To stay up to date you can also follow on Mastodon.

🔗 History 🔗 East Asia 🔗 Middle Ages 🔗 Middle Ages/History 🔗 Mongols

The Pax Mongolica (Latin for "Mongol Peace"), less often known as Pax Tatarica ("Tatar Peace"), is a historiographical term modelled after the original phrase Pax Romana which describes the stabilizing effects of the conquests of the Mongol Empire on the social, cultural and economic life of the inhabitants of the vast Eurasian territory that the Mongols conquered in the 13th and 14th centuries. The term is used to describe the eased communication and commerce the unified administration helped to create and the period of relative peace that followed the Mongols' vast conquests.

The conquests of Genghis Khan (r. 1206–1227) and his successors, spanning from Southeast Asia to Eastern Europe, effectively connected the Eastern world with the Western world. The Silk Road, connecting trade centres across Asia and Europe, came under the sole rule of the Mongol Empire. It was commonly said that "a maiden bearing a nugget of gold on her head could wander safely throughout the realm". Despite the political fragmentation of the Mongol Empire into four khanates (Yuan dynasty, Golden Horde, Chagatai Khanate and Ilkhanate), nearly a century of conquest and civil war was followed by relative stability in the early 14th century. The end of the Pax Mongolica was marked by the disintegration of the khanates and the outbreak of the Black Death in Asia which spread along trade routes to much of the world in the mid-14th century.

During this time, Mongol elements including the ʼPhags-pa script made numerous appearances in western art (see Mongol elements in Western medieval art).

🔗 Biography 🔗 Espionage 🔗 Aviation 🔗 Physics 🔗 Systems 🔗 Biography/science and academia 🔗 Aviation/aerospace biography 🔗 Physics/Biographies 🔗 Physics/Fluid Dynamics 🔗 Systems/Systems engineering 🔗 Pritzker Military Library

Clarence Leonard "Kelly" Johnson (February 27, 1910 – December 21, 1990) was an American aeronautical and systems engineer. He is recognized for his contributions to a series of important aircraft designs, most notably the Lockheed U-2 and SR-71 Blackbird. Besides the first production aircraft to exceed Mach 3, he also produced the first fighter capable of Mach 2, the United States' first operational jet fighter, as well as the first fighter to exceed 400 mph, and many other contributions to various aircraft. As a member and first team leader of the Lockheed Skunk Works, Johnson worked for more than four decades and is said to have been an "organizing genius". He played a leading role in the design of over forty aircraft, including several honored with the prestigious Collier Trophy, acquiring a reputation as one of the most talented and prolific aircraft design engineers in the history of aviation. In 2003, as part of its commemoration of the 100th anniversary of the Wright Brothers' flight, Aviation Week & Space Technology ranked Johnson eighth on its list of the top 100 "most important, most interesting, and most influential people" in the first century of aerospace. Hall Hibbard, Johnson's Lockheed boss, referring to Johnson's Swedish ancestry, once remarked to Ben Rich: "That damned Swede can actually see air."

🔗 United States 🔗 Spaceflight 🔗 Telecommunications

The Iridium satellite constellation provides L-band voice and data information coverage to satellite phones, pagers and integrated transceivers over the entire Earth surface. Iridium Communications owns and operates the constellation, additionally selling equipment and access to its services. It was originally conceived by Bary Bertiger, Raymond J. Leopold and Ken Peterson in late 1987 (in 1988 protected by patents Motorola filed in their names) and then developed by Motorola on a fixed-price contract from July 29, 1993, to November 1, 1998, when the system became operational and commercially available.

The constellation consists of 66 active satellites in orbit, required for global coverage, and additional spare satellites to serve in case of failure. Satellites are in low Earth orbit at a height of approximately 781 km (485 mi) and inclination of 86.4°. Orbital velocity of the satellites is approximately 27,000 km/h (17,000 mph). Satellites communicate with neighboring satellites via K_a band inter-satellite links. Each satellite can have four inter-satellite links: one each to neighbors fore and aft in the same orbital plane, and one each to satellites in neighboring planes to either side. The satellites orbit from pole to same pole with an orbital period of roughly 100 minutes. This design means that there is excellent satellite visibility and service coverage especially at the North and South poles. The over-the-pole orbital design produces "seams" where satellites in counter-rotating planes next to one another are traveling in opposite directions. Cross-seam inter-satellite link hand-offs would have to happen very rapidly and cope with large Doppler shifts; therefore, Iridium supports inter-satellite links only between satellites orbiting in the same direction. The constellation of 66 active satellites has six orbital planes spaced 30° apart, with 11 satellites in each plane (not counting spares). The original concept was to have 77 satellites, which is where the name Iridium came from, being the element with the atomic number 77 and the satellites evoking the Bohr model image of electrons orbiting around the Earth as its nucleus. This reduced set of six planes is sufficient to cover the entire Earth surface at every moment.

Because of the shape of the original Iridium satellites' reflective antennas, the first generation satellites focus sunlight on a small area of the Earth surface in an incidental manner. This results in an effect called Iridium flares, where the satellite momentarily appears as one of the brightest objects in the night sky and can be seen even during daylight. Newer Iridium satellites do not produce flares.

🔗 Computing 🔗 Computing/Software 🔗 Writing systems 🔗 Typography

A bidirectional text contains both text directionalities, right-to-left (RTL or dextrosinistral) and left-to-right (LTR or sinistrodextral). It generally involves text containing different types of alphabets, but may also refer to boustrophedon, which is changing text direction in each row.

Some writing systems including the Arabic and Hebrew scripts or derived systems such as the Persian, Urdu, and Yiddish scripts, are written in a form known as right-to-left (RTL), in which writing begins at the right-hand side of a page and concludes at the left-hand side. This is different from the left-to-right (LTR) direction used by the dominant Latin script. When LTR text is mixed with RTL in the same paragraph, each type of text is written in its own direction, which is known as bidirectional text. This can get rather complex when multiple levels of quotation are used.

Many computer programs fail to display bidirectional text correctly. For example, the Hebrew name Sarah (שרה) is spelled: sin (ש) (which appears rightmost), then resh (ר), and finally heh (ה) (which should appear leftmost).

Note: Some web browsers may display the Hebrew text in this article in the opposite direction.

🔗 Physics 🔗 Physics/Acoustics

Thermoacoustic engines (sometimes called "TA engines") are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another (this requires work, which is provided by the loudspeaker) or use a heat difference to produce work in the form of sound waves (these waves can then be converted into electrical current the same way as a microphone does).

These devices can be designed to use either standing wave or travelling wave.

Compared to vapor refrigerators, thermoacoustic refrigerators have no coolant and few moving parts (only the loudspeaker), therefore require no dynamic sealing or lubrication.

🔗 Australia 🔗 Military history 🔗 Agriculture 🔗 Australia/Western Australia 🔗 Birds 🔗 Military history/Australia, New Zealand and South Pacific military history 🔗 Australia/Australian history 🔗 Australia/Australian biota 🔗 Australia/Australian politics

The Emu War, also known as the Great Emu War, was a nuisance wildlife management military operation undertaken in Australia over the latter part of 1932 to address public concern over the number of emus said to be running amok in the Campion district of Western Australia. The unsuccessful attempts to curb the population of emus, a large flightless bird indigenous to Australia, employed soldiers armed with Lewis guns—leading the media to adopt the name "Emu War" when referring to the incident. While a number of the birds were killed, the emu population persisted and continued to cause crop destruction.

🔗 Physics 🔗 Alternative Views

The Biefeld–Brown effect is an electrical phenomenon that produces an ionic wind that transfers its momentum to surrounding neutral particles. It describes a force observed on an asymmetric capacitor when high voltage is applied to the capacitor's electrodes. Once suitably charged up to high DC potentials, a thrust at the negative terminal, pushing it away from the positive terminal, is generated. The effect was named by inventor Thomas Townsend Brown who claimed that he did a series of experiments with professor of astronomy Paul Alfred Biefeld, a former teacher of Brown whom Brown claimed was his mentor and co-experimenter at Denison University in Ohio.

The use of an asymmetric capacitor, with the negative electrode being larger than the positive electrode, allowed for more thrust to be produced in the direction from the low-flux to the high-flux region compared to a conventional capacitor. These asymmetric capacitors became known as Asymmetrical Capacitor Thrusters (ACT). The Biefeld–Brown effect can be observed in ionocrafts and lifters, which utilize the effect to produce thrust in the air without requiring any combustion or moving parts.

In his 1960 patent titled "Electrokinetic Apparatus," Brown refers to electrokinesis to describe the Biefeld–Brown effect, linking the phenomenon to the field of electrohydrodynamics (EHD). Brown also believed the Biefeld–Brown effect could produce an anti-gravity force, referred to as "electrogravitics" based on it being an electricity/gravity phenomenon. However, there is little evidence that supports Brown's claim on the effect's anti-gravity properties.

🔗 Amateur radio 🔗 Michigan

Heathkit is the brand name of kits and other electronic products produced and marketed by the Heath Company. The products over the decades have included electronic test equipment, high fidelity home audio equipment, television receivers, amateur radio equipment, robots, electronic ignition conversion modules for early model cars with point style ignitions, and the influential Heath H-8, H-89, and H-11 hobbyist computers, which were sold in kit form for assembly by the purchaser.

Heathkit manufactured electronic kits from 1947 until 1992. After closing that business, the Heath Company continued with its products for education, and motion-sensor lighting controls. The lighting control business was sold around 2000. The company announced in 2011 that they were reentering the kit business after a 20-year hiatus but then filed for bankruptcy in 2012, and under new ownership began restructuring in 2013. As of 2019, the company has a live website with newly-designed products, services, vintage kits, and replacement parts for sale.

🔗 Cryptography 🔗 Cryptography/Computer science 🔗 Virginia

The Beale ciphers (or Beale Papers) are a set of three ciphertexts, one of which allegedly states the location of a buried treasure of gold, silver and jewels estimated to be worth over US$43 million as of January 2018. Comprising three ciphertexts, the first (unsolved) text describes the location, the second (solved) ciphertext the content of the treasure, and the third (unsolved) lists the names of the treasure's owners and their next of kin.

The story of the three ciphertexts originates from an 1885 pamphlet detailing treasure being buried by a man named Thomas J. Beale in a secret location in Bedford County, Virginia, in the 1820s. Beale entrusted a box containing the encrypted messages to a local innkeeper named Robert Morriss and then disappeared, never to be seen again. According to the story, the innkeeper opened the box 23 years later, and then decades after that gave the three encrypted ciphertexts to a friend before he died. The friend then spent the next twenty years of his life trying to decode the messages, and was able to solve only one of them which gave details of the treasure buried and the general location of the treasure. The unnamed friend then published all three ciphertexts in a pamphlet which was advertised for sale in the 1880s.

Since the publication of the pamphlet, a number of attempts have been made to decode the two remaining ciphertexts and to locate the treasure, but all efforts have resulted in failure.

There are many arguments that the entire story is a hoax, including the 1980 article "A Dissenting Opinion" by cryptographer Jim Gillogly, and a 1982 scholarly analysis of the Beale Papers and their related story by Joe Nickell, using historical records that cast doubt on the existence of Thomas J. Beale. Nickell also presents linguistic evidence demonstrating that the documents could not have been written at the time alleged (words such as "stampeding", for instance, are of later vintage). His analysis of the writing style showed that Beale was almost certainly James B. Ward, whose 1885 pamphlet brought the Beale Papers to light. Nickell argues that the tale is thus a work of fiction; specifically, a "secret vault" allegory of the Freemasons; James B. Ward was a Mason himself.

🔗 Biography 🔗 Russia 🔗 Statistics 🔗 Biography/science and academia 🔗 Russia/science and education in Russia

Alexey Yakovlevich Chervonenkis (Russian: Алексей Яковлевич Червоненкис; 7 September 1938 – 22 September 2014) was a Soviet and Russian mathematician, and, with Vladimir Vapnik, was one of the main developers of the Vapnik–Chervonenkis theory, also known as the "fundamental theory of learning" an important part of computational learning theory. Chervonenkis held joint appointments with the Russian Academy of Sciences and Royal Holloway, University of London.

Alexey Chervonenkis got lost in Losiny Ostrov National Park on 22 September 2014, and later during a search operation was found dead near Mytishchi, a suburb of Moscow. He had died of hypothermia.