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🔗 Professional sound production

A Shepard tone, named after Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves. When played with the bass pitch of the tone moving upward or downward, it is referred to as the Shepard scale. This creates the auditory illusion of a tone that continually ascends or descends in pitch, yet which ultimately seems to get no higher or lower.

🔗 United States 🔗 Aviation 🔗 Military history 🔗 Disaster management 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Aviation/Aviation accident 🔗 Iran 🔗 Military history/Maritime warfare

Iran Air Flight 655 was a scheduled passenger flight from Tehran to Dubai via Bandar Abbas that was shot down on 3 July 1988 by an SM-2MR surface-to-air missile fired from USS Vincennes, a guided-missile cruiser of the United States Navy. The aircraft, an Airbus A300, was destroyed and all 290 people on board were killed. The jet was hit while flying over Iran's territorial waters in the Persian Gulf, along the flight's usual route, shortly after departing Bandar Abbas International Airport, the flight's stopover location. The incident occurred during the final stages of the Iran–Iraq War, which had been continuing for nearly eight years. Vincennes had entered Iranian territory after one of its helicopters drew warning fire from Iranian speedboats operating within Iranian territorial limits.

The reason for the shootdown has been disputed between the governments of the two countries. According to the U.S., the Vincennes crew had incorrectly identified the Airbus as an attacking F-14 Tomcat, a U.S.-made jet fighter that had been part of the Iranian Air Force inventory since the 1970s. While the F-14s had been supplied to Iran in an air-to-air configuration, the Vincennes crew had been briefed that the Iranian F-14s were equipped with air-to-ground ordnance. Vincennes had made ten attempts to contact the aircraft both on military and on civilian frequencies, but had received no response. According to Iran, the cruiser negligently shot down the aircraft, which was transmitting IFF squawks in Mode III, a signal that identified it as a civilian aircraft, and not Mode II as used by Iranian military aircraft. The event generated a great deal of criticism of the United States. Some analysts blamed the captain of Vincennes, William C. Rogers III, for overly aggressive behavior in a tense and dangerous environment. In the days immediately following the incident, President Ronald Reagan issued a written diplomatic note to the Iranian government, expressing deep regret. However, the U.S. continued to insist that Vincennes was acting in self-defense in international waters.

In 1996, the governments of the U.S. and Iran reached a settlement at the International Court of Justice which included the statement "... the United States recognized the aerial incident of 3 July 1988 as a terrible human tragedy and expressed deep regret over the loss of lives caused by the incident ..." When President Ronald Reagan was directly asked if he considered the statement an apology, Reagan replied, "Yes." As part of the settlement, even though the U.S. government did not admit legal liability or formally apologize to Iran, it still agreed to pay US$61.8 million on an ex gratia basis in compensation to the families of the Iranian victims. The shootdown was the deadliest aviation disaster involving an Airbus A300.

🔗 Physics

In physics, the fourth, fifth and sixth derivatives of position are defined as derivatives of the position vector with respect to time – with the first, second, and third derivatives being velocity, acceleration, and jerk, respectively. Unlike the first three derivatives, the higher-order derivatives are less common, thus their names are not as standardized, though the concept of a minimum snap trajectory has been used in robotics and is implemented in MATLAB.

The fourth derivative is often referred to as snap or jounce. The name "snap" for the fourth derivative led to crackle and pop for the fifth and sixth derivatives respectively, inspired by the Rice Krispies mascots Snap, Crackle, and Pop. These terms are occasionally used, though "sometimes somewhat facetiously".

🔗 Mathematics

In mathematics, the Gibbs phenomenon, discovered by Henry Wilbraham (1848) and rediscovered by J. Willard Gibbs (1899), is the peculiar manner in which the Fourier series of a piecewise continuously differentiable periodic function behaves at a jump discontinuity. The nth partial sum of the Fourier series has large oscillations near the jump, which might increase the maximum of the partial sum above that of the function itself. The overshoot does not die out as n increases, but approaches a finite limit. This sort of behavior was also observed by experimental physicists, but was believed to be due to imperfections in the measuring apparatus.

This is one cause of ringing artifacts in signal processing.

🔗 United States 🔗 Mathematics 🔗 Education 🔗 United States/Massachusetts 🔗 Higher Education

Math 55 is a two-semester long first-year undergraduate mathematics course at Harvard University, founded by Lynn Loomis and Shlomo Sternberg. The official titles of the course are Honors Abstract Algebra (Math 55a) and Honors Real and Complex Analysis (Math 55b). Previously, the official title was Honors Advanced Calculus and Linear Algebra.

🔗 China 🔗 Linguistics 🔗 Food and drink 🔗 Linguistics/Etymology 🔗 Food and drink/Beverages

The etymology of the word tea can be traced back to the various Chinese pronunciations of the word. Nearly all the words for tea worldwide, fall into three broad groups: te, cha and chai, which reflected the history of transmission of tea drinking culture and trade from China to countries around the world. The few exceptions of words for tea that do not fall into these three broad groups are mostly from the minor languages from the botanical homeland of the tea plant, and likely to be the ultimate origin of the Chinese words for tea. Notably, none of these words mean 'dinner' or a late afternoon meal.

🔗 Transhumanism 🔗 Alternative Views 🔗 Futures studies

American author, inventor and futurist Raymond Kurzweil has become well known for his predictions about artificial intelligence and the human species, mainly concerning the technological singularity. He predicts that Artificial Intelligence would outsmart the human brain in computational capabilities by mid-21st century. His first book, The Age of Intelligent Machines, published in 1990, put forth his theories on the results of the increasing use of technology and predicted the explosive growth in the internet, among other predictions. Later works, 1999's The Age of Spiritual Machines and 2005's The Singularity is Near outlined other theories including the rise of clouds of nano-robots (nanobots) called foglets and the development of Human Body 2.0 and 3.0, whereby nanotechnology is incorporated into many internal organs.

🔗 Electronics 🔗 Electrical engineering

A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, producing a phenomenon known as a Townsend discharge. Gases used include mercury vapor, xenon, neon, and (in special high-voltage applications or applications requiring very short switching times) hydrogen. Unlike a vacuum tube (valve), a thyratron cannot be used to amplify signals linearly.

In the 1920s, thyratrons were derived from early vacuum tubes such as the UV-200, which contained a small amount of argon gas to increase its sensitivity as a radio signal detector, and the German LRS relay tube, which also contained argon gas. Gas rectifiers, which predated vacuum tubes, such as the argon-filled General Electric "Tungar bulb" and the Cooper-Hewitt mercury-pool rectifier, also provided an influence. Irving Langmuir and G. S. Meikle of GE are usually cited as the first investigators to study controlled rectification in gas tubes, about 1914. The first commercial thyratrons appeared circa 1928.

The term "thyratron" is derived from Ancient Greek "θύρα" ("thyra"), meaning "door" or "valve". The term "thyristor" was further derived from a combination of "thyratron" and "transistor". Since the 1960s thyristors have replaced thyratrons in most low- and medium-power applications.

🔗 Computing 🔗 Computing/Computer hardware 🔗 Computing/Software 🔗 Travel and Tourism

Sabre Global Distribution System, owned by Sabre Corporation, is used by travel agents and companies around the world to search, price, book, and ticket travel services provided by airlines, hotels, car rental companies, rail providers and tour operators. Sabre aggregates airlines, hotels, online and offline travel agents and travel buyers.

🔗 Writing systems

Scriptio continua (Latin for "continuous script"), also known as scriptura continua or scripta continua, is a style of writing without spaces or other marks between the words or sentences. The form also lacks punctuation, diacritics, or distinguished letter case. In the West, the oldest Greek and Latin inscriptions used word dividers to separate words in sentences; however, Classical Greek and late Classical Latin both employed scriptio continua as the norm.