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🔗 Aviation 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/Military science, technology, and theory 🔗 Aviation/aircraft

In aerobatics the Cobra maneuver, also known as just the Cobra, is a dramatic and demanding maneuver in which an airplane flying at a moderate speed suddenly raises the nose momentarily to the vertical position and slightly beyond, before dropping it back to normal, effectively making the plane a full body air brake.

The maneuver relies on the ability of the plane to be able to quickly change alpha which momentarily stalls the plane without overloading the airframe and powerful engine thrust to maintain approximately constant altitude through the entire move. It is an impressive maneuver to demonstrate an aircraft's pitch control authority, high alpha stability and engine-versus-inlet compatibility, as well as the pilot's skill.

Although the maneuver is mainly performed at air shows it has use in close range air combat as a last ditch maneuver to make a pursuing plane overshoot. There is currently no widely spread or readily available evidence of the Cobra being used in real combat, although, there are records of it being used during mockup-dogfights and during border protection.

🔗 Computer science

Floyd–Steinberg dithering is an image dithering algorithm first published in 1976 by Robert W. Floyd and Louis Steinberg. It is commonly used by image manipulation software, for example when an image is converted into GIF format that is restricted to a maximum of 256 colors.

The algorithm achieves dithering using error diffusion, meaning it pushes (adds) the residual quantization error of a pixel onto its neighboring pixels, to be dealt with later. It spreads the debt out according to the distribution (shown as a map of the neighboring pixels):

${\displaystyle {\begin{bmatrix}&&*&{\frac {\displaystyle 7}{\displaystyle 16}}&\ldots \\\ldots &{\frac {\displaystyle 3}{\displaystyle 16}}&{\frac {\displaystyle 5}{\displaystyle 16}}&{\frac {\displaystyle 1}{\displaystyle 16}}&\ldots \\\end{bmatrix}}}$

The pixel indicated with a star (*) indicates the pixel currently being scanned, and the blank pixels are the previously-scanned pixels. The algorithm scans the image from left to right, top to bottom, quantizing pixel values one by one. Each time the quantization error is transferred to the neighboring pixels, while not affecting the pixels that already have been quantized. Hence, if a number of pixels have been rounded downwards, it becomes more likely that the next pixel is rounded upwards, such that on average, the quantization error is close to zero.

The diffusion coefficients have the property that if the original pixel values are exactly halfway in between the nearest available colors, the dithered result is a checkerboard pattern. For example, 50% grey data could be dithered as a black-and-white checkerboard pattern. For optimal dithering, the counting of quantization errors should be in sufficient accuracy to prevent rounding errors from affecting the result.

In some implementations, the horizontal direction of scan alternates between lines; this is called "serpentine scanning" or boustrophedon transform dithering.

In the following pseudocode we can see the algorithm described above. This works for any approximately linear encoding of pixel values, such as 8-bit integers, 16-bit integers or real numbers in the range [0,1].

for each y from top to bottom do
    for each x from left to right do
        oldpixel := pixel[x][y]
        newpixel := find_closest_palette_color(oldpixel)
        pixel[x][y] := newpixel
        quant_error := oldpixel - newpixel
        pixel[x + 1][y    ] := pixel[x + 1][y    ] + quant_error × 7 / 16
        pixel[x - 1][y + 1] := pixel[x - 1][y + 1] + quant_error × 3 / 16
        pixel[x    ][y + 1] := pixel[x    ][y + 1] + quant_error × 5 / 16
        pixel[x + 1][y + 1] := pixel[x + 1][y + 1] + quant_error × 1 / 16

When converting 16 bit greyscale to 8 bit, find_closest_palette_color() may perform just a simple rounding, for example:

find_closest_palette_color(oldpixel) = round(oldpixel / 256)

The pseudocode can result in pixel values exceeding the valid values (such as greater than 1 in a [0,1] representation). Such values should ideally be clipped by the find_closest_palette_color() function, rather than clipping the intermediate values, since a subsequent error may bring the value back into range. However, if fixed-width integers are used, wrapping of intermediate values would cause inversion of black and white, and so should be avoided.

🔗 Video games

42 is a private, nonprofit and tuition-free computer programming school created and funded by French billionaire Xavier Niel (founder of the telecommunication company Illiad) with several partners including Nicolas Sadirac (previous director-general of the Epitech school in France), Kwame Yamgnane and Florian Bucher (former executives of Epitech). The school was first opened in Paris in 2013.

Out of more than 80,000 candidates in France, 3,000 were selected to complete a four-week intensive computer programming bootcamp called piscine (swimming-pool). Any person older than 18 can register for the piscine after completing the logical reasoning tests on the website.

The school does not have any professors, and is open 24/7. The training is inspired by new modern ways to teach which include peer-to-peer pedagogy and project-based learning. The School has been endorsed by many high-profile people in Silicon Valley including Evan Spiegel the co-founder and CEO of Snapchat, Keyvon Beykpour the co-founder and CEO of Periscope, Stewart Butterfield the co-founder and CEO of Slack, Brian Chesky the co-founder and CEO of Airbnb, Tony Fadell the founder and CEO of Nest Labs, Jack Dorsey the co-Founder and CEO of Twitter, Paul Graham, venture capitalist and co-Founder of Y Combinator, Bill Gurley venture capitalist and general partner at Benchmark.

The school is a non-profit organization and is entirely free, being funded by billionaire Xavier Niel with hundreds of millions of dollars. All the intellectual property belongs to the students. 42 Silicon Valley is the American campus of 42 chartered as a public-benefit nonprofit corporation in the State of California and has been created and funded by the same team from France, in addition to a new partner, the chief operating officer of the American school and former 42 Paris student Brittany Bir. 42 Silicon Valley opened in summer 2016 in Fremont, California in the San Francisco Bay Area.

42's name is a reference to the science fiction book The Hitchhiker's Guide to the Galaxy written by British author Douglas Adams: in the book 42 is the Answer to the Ultimate Question of Life, the Universe, and Everything.

In addition to the two official campuses in Paris, France and Fremont, California, the school model was adopted in Lyon, Reims, and Mulhouse, France, as well as in Romania, South Africa, Ukraine, Bulgaria, Moldova, Belgium, Russia, Morocco, the Netherlands, Indonesia, and Finland with the help and support of 42.

🔗 Vietnam

The Đông Yên Châu inscription is an Old Cham inscription written in Pallava script, found in 1936 at Đông Yên Châu, northwest of Trà Kiệu, which used to be the old Champa capital known as Simhapura, in central Vietnam. The inscription was written in prose, is the oldest document of Cham (and indeed of any Austronesian language), and testifies to the existence of indigenous beliefs among the ancient Cham people of the Champa kingdom. Though not itself dated, the phrasing of the inscription is identical to those of dated Sanskrit inscriptions of Bhadravarman I of the second dynasty, who ruled Champa at the end of the 4th century CE. It contains an imprecatory formula ordering respect for the "naga of the king", undoubtedly a reference to the protective divinity of a spring or well. This vernacular text shows that in the 4th century, the land that now constitutes modern-day central Vietnam was inhabited by an Austronesian-speaking population. The evidence, both monumental and palaeographic, also suggests that Hinduism was the predominant religious system.

The fact that the language in the inscription shares some basic grammar and vocabulary with Malay has led some scholars to argue that the inscription contains the oldest specimen of Malay words in the form of Old Malay, older by three centuries than the earliest Srivijayan inscriptions from southeastern Sumatra. However, most scholars consider it established that this inscription was written in Old Cham instead. The shared basic grammar and vocabulary comes as no surprise, since Chamic and Malayic languages are closely related; both are the two subgroups of a Malayic–Chamic group within the Malayo-Polynesian branch of the Austronesian family.

🔗 Mathematics 🔗 Statistics

In statistics, the 68–95–99.7 rule, also known as the empirical rule, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean, respectively.

In mathematical notation, these facts can be expressed as follows, where Pr() is the probability function, Χ is an observation from a normally distributed random variable, μ (mu) is the mean of the distribution, and σ (sigma) is its standard deviation:

${\displaystyle {\begin{aligned}\Pr(\mu -1\sigma \leq X\leq \mu +1\sigma )&\approx 68.27\%\\\Pr(\mu -2\sigma \leq X\leq \mu +2\sigma )&\approx 95.45\%\\\Pr(\mu -3\sigma \leq X\leq \mu +3\sigma )&\approx 99.73\%\end{aligned}}}$

The usefulness of this heuristic especially depends on the question under consideration.

In the empirical sciences, the so-called three-sigma rule of thumb (or 3σ rule) expresses a conventional heuristic that nearly all values are taken to lie within three standard deviations of the mean, and thus it is empirically useful to treat 99.7% probability as near certainty.

In the social sciences, a result may be considered "significant" if its confidence level is of the order of a two-sigma effect (95%), while in particle physics, there is a convention of a five-sigma effect (99.99994% confidence) being required to qualify as a discovery.

A weaker three-sigma rule can be derived from Chebyshev's inequality, stating that even for non-normally distributed variables, at least 88.8% of cases should fall within properly calculated three-sigma intervals. For unimodal distributions, the probability of being within the interval is at least 95% by the Vysochanskij–Petunin inequality. There may be certain assumptions for a distribution that force this probability to be at least 98%.

🔗 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).

🔗 Geography 🔗 Arctic 🔗 Islands 🔗 Greenland

Kaffeklubben Island or Coffee Club Island (Danish: Kaffeklubben Ø; Greenlandic: Inuit Qeqertaat) is an uninhabited island lying off the northern shore of Greenland. It contains the northernmost undisputed point of land on Earth.

🔗 Mathematics

Modern Arabic mathematical notation is a mathematical notation based on the Arabic script, used especially at pre-university levels of education. Its form is mostly derived from Western notation, but has some notable features that set it apart from its Western counterpart. The most remarkable of those features is the fact that it is written from right to left following the normal direction of the Arabic script. Other differences include the replacement of the Greek and Latin alphabet letters for symbols with Arabic letters and the use of Arabic names for functions and relations.

🔗 France

La Bougie du Sapeur (French: [la bu.ʒi dy sa.pœʁ]) is a French satirical newspaper launched in 1980 that is published only on Leap Day, making it the world's least frequently published newspaper. The editor-in-chief is Jean d'Indy, who works for France Galop and has been involved in producing the paper since 1992.

🔗 Africa 🔗 Ancient Near East 🔗 Ancient Egypt 🔗 Greece 🔗 Turkey 🔗 Archaeology

The Late Bronze Age collapse was a dark age transition in a large area covering much of Southeast Europe, West Asia and North Africa (comprising the overlapping regions of the Near East, the Eastern Mediterranean and North Africa, with the Balkans, the Aegean, Anatolia, and the Caucasus), which took place from the Late Bronze Age to the emerging Early Iron Age. It was a transition which historians believe was violent, sudden, and culturally disruptive, and involved societal collapse for some civilizations during the 12th century BCE. The palace economy of Mycenaean Greece, the Aegean region and Anatolia that characterized the Late Bronze Age disintegrated, transforming into the small isolated village cultures of the Greek Dark Ages. The Hittite Empire of Anatolia and the Levant collapsed, while states such as the Middle Assyrian Empire in Mesopotamia and the New Kingdom of Egypt survived but were considerably weakened.

Competing and even mutually compatible theories for the ultimate cause of the Late Bronze Age collapse have been made since the 19th century. These include volcanic eruptions, droughts, invasions by the Sea Peoples or migrations of Dorians, economic disruptions due to the rising use of ironworking, and changes in military technology and methods of war that saw the decline of chariot warfare.