed that it is multiple discoveries, rather than unique ones, that represent the common pattern in science.

Merton contrasted a "multiple" with a "singleton"—a discovery that has been made uniquely by a single scientist or group of scientists working together.

A distinction is drawn between a discovery and an invention, as discussed for example by Bolesław Prus. However, discoveries and inventions are inextricably related, in that discoveries lead to inventions, and inventions facilitate discoveries; and since the same phenomenon of multiplicity occurs in relation to both discoveries and inventions, this article lists both multiple discoveries and multiple inventions.

🔗 Numbers

In number theory, a narcissistic number (also known as a pluperfect digital invariant (PPDI), an Armstrong number (after Michael F. Armstrong) or a plus perfect number) in a given number base ${\displaystyle b}$ is a number that is the sum of its own digits each raised to the power of the number of digits.

🔗 Economics 🔗 Statistics

The St. Petersburg paradox or St. Petersburg lottery is a paradox related to probability and decision theory in economics. It is based on a particular (theoretical) lottery game that leads to a random variable with infinite expected value (i.e., infinite expected payoff) but nevertheless seems to be worth only a very small amount to the participants. The St. Petersburg paradox is a situation where a naive decision criterion which takes only the expected value into account predicts a course of action that presumably no actual person would be willing to take. Several resolutions are possible.

The paradox takes its name from its resolution by Daniel Bernoulli, one-time resident of the eponymous Russian city, who published his arguments in the Commentaries of the Imperial Academy of Science of Saint Petersburg (Bernoulli 1738). However, the problem was invented by Daniel's cousin, Nicolas Bernoulli, who first stated it in a letter to Pierre Raymond de Montmort on September 9, 1713 (de Montmort 1713).