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🔗 Spaceflight 🔗 Physics 🔗 Science Fiction

A black hole starship is a theoretical idea for enabling interstellar travel by propelling a starship by using a black hole as the energy source. The concept was first discussed in science fiction, notably in the book Imperial Earth by Arthur C. Clarke, and in the work of Charles Sheffield, in which energy extracted from a Kerr-Newman black hole is described as powering the rocket engines in the story "Killing Vector" (1978).

In a more detailed analysis, a proposal to create an artificial black hole and using a parabolic reflector to reflect its Hawking radiation was discussed in 2009 by Louis Crane and Shawn Westmoreland. Their conclusion was that it was on the edge of possibility, but that quantum gravity effects that are presently unknown will either make it easier, or make it impossible. Similar concepts were also sketched out by Bolonkin.

🔗 Australia 🔗 Australia/Western Australia

The State Barrier Fence of Western Australia, formerly known as the Rabbit Proof Fence, the State Vermin Fence, and the Emu Fence, is a pest-exclusion fence constructed between 1901 and 1907 to keep rabbits and other agricultural pests, from the east, out of Western Australian pastoral areas.

There are three fences in Western Australia: the original No. 1 Fence crosses the state from north to south, No. 2 Fence is smaller and further west, and No. 3 Fence is smaller still and runs east–west. The fences took six years to build. When completed in 1907, the rabbit-proof fence (including all three fences) stretched 2,023 miles (3,256 km). The cost to build the fences at the time was about £168 per mile ($250/km).

When it was completed in 1907, the 1,139-mile (1,833 km) No. 1 Fence was the longest unbroken fence in the world.

🔗 Computing 🔗 Time 🔗 Linux

Unix time (also known as Epoch time, POSIX time, seconds since the Epoch, or UNIX Epoch time) is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, that is the time 00:00:00 UTC on 1 January 1970, minus leap seconds. Leap seconds are ignored, with a leap second having the same Unix time as the second before it, and every day is treated as if it contains exactly 86400 seconds. Due to this treatment, Unix time is not a true representation of UTC.

Unix time is widely used in operating systems and file formats. In Unix-like operating systems, date is a command which will print or set the current time; by default, it prints or sets the time in the system time zone, but with the -u flag, it prints or sets the time in UTC and, with the TZ environment variable set to refer to a particular time zone, prints or sets the time in that time zone.

🔗 Computer science 🔗 Statistics

A Boltzmann machine (also called stochastic Hopfield network with hidden units) is a type of stochastic recurrent neural network. It is a Markov random field. It was translated from statistical physics for use in cognitive science. The Boltzmann machine is based on stochastic spin-glass model with an external field, i.e., a Sherrington–Kirkpatrick model that is a stochastic Ising Model and applied to machine learning.

Boltzmann machines can be seen as the stochastic, generative counterpart of Hopfield networks. They were one of the first neural networks capable of learning internal representations, and are able to represent and (given sufficient time) solve combinatoric problems.

They are theoretically intriguing because of the locality and Hebbian nature of their training algorithm (being trained by Hebb's rule), and because of their parallelism and the resemblance of their dynamics to simple physical processes. Boltzmann machines with unconstrained connectivity have not proven useful for practical problems in machine learning or inference, but if the connectivity is properly constrained, the learning can be made efficient enough to be useful for practical problems.

They are named after the Boltzmann distribution in statistical mechanics, which is used in their sampling function. That's why they are called "energy based models" (EBM). They were invented in 1985 by Geoffrey Hinton, then a Professor at Carnegie Mellon University, and Terry Sejnowski, then a Professor at Johns Hopkins University.

🔗 Biography 🔗 Psychology 🔗 Biography/science and academia 🔗 Anti-war

Julian Jaynes (February 27, 1920 – November 21, 1997) was an American researcher in psychology at Yale and Princeton for nearly 25 years and best known for his 1976 book The Origin of Consciousness in the Breakdown of the Bicameral Mind. His career was dedicated to the problem of consciousness, “…the difference between what others see of us and our sense of our inner selves and the deep feelings that sustain it. … Men have been conscious of the problem of consciousness almost since consciousness began.” Jaynes's solution touches on many disciplines, including neuroscience, linguistics, psychology, archeology, history, religion and analysis of ancient texts.

🔗 Biography 🔗 Mathematics 🔗 Biography/science and academia 🔗 Astronomy 🔗 Linguistics 🔗 Linguistics/Applied Linguistics 🔗 Indigenous peoples of North America 🔗 University of Oxford

Thomas Harriot (Oxford, c. 1560 – London, 2 July 1621), also spelled Harriott, Hariot or Heriot, was an English astronomer, mathematician, ethnographer and translator who made advances within the scientific field. Thomas Harriot was recognized for his contributions in astronomy, mathematics, and navigational techniques. Harriot worked closely with John White to create advanced maps for navigation. While Harriot worked extensively on numerous papers on the subjects of astronomy, mathematics, and navigation the amount of work that was actually published was sparse. So sparse that the only publication that has been produced by Harriot was The Briefe and True Report of the New Found Land of Virginia. The premise of the book includes descriptions of English settlements and financial issues in Virginia at the time. He is sometimes credited with the introduction of the potato to the British Isles. Harriot was the first person to make a drawing of the Moon through a telescope, on 26 July 1609, over four months before Galileo Galilei.

After graduating from St Mary Hall, Oxford, Harriot travelled to the Americas, accompanying the 1585 expedition to Roanoke island funded by Sir Walter Raleigh and led by Sir Ralph Lane. Harriot was a vital member of the venture, having learned and translating the Carolina Algonquian language from two Native Americans: Wanchese and Manteo. On his return to England, he worked for the 9th Earl of Northumberland. At the Earl's house, he became a prolific mathematician and astronomer to whom the theory of refraction is attributed.

🔗 Computing 🔗 Computing/Computer hardware

Model M designates a group of computer keyboards designed and manufactured by IBM starting in 1984, and later by Lexmark International, Maxi Switch, and Unicomp. The keyboard's many variations have their own distinct characteristics, with the vast majority having a buckling-spring key design and swappable keycaps. Model M keyboards have been praised by computer enthusiasts and frequent typists due to their durability and consistency, and the tactile and auditory feedback they provide.

The Model M is also regarded as a timeless and durable piece of hardware. Although the computers and computer peripherals produced concurrently with the Model M are considered obsolete, many Model M keyboards are still in use due to their physical durability and the continued validity of their ANSI 101-key and ISO 102-key layouts, through the use of a PS/2 female to USB male adapter with a built-in level converter. Since their original popularity, new generations of writers and computer technicians have rediscovered their unique functionality and aesthetics. The Kentucky-based company Unicomp continues to manufacture and sell Model M keyboards.

🔗 United States 🔗 Library of Congress 🔗 Geography 🔗 Maps 🔗 Libraries

The Waldseemüller map or Universalis Cosmographia ("Universal Cosmography") is a printed wall map of the world by German cartographer Martin Waldseemüller, originally published in April 1507. It is known as the first map to use the name "America". The name America is placed on what is now called South America on the main map. As explained in Cosmographiae Introductio, the name was bestowed in honor of the Italian Amerigo Vespucci.

The map is drafted on a modification of Ptolemy's second projection, expanded to accommodate the Americas and the high latitudes. A single copy of the map survives, presently housed at the Library of Congress in Washington, D.C.

Waldseemüller also created globe gores, printed maps designed to be cut out and pasted onto spheres to form globes of the Earth. The wall map, and his globe gores of the same date, depict the American continents in two pieces. These depictions differ from the small inset map in the top border of the wall map, which shows the two American continents joined by an isthmus.

🔗 Africa 🔗 Philosophy 🔗 Philosophy/Anarchism 🔗 Somalia

Xeer (pronounced [ħeːr]) is the traditional legal system of Somalia, and one of the three systems from which formal Somali law draws its inspiration, the others being civil law and Islamic law. It is believed to pre-date Islam, although it was influenced by Islam and retains many of the faith's conservative elements. Under this system, elders, known as the xeer begti serve as mediator judges and help settle court cases, taking precedent and custom into account. Xeer is polycentric in that different groups within Somali society have different interpretations of xeer.

🔗 Computer science

In computer science, corecursion is a type of operation that is dual to recursion. Whereas recursion works analytically, starting on data further from a base case and breaking it down into smaller data and repeating until one reaches a base case, corecursion works synthetically, starting from a base case and building it up, iteratively producing data further removed from a base case. Put simply, corecursive algorithms use the data that they themselves produce, bit by bit, as they become available, and needed, to produce further bits of data. A similar but distinct concept is generative recursion which may lack a definite "direction" inherent in corecursion and recursion.

Where recursion allows programs to operate on arbitrarily complex data, so long as they can be reduced to simple data (base cases), corecursion allows programs to produce arbitrarily complex and potentially infinite data structures, such as streams, so long as it can be produced from simple data (base cases) in a sequence of finite steps. Where recursion may not terminate, never reaching a base state, corecursion starts from a base state, and thus produces subsequent steps deterministically, though it may proceed indefinitely (and thus not terminate under strict evaluation), or it may consume more than it produces and thus become non-productive. Many functions that are traditionally analyzed as recursive can alternatively, and arguably more naturally, be interpreted as corecursive functions that are terminated at a given stage, for example recurrence relations such as the factorial.

Corecursion can produce both finite and infinite data structures as results, and may employ self-referential data structures. Corecursion is often used in conjunction with lazy evaluation, to produce only a finite subset of a potentially infinite structure (rather than trying to produce an entire infinite structure at once). Corecursion is a particularly important concept in functional programming, where corecursion and codata allow total languages to work with infinite data structures.