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🔗 Physics 🔗 Chemistry 🔗 Geology 🔗 Rocks and minerals

A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical crystallographic restriction theorem, can possess only two-, three-, four-, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders—for instance, five-fold.

Aperiodic tilings were discovered by mathematicians in the early 1960s, and, some twenty years later, they were found to apply to the study of natural quasicrystals. The discovery of these aperiodic forms in nature has produced a paradigm shift in the fields of crystallography. Quasicrystals had been investigated and observed earlier, but, until the 1980s, they were disregarded in favor of the prevailing views about the atomic structure of matter. In 2009, after a dedicated search, a mineralogical finding, icosahedrite, offered evidence for the existence of natural quasicrystals.

Roughly, an ordering is non-periodic if it lacks translational symmetry, which means that a shifted copy will never match exactly with its original. The more precise mathematical definition is that there is never translational symmetry in more than n – 1 linearly independent directions, where n is the dimension of the space filled, e.g., the three-dimensional tiling displayed in a quasicrystal may have translational symmetry in two directions. Symmetrical diffraction patterns result from the existence of an indefinitely large number of elements with a regular spacing, a property loosely described as long-range order. Experimentally, the aperiodicity is revealed in the unusual symmetry of the diffraction pattern, that is, symmetry of orders other than two, three, four, or six. In 1982 materials scientist Dan Shechtman observed that certain aluminium-manganese alloys produced the unusual diffractograms which today are seen as revelatory of quasicrystal structures. Due to fear of the scientific community's reaction, it took him two years to publish the results for which he was awarded the Nobel Prize in Chemistry in 2011. On 25 October 2018, Luca Bindi and Paul Steinhardt were awarded the Aspen Institute 2018 Prize for collaboration and scientific research between Italy and the United States.

🔗 Physics 🔗 Astronomy

Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction. The theory, based on string theory, black hole physics, and quantum information theory, describes gravity as an emergent phenomenon that springs from the quantum entanglement of small bits of spacetime information. As such, entropic gravity is said to abide by the second law of thermodynamics under which the entropy of a physical system tends to increase over time.

At its simplest, the theory holds that when gravity becomes vanishingly weak—levels seen only at interstellar distances—it diverges from its classically understood nature and its strength begins to decay linearly with distance from a mass.

Entropic gravity provides the underlying framework to explain Modified Newtonian Dynamics, or MOND, which holds that at a gravitational acceleration threshold of approximately 1.2×10⁻¹⁰ m/s², gravitational strength begins to vary inversely (linearly) with distance from a mass rather than the normal inverse-square law of the distance. This is an exceedingly low threshold, measuring only 12 trillionths gravity's strength at earth's surface; an object dropped from a height of one meter would fall for 36 hours were earth's gravity this weak. It is also 3,000 times less than exists at the point where Voyager 1 crossed our solar system's heliopause and entered interstellar space.

The theory claims to be consistent with both the macro-level observations of Newtonian gravity as well as Einstein's theory of general relativity and its gravitational distortion of spacetime. Importantly, the theory also explains (without invoking the existence of dark matter and its accompanying math featuring new free parameters that are tweaked to obtain the desired outcome) why galactic rotation curves differ from the profile expected with visible matter.

The theory of entropic gravity posits that what has been interpreted as unobserved dark matter is the product of quantum effects that can be regarded as a form of positive dark energy that lifts the vacuum energy of space from its ground state value. A central tenet of the theory is that the positive dark energy leads to a thermal-volume law contribution to entropy that overtakes the area law of anti-de Sitter space precisely at the cosmological horizon.

The theory has been controversial within the physics community but has sparked research and experiments to test its validity.

🔗 Software 🔗 Software/Computing

In the context of Unix-like systems, the term rc stands for the phrase "run commands". It is used for any file that contains startup information for a command. It is believed to have originated sometime in 1965 at a runcom facility from the MIT Compatible Time-Sharing System (CTSS).

From Brian Kernighan and Dennis Ritchie:

There was a facility that would execute a bunch of commands stored in a file; it was called runcom for "run commands", and the file began to be called "a runcom". rc in Unix is a fossil from that usage.

Tom Van Vleck, a Multics engineer, has also reminisced about the extension rc: "The idea of having the command processing shell be an ordinary slave program came from the Multics design, and a predecessor program on CTSS by Louis Pouzin called RUNCOM, the source of the '.rc' suffix on some Unix configuration files."

This is also the origin of the name of the Plan 9 from Bell Labs shell by Tom Duff, the rc shell. It is called "rc" because the main job of a shell is to "run commands".

While not historically precise, rc may also be expanded as "run control", because an rc file controls how a program runs. For instance, the editor Vim looks for and reads the contents of the .vimrc file to determine its initial configuration. In The Art of Unix Programming, Eric S. Raymond consistently refers to rc files as "run-control" files.

🔗 Computing 🔗 Computing/Amiga

The Smart File System (SFS) is a journaling filesystem used on Amiga computers and AmigaOS-derived operating systems (though some support also exists for IBM PC compatibles). It is designed for performance, scalability and integrity, offering improvements over standard Amiga filesystems as well as some special or unique features.

🔗 Computing 🔗 Computing/Computer hardware

Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory.

FeRAM's advantages over Flash include: lower power usage, faster write performance and a much greater maximum read/write endurance (about 10¹⁰ to 10¹⁴ cycles). FeRAMs have data retention times of more than 10 years at +85 °C (up to many decades at lower temperatures). Market disadvantages of FeRAM are much lower storage densities than flash devices, storage capacity limitations and higher cost. Like DRAM, FeRAM's read process is destructive, necessitating a write-after-read architecture.

🔗 Russia 🔗 Europe 🔗 Food and drink 🔗 Wine 🔗 Russia/demographics and ethnography of Russia

The alcohol belts of Europe divide Europe by their traditional alcoholic beverages: beer, wine, or spirits. They do not necessarily correspond with current drinking habits, as beer has become the most popular alcoholic drink world-wide. The definitions of these belts are not completely objective.

🔗 Economics

The Penn effect is the economic finding that real income ratios between high and low income countries are systematically exaggerated by gross domestic product (GDP) conversion at market exchange rates. It is associated with what became the Penn World Table, and it has been a consistent econometric result since at least the 1950s.

The "Balassa–Samuelson effect" is a model cited as the principal cause of the Penn effect by neo-classical economics, as well as being a synonym of "Penn effect".

🔗 Statistics 🔗 Sociology

The Anna Karenina principle states that a deficiency in any one of a number of factors dooms an endeavor to failure. Consequently, a successful endeavor (subject to this principle) is one where every possible deficiency has been avoided.

The name of the principle derives from Leo Tolstoy's book Anna Karenina, which begins:

All happy families are alike; each unhappy family is unhappy in its own way.

In other words: happy families share a common set of attributes which lead to happiness, while any of a variety of attributes can cause an unhappy family. This concept has been generalized to apply to several fields of study.

In statistics, the term Anna Karenina principle is used to describe significance tests: there are any number of ways in which a dataset may violate the null hypothesis and only one in which all the assumptions are satisfied.

🔗 Biography 🔗 Portugal 🔗 Numismatics

Artur Virgílio Alves Reis (Lisbon, 8 September 1896 – 9 June 1955) was a Portuguese criminal who perpetrated one of the largest frauds in history, against the Bank of Portugal in 1925, often called the Portuguese Bank Note Crisis.

🔗 Soviet Union 🔗 Socialism 🔗 Latvia 🔗 Estonia 🔗 Soviet Union/history of Russia 🔗 Soviet Union/Russia 🔗 Lithuania

The Baltic Way or Baltic Chain (also Chain of Freedom; Estonian: Balti kett; Latvian: Baltijas ceļš; Lithuanian: Baltijos kelias; Russian: Балтийский путь Baltiysky put) was a peaceful political demonstration that occurred on 23 August 1989. Approximately two million people joined their hands to form a human chain spanning 675.5 kilometres (419.7 mi) across the three Baltic states – Estonia, Latvia, and Lithuania, which were considered at the time to be constituent republics of the Soviet Union.

The demonstration originated in "Black Ribbon Day" protests held in the western cities in the 1980s. It marked the 50th anniversary of the Molotov–Ribbentrop Pact between the Soviet Union and Nazi Germany. The pact and its secret protocols divided Eastern Europe into spheres of influence and led to the occupation of the Baltic states in 1940. The event was organised by Baltic pro-independence movements: Rahvarinne of Estonia, the Tautas fronte of Latvia, and Sąjūdis of Lithuania. The protest was designed to draw global attention by demonstrating a popular desire for independence and showcasing solidarity among the three nations. It has been described as an effective publicity campaign, and an emotionally captivating and visually stunning scene. The event presented an opportunity for the Baltic activists to publicise the Soviet rule and position the question of Baltic independence not only as a political matter, but also as a moral issue. The Soviet authorities responded to the event with intense rhetoric, but failed to take any constructive actions that could bridge the widening gap between the Baltic republics and the rest of the Soviet Union. Within seven months of the protest, Lithuania became the first of the Soviet republics to declare independence.

After the Revolutions of 1989, 23 August has become an official remembrance day both in the Baltic countries, in the European Union and in other countries, known as the Black Ribbon Day or as the European Day of Remembrance for Victims of Stalinism and Nazism.