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🔗 Physics

The green flash and green ray are meteorological optical phenomena that sometimes occur transiently around the moment of sunset or sunrise. When the conditions are right, a distinct green spot is briefly visible above the upper rim of the Sun's disk; the green appearance usually lasts for no more than two seconds. Rarely, the green flash can resemble a green ray shooting up from the sunset or sunrise point.

Green flashes occur because the earth's atmosphere can cause the light from the Sun to separate out into different colors. Green flashes are a group of similar phenomena that stem from slightly different causes, and therefore, some types of green flashes are more common than others.

🔗 Palaeontology 🔗 Amphibians and Reptiles 🔗 Mammals

Dimetrodon ( (listen) or , meaning "two measures of teeth") is an extinct genus of non-mammalian synapsids that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Ma). It is a member of the family Sphenacodontidae. The most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the southwestern United States, the majority coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878.

Dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the first appearance of dinosaurs. Reptile-like in appearance and physiology, Dimetrodon is nevertheless more closely related to mammals than to modern reptiles, though it is not a direct ancestor of mammals. Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally called "mammal-like reptiles". This groups Dimetrodon together with mammals in a clade (evolutionary group) called Synapsida, while placing dinosaurs, reptiles and birds in a separate clade, Sauropsida. Single openings in the skull behind each eye, known as temporal fenestrae, and other skull features distinguish Dimetrodon and mammals from most of the earliest sauropsids.

Dimetrodon was probably one of the apex predators of the Cisuralian ecosystems, feeding on fish and tetrapods, including reptiles and amphibians. Smaller Dimetrodon species may have had different ecological roles. The sail of Dimetrodon may have been used to stabilize its spine or to heat and cool its body as a form of thermoregulation. Some recent studies argue that the sail would have been ineffective at removing heat from the body due to large species being discovered with small sails and small species being discovered with large sails, essentially ruling out heat regulation as its main purpose. The sail was most likely used in courtship display with methods such as threatening rivals or showing off to potential mates.

🔗 Lists 🔗 Science Fiction 🔗 Transhumanism 🔗 Sociology 🔗 Futures studies 🔗 Science 🔗 Popular Culture

This is a list of fictional stories that, when written, were set in the future, but the future they predicted is now present or past. The list excludes works that were alternate histories, which were composed after the dates they depict, alternative futures, as depicted in time travel fiction, as well as any works that make no predictions of the future, such as those focusing solely on the future lives of specific fictional characters, or works which, despite their claimed dates, are contemporary in all but name. Entries referencing the current year may be added if their month and day were not specified or have already occurred.

🔗 Computing 🔗 Computing/Networking

Internet 0 is a low-speed physical layer designed to route 'IP over anything.' It was developed at MIT's Center for Bits and Atoms by Neil Gershenfeld, Raffi Krikorian, and Danny Cohen. When it was invented, a number of other proposals were being labelled as "internet 2." The name was chosen to emphasize that this was designed to be a slow, but very inexpensive internetworking system, and forestall "high-performance" comparison questions such as "how fast is it?"

Effectively, it would enable a platform for pervasive computing -- everything in a building could be on the same network to share data gathering and actuation. A light switch could turn on a light bulb by sending a packet to it, they can be linked together by the user.

🔗 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.

Mental poker is the common name for a set of cryptographic problems that concerns playing a fair game over distance without the need for a trusted third party. The term is also applied to the theories surrounding these problems and their possible solutions. The name comes from the card game poker which is one of the games to which this kind of problem applies. Similar problems described as two party games are Blum's flipping a coin over a distance, Yao's Millionaires' Problem, and Rabin's oblivious transfer.

The problem can be described thus: "How can one allow only authorized actors to have access to certain information while not using a trusted arbiter?" (Eliminating the trusted third-party avoids the problem of trying to determine whether the third party can be trusted or not, and may also reduce the resources required.)

In poker, this could translate to: "How can we make sure no player is stacking the deck or peeking at other players' cards when we are shuffling the deck ourselves?". In a physical card game, this would be relatively simple if the players were sitting face to face and observing each other, at least if the possibility of conventional cheating can be ruled out. However, if the players are not sitting at the same location but instead are at widely separate locations and pass the entire deck between them (using the postal mail, for instance), this suddenly becomes very difficult. And for electronic card games, such as online poker, where the mechanics of the game are hidden from the user, this is impossible unless the method used is such that it cannot allow any party to cheat by manipulating or inappropriately observing the electronic "deck".

Several protocols for doing this have been suggested, the first by Adi Shamir, Ron Rivest and Len Adleman (the creators of the RSA-encryption protocol). This protocol was the first example of two parties conducting secure computation rather than secure message transmission, employing cryptography; later on due to leaking partial information in the original protocol, this led to the definition of semantic security by Shafi Goldwasser and Silvio Micali. The concept of multi-player mental poker was introduced in Moti Yung's 1984 book Cryptoprotocols. The area has later evolved into what is known as secure multi-party computation protocols (for two parties, and multi parties as well).

🔗 Medicine 🔗 Death 🔗 Health and fitness 🔗 Japan 🔗 Medicine/Society and Medicine 🔗 Japan/Culture 🔗 Japan/Science and technology

Karoshi (過労死, Karōshi), which can be translated literally as "overwork death" in Japanese, is occupational sudden mortality. The major medical causes of karoshi deaths are heart attack and stroke due to stress and a starvation diet. This phenomenon is also widespread in other parts of Asia.

🔗 Food and drink 🔗 Plants

Romanesco broccoli (also known as Roman cauliflower, Broccolo Romanesco, Romanesque cauliflower, or simply Romanesco) is an edible flower bud of the species Brassica oleracea. First documented in Italy in the 16th century, it is chartreuse in color, and has a form naturally approximating a fractal. When compared to a traditional cauliflower, it has a firmer texture and delicate, nutty flavor.

🔗 Novels 🔗 Novels/Science fiction 🔗 Science Fiction 🔗 Solar System/Mars 🔗 Solar System

The Mars trilogy is a series of science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the personal and detailed viewpoints of a wide variety of characters spanning almost two centuries. Ultimately more utopian than dystopian, the story focuses on egalitarian, sociological, and scientific advances made on Mars, while Earth suffers from overpopulation and ecological disaster.

The three novels are Red Mars (1992), Green Mars (1993), and Blue Mars (1996). The Martians (1999) is a collection of short stories set in the same fictional universe. Red Mars won the BSFA Award in 1992 and Nebula Award for Best Novel in 1993. Green Mars won the Hugo Award for Best Novel and Locus Award for Best Science Fiction Novel in 1994. Blue Mars also won the Hugo and Locus Awards in 1997.

Icehenge (1984), Robinson's first novel about Mars, is not set in this universe but deals with similar themes and plot elements. The trilogy shares some similarities with Robinson's more recent novel 2312 (2012); for instance, the terraforming of Mars and the extreme longevity of the characters in both novels.

🔗 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.