Have a deep view into what people are curious about.

🔗 Biography 🔗 Physics 🔗 Biography/science and academia 🔗 Physics/Biographies

Sir James Dewar (20 September 1842 – 27 March 1923) was a Scottish chemist and physicist. He is best known for his invention of the vacuum flask, which he used in conjunction with research into the liquefaction of gases. He also studied atomic and molecular spectroscopy, working in these fields for more than 25 years.

🔗 Biography 🔗 Philosophy 🔗 Middle Ages 🔗 Islam 🔗 Middle Ages/History 🔗 Philosophy/Philosophers 🔗 Philosophy/Philosophy of religion 🔗 Syria 🔗 Philosophy/Ancient philosophy

Abū al-ʿAlāʾ al-Maʿarrī (Arabic: أبو العلاء المعري‎‎, full name أبو العلاء أحمد بن عبد الله بن سليمان التنوخي المعري‎ Abū al-ʿAlāʾ Aḥmad ibn ʿAbd Allāh ibn Sulaymān al-Tanūkhī al-Maʿarrī; December 973 – May 1057) was a blind Arab philosopher, poet, and writer. Despite holding a controversially irreligious worldview, he is regarded as one of the greatest classical Arabic poets.

Born in the city of Ma'arra during the Abbasid era, he studied in nearby Aleppo, then in Tripoli and Antioch. Producing popular poems in Baghdad, he nevertheless refused to sell his texts. In 1010, he returned to Syria after his mother began declining in health, and continued writing which gained him local respect.

Described as a "pessimistic freethinker", al-Ma'arri was a controversial rationalist of his time, citing reason as the chief source of truth and divine revelation. He was pessimistic about life, describing himself as "a double prisoner" of blindness and isolation. He attacked religious dogmas and practices, was equally critical and sarcastic about Judaism, Christianity, Islam and Zoroastrianism, and became a Deist.

He advocated social justice and lived a secluded, ascetic lifestyle. He was a vegan, known in his time as moral vegetarianism, entreating: "do not desire as food the flesh of slaughtered animals / Or the white milk of mothers who intended its pure draught / for their young". Al-Ma'arri held an antinatalist outlook, in line with his general pessimism, suggesting that children should not be born to spare them of the pains and suffering of life.

Al-Ma'arri wrote three main works that were popular in his time. Among his works are The Tinder Spark, Unnecessary Necessity, and The Epistle of Forgiveness. Al-Ma'arri never married and died at the age of 83 in the city where he was born, Ma'arrat al-Nu'man. In 2013, a statue of al-Ma'arri located in his Syrian hometown was beheaded by jihadists from the al-Nusra Front.

🔗 Computer Security 🔗 Computer Security/Computing 🔗 Crime and Criminal Biography

The Morris worm or Internet worm of November 2, 1988, is one of the oldest computer worms distributed via the Internet, and the first to gain significant mainstream media attention. It resulted in the first felony conviction in the US under the 1986 Computer Fraud and Abuse Act. It was written by a graduate student at Cornell University, Robert Tappan Morris, and launched on 8:30 pm November 2, 1988, from the Massachusetts Institute of Technology network.

Clifford Stoll of Harvard wrote that "Rumors have it that [Morris] worked with a friend or two at Harvard's computing department (Harvard student Paul Graham sent him mail asking for 'Any news on the brilliant project')."

🔗 Computer science

Pearson hashing is a hash function designed for fast execution on processors with 8-bit registers. Given an input consisting of any number of bytes, it produces as output a single byte that is strongly dependent on every byte of the input. Its implementation requires only a few instructions, plus a 256-byte lookup table containing a permutation of the values 0 through 255.

This hash function is a CBC-MAC that uses an 8-bit substitution cipher implemented via the substitution table. An 8-bit cipher has negligible cryptographic security, so the Pearson hash function is not cryptographically strong, but it is useful for implementing hash tables or as a data integrity check code, for which purposes it offers these benefits:

• It is extremely simple.
• It executes quickly on resource-limited processors.
• There is no simple class of inputs for which collisions (identical outputs) are especially likely.
• Given a small, privileged set of inputs (e.g., reserved words for a compiler), the permutation table can be adjusted so that those inputs yield distinct hash values, producing what is called a perfect hash function.
• Two input strings differing by exactly one character never collide. E.g., applying the algorithm on the strings ABC and AEC will never produce the same value.

One of its drawbacks when compared with other hashing algorithms designed for 8-bit processors is the suggested 256 byte lookup table, which can be prohibitively large for a small microcontroller with a program memory size on the order of hundreds of bytes. A workaround to this is to use a simple permutation function instead of a table stored in program memory. However, using a too simple function, such as T[i] = 255-i, partly defeats the usability as a hash function as anagrams will result in the same hash value; using a too complex function, on the other hand, will affect speed negatively. Using a function rather than a table also allows extending the block size. Such functions naturally have to be bijective, like their table variants.

The algorithm can be described by the following pseudocode, which computes the hash of message C using the permutation table T:

algorithm pearson hashing is
    h := 0

    for each c in C loop
        h := T[ h xor c ]
    end loop

    return h

The hash variable (h) may be initialized differently, e.g. to the length of the data (C) modulo 256; this particular choice is used in the Python implementation example below.

🔗 France 🔗 Environment 🔗 Military history 🔗 Military history/World War I 🔗 Military history/French military history 🔗 Military history/European military history

The Zone Rouge (English: Red Zone) is a chain of non-contiguous areas throughout northeastern France that the French government isolated after the First World War. The land, which originally covered more than 1,200 square kilometres (460 sq mi), was deemed too physically and environmentally damaged by conflict for human habitation. Rather than attempt to immediately clean up the former battlefields, the land was allowed to return to nature. Restrictions within the Zone Rouge still exist today, although the control areas have been greatly reduced.

The Zone Rouge was defined just after the war as "Completely devastated. Damage to properties: 100%. Damage to Agriculture: 100%. Impossible to clean. Human life impossible".

Under French law, activities such as housing, farming, or forestry were temporarily or permanently forbidden in the Zone Rouge, because of the vast amounts of human and animal remains, and millions of items of unexploded ordnance contaminating the land. Some towns and villages were never permitted to be rebuilt after the war.

🔗 Computing 🔗 Computing/Software

In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it. The term is a pun on the name of Werner Heisenberg, the physicist who first asserted the observer effect of quantum mechanics, which states that the act of observing a system inevitably alters its state. In electronics the traditional term is probe effect, where attaching a test probe to a device changes its behavior.

Similar terms, such as bohrbug, mandelbug, hindenbug, and schrödinbug (see the section on related terms) have been occasionally proposed for other kinds of unusual software bugs, sometimes in jest; however, unlike the term heisenbug, they are not widely known or used.

🔗 Ancient Near East 🔗 Turkey 🔗 Archaeology

Göbekli Tepe (Turkish: [ɟœbecˈli teˈpe], "Potbelly Hill") is an archaeological site in the Southeastern Anatolia Region of Turkey approximately 12 km (7 mi) northeast of the city of Şanlıurfa. The tell (artificial mound) has a height of 15 m (49 ft) and is about 300 m (980 ft) in diameter. It is approximately 760 m (2,490 ft) above sea level.

The tell includes two phases of use, believed to be of a social or ritual nature by site discoverer and excavator Klaus Schmidt, dating back to the 10th–8th millennium BCE. During the first phase, belonging to the Pre-Pottery Neolithic A (PPNA), circles of massive "T-shaped" stone pillars were erected – the world's oldest known megaliths.

More than 200 pillars in about 20 circles are currently known through geophysical surveys. Each pillar has a height of up to 6 m (20 ft) and weighs up to 10 tons. They are fitted into sockets that were hewn out of the bedrock. In the second phase, belonging to the Pre-Pottery Neolithic B (PPNB), the erected pillars are smaller and stood in rectangular rooms with floors of polished lime. The site was abandoned after the Pre-Pottery Neolithic B (PPNB). Younger structures date to classical times.

The details of the structure's function remain a mystery. The excavations have been ongoing since 1996 by the German Archaeological Institute, but large parts still remain unexcavated. In 2018, the site was designated a UNESCO World Heritage Site.

🔗 Software 🔗 Software/Computing

GNU Guix System or Guix System (previously GuixSD) is a rolling release, free and open source Linux distribution built around the GNU Guix package manager. It enables a declarative operating system configuration and allows reliable system upgrades that can easily be rolled back. It uses the GNU Shepherd init system and the Linux-libre kernel, with support for the GNU Hurd kernel under development. On February 3, 2015, the distribution was added to the Free Software Foundation's list of free Linux distributions. The Guix package manager and the Guix System drew inspiration from the Nix package manager and NixOS respectively.

Deletion review (DRV) is a forum designed primarily to appeal disputed speedy deletions and disputed decisions made as a result of deletion discussions; this includes appeals to delete pages kept after a prior discussion.

If you are considering a request for a deletion review, please read the "Purpose" section below to make sure that is what you wish to do. Then, follow the instructions below.

🔗 Mathematics 🔗 Physics

Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic fields, but was first applied to electrostatic fields.

Earnshaw's theorem applies to classical inverse-square law forces (electric and gravitational) and also to the magnetic forces of permanent magnets, if the magnets are hard (the magnets do not vary in strength with external fields). Earnshaw's theorem forbids magnetic levitation in many common situations.

If the materials are not hard, Braunbeck's extension shows that materials with relative magnetic permeability greater than one (paramagnetism) are further destabilising, but materials with a permeability less than one (diamagnetic materials) permit stable configurations.