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🔗 United States 🔗 Companies 🔗 Business 🔗 Philately

The American Letter Mail Company was started by Lysander Spooner in 1844, competing with the presumed legal monopoly of the United States Post Office (USPO, now the USPS).

🔗 Chess

The Immortal Game was a chess game played by Adolf Anderssen and Lionel Kieseritzky on 21 June 1851 in London, during a break of the first international tournament. The bold sacrifices made by Anderssen to secure victory have made it one of the most famous chess games of all time. Anderssen gave up both rooks and a bishop, then his queen, checkmating his opponent with his three remaining minor pieces. In 1996, Bill Hartston called the game an achievement "perhaps unparalleled in chess literature".

🔗 Birds

Wisdom is a wild female Laysan albatross. She is the oldest confirmed wild bird in the world as well as the oldest banded bird in the world.

🔗 Computing 🔗 Computer science

Esterel is a synchronous programming language for the development of complex reactive systems. The imperative programming style of Esterel allows the simple expression of parallelism and preemption. As a consequence, it is well suited for control-dominated model designs.

The development of the language started in the early 1980s, and was mainly carried out by a team of Ecole des Mines de Paris and INRIA led by Gérard Berry in France. Current compilers take Esterel programs and generate C code or hardware (RTL) implementations (VHDL or Verilog).

The language is still under development, with several compilers out. The commercial version of Esterel is the development environment Esterel Studio. The company that commercialize it (Synfora) initiated a normalization process with the IEEE in April 2007 however the working group (P1778) dissolved March 2011. The Esterel v7 Reference Manual Version v7 30 – initial IEEE standardization proposal is publicly available.

🔗 Spaceflight

A porkchop plot (also pork-chop plot) is a chart that shows contours of equal characteristic energy (C₃) against combinations of launch date and arrival date for a particular interplanetary flight.

By examining the results of the porkchop plot, engineers can determine when launch opportunities exist (a launch window) that is compatible with the capabilities of a particular spacecraft. A given contour, called a porkchop curve, represents constant C₃, and the center of the porkchop the optimal minimum C₃. The orbital elements of the solution, where the fixed values are the departure date, the arrival date, and the length of the flight, were first solved mathematically in 1761 by Johann Heinrich Lambert, and the equation is generally known as Lambert's problem (or theorem).

🔗 Time

The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 (last revised in 2004) and, before that, it was defined in ISO (R) 2015 since 1971. It is used (mainly) in government and business for fiscal years, as well as in timekeeping. This was previously known as "Industrial date coding". The system specifies a week year atop the Gregorian calendar by defining a notation for ordinal weeks of the year.

The Gregorian leap cycle, which has 97 leap days spread across 400 years, contains a whole number of weeks (20871). In every cycle there are 71 years with an additional 53rd week (corresponding to the Gregorian years that contain 53 Thursdays). An average year is exactly 52.1775 weeks long; months (​¹⁄₁₂ year) average at exactly 4.348125 weeks.

An ISO week-numbering year (also called ISO year informally) has 52 or 53 full weeks. That is 364 or 371 days instead of the usual 365 or 366 days. The extra week is sometimes referred to as a leap week, although ISO 8601 does not use this term.

Weeks start with Monday. Each week's year is the Gregorian year in which the Thursday falls. The first week of the year, hence, always contains 4 January. ISO week year numbering therefore slightly deviates from the Gregorian for some days close to 1 January.

A precise date is specified by the ISO week-numbering year in the format YYYY, a week number in the format ww prefixed by the letter 'W', and the weekday number, a digit d from 1 through 7, beginning with Monday and ending with Sunday. For example, the Gregorian date Monday 23 December 2019 corresponds to Monday in the 52nd week of 2019, and is written 2019-W52-1 (in extended form) or 2019W521 (in compact form). The ISO year is slightly offset to the Gregorian year; for example, Monday 30 December 2019 in the Gregorian calendar is the first day of week 1 of 2020 in the ISO calendar, and is written as 2020-W01-1 or 2020W011.

🔗 Physics 🔗 Spectroscopy

Silicon drift detectors (SDDs) are X-ray radiation detectors used in x-ray spectrometry (XRF and EDS) and electron microscopy. Their chief characteristics compared with other X-ray detectors are:

• high count rates
• comparatively high energy resolution (e.g. 125 eV for Mn Kα wavelength)
• Peltier cooling

🔗 Computing

In computer science, the ostrich algorithm is a strategy of ignoring potential problems on the basis that they may be exceedingly rare. It is named for the ostrich effect which is defined as "to stick one's head in the sand and pretend there is no problem". It is used when it is more cost-effective to allow the problem to occur than to attempt its prevention.

🔗 Soviet Union 🔗 Russia 🔗 Death 🔗 Guild of Copy Editors 🔗 Russia/physical geography of Russia 🔗 Russia/history of Russia 🔗 Russia/sports and games in Russia

The Dyatlov Pass incident (Russian: Гибель тургруппы Дятлова) was an event where nine Russian hikers died in the northern Ural Mountains between 1 and 2 February 1959, in uncertain circumstances. The experienced trekking group, who were all from the Ural Polytechnical Institute, had established a camp on the slopes of Kholat Syakhl, in an area now named in honor of the group's leader, Igor Dyatlov. During the night, something caused them to tear their way out of their tents and flee the campsite, all while inadequately dressed for the heavy snowfall and sub-zero temperatures.

After the group's bodies were discovered, an investigation by Soviet authorities determined that six had died from hypothermia while the other three showed signs of physical trauma. One victim had a fractured skull; two others had major chest fractures and the body of one of the group was missing both its eyes. One of the victims was missing a tongue. The investigation concluded that a "compelling natural force" had caused the deaths. Numerous theories have been put forward to account for the unexplained deaths, including animal attacks, hypothermia, avalanche, katabatic winds, infrasound-induced panic, military involvement, or some combination of these.

🔗 Computer science 🔗 Mathematics

In numerical analysis, the Kahan summation algorithm, also known as compensated summation, significantly reduces the numerical error in the total obtained by adding a sequence of finite-precision floating-point numbers, compared to the obvious approach. This is done by keeping a separate running compensation (a variable to accumulate small errors).

In particular, simply summing n numbers in sequence has a worst-case error that grows proportional to n, and a root mean square error that grows as ${\displaystyle {\sqrt {n}}}$ for random inputs (the roundoff errors form a random walk). With compensated summation, the worst-case error bound is effectively independent of n, so a large number of values can be summed with an error that only depends on the floating-point precision.

The algorithm is attributed to William Kahan. Similar, earlier techniques are, for example, Bresenham's line algorithm, keeping track of the accumulated error in integer operations (although first documented around the same time) and the delta-sigma modulation (integrating, not just summing the error).