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🔗 Game theory

The Price of Anarchy (PoA) is a concept in economics and game theory that measures how the efficiency of a system degrades due to selfish behavior of its agents. It is a general notion that can be extended to diverse systems and notions of efficiency. For example, consider the system of transportation of a city and many agents trying to go from some initial location to a destination. Let efficiency in this case mean the average time for an agent to reach the destination. In the 'centralized' solution, a central authority can tell each agent which path to take in order to minimize the average travel time. In the 'decentralized' version, each agent chooses its own path. The Price of Anarchy measures the ratio between average travel time in the two cases.

Usually the system is modeled as a game and the efficiency is some function of the outcomes (e.g. maximum delay in a network, congestion in a transportation system, social welfare in an auction, ...). Different concepts of equilibrium can be used to model the selfish behavior of the agents, among which the most common is the Nash equilibrium. Different flavors of Nash equilibrium lead to variations of the notion of Price of Anarchy as Pure Price of Anarchy (for deterministic equilibria), Mixed Price of Anarchy (for randomized equilibria), and Bayes–Nash Price of Anarchy (for games with incomplete information). Solution concepts other than Nash equilibrium lead to variations such as the Price of Sinking.

The term Price of Anarchy was first used by Elias Koutsoupias and Christos Papadimitriou, but the idea of measuring inefficiency of equilibrium is older. The concept in its current form was designed to be the analogue of the 'approximation ratio' in an approximation algorithm or the 'competitive ratio' in an online algorithm. This is in the context of the current trend of analyzing games using algorithmic lenses (algorithmic game theory).

🔗 Technology 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Maritime warfare

Communication with submarines is a field within military communications that presents technical challenges and requires specialized technology. Because radio waves do not travel well through good electrical conductors like salt water, submerged submarines are cut off from radio communication with their command authorities at ordinary radio frequencies. Submarines can surface and raise an antenna above the sea level, then use ordinary radio transmissions, however this makes them vulnerable to detection by anti-submarine warfare forces. Early submarines during World War II mostly traveled on the surface because of their limited underwater speed and endurance; they dove mainly to evade immediate threats. During the Cold War, however, nuclear-powered submarines were developed that could stay submerged for months. Transmitting messages to these submarines is an active area of research. Very low frequency (VLF) radio waves can penetrate seawater a few hundred feet, and many navies use powerful VLF transmitters for submarine communications. A few nations have built transmitters which use extremely low frequency (ELF) radio waves, which can penetrate seawater to reach submarines at operating depths, but these require huge antennas. Other techniques that have been used include sonar and blue lasers.

🔗 Mathematics 🔗 Books 🔗 Systems

How to Solve It (1945) is a small volume by mathematician George Pólya describing methods of problem solving.

🔗 Biography 🔗 Soviet Union 🔗 Russia 🔗 Military history 🔗 Military history/Military biography 🔗 Biography/military biography 🔗 Military history/Maritime warfare 🔗 Military history/Cold War 🔗 Cold War 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Military history/Russian, Soviet and CIS military history 🔗 Russia/history of Russia

Vasily Arkhipov (Russian: Василий Архипов) may refer to:

• Vasily Arkhipov (vice admiral) (1926–1998), Soviet Navy officer credited with casting the single vote that prevented a Soviet nuclear strike
• Vasily Arkhipov (general) (1906–1985), Commander of the 53rd Guards Tank Brigade of the Red Army during World War II, twice Hero of the Soviet Union

🔗 Biology 🔗 Molecular and Cell Biology 🔗 Genetics

DNA origami is the nanoscale folding of DNA to create non-arbitrary two- and three-dimensional shapes at the nanoscale. The specificity of the interactions between complementary base pairs make DNA a useful construction material, through design of its base sequences. DNA is a well-understood material that is suitable for creating scaffolds that hold other molecules in place or to create structures all on its own.

DNA origami was the cover story of Nature on March 16, 2006. Since then, DNA origami has progressed past an art form and has found a number of applications from drug delivery systems to uses as circuitry in plasmonic devices; however, most applications remain in a concept or testing phase.

🔗 Internet culture 🔗 Telecommunications 🔗 Websites 🔗 Websites/Computing

This is a list of notable active virtual communities with more than 1 million registered members.

Defunct

🔗 United States 🔗 United States/North Carolina 🔗 Aviation 🔗 Military history 🔗 Disaster management 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 United States/Military history - U.S. military history 🔗 Aviation/Aviation accident 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry

The 1961 Goldsboro B-52 crash was an accident that occurred near Goldsboro, North Carolina, on 23 January 1961. A Boeing B-52 Stratofortress carrying two 3–4-megaton Mark 39 nuclear bombs broke up in mid-air, dropping its nuclear payload in the process. The pilot in command, Walter Scott Tulloch, ordered the crew to eject at 9,000 feet (2,700 m). Five crewmen successfully ejected or bailed out of the aircraft and landed safely, another ejected, but did not survive the landing, and two died in the crash. Information declassified in 2013 showed that one of the bombs came very close to detonating.

🔗 Telecommunications

The Strowger switch is the first commercially successful electromechanical stepping switch telephone exchange system. It was developed by the Strowger Automatic Telephone Exchange Company founded in 1891 by Almon Brown Strowger. Because of its operational characteristics it is also known as a step-by-step (SXS) switch.