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🔗 Aviation 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Aviation/aircraft 🔗 Military history/World War II 🔗 Japan 🔗 Japan/Japanese military history 🔗 Military history/Asian military history 🔗 Military history/Japanese military history

A Fu-Go (ふ号[兵器], fugō [heiki], lit. "Code Fu [Weapon]"), or fire balloon (風船爆弾, fūsen bakudan, lit. "balloon bomb"), was a weapon launched by Japan during World War II. A hydrogen balloon with a load varying from a 33 lb (15 kg) antipersonnel bomb to one 26-pound (12 kg) incendiary bomb and four 11 lb (5.0 kg) incendiary devices attached, it was designed as a cheap weapon intended to make use of the jet stream over the Pacific Ocean and drop bombs on American cities, forests, and farmland. Canada and Mexico reported fire balloon sightings as well.

The Japanese fire balloon was the first ever weapon possessing intercontinental range (the second being the Convair B-36 Peacemaker and the third being the R-7 ICBM). The Japanese balloon attacks on North America were at that time the longest ranged attacks ever conducted in the history of warfare, a record which was not broken until the 1982 Operation Black Buck raids during the Falkland Islands War.

The balloons were intended to instill fear and terror in the U.S., though the bombs were relatively ineffective as weapons of destruction due to extreme weather conditions.

🔗 Mathematics 🔗 Festivals

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π. In 2009, the United States House of Representatives supported the designation of Pi Day. UNESCO's 40th General Conference decided Pi Day as the International Day of Mathematics in November 2019.

Pi Approximation Day is observed on July 22 (22/7 in the day/month format), since the fraction ​²²⁄₇ is a common approximation of π, which is accurate to two decimal places and dates from Archimedes.

Two Pi Day, also known as Tau Day for the mathematical constant Tau, is observed on June 28 (6/28 in the month/day format).

🔗 Cognitive science 🔗 Neuroscience

Sparse distributed memory (SDM) is a mathematical model of human long-term memory introduced by Pentti Kanerva in 1988 while he was at NASA Ames Research Center. It is a generalized random-access memory (RAM) for long (e.g., 1,000 bit) binary words. These words serve as both addresses to and data for the memory. The main attribute of the memory is sensitivity to similarity, meaning that a word can be read back not only by giving the original write address but also by giving one close to it, as measured by the number of mismatched bits (i.e., the Hamming distance between memory addresses).

SDM implements transformation from logical space to physical space using distributed data representation and storage, similarly to encoding processes in human memory. A value corresponding to a logical address is stored into many physical addresses. This way of storing is robust and not deterministic. A memory cell is not addressed directly. If input data (logical addresses) are partially damaged at all, we can still get correct output data.

The theory of the memory is mathematically complete and has been verified by computer simulation. It arose from the observation that the distances between points of a high-dimensional space resemble the proximity relations between concepts in human memory. The theory is also practical in that memories based on it can be implemented with conventional RAM-memory elements.

Vector 2022 is a desktop skin developed between 2019 and 2023 by the Wikimedia Foundation Web team with the goal of making the interface more welcoming and usable for readers and maintaining utility for existing editors.

It introduces changes to the navigation and layout of the site, adds persistent elements such as a sticky header and Table of Contents, and makes changes to the overall styling of the page. Currently (early January 2023), the skin is the default on more than 300 projects of various sizes, accounting for about 1.5 billion page views per month. Before the deployment, on English Wikipedia, it was the most popular non-default skin, with more active editors using it than any other non-default skin (Monobook, Timeless, etc).

The skin was ready for deployment to English Wikipedia after completing the changes specified by the consensus of the Request for Comment. Today (January 18, 2023), the skin was turned on as the default on the desktop site. Users of non-default skins (Monobook, Timeless, etc.) will not see any changes.

If you decide to try it out, we, the Web team, suggest trying it for at least one week prior to deciding whether to switch to one of our older skins. It usually takes a few days to begin feeling comfortable with the new interface. That said, if you are unsatisfied, you can switch to any of our other skins at any time.

🔗 Internet 🔗 Internet culture

The Society for Preventing Parents from Naming Their Children Jennifer (SPPNTCJ) was a popular and sometimes controversial website that contributed to early web culture, online from 1996 to 2000. The SPPNTCJ home page was created and updated by Jennifer Farwell, one of the three founding members of the SPPNTCJ. Other founding members were Jennifer Rich and Jennifer Ang.

The SPPNTCJ began as an inside joke on an email discussion list that both Farwell and Rich subscribed to, which included five or more Jennifers who actively posted at that time. One of the Jennifers tossed out the comment that there should be "a society for preventing parents from naming their children Jennifer." The idea took off, and Farwell created the SPPNTCJ's website. It welcomed more than 2 million visitors while online.

During its run, the SPPNTCJ was noted by the Richmond Times-Dispatch, Yahoo! Internet Life magazine, Thunder Bay Television News, 580 CKPR radio program Tech Talk, California State University, Chico, SignsOnSanDiego.com, WebMD and more. It received several Internet "cool site" acknowledgments, from Cool Central, Seven Wonders, Twoeys, Fallen Thinkers, and Secret Einstein.

🔗 Volcanoes 🔗 Meteorology

The year 1816 is known as the Year Without a Summer (also the Poverty Year and Eighteen Hundred and Froze To Death) because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.72–1.26 °F). This resulted in major food shortages across the Northern Hemisphere.

Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in April in the Dutch East Indies (now Indonesia). This eruption was the largest eruption in at least 1,300 years (after the hypothesized eruption causing the extreme weather events of 535–536), and perhaps exacerbated by the 1814 eruption of Mayon in the Philippines.

🔗 Scotland 🔗 Theatre 🔗 Shakespeare

The Scottish play and the Bard's play are euphemisms for William Shakespeare's Macbeth. The first is a reference to the play's Scottish setting, the second a reference to Shakespeare’s popular nickname. According to a theatrical superstition, called the Scottish curse, speaking the name Macbeth inside a theatre, other than as called for in the script while rehearsing or performing, will cause disaster. A variation of the superstition also forbids quoting lines from the play within a theatre except as part of an actual rehearsal or performance of the play.

Because of this superstition, the lead character is often referred to as the Scottish King or Scottish Lord. Lady Macbeth is often referred to as the Scottish Lady. Sometimes Mackers or MacB is used to avoid saying the name.

🔗 China 🔗 Writing systems

Since the second half of the 20th century, inscriptions have been found on pottery in a variety of locations in China, such as Banpo near Xi'an, as well as on bone and bone marrows at Hualouzi, Chang'an County near Xi'an. These simple, often geometric, marks have been frequently compared to some of the earliest known Chinese characters appearing on the oracle bones, and some have taken them to mean that the history of Chinese writing extends back over six millennia. However, only isolated instances of these symbols have been found, and they show no indication of representing speech or of the non-pictorial processes that a writing system requires.

🔗 Mathematics

In linear algebra, the singular value decomposition (SVD) is a factorization of a real or complex matrix that generalizes the eigendecomposition of a square normal matrix to any ${\displaystyle m\times n}$ matrix via an extension of the polar decomposition.

Specifically, the singular value decomposition of an ${\displaystyle m\times n}$ real or complex matrix ${\displaystyle \mathbf {M} }$ is a factorization of the form ${\displaystyle \mathbf {U\Sigma V^{*}} }$, where ${\displaystyle \mathbf {U} }$ is an ${\displaystyle m\times m}$ real or complex unitary matrix, ${\displaystyle \mathbf {\Sigma } }$ is an ${\displaystyle m\times n}$ rectangular diagonal matrix with non-negative real numbers on the diagonal, and ${\displaystyle \mathbf {V} }$ is an ${\displaystyle n\times n}$ real or complex unitary matrix. If ${\displaystyle \mathbf {M} }$ is real, ${\displaystyle \mathbf {U} }$ and ${\displaystyle \mathbf {V} =\mathbf {V^{*}} }$ are real orthonormal matrices.

The diagonal entries ${\displaystyle \sigma _{i}=\Sigma _{ii}}$ of ${\displaystyle \mathbf {\Sigma } }$ are known as the singular values of ${\displaystyle \mathbf {M} }$. The number of non-zero singular values is equal to the rank of ${\displaystyle \mathbf {M} }$. The columns of ${\displaystyle \mathbf {U} }$ and the columns of ${\displaystyle \mathbf {V} }$ are called the left-singular vectors and right-singular vectors of ${\displaystyle \mathbf {M} }$, respectively.

The SVD is not unique. It is always possible to choose the decomposition so that the singular values ${\displaystyle \Sigma _{ii}}$are in descending order. In this case, Σ (but not always U and V) is uniquely determined by M.

The term sometimes refers to the compact SVD, a similar decomposition ${\displaystyle \mathbf {M} =\mathbf {U\Sigma V^{*}} }$ in which Σ is square diagonal of size ${\displaystyle r\times r}$, where ${\displaystyle r\leq \min\{m,n\}}$ is the rank of M, and has only the non-zero singular values. In this variant, ${\displaystyle \mathbf {U} }$ is an ${\displaystyle m\times r}$ matrix and ${\displaystyle \mathbf {V} }$ is an ${\displaystyle n\times r}$ matrix, such that ${\displaystyle \mathbf {U^{*}U} =\mathbf {V^{*}V} =\mathbf {I} _{r\times r}}$.

Mathematical applications of the SVD include computing the pseudoinverse, matrix approximation, and determining the rank, range, and null space of a matrix. The SVD is also extremely useful in all areas of science, engineering, and statistics, such as signal processing, least squares fitting of data, and process control.

🔗 Germany 🔗 Astronomy 🔗 Archaeology 🔗 Visual arts

The Nebra sky disk is a bronze disk of around 30 centimeters (11 ³⁄₄ in) diameter and a weight of 2.2 kilograms (4.9 lb), having a blue-green patina and inlaid with gold symbols. These symbols are interpreted generally as the Sun or full moon, a lunar crescent, and stars (including a cluster of seven interpreted as the Pleiades). Two golden arcs along the sides, interpreted to mark the angle between the solstices, were added later. A final addition was another arc at the bottom surrounded with multiple strokes (of uncertain meaning, variously interpreted as a Solar Barge with numerous oars, the Milky Way, or a rainbow).

The disk is attributed to a site in present-day Germany near Nebra, Saxony-Anhalt, and dated by Archaeological association to c. 1600 BC. Researchers suggest the disk is an artifact of the Bronze Age Unetice culture.

The style in which the disk is executed was unlike any artistic style then known from the period, with the result that the object was initially suspected of being a forgery, but is now widely accepted as authentic.

The Nebra sky disk features the oldest concrete depiction of the cosmos yet known from anywhere in the world. In June 2013 it was included in the UNESCO Memory of the World Register and termed "one of the most important archaeological finds of the twentieth century."