Deca

Deca or DECA may refer to:

See also

Deca-

Deca- or deka- (symbol da) is a decimal unit prefix in the metric system, denoting a factor of ten. The term is derived from the Greek deka (δέκα), meaning "ten".

The prefix was a part of the original metric system in 1795. It is not in very common usage, although the decapascal is occasionally used by audiologists. The decanewton is also encountered occasionally, probably because it is an SI approximation of the kilogram-force. Its use is more common in Central Europe. In German, Polish (deka, deko), Czech, Slovak and Hungarian, deca is common (and used a word on its own always means decagram). A runway number typically indicates its heading in decadegrees.

Before the symbol as an SI prefix was standardized as "da" with the introduction of the International System of Units in 1960, various other symbols were more common, such as "dk" (f.e. in the UK and Austria), "D" (f.e. in Germany), and "Da". For syntactical reasons, the HP 48, 49, 50 series as well as the HP 39gII and Prime calculators use the unit prefix "D".

Deca (journalism collective)

Deca is a cooperative of magazine writers co-owned and managed by its members. Their cooperative model is based on photo agencies like Magnum and NOOR. Each journalist reports and writes independently but stories are edited and promoted collectively. Their writers are based all over the world, including Rome, London, Shanghai, Barcelona, Beirut, Abu Dhabi, Los Angeles, New York, Seattle, and Washington, D.C. Collectively, they have reported from more than 90 countries and every continent but Antarctica. Deca's tagline is "The world, firsthand." They offer a subscription service to their stories as well as an iOS app, with an Android app in development. Readers can also purchase the stories for download as Kindle singles on Amazon.com.

History

Deca launched in June 2014 with the story "And The City Swallowed Them" by Mara Hvistendahl and a Kickstarter campaign that raised $32,627.

And The City Swallowed Them

"And The City Swallowed Them" is Deca's debut story, written by Mara Hvistendahl, published in June, 2014. It is a true crime nonfiction story about the murder of 22-year-old model Diana O'brien in Shanghai on July 6, 2008 based on dozens of interviews with investigators, models, and both the victim's and the convicted murderer's families. The short book touches on issues of urbanization, migration and underground economies, anchored by the narrative of the lives of the Diana O'Brien and her murderer. The Wall Street Journal, China Real Time blog wrote about the book: "And The City Swallowed Them looks at the world that brought two different kinds of newcomers together—foreigners, including young models fighting for emerging opportunities in high fashion, and China’s own migrants, including those traveling from poor villages who were willing to go to desperate measures to scrape together their own living.” Hvistendahl is the author of Unnatural Selection: Choosing Boys Over Girls, and the Consequences of a World Full of Men.

Crab

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (Greek: βραχύς / brachys = short,οὐρά / οura = tail), usually entirely hidden under the thorax. They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of claws. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs and crab lice – are not true crabs.

Evolution

Crabs are generally covered with a thick exoskeleton, composed primarily of calcium carbonate, and armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft).

About 850 species of crab are freshwater, terrestrial or semi-terrestrial species; they are found throughout the world's tropical and semi-tropical regions. They were previously thought to be a monophyletic group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World.

Crab (unit)

A Crab is a standard astrophotometrical unit for measurement of the intensity of Astrophysical X-ray sources. One Crab is defined as the intensity of the Crab Nebula at the corresponding X-ray photon energy.

The Crab Nebula, and the Crab Pulsar within it, is an intense space X-ray source. It is used as a standard candle in the calibration procedure of X-ray instruments in space. However, because of the Crab Nebula's variable intensity at different X-ray energies, conversion of the Crab to another units depends on the X-ray energy range of interest.

In the photon energy range from 2 to 10 keV, 1 Crab equals 2.4 · 10⁻⁸erg cm⁻²s⁻¹ = 15 keV cm⁻² s⁻¹ = 2.4 · 10⁻¹¹W m⁻². For energies greater than ~30 keV, the Crab Nebula becomes unsuitable for calibration purposes, as its flux can no longer be characterized by a single coherent model.

The unit mCrab, or milliCrab, is sometimes used instead of the Crab.

References

Crab (cipher)

In cryptography, Crab is a block cipher proposed by Burt Kaliski and Matt Robshaw at the first Fast Software Encryption workshop in 1993. Not really intended for use, Crab was developed to demonstrate how ideas from hash functions could be used to create a fast cipher.

Crab has an unusually large block size of 8192 bits. Its creators suggested using an 80-bit key, but the cipher could use any key size. The authors didn't specify an actual key schedule, only that the key is used to generate two large sets of subkeys: a permutation of the numbers 0 through 255, and an array of 2048 32-bit numbers. The block is divided into 256 32-bit subblocks, which are permuted at the beginning. Then the algorithm makes four passes over the data, each time applying one of four transformations adapted from MD5.

A brief note on the cryptanalysis of Crab is included in Markku-Juhani Saarinen's paper on block ciphers based on SHA-1 and MD5, published at FSE 2003. The author demonstrates a weakness in Crab that permits a distinguisher using no more than a dozen chosen plaintexts, and speculates that this can be converted into a full key-recovery attack using no more than 2¹⁶ chosen plaintexts. Such an attack would depend on the key schedule used.