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🔗 Biography 🔗 Canada 🔗 Physics 🔗 Women 🔗 Women scientists 🔗 Biography/science and academia 🔗 Physics/Biographies 🔗 Canada/Ontario

Donna Theo Strickland, (born 27 May 1959) is a Canadian optical physicist and pioneer in the field of pulsed lasers. She was awarded the Nobel Prize in Physics in 2018, together with Gérard Mourou, for the invention of chirped pulse amplification. She is a professor at the University of Waterloo.

She served as fellow, vice president, and president of The Optical Society, and is currently chair of their Presidential Advisory Committee. In 2018, she was listed as one of BBC's 100 Women.

🔗 Computing

The Fletcher checksum is an algorithm for computing a position-dependent checksum devised by John G. Fletcher (1934–2012) at Lawrence Livermore Labs in the late 1970s. The objective of the Fletcher checksum was to provide error-detection properties approaching those of a cyclic redundancy check but with the lower computational effort associated with summation techniques.

🔗 Europe 🔗 Maps 🔗 Sociology

The Hajnal line is a border that links Saint Petersburg, Russia and Trieste, Italy. In 1965, John Hajnal discovered it divides Europe into two areas characterized by different levels of nuptiality. To the west of the line, marriage rates and thus fertility were comparatively low and a significant minority of women married late or remained single; to the east of the line and in the Mediterranean and select pockets of Northwestern Europe, early marriage was the norm and high fertility was countered by high mortality.

🔗 United States/U.S. Government 🔗 United States 🔗 Spaceflight 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 United States/Military history - U.S. military history 🔗 Cold War

Project West Ford (also known as Westford Needles and Project Needles) was a test carried out by Massachusetts Institute of Technology's Lincoln Laboratory on behalf of the United States Military in 1961 and 1963 to create an artificial ionosphere above the Earth. This was done to solve a major weakness that had been identified in US military communications.

🔗 Mathematics

Legendre's constant is a mathematical constant occurring in a formula conjectured by Adrien-Marie Legendre to capture the asymptotic behavior of the prime-counting function ${\displaystyle \pi (x)}$. Its value is now known to be exactly 1.

Examination of available numerical evidence for known primes led Legendre to suspect that ${\displaystyle \pi (x)}$ satisfies an approximate formula.

Legendre conjectured in 1808 that

${\displaystyle \pi (x)={\frac {x}{\ln(x)-B(x)}}}$

where ${\displaystyle \lim _{x\to \infty }B(x)=1.08366}$....OEIS: A228211

Or similarly,

${\displaystyle \lim _{n\to \infty }\left(\ln(n)-{n \over \pi (n)}\right)=B}$

where B is Legendre's constant. He guessed B to be about 1.08366, but regardless of its exact value, the existence of B implies the prime number theorem.

Pafnuty Chebyshev proved in 1849 that if the limit B exists, it must be equal to 1. An easier proof was given by Pintz in 1980.

It is an immediate consequence of the prime number theorem, under the precise form with an explicit estimate of the error term

${\displaystyle \pi (x)={\rm {Li}}(x)+O\left(xe^{-a{\sqrt {\ln x}}}\right)\quad {\text{as }}x\to \infty }$

(for some positive constant a, where O(…) is the big O notation), as proved in 1899 by Charles de La Vallée Poussin, that B indeed is equal to 1. (The prime number theorem had been proved in 1896, independently by Jacques Hadamard and La Vallée Poussin, but without any estimate of the involved error term).

Being evaluated to such a simple number has made the term Legendre's constant mostly only of historical value, with it often (technically incorrectly) being used to refer to Legendre's first guess 1.08366... instead.

Pierre Dusart proved in 2010

${\displaystyle {\frac {x}{\ln x-1}}<\pi (x)}$ for ${\displaystyle x\geq 5393}$, and

${\displaystyle \pi (x)<{\frac {x}{\ln x-1.1}}}$ for ${\displaystyle x\geq 60184}$. This is of the same form as

${\displaystyle \pi (x)={\frac {x}{\ln(x)-B(x)}}}$ with ${\displaystyle 1<B(x)<1.1}$.

🔗 Architecture

The Frankfurt kitchen was a milestone in domestic architecture, considered the forerunner of modern fitted kitchens, for it realised for the first time a kitchen built after a unified concept, designed to enable efficient work and to be built at low cost. It was designed in 1926 by Austrian architect Margarete Schütte-Lihotzky for architect Ernst May's social housing project New Frankfurt in Frankfurt, Germany. Some 10,000 units were built in the late 1920s in Frankfurt.

🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry

Improvised firearms (sometimes called zip guns or pipe guns) are firearms manufactured other than by a firearms manufacturer or a gunsmith, and are typically constructed by adapting existing materials to the purpose. They range in quality from crude weapons that are as much a danger to the user as the target to high-quality arms produced by cottage industries using salvaged and repurposed materials.

Improvised firearms are commonly used as tools by criminals and insurgents and are often associated with such groups; other uses include self-defense in lawless areas and hunting game in poor rural areas.

🔗 France 🔗 Atheism

The Cult of Reason (French: Culte de la Raison) was France's first established state-sponsored atheistic religion, intended as a replacement for Catholicism during the French Revolution. After holding sway for barely a year, in 1794 it was officially replaced by the rival Cult of the Supreme Being, promoted by Robespierre. Both cults were officially banned in 1802 by Napoleon Bonaparte with his Law on Cults of 18 Germinal, Year X.

🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Military history/Cold War 🔗 Pritzker Military Library 🔗 Firearms

The M-28 or M-29 Davy Crockett Weapon System was the tactical nuclear recoilless gun (smoothbore) for firing the M-388 nuclear projectile that was deployed by the United States during the Cold War. It was one of the smallest nuclear weapon systems ever built, with a yield between 10 and 20 tons TNT equivalent (40–80 gigajoules). It is named after American folk hero, soldier, and congressman Davy Crockett.

🔗 Archaeology 🔗 Paranormal

A thunderstone is a flint tool or fossil turned up by farmer's plow that was thought to have fallen from the sky. They were often thought to be thunderbolts. It was not until travelers returned from far-away places where these implements were in use among primitive cultures that the origins of these objects became known. Even then, these travelers' tales received little popular credence.