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🔗 Computing

In computing, the Two Generals' Problem is a thought experiment meant to illustrate the pitfalls and design challenges of attempting to coordinate an action by communicating over an unreliable link. In the experiment, two generals are only able to communicate with one another by sending a messenger through enemy territory. The experiment asks how they might reach an agreement on the time to launch an attack, while knowing that any messenger they send could be captured.

It is related to the more general Byzantine Generals Problem and appears often in introductory classes about computer networking (particularly with regard to the Transmission Control Protocol, where it shows that TCP can't guarantee state consistency between endpoints and why this is the case), though it applies to any type of two-party communication where failures of communication are possible. A key concept in epistemic logic, this problem highlights the importance of common knowledge. Some authors also refer to this as the Two Generals' Paradox, the Two Armies Problem, or the Coordinated Attack Problem. The Two Generals' Problem was the first computer communication problem to be proved to be unsolvable. An important consequence of this proof is that generalizations like the Byzantine Generals problem are also unsolvable in the face of arbitrary communication failures, thus providing a base of realistic expectations for any distributed consistency protocols.

🔗 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.

🔗 Computing

The IBM 5100 Portable Computer is a portable computer (one of the first) introduced in September 1975, six years before the IBM Personal Computer. It was the evolution of a prototype called the SCAMP (Special Computer APL Machine Portable) that was developed at the IBM Palo Alto Scientific Center in 1973. In January 1978, IBM announced the IBM 5110, its larger cousin, and in February 1980 IBM announced the IBM 5120. The 5100 was withdrawn in March 1982.

When the IBM PC was introduced in 1981, it was originally designated as the IBM 5150, putting it in the "5100" series, though its architecture was unrelated to the IBM 5100's.

🔗 Psychology

In psychology, the four stages of competence, or the "conscious competence" learning model, relates to the psychological states involved in the process of progressing from incompetence to competence in a skill. People may have several skills, some unrelated to each other, and each skill will typically be at one of the stages at a given time. Many skills require practice to remain at a high level of competence.

The four stages suggest that individuals are initially unaware of how little they know, or unconscious of their incompetence. As they recognize their incompetence, they consciously acquire a skill, then consciously use it. Eventually, the skill can be utilized without it being consciously thought through: the individual is said to have then acquired unconscious competence.

🔗 United States 🔗 Finance & Investment 🔗 Lists 🔗 Business

This is a list of the largest United States bank failures with respect to total assets under management at the time of the bank failure (banks with $1.0 billion or more in assets are listed here). Assets of the banks listed here are figures provided by the Federal Deposit Insurance Corporation.

🔗 International relations 🔗 Human rights 🔗 History 🔗 Islam 🔗 International relations/International law 🔗 Sociology 🔗 Discrimination 🔗 International relations/United Nations

The history of slavery in the Muslim world began with institutions inherited from pre-Islamic Arabia; and the practice of keeping slaves subsequently developed in radically different ways, depending on social-political factors such as the Arab slave trade. Any non-Muslim could be enslaved. Throughout Islamic history, slaves served in various social and economic roles, from powerful emirs to harshly treated manual laborers. Early on in Muslim history slaves provided plantation labor similar to that in the early-modern Americas, but this practice was abandoned after harsh treatment led to destructive slave revolts, the most notable being the Zanj Rebellion of 869–883. Slaves were widely employed in irrigation, mining, and animal husbandry, but most commonly as soldiers, guards, domestic workers, concubines and sex slaves. Many rulers relied on military slaves (often in huge standing armies) and on slaves in administration - to such a degree that the slaves could sometimes seize power. Among black slaves, there were roughly two females to every one male. Two rough estimates by scholars of the numbers of just one group - black slaves held over twelve centuries in the Muslim world - are 11.5 million and 14 million, while other estimates indicate a number between 12 and 15 million African slaves prior to the 20th century.

Islam encouraged the manumission of Muslim slaves as a way of expiating sins. Many early converts to Islam, such as Bilal, were former slaves. In theory, slavery in Islamic law does not have a racial or color basis, although this has not always been the case in practice. In 1990 the Cairo Declaration on Human Rights in Islam declared that "no one has the right to enslave" another human being. Many slaves were imported from outside the Muslim world.

The Arab slave trade was most active in West Asia, North Africa, and Southeast Africa. The Ottoman slave trade exploited the human resources of eastern and central Europe and the Caucasus; the Barbary Coast slave traders raided the Mediterranean coasts of Europe and as far afield as the British Isles and Iceland. In the early 20th century (post-World War I), authorities gradually outlawed and suppressed slavery in Muslim lands, largely due to pressure exerted by Western nations such as Britain and France. Slavery in the Ottoman Empire was abolished in 1924 when the new Turkish Constitution disbanded the Imperial Harem and made the last concubines and eunuchs free citizens of the newly proclaimed republic. Slavery in Iran was abolished in 1929. Mauritania became the last state to abolish slavery - in 1905, 1981, and again in August 2007. Oman abolished slavery in 1970, and Saudi Arabia and Yemen abolished slavery in 1962 under pressure from Britain. However, slavery claiming the sanction of Islam is documented at present in the predominantly Islamic countries of the Sahel, and is also practiced by ISIS and Boko Haram. It is also practiced in countries like Libya and Mauritania - despite being outlawed.

🔗 Psychology 🔗 Sociology 🔗 Media

The spiral of silence theory is a political science and mass communication theory proposed by the German political scientist Elisabeth Noelle-Neumann. It states that an individual's perception of the distribution of public opinion influences that individual's willingness to express their own opinions, which in turn affects the perceptions and, ultimately, willingness of others to express their opinions. The main idea is that people influence each other's willingness to express opinions through social interaction. According to the spiral of silence theory, individuals will be more confident and outward with their opinion when they notice that their personal opinion is shared throughout a group. But if the individual notices that their opinion is unpopular with the group they will be more inclined to be reserved and remain silent. In other words, from the individual's perspective, "not isolating himself is more important than his own judgement", meaning his perception of how others in the group perceive him is more important to himself than the need for his opinion to be heard.

According to Glynn (1995), "the major components of the spiral of silence include (1) an issue of public interest; (2) divisiveness on the issue; (3) a quasi-statistical sense that helps an individual perceive the climate of opinion as well as estimate the majority and minority opinion; (4) 'fear of isolation' from social interaction "(though, whether this is a causal factor in the willingness to speak out is contested)"; (5) an individual's belief that a minority (or 'different') opinion isolates oneself from others; and (6) a 'hardcore' group of people whose opinions are unaffected by others' opinions."

🔗 China 🔗 Psychology

Guanxi (simplified Chinese: 关系; traditional Chinese: 關係; pinyin: guānxi) defines the fundamental dynamic in personalized social networks of power, and is a crucial system of beliefs in Chinese culture. In Western media, the pinyin romanization of this Chinese word is becoming more widely used instead of the two common translations of it—"connections" and "relationships"—as neither of those terms sufficiently reflects the wide cultural implications that guanxi describes.

Guanxi plays a fundamental role within the Confucian doctrine, which sees the individual as part of a community and a set of family, hierarchical and friendly relationships. In particular, there is a focus on tacit mutual commitments, reciprocity, and trust, which are the grounds of guanxi and guanxi networks.

Guanxi also has a major influence on the management of businesses based in Mainland China, and businesses owned by Overseas Chinese in Southeast Asia (the latter is known as the bamboo network).

Closely related concepts include that of ganqing, a measure which reflects the depth of feeling within an interpersonal relationship, renqing (人情 rénqíng/jen-ch'ing), the moral obligation to maintain a relationship, and the idea of "face" (面子, miànzi/mien-tzu), which refers to social status, propriety, prestige, or a combination of all three. Other related concepts include wu-lune, which supports the idea of a long term, developing relationship between a business and its client, and yi-ren and ren, which respectively support reciprocity and empathy.

🔗 Technology 🔗 Energy

In pipeline transportation, pigging is the practice of using devices known as pigs or scrapers to perform various maintenance operations. This is done without stopping the flow of the product in the pipeline. These devices are known as pigs because they scrape or clean just like a normal pig.

These operations include but are not limited to cleaning and inspecting the pipeline. This is accomplished by inserting the pig into a "pig launcher" (or "launching station") — an oversized section in the pipeline, reducing to the normal diameter. The launching station is then closed and the pressure-driven flow of the product in the pipeline is used to push the pig along down the pipe until it reaches the receiving trap — the "pig catcher" (or "receiving station").

🔗 Computer science

In distributed computing, a conflict-free replicated data type (CRDT) is a data structure which can be replicated across multiple computers in a network, where the replicas can be updated independently and concurrently without coordination between the replicas, and where it is always mathematically possible to resolve inconsistencies which might result.

The CRDT concept was formally defined in 2011 by Marc Shapiro, Nuno Preguiça, Carlos Baquero and Marek Zawirski. Development was initially motivated by collaborative text editing and mobile computing. CRDTs have also been used in online chat systems, online gambling, and in the SoundCloud audio distribution platform. The NoSQL distributed databases Redis, Riak and Cosmos DB have CRDT data types.