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🔗 Computer science

In computer science, the Knuth–Morris–Pratt string-searching algorithm (or KMP algorithm) searches for occurrences of a "word" W within a main "text string" S by employing the observation that when a mismatch occurs, the word itself embodies sufficient information to determine where the next match could begin, thus bypassing re-examination of previously matched characters.

The algorithm was conceived by James H. Morris and independently discovered by Donald Knuth "a few weeks later" from automata theory. Morris and Vaughan Pratt published a technical report in 1970. The three also published the algorithm jointly in 1977. Independently, in 1969, Matiyasevich discovered a similar algorithm, coded by a two-dimensional Turing machine, while studying a string-pattern-matching recognition problem over a binary alphabet. This was the first linear-time algorithm for string matching.

🔗 Companies 🔗 Computing 🔗 United Kingdom

Andrews & Arnold Ltd (also known as AAISP) is an Internet service provider based in Bracknell in the United Kingdom founded in 1997 and launched in 1998, primarily serving businesses and "technical" home users.

In 2009 the company was judged the best niche provider in the Thinkbroadband Customer Service Awards, based on customer ratings and again in 2010.

The company's owner, Adrian Kennard (RevK), stated in a blog post that as of October 2010 the company is "xkcd/806" compliant, referring to xkcd comic number 806. This means that technical support callers who say the code word "shibboleet" will be transferred to a technical support representative who knows at least two programming languages, and presumably can offer more useful advice than a standard tech support script.

Andrews & Arnold provides IPv6 to all customers, for no additional charge.

Andrews & Arnold provides optional bonded multiple-link internet access. This allows multiple links to be used together to vastly increase speed and reliability. Special routers distribute individual IP packets between the available links in such a way that even one single download or upload operation will benefit fully from multiple speed, and it is not necessary to have several users, several running programs or computers to gain the speed benefit. Links can be of different types, each needs only to be a pipe that can carry IP packets. Multiple links can either be used together all the time, or some can be brought up as a back up if other links fail, so-called 'failover', or a combination of the two approaches can be set up.

Andrews & Arnold are strong advocates of not censoring Internet connections. Adrian Kennard has several blog posts discussing why Internet censorship as discussed in the UK is not workable, providing background for AAISP's decision.

🔗 Computing 🔗 Computing/Software

In software development, the yo-yo problem is an anti-pattern that occurs when a programmer has to read and understand a program whose inheritance graph is so long and complicated that the programmer has to keep flipping between many different class definitions in order to follow the control flow of the program. It often happens in object-oriented programming. The term comes from comparing the bouncing attention of the programmer to the up-down movement of a toy yo-yo. Taenzer, Ganti, and Podar described the problem by name, explaining: "Often we get the feeling of riding a yoyo when we try to understand one of these message trees."

Most practices of object-oriented programming recommend keeping the inheritance graph as shallow as possible, in part to avoid this problem. The use of composition instead of inheritance is also strongly preferred, although this still requires that a programmer keep multiple class definitions in mind at once.

More generally, the yo-yo problem can also refer to any situation where a person must keep flipping between different sources of information in order to understand a concept.

Object-oriented design techniques such as documenting layers of the inheritance hierarchy can reduce the effect of this problem, as they collect in one place the information that the programmer is required to understand.

🔗 Biography 🔗 Military history 🔗 Military history/Military biography 🔗 Military history/World War II

Sir Basil Zaharoff, GCB, GBE, born Vasileios Zacharias (Greek: Βασίλειος Zαχαρίας Ζαχάρωφ; October 6, 1849 – November 27, 1936), was a Greek arms dealer and industrialist. One of the richest men in the world during his lifetime, Zaharoff was described as a "merchant of death" and "mystery man of Europe". His success was forged through his cunning, often aggressive and sharp, business tactics. These included the sale of arms to opposing sides in conflicts, sometimes delivering fake or faulty machinery and skilfully using the press to attack business rivals.

Zaharoff maintained close contacts with many powerful political leaders, including British Prime Minister David Lloyd George, Greek Prime Minister Eleftherios Venizelos and Ottoman Sultan Abdul Hamid II; he served as a primary inspiration for Ian Fleming's fictional James Bond villain Ernst Stavro Blofeld.

🔗 Physics 🔗 Systems 🔗 Systems/Chaos theory

In condensed matter physics, Hofstadter's butterfly describes the spectral properties of non-interacting two dimensional electrons in a magnetic field. The fractal, self-similar, nature of the spectrum was discovered in the 1976 Ph.D. work of Douglas Hofstadter and is one of the early examples of computer graphics. The name reflects the visual resemblance of the figure on the right to a swarm of butterflies flying to infinity.

The Hofstadter butterfly plays an important role in the theory of the integer quantum Hall effect, and D.J. Thouless has been awarded the Nobel prize in physics in 2016 for the discovery that the wings of the butterfly are characterized by Chern integers, the quantized Hall conductances discovered in 1980 by Klaus von Klitzing for which he has been awarded the Nobel prize in 1985. The colors in the diagram reflect the different Chern numbers.

🔗 Biography 🔗 Bangladesh 🔗 Architecture 🔗 Skyscrapers 🔗 Civil engineering 🔗 Chicago 🔗 Illinois

Fazlur Rahman Khan (Bengali: ফজলুর রহমান খান, Fozlur Rôhman Khan) (3 April 1929 – 27 March 1982) was a Bangladeshi-American structural engineer and architect, who initiated important structural systems for skyscrapers. Considered the "father of tubular designs" for high-rises, Khan was also a pioneer in computer-aided design (CAD). He was the structural engineer of the Sears Tower working with Architect Bruce Graham, since renamed Willis Tower, the tallest building in the world from 1973 until 1998, and the 100-story John Hancock Center.

Khan, more than any other individual, ushered in a renaissance in skyscraper construction during the second half of the 20th century. He has been called the "Einstein of structural engineering" and the "Greatest Structural Engineer of the 20th Century" for his innovative use of structural systems that remain fundamental to modern skyscraper design and construction. In his honor, the Council on Tall Buildings and Urban Habitat established the Fazlur Khan Lifetime Achievement Medal, as one of their CTBUH Skyscraper Awards.

Although best known for skyscrapers, Khan was also an active designer of other kinds of structures, including the Hajj airport terminal, the McMath–Pierce solar telescope, and several stadium structures.

🔗 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.