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🔗 Mathematics

John von Neumann's universal constructor is a self-replicating machine in a cellular automata (CA) environment. It was designed in the 1940s, without the use of a computer. The fundamental details of the machine were published in von Neumann's book Theory of Self-Reproducing Automata, completed in 1966 by Arthur W. Burks after von Neumann's death.

Von Neumann's goal was to specify an abstract machine which, when run, would replicate itself. In his design, the machine consists of three parts: a 'blueprint' for itself, a mechanism that can read any blueprint and construct the machine (sans blueprint) specified by that blueprint, and a 'copy machine' that can make copies of any blueprint. After the mechanism has been used to construct the machine specified by the blueprint, the copy machine is used to create a copy of that blueprint, and this copy is placed into the new machine, resulting in a working replication of the original machine. Some machines will do this backwards, copying the blueprint and then building a machine.

To define his machine in more detail, von Neumann invented the concept of a cellular automaton. The one he used consists of a two-dimensional grid of cells, each of which can be in one of 29 states at any point in time. At each timestep, each cell updates its state depending on the states of the surrounding cells at the prior timestep. The rules governing these updates are identical for all cells.

The universal constructor is a certain pattern of cell states in this cellular automaton. It contains one line of cells that serve as a 'tape', encoding a sequence of instructions that serve as a 'blueprint' for the machine. The machine reads these instructions one by one and performs the corresponding actions. The instructions direct the machine to use its 'construction arm' to build a copy of the machine, without tape, at some other location in the cell grid. The tape can't contain instructions to build an equally long tape, just as a container can't contain a container of the same size. Therefore, the machine contains a separate 'copy machine' which reads the tape and places a copy into the newly constructed machine. The resulting new machine and tape is identical to the old one, and it proceeds to replicate again.

🔗 Computing 🔗 Mathematics 🔗 Computing/Networking

In mathematics, the Cheeger constant (also Cheeger number or isoperimetric number) of a graph is a numerical measure of whether or not a graph has a "bottleneck". The Cheeger constant as a measure of "bottleneckedness" is of great interest in many areas: for example, constructing well-connected networks of computers, card shuffling. The graph theoretical notion originated after the Cheeger isoperimetric constant of a compact Riemannian manifold.

The Cheeger constant is named after the mathematician Jeff Cheeger.

🔗 Biology 🔗 Evolutionary biology 🔗 Tree of Life

The three-domain system is a biological classification introduced by Carl Woese et al. in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea). Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated each as a domain, divided into several different kingdoms. Woese initially used the term "kingdom" to refer to the three primary phylogenic groupings, and this nomenclature was widely used until the term "domain" was adopted in 1990.

Parts of the three-domain theory have been fiercly challenged by scientists such as Radhey S. Gupta, who argues that the primary division within prokaryotes should be between those surrounded by a single membrane, and those with two membranes.

🔗 Extinction

An endling is the last known individual of a species or subspecies. Once the endling dies, the species becomes extinct. The word was coined in correspondence in the scientific journal Nature. Alternative names put forth for the last individual of its kind include ender and terminarch.

The word relict may also be used, but usually refers to a population, rather than an individual, that is the last of a species.

🔗 Psychology 🔗 Education 🔗 Homeschooling 🔗 Alternative education

Autodidacticism (also autodidactism) or self-education (also self-learning and self-teaching) is education without the guidance of masters (such as teachers and professors) or institutions (such as schools). Generally, an autodidact is an individual who chooses the subject they will study, their studying material, and the studying rhythm and time. An autodidact may or may not have formal education, and their study may be either a complement or an alternative to formal education. Many notable contributions have been made by autodidacts.

🔗 Computer science

Boids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference. The name "boid" corresponds to a shortened version of "bird-oid object", which refers to a bird-like object. Incidentally, "boid" is also a New York Metropolitan dialect pronunciation for "bird".

As with most artificial life simulations, Boids is an example of emergent behavior; that is, the complexity of Boids arises from the interaction of individual agents (the boids, in this case) adhering to a set of simple rules. The rules applied in the simplest Boids world are as follows:

• separation: steer to avoid crowding local flockmates
• alignment: steer towards the average heading of local flockmates
• cohesion: steer to move towards the average position (center of mass) of local flockmates

More complex rules can be added, such as obstacle avoidance and goal seeking.

The basic model has been extended in several different ways since Reynolds proposed it. For instance, Delgado-Mata et al. extended the basic model to incorporate the effects of fear. Olfaction was used to transmit emotion between animals, through pheromones modelled as particles in a free expansion gas. Hartman and Benes introduced a complementary force to the alignment that they call the change of leadership. This steer defines the chance of the boid to become a leader and try to escape.

The movement of Boids can be characterized as either chaotic (splitting groups and wild behaviour) or orderly. Unexpected behaviours, such as splitting flocks and reuniting after avoiding obstacles, can be considered emergent.

The boids framework is often used in computer graphics, providing realistic-looking representations of flocks of birds and other creatures, such as schools of fish or herds of animals. It was for instance used in the 1998 video game Half-Life for the flying bird-like creatures seen at the end of the game on Xen, named "boid" in the game files.

The Boids model can be used for direct control and stabilization of teams of simple Unmanned Ground Vehicles (UGV) or Micro Aerial Vehicles (MAV) in swarm robotics. For stabilization of heterogeneous UAV-UGV teams, the model was adapted for using onboard relative localization by Saska et al.

At the time of proposal, Reynolds' approach represented a giant step forward compared to the traditional techniques used in computer animation for motion pictures. The first animation created with the model was Stanley and Stella in: Breaking the Ice (1987), followed by a feature film debut in Tim Burton's film Batman Returns (1992) with computer generated bat swarms and armies of penguins marching through the streets of Gotham City.

The boids model has been used for other interesting applications. It has been applied to automatically program Internet multi-channel radio stations. It has also been used for visualizing information and for optimization tasks.

🔗 Novels

The 480 is a political fiction novel by Eugene Burdick (1964).

The plot evolves around the political turmoil after John F. Kennedy assassination in 1963. In the novel, a fictitious charismatic character, John Thatch, an engineer, is seeking nomination for the Republican Party candidate at 1964 presidential elections. He is described as being contaminated with the "political virus". A handful of political professionals are promoting his nomination, in confrontation with the Party establishment. There exist apparent parallels between Thatch and Henry Cabot Lodge, Jr., a write-in hero at New Hampshire primary.

The novel criticizes the socio-political effects on society at large from the use of computers to run massive simulations, which predict the public reaction to certain (proposed) political moves before implementing them. Such simulations make it easy to manipulate the public consciousness.

The "480" in the title denotes the number of groups (by party affiliation, socioeconomic status, location, origin, etc.) that the computer simulation uses to classify the American electorate. The full list of these is reproduced in the Appendix, claimed by the author to be the true list used by the Simulmatics Corporation (real name) in Senator John F. Kennedy's Presidential campaign in 1960. The cover features an IBM 5081 punched card.

The Simulmatics Corporation was created by MIT Professor Ithiel de Sola Pool, who provided a non-fiction backup to "The 480" in "Candidates, Issues, and Strategies: A Computer Simulation of the 1960 Presidential Election," MIT Press, 1964 (with co-authors Robert P. Abelson and Samuel L. Popkin). They built their model from 130,000 archived interviews in Gallup and Roper polls over a ten-year period. Based on its output, they advised Kennedy that he would benefit from a strong civil rights stand and that he had nothing to lose, and much to gain, by attacking religious bigotry and dealing frankly with his Catholicism.

The 480 has been cited as prefiguring the effect of modern social media and data gathering on politics.

🔗 United States 🔗 History 🔗 Philosophy 🔗 Philosophy/Social and political philosophy 🔗 British Empire 🔗 Sociology 🔗 United States History 🔗 United States/U.S. history

The Strauss–Howe generational theory, also known as the Fourth Turning theory or simply the Fourth Turning, which was created by authors William Strauss and Neil Howe, describes a theorized recurring generation cycle in American history. According to the theory, historical events are associated with recurring generational personas (archetypes). Each generational persona unleashes a new era (called a turning) lasting around 20–22 years, in which a new social, political, and economic climate exists. They are part of a larger cyclical "saeculum" (a long human life, which usually spans between 80 and 90 years, although some saecula have lasted longer). The theory states that after every saeculum, a crisis recurs in American history, which is followed by a recovery (high). During this recovery, institutions and communitarian values are strong. Ultimately, succeeding generational archetypes attack and weaken institutions in the name of autonomy and individualism, which ultimately creates a tumultuous political environment that ripens conditions for another crisis.

Strauss and Howe laid the groundwork for their theory in their 1991 book Generations, which discusses the history of the United States as a series of generational biographies going back to 1584. In their 1997 book The Fourth Turning, the authors expanded the theory to focus on a fourfold cycle of generational types and recurring mood eras to describe the history of the United States, including the Thirteen Colonies and their British antecedents. However, the authors have also examined generational trends elsewhere in the world and described similar cycles in several developed countries.

Academic response to the theory has been mixed—some applauding Strauss and Howe for their "bold and imaginative thesis" and others criticizing the theory as being overly-deterministic, non-falsifiable, and unsupported by rigorous evidence, "about as scientific as astrology or a Nostradamus text." Strauss–Howe generational theory has also been described by some historians and journalists as a "pseudoscience" "kooky", and "an elaborate historical horoscope that will never withstand scholarly scrutiny."

Academic criticism has focused on the lack of rigorous empirical evidence for their claims, and the authors' view that generational groupings are far more powerful than other social groupings such as economic class, race, sex, religion and political parties.

🔗 Economics 🔗 Business 🔗 Marketing & Advertising 🔗 Guild of Copy Editors

In marketing strategy, first-mover advantage (FMA) is the advantage gained by the initial ("first-moving") significant occupant of a market segment. First-mover advantage may be gained by technological leadership, or early purchase of resources.

A market participant has first-mover advantage if it is the first entrant and gains a competitive advantage through control of resources. With this advantage, first-movers can be rewarded with huge profit margins and a monopoly-like status.

Not all first-movers are rewarded. If the first-mover does not capitalize on its advantage, its "first-mover disadvantages" leave opportunity for new entrants to enter the market and compete more effectively and efficiently than the first-movers; such firms have "second-mover advantage".

🔗 Japan 🔗 Japan/Culture 🔗 Textile Arts

Shibori (しぼり / 絞り) is a Japanese manual resist dyeing technique, which produces a number of different patterns on fabric.