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For non-linear autonomous ODEs it is possible under some conditions to develop solutions of finite duration, meaning here that from its own dynamics, the system will reach the value zero at an ending time and stays there in zero forever after. These finite-duration solutions can't be analytical functions on the whole r... | Ordinary differential equation | Wikipedia | 414 | 32742753 | https://en.wikipedia.org/wiki/Ordinary%20differential%20equation | Mathematics | Calculus and analysis | null |
Two memoirs by Fuchs inspired a novel approach, subsequently elaborated by Thomé and Frobenius. Collet was a prominent contributor beginning in 1869. His method for integrating a non-linear system was communicated to Bertrand in 1868. Clebsch (1873) attacked the theory along lines parallel to those in his theory of Abe... | Ordinary differential equation | Wikipedia | 371 | 32742753 | https://en.wikipedia.org/wiki/Ordinary%20differential%20equation | Mathematics | Calculus and analysis | null |
Sturm–Liouville theory is a theory of a special type of second-order linear ordinary differential equation. Their solutions are based on eigenvalues and corresponding eigenfunctions of linear operators defined via second-order homogeneous linear equations. The problems are identified as Sturm–Liouville problems (SLP) a... | Ordinary differential equation | Wikipedia | 502 | 32742753 | https://en.wikipedia.org/wiki/Ordinary%20differential%20equation | Mathematics | Calculus and analysis | null |
For each initial condition there exists a unique maximum (possibly infinite) open interval
such that any solution that satisfies this initial condition is a restriction of the solution that satisfies this initial condition with domain .
In the case that , there are exactly two possibilities
explosion in finite time... | Ordinary differential equation | Wikipedia | 467 | 32742753 | https://en.wikipedia.org/wiki/Ordinary%20differential%20equation | Mathematics | Calculus and analysis | null |
When all other methods for solving an ODE fail, or in the cases where we have some intuition about what the solution to a DE might look like, it is sometimes possible to solve a DE simply by guessing the solution and validating it is correct. To use this method, we simply guess a solution to the differential equation, ... | Ordinary differential equation | Wikipedia | 429 | 32742753 | https://en.wikipedia.org/wiki/Ordinary%20differential%20equation | Mathematics | Calculus and analysis | null |
Structural coloration in animals, and a few plants, is the production of colour by microscopically structured surfaces fine enough to interfere with visible light instead of pigments, although some structural coloration occurs in combination with pigments. For example, peacock tail feathers are pigmented brown, but the... | Structural coloration | Wikipedia | 467 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Thomas Young (1773–1829) extended Newton's particle theory of light by showing that light could also behave as a wave. He showed in 1803 that light could diffract from sharp edges or slits, creating interference patterns.
In his 1892 book Animal Coloration, Frank Evers Beddard (1858–1925) acknowledged the existence of... | Structural coloration | Wikipedia | 399 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Iridescence, as explained by Thomas Young in 1803, is created when extremely thin films reflect part of the light falling on them from their top surfaces. The rest of the light goes through the films, and a further part of it is reflected from their bottom surfaces. The two sets of reflected waves travel back upwards i... | Structural coloration | Wikipedia | 334 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
A diffraction grating constructed of layers of chitin and air gives rise to the iridescent colours of various butterfly wing scales as well as to the tail feathers of birds such as the peacock. Hooke and Newton were correct in their claim that the peacock's colours are created by interference, but the structures respon... | Structural coloration | Wikipedia | 450 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Selective mirrors to create interference effects are formed of micron-sized bowl-shaped pits lined with multiple layers of chitin in the wing scales of Papilio palinurus, the emerald swallowtail butterfly. These act as highly selective mirrors for two wavelengths of light. Yellow light is reflected directly from the ce... | Structural coloration | Wikipedia | 317 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Spiral coils, formed of helicoidally stacked cellulose microfibrils, create Bragg reflection in the "marble berries" of the African herb Pollia condensata, resulting in the most intense blue coloration known in nature. The berry's surface has four layers of cells with thick walls, containing spirals of transparent cell... | Structural coloration | Wikipedia | 418 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Surface gratings, consisting of ordered surface features due to exposure of ordered muscle cells on cuts of meat. The structural coloration on meat cuts appears only after the ordered pattern of muscle fibrils is exposed and light is diffracted by the proteins in the fibrils. The coloration or wavelength of the diffrac... | Structural coloration | Wikipedia | 482 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Gabriel Lippmann won the Nobel Prize in Physics in 1908 for his work on a structural coloration method of colour photography, the Lippmann plate. This used a photosensitive emulsion fine enough for the interference caused by light waves reflecting off the back of the glass plate to be recorded in the thickness of the e... | Structural coloration | Wikipedia | 425 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
The surface of the compound eye of the housefly is densely packed with microscopic projections that have the effect of reducing reflection and hence increasing transmission of incident light. Similarly, the eyes of some moths have antireflective surfaces, again using arrays of pillars smaller than the wavelength of lig... | Structural coloration | Wikipedia | 136 | 32747596 | https://en.wikipedia.org/wiki/Structural%20coloration | Biology and health sciences | Biological pigments | Biology |
Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying directions on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of different operations and machines, on scales from small individual parts to... | Milling (machining) | Wikipedia | 440 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
The milling process removes material by performing many separate, small cuts. This is accomplished by using a cutter with many teeth, spinning the cutter at high speed, or advancing the material through the cutter slowly; most often it is some combination of these three approaches. The speeds and feeds used are varied ... | Milling (machining) | Wikipedia | 483 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
As material passes through the cutting area of a milling machine, the blades of the cutter take swarfs of material at regular intervals. Surfaces cut by the side of the cutter (as in peripheral milling) therefore always contain regular ridges. The distance between ridges and the height of the ridges depend on the feed ... | Milling (machining) | Wikipedia | 467 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Types and nomenclature
Mill orientation is the primary classification for milling machines. The two basic configurations are vertical and horizontal – referring to the orientation of the rotating spindle upon which the cutter is mounted. However, there are alternative classifications according to method of control, si... | Milling (machining) | Wikipedia | 297 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
A third type also exists, a lighter, more versatile machine, called a mill-drill. The mill-drill is a close relative of the vertical mill and quite popular in light industry; and with hobbyists. A mill-drill is similar in basic configuration to a very heavy drill press, but equipped with an X-Y table and a much larger ... | Milling (machining) | Wikipedia | 343 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
A horizontal mill has the same short but the cutters are mounted on a horizontal spindle, or arbor, mounted across the table. Many horizontal mills also feature a built-in rotary table that allows milling at various angles; this feature is called a universal table. While endmills and the other types of tools availabl... | Milling (machining) | Wikipedia | 413 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Comparative merits
The choice between vertical and horizontal spindle orientation in milling machine design usually hinges on the shape and size of a workpiece and the number of sides of the workpiece that require machining. Work in which the spindle's axial movement is normal to one plane, with an endmill as the cutte... | Milling (machining) | Wikipedia | 251 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Bed mill This refers to any milling machine where the spindle is on a pendant that moves up and down to move the cutter into the work, while the table sits on a stout bed that rests on the floor. These are generally more rigid than a knee mill. Gantry mills can be included in this bed mill category.
Box mill or colu... | Milling (machining) | Wikipedia | 406 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Horizontal boring mill Large, accurate bed horizontal mills that incorporate many features from various machine tools. They are predominantly used to create large manufacturing jigs, or to modify large, high precision parts. They have a spindle stroke of several (usually between four and six) feet, and many are equip... | Milling (machining) | Wikipedia | 488 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Alternative terminology
A milling machine is often called a mill by machinists. The archaic term miller was commonly used in the 19th and early 20th centuries.
Since the 1960s there has developed an overlap of usage between the terms milling machine and machining center. NC/CNC machining centers evolved from milling ... | Milling (machining) | Wikipedia | 434 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
The operating system of such machines is a closed loop system and functions on feedback.
These machines have developed from the basic NC (NUMERIC CONTROL) machines. A computerized form of NC machines is known as CNC machines. A set of instructions (called a program) is used to guide the machine for desired operations. ... | Milling (machining) | Wikipedia | 383 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
CNC milling machines nearly always use SK (or ISO), CAT, BT or HSK tooling. SK tooling is the most common in Europe, while CAT tooling, sometimes called V-Flange Tooling, is the oldest and probably most common type in the USA. CAT tooling was invented by Caterpillar Inc. of Peoria, Illinois, in order to standardize the... | Milling (machining) | Wikipedia | 408 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
For manual milling machines, there is less standardization, because a greater plurality of formerly competing standards exist. Newer and larger manual machines usually use NMTB tooling. This tooling is somewhat similar to CAT tooling but requires a drawbar within the milling machine. Furthermore, there are a number of... | Milling (machining) | Wikipedia | 512 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Zig
In zig milling, the tool moves only in one direction. The tool has to be lifted and retracted after each cut, due to which machining time increases. However, in case of zig milling surface quality is better.
Non-linear tool path
In this approach, tool movement is multi-directional. One example of non-linear tool p... | Milling (machining) | Wikipedia | 440 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Milling machines evolved from the practice of rotary filing—that is, running a circular cutter with file-like teeth in the headstock of a lathe. Rotary filing and, later, true milling were developed to reduce time and effort spent hand-filing. The full story of milling machine development may never be known, because mu... | Milling (machining) | Wikipedia | 336 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
It is clear that milling machines as a distinct class of machine tool (separate from lathes running rotary files) first appeared between 1814 and 1818. The centers of earliest development of true milling machines were two federal armories of the U.S. (Springfield and Harpers Ferry) together with the various private arm... | Milling (machining) | Wikipedia | 427 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
The late teens of the 19th century were a pivotal time in the history of machine tools, as the period of 1814 to 1818 is also the period during which several contemporary pioneers (Fox, Murray, and Roberts) were developing the planer, and as with the milling machine, the work being done in various shops was undocumente... | Milling (machining) | Wikipedia | 497 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
During this era there was a continued blind spot in milling machine design, as various designers failed to develop a truly simple and effective means of providing slide travel in all three of the archetypal milling axes (X, Y, and Z—or as they were known in the past, longitudinal, traverse, and vertical). Vertical posi... | Milling (machining) | Wikipedia | 412 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
In these decades, Brown & Sharpe and the Cincinnati Milling Machine Company dominated the American milling machine field. However, hundreds of other firms also built milling machines at the time, and many were significant in various ways. Besides a wide variety of specialized production machines, the archetypal multipu... | Milling (machining) | Wikipedia | 414 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
Bridgeport milling machine
In 1936, Rudolph Bannow (1897–1962) conceived of a major improvement to the milling machine. His company commenced manufacturing a new knee-and-column vertical mill in 1938. This was the Bridgeport milling machine, often called a ram-type or turret-type mill because its head has sliding-ram a... | Milling (machining) | Wikipedia | 503 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
During the 1950s, numerical control moved slowly from the laboratory into commercial service. For its first decade, it had rather limited impact outside of aerospace work. But during the 1960s and 1970s, NC evolved into CNC, data storage and input media evolved, computer processing power and memory capacity steadily in... | Milling (machining) | Wikipedia | 422 | 38360943 | https://en.wikipedia.org/wiki/Milling%20%28machining%29 | Technology | Industrial machinery | null |
The evolution of bacteria has progressed over billions of years since the Precambrian time with their first major divergence from the archaeal/eukaryotic lineage roughly 3.2-3.5 billion years ago. This was discovered through gene sequencing of bacterial nucleoids to reconstruct their phylogeny. Furthermore, evidence of... | Evolution of bacteria | Wikipedia | 433 | 60456582 | https://en.wikipedia.org/wiki/Evolution%20of%20bacteria | Biology and health sciences | Basics_4 | Biology |
Bacteria are prokaryotic microorganisms that can either have a bacilli, spirilli, or cocci shape and measure between 0.5-20 micrometers. They were one of the first living cells to evolve and have spread to inhabit a variety of different habitats including hydrothermal vents, glacial rocks, and other organisms. They sha... | Evolution of bacteria | Wikipedia | 345 | 60456582 | https://en.wikipedia.org/wiki/Evolution%20of%20bacteria | Biology and health sciences | Basics_4 | Biology |
Thermotogales
Thermotogota bacteria are typically thermophilic or hyperthermophilic, gram-negative staining, anaerobic organisms that can live near hydrothermal vents where temperatures can range between 55-95 °C. They are thought to be some of the earliest forms of life. Evidence of bacteria has been discovered in the... | Evolution of bacteria | Wikipedia | 370 | 60456582 | https://en.wikipedia.org/wiki/Evolution%20of%20bacteria | Biology and health sciences | Basics_4 | Biology |
Cyanobacteria
Cyanobacteria or blue green-algae is a gram negative bacteria, a phylum of photosynthetic bacteria that evolved between 2.3-2.7 billion years ago. This prokaryote produces oxygen as a byproduct of its photosynthetic processes. They have made a distinctive impact in pharmaceutical and agricultural industry... | Evolution of bacteria | Wikipedia | 349 | 60456582 | https://en.wikipedia.org/wiki/Evolution%20of%20bacteria | Biology and health sciences | Basics_4 | Biology |
HWB (Hue, Whiteness, Blackness) is a cylindrical-coordinate representation of points in an RGB color model, similar to HSL and HSV. It was developed by HSV’s creator Alvy Ray Smith in 1996 to address some of the issues with HSV. HWB was designed to be more intuitive for humans to use and slightly faster to compute. The... | HWB color model | Wikipedia | 248 | 42593487 | https://en.wikipedia.org/wiki/HWB%20color%20model | Physical sciences | Basics | Physics |
Pollen beetle is an informal term for any species of beetle associated intimately with suitably pollen-rich species of flowers. Typically such a beetle is adapted to the pollen as a major part of its diet. Species in at least sixteen families of the order Coleoptera could be counted as pollen beetles, and "pollen beetl... | Pollen beetle | Wikipedia | 440 | 42593531 | https://en.wikipedia.org/wiki/Pollen%20beetle | Biology and health sciences | Beetles (Coleoptera) | Animals |
Among the Melyridae the most prominent example of a species commonly referred to as a pollen beetle is Astylus atromaculatus. It feeds particularly on the large amounts of pollen produced by members of the grass family Poaceae, and related wind-pollinated families such as the Cyperaceae. It does however also visit many... | Pollen beetle | Wikipedia | 322 | 42593531 | https://en.wikipedia.org/wiki/Pollen%20beetle | Biology and health sciences | Beetles (Coleoptera) | Animals |
Power-to-X (also P2X and P2Y) are electricity conversion, energy storage, and reconversion pathways from surplus renewable energy.
Power-to-X conversion technologies allow for the decoupling of power from the electricity sector for use in other sectors (such as transport or chemicals), possibly using power that has be... | Power-to-X | Wikipedia | 427 | 50375026 | https://en.wikipedia.org/wiki/Power-to-X | Technology | Energy storage | null |
Reconversion technologies include gas turbines, combined cycle plants, reciprocating engines and fuel cells.
Power-to-power refers to the round-trip reconversion efficiency. For hydrogen storage, the round-trip efficiency remains limited at 35–50%. Electrolysis is expensive and power-to-gas processes need substantial ... | Power-to-X | Wikipedia | 385 | 50375026 | https://en.wikipedia.org/wiki/Power-to-X | Technology | Energy storage | null |
Power-to-heat involves contributing to the heat sector, either by resistance heating or via a heat pump. Resistance heaters have unity efficiency, and the corresponding coefficient of performance (COP) of heat pumps is 2–5. Back-up immersion heating of both domestic hot water and district heating offers a cheap way of ... | Power-to-X | Wikipedia | 375 | 50375026 | https://en.wikipedia.org/wiki/Power-to-X | Technology | Energy storage | null |
Xenacoelomorpha () is a small phylum of bilaterian invertebrate animals, consisting of two sister groups: xenoturbellids and acoelomorphs. This new phylum was named in February 2011 and suggested based on morphological synapomorphies (physical appearances shared by the animals in the clade), which was then confirmed by... | Xenacoelomorpha | Wikipedia | 421 | 38386085 | https://en.wikipedia.org/wiki/Xenacoelomorpha | Biology and health sciences | Other | Animals |
Internal phylogeny
For multiple decades, the genus Xenoturbella contained only one species, X. bocki. In 2016 however, a team reported the discovery of four new species from the Gulf of California and sequenced each new species' mitogenome and upon analysis found that the two species that lived in shallow water (X. boc... | Xenacoelomorpha | Wikipedia | 421 | 38386085 | https://en.wikipedia.org/wiki/Xenacoelomorpha | Biology and health sciences | Other | Animals |
The phylum is hermaphroditic (all individuals have both male and female sex organs) and reproduces sexually with direct development, meaning they skip a potentially vulnerable larval stage. Xenoturbella have external fertilization, and Acoelomorpha has internal fertilization. All xenacoelomorphs are bilateral, meaning ... | Xenacoelomorpha | Wikipedia | 510 | 38386085 | https://en.wikipedia.org/wiki/Xenacoelomorpha | Biology and health sciences | Other | Animals |
The epidermis of all species within the phylum is ciliated. The cilia are composed of a set of nine pairs of peripheral microtubules and one or two central microtubules (patterns 9+1 and 9+2, respectively). The pairs 4–7 terminate before the tip, creating a structure called a "shelf". | Xenacoelomorpha | Wikipedia | 73 | 38386085 | https://en.wikipedia.org/wiki/Xenacoelomorpha | Biology and health sciences | Other | Animals |
Deforestation is a primary contributor to climate change, and climate change affects the health of forests. Land use change, especially in the form of deforestation, is the second largest source of carbon dioxide emissions from human activities, after the burning of fossil fuels. Greenhouse gases are emitted from defor... | Deforestation and climate change | Wikipedia | 444 | 44035599 | https://en.wikipedia.org/wiki/Deforestation%20and%20climate%20change | Physical sciences | Climate change | Earth science |
Deforestation, particularly in large swaths of the Amazon, where nearly 20% of the rainforest has been clear cut, has climactic effects and effects on water sources as well as on the soil. Moreover, the type of land usage after deforestation also produces varied results. When deforested land is converted to pasture lan... | Deforestation and climate change | Wikipedia | 500 | 44035599 | https://en.wikipedia.org/wiki/Deforestation%20and%20climate%20change | Physical sciences | Climate change | Earth science |
According to a study published in 2023, tropical deforestation has led to a significant decrease in the amount of observed precipitation. By the year 2100, researchers anticipate that deforestation in the Congo will diminish regional precipitation levels by up to 8-10%.
Decreasing albedo
Deforestation changes the lan... | Deforestation and climate change | Wikipedia | 413 | 44035599 | https://en.wikipedia.org/wiki/Deforestation%20and%20climate%20change | Physical sciences | Climate change | Earth science |
Objective-C is a high-level general-purpose, object-oriented programming language that adds Smalltalk-style message passing (messaging) to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTSTEP operating system. Due to Apple macOS’s direct ... | Objective-C | Wikipedia | 366 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Cox began writing a pre-processor for C to add some of the abilities of Smalltalk. He soon had a working implementation of an object-oriented extension to the C language, which he named Object-Oriented Pre-Compiler (OOPC).
Love was hired by Schlumberger Research in 1982 and had the opportunity to acquire the first comm... | Objective-C | Wikipedia | 452 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
The work to extend GNU Compiler Collection (GCC) was led by Steve Naroff, who joined NeXT from StepStone. The compiler changes were made available as per GNU General Public License (GPL) terms, but the runtime libraries were not, rendering the open source contribution unusable to the general public. This led to other p... | Objective-C | Wikipedia | 439 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Messages
The Objective-C model of object-oriented programming is based on message passing to object instances. In Objective-C, one does not call a method; one sends a message. This is unlike the Simula-style programming model used by C++. The difference between these two concepts is in how the code referenced by the me... | Objective-C | Wikipedia | 502 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Interfaces and implementations
Objective-C requires that the interface and implementation of a class be in separately declared code blocks. By convention, developers place the interface in a header file and the implementation in a code file. The header files, normally suffixed .h, are similar to C header files while th... | Objective-C | Wikipedia | 512 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Note that demonstrates the interleaving of selector segments with argument expressions, for which there is no direct equivalent in C/C++.
Return types can be any standard C type, a pointer to a generic Objective-C object, a pointer to a specific type of object such as NSArray *, NSImage *, or NSString *, or a pointer... | Objective-C | Wikipedia | 431 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Internal representations of a method vary between different implementations of Objective-C. If myColor is of the class , instance method might be internally labeled . The is to refer to an instance method, with the class and then method names appended and colons changed to underscores. As the order of parameters is p... | Objective-C | Wikipedia | 508 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
The init message performs the set-up of the instance upon creation. The init method is often written as follows:
- (id)init {
self = [super init];
if (self) {
// perform initialization of object here
}
return self;
}
In the above example, notice the return type. This type stands for pointer t... | Objective-C | Wikipedia | 405 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
An informal protocol is a list of methods that a class can opt to implement. It is specified in the documentation, since it has no presence in the language. Informal protocols are implemented as a category (see below) on NSObject and often include optional methods, which, if implemented, can change the behavior of a cl... | Objective-C | Wikipedia | 397 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Dynamic typing
Objective-C, like Smalltalk, can use dynamic typing: an object can be sent a message that is not specified in its interface. This can allow for increased flexibility, as it allows an object to "capture" a message and send the message to a different object that can respond to the message appropriately, or... | Objective-C | Wikipedia | 472 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
Forwarding
Objective-C permits the sending of a message to an object that may not respond. Rather than responding or simply dropping the message, an object can forward the message to an object that can respond. Forwarding can be used to simplify implementation of certain design patterns, such as the observer pattern or... | Objective-C | Wikipedia | 423 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
@implementation Forwarder
- (retval_t)forward:(SEL)sel args:(arglist_t)args {
/*
* Check whether the recipient actually responds to the message.
* This may or may not be desirable, for example, if a recipient
* in turn does not respond to the message, it might do forwarding
* itself.
*/
if ([recipient res... | Objective-C | Wikipedia | 385 | 39809523 | https://en.wikipedia.org/wiki/Objective-C | Technology | Programming languages | null |
In theoretical physics, the problem of time is a conceptual conflict between quantum mechanics and general relativity. Quantum mechanics regards the flow of time as universal and absolute, whereas general relativity regards the flow of time as malleable and relative. This problem raises the question of what time reall... | Problem of time | Wikipedia | 449 | 42598658 | https://en.wikipedia.org/wiki/Problem%20of%20time | Physical sciences | Quantum mechanics | Physics |
where the operator varies throughout space, but the wavefunction here, called the wavefunction of the universe, is constant. Consequently this cosmic universal wavefunction is frozen and does not evolve. Somehow, at a smaller scale, the laws of physics, including a concept of time, apply within the universe while the ... | Problem of time | Wikipedia | 291 | 42598658 | https://en.wikipedia.org/wiki/Problem%20of%20time | Physical sciences | Quantum mechanics | Physics |
Consistent discretizations approach developed by Jorge Pullin and Rodolfo Gambini have no constraints. These are lattice approximation techniques for quantum gravity. In the canonical approach, if one discretizes the constraints and equations of motion, the resulting discrete equations are inconsistent: they cannot be ... | Problem of time | Wikipedia | 475 | 42598658 | https://en.wikipedia.org/wiki/Problem%20of%20time | Physical sciences | Quantum mechanics | Physics |
Avshalom Elitzur and Shahar Dolev argue that quantum-mechanical experiments such as the "quantum liar" provide evidence of inconsistent histories, and that spacetime itself may therefore be subject to change affecting entire histories. Elitzur and Dolev also believe that an objective passage of time and relativity can ... | Problem of time | Wikipedia | 403 | 42598658 | https://en.wikipedia.org/wiki/Problem%20of%20time | Physical sciences | Quantum mechanics | Physics |
Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish. Consistent with this definition, there are ... | Pregnancy in fish | Wikipedia | 399 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Five modes of reproduction can be differentiated in fish based on relations between the zygote(s) and parents:
Ovuliparity: Fertilization of eggs is external; zygotes develop externally.
Oviparity: Fertilization of eggs is internal; zygotes develop externally as eggs with large vitellus.
Ovoviviparity: Fertilization... | Pregnancy in fish | Wikipedia | 372 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Viviparous fish
Viviparous fish include the families Goodeidae, Anablepidae, Jenynsiidae, Poeciliidae, Embiotocidae and some sharks (some species of the requiem sharks, Carcharinidae and the hammerheads, Sphyrnidae, among others). The halfbeaks, Hemiramphidae, are found in both marine and freshwaters and those species ... | Pregnancy in fish | Wikipedia | 491 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
"Matrotrophy" (mother feeding) occurs when the embryo exhausts its yolk supply early in gestation and the mother provides additional nutrition. Post-fertilization transfer of nutrients has been reported in several species within the genera Gambusia and Poecilia, specifically, G. affinis, G. clarkhubbsi, G. holbrooki, G... | Pregnancy in fish | Wikipedia | 486 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Poeciliopsis
Members of the genus Poeciliopsis (amongst others) show variable reproductive life history adaptations. P. monacha can be considered to be lecithotrophic because the female does not really provide any resources for her offspring after fertilization. P. lucida shows an intermediate level of matrotrophy, mea... | Pregnancy in fish | Wikipedia | 440 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Elasmobranchs
The majority of elasmobranchs are viviparous and show a wide range of strategies to provide their offspring with nourishment and respiratory requirements. Some sharks simply retain their young in the dilated posterior segment of the oviduct. In its simplest form, the uterus does not provide any additional... | Pregnancy in fish | Wikipedia | 431 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
When a female's eggs reach maturity, she squirts them from a chamber in her trunk via her ovipositor into his brood pouch or egg pouch, sometimes called a "marsupium". During a mammalian pregnancy, the placenta allows the female to nourish her progeny in the womb, and remove their waste products. If male pipefish and s... | Pregnancy in fish | Wikipedia | 374 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Pipefish brood their offspring either on distinct region of its body or in a brood pouch. Brood pouches vary significantly among different species of pipefish, but all contain a small opening through which the female's eggs can be deposited. The location of the brood pouch can be along the entire underside of the pipef... | Pregnancy in fish | Wikipedia | 170 | 44046994 | https://en.wikipedia.org/wiki/Pregnancy%20in%20fish | Biology and health sciences | Animal reproduction | Biology |
Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, polonium, and livermorium). Water, the first chemical compound in this series, contains one oxygen atom and two hydrogen atoms, and is ... | Hydrogen chalcogenide | Wikipedia | 487 | 48894713 | https://en.wikipedia.org/wiki/Hydrogen%20chalcogenide | Physical sciences | Hydrogen compounds | Chemistry |
The other hydrogen chalcogenides are highly toxic, malodorous gases. Hydrogen sulfide occurs commonly in nature and its properties compared with water reveal a lack of any significant hydrogen bonding. Since they are both gases at STP, hydrogen can be simply burned in the presence of oxygen to form water in a highly ex... | Hydrogen chalcogenide | Wikipedia | 399 | 48894713 | https://en.wikipedia.org/wiki/Hydrogen%20chalcogenide | Physical sciences | Hydrogen compounds | Chemistry |
The most important of these is hydrogen peroxide, H2O2, a pale blue, nearly colourless liquid that has a lower volatility than water and a higher density and viscosity. It is important chemically as it can be either oxidised or reduced in solutions of any pH, can readily form peroxometal complexes and peroxoacid comple... | Hydrogen chalcogenide | Wikipedia | 419 | 48894713 | https://en.wikipedia.org/wiki/Hydrogen%20chalcogenide | Physical sciences | Hydrogen compounds | Chemistry |
Beyond and , many higher polysulfanes (n = 3–8) are known as stable compounds. They feature unbranched sulfur chains, reflecting sulfur's tendency for catenation. Starting with , all known polysulfanes are liquids at room temperature. is colourless while the other polysulfanes are yellow; the colour becomes richer a... | Hydrogen chalcogenide | Wikipedia | 414 | 48894713 | https://en.wikipedia.org/wiki/Hydrogen%20chalcogenide | Physical sciences | Hydrogen compounds | Chemistry |
One or both of the protium atoms in water can be substituted with the isotope deuterium, yielding respectively semiheavy water and heavy water, the latter being one of the most famous deuterium compounds. Due to the high difference in density between deuterium and regular protium, heavy water exhibits many anomalous pr... | Hydrogen chalcogenide | Wikipedia | 340 | 48894713 | https://en.wikipedia.org/wiki/Hydrogen%20chalcogenide | Physical sciences | Hydrogen compounds | Chemistry |
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! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
|- style="vertical-align:top"
! style="text-align:left" | Evolutionary stage
| Main sequence
|- style="vertical-align:top"
! style="text-align:left" | Spectral type
| M8V
|- style="vertical-align:top"
! style="text-align:left" | Ap... | TRAPPIST-1 | Wikipedia | 450 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Observations in 2016 from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at La Silla Observatory in Chile and other telescopes led to the discovery of two terrestrial planets in orbit around TRAPPIST-1. In 2017, further analysis of the original observations identified five more terrestrial planets.... | TRAPPIST-1 | Wikipedia | 385 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Its planetary system was discovered by a team led by Michaël Gillon, a Belgian astronomer at the University of Liege, in 2016 during observations made at the La Silla Observatory, Chile, using the TRAPPIST telescope. The discovery was based on anomalies in the light curves measured by the telescope in 2015. These were ... | TRAPPIST-1 | Wikipedia | 493 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
There is no evidence that it has a stellar cycle. Its luminosity, emitted mostly as infrared radiation, is about 0.055% that of the Sun. Low-precision measurements from the XMM-Newton satellite and other facilities show that the star emits faint radiation at short wavelengths such as x-rays and UV radiation. There are ... | TRAPPIST-1 | Wikipedia | 489 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
TRAPPIST-1 is orbited by seven planets, designated TRAPPIST-1b, 1c, 1d, 1e, 1f, 1g and 1h in alphabetic order going out from the star. These planets have orbital periods ranging from 1.5 to 19 days, at distances of 0.011–0.059 astronomical units (1.7–8.9 million km).
All the planets are much closer to their star than ... | TRAPPIST-1 | Wikipedia | 363 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
The TRAPPIST-1 planets are expected to have compositions that resemble each other as well as that of Earth. The estimated densities of the planets are lower than Earth's which may imply that they have large amounts of volatile chemicals. Alternatively, their cores may be smaller than that of Earth and therefore they ma... | TRAPPIST-1 | Wikipedia | 452 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
The closeness of the planets to TRAPPIST-1 results in tidal interactions stronger than those on Earth.
All the planets have reached an equilibrium with slow planetary rotations and tidal locking, which can lead to the synchronisation of a planet's rotation to its revolution around its star. However, the mutual interact... | TRAPPIST-1 | Wikipedia | 509 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Because most of TRAPPIST-1's radiation is in the infrared region, there may be very little visible light on the planets' surfaces; Amaury Triaud, one of the system's co-discoverers, said the skies would never be brighter than Earth's sky at sunset and only a little brighter than a night with a full moon. Ignoring atmos... | TRAPPIST-1 | Wikipedia | 302 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
For a dim star like TRAPPIST-1, the habitable zone is located closer to the star than for the Sun. Three or four planets might be located in the habitable zone; these include , and ; or , and . , this is the largest-known number of planets within the habitable zone of any known star or star system. The presence of li... | TRAPPIST-1 | Wikipedia | 433 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Moons
No moons with a size comparable to Earth's have been detected in the TRAPPIST-1 system, and they are unlikely in such a densely packed planetary system. This is because moons would likely be either destroyed by their planet's gravity after entering its Roche limit or stripped from the planet by leaving its Hill ... | TRAPPIST-1 | Wikipedia | 288 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Formation history
The TRAPPIST-1 planets most likely formed further from the star and migrated inwards, although it is possible they formed in their current locations. According to the most popular theory on the formation of the TRAPPIST-1 planets (Ormel et al. (2017)), the planets formed when a streaming instability ... | TRAPPIST-1 | Wikipedia | 499 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Due to a combination of high insolation, the greenhouse effect of water vapour atmospheres and remnant heat from the process of planet assembly, the TRAPPIST-1 planets would likely have initially had molten surfaces. Eventually the surfaces would cool until the magma oceans solidified, which in the case of TRAPPIST-1b ... | TRAPPIST-1 | Wikipedia | 370 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
TRAPPIST-1c has a semi-major axis of and orbits its star every 2.42 Earth days. It is close enough to TRAPPIST-1 to be tidally locked. JWST observations have ruled out the existence of Venus-like atmospheres, or CO2-rich atmospheres without a temperature inversion. Airlessness is possible, but only if the surface is s... | TRAPPIST-1 | Wikipedia | 466 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
TRAPPIST-1e has a semi-major axis of and orbits its star every 6.10 Earth days. It has density similar that of Earth. Based on several climate models, the planet is the most likely of the system to have retained its water, and the most likely to have liquid water for many climate states. A dedicated climate model proj... | TRAPPIST-1 | Wikipedia | 491 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
TRAPPIST-1h has a semi-major axis of ; it is the system's least-massive-known planet and orbits its star every 18.9 Earth days. It is likely too distant from its host star to sustain liquid water and may be a snowball planet, or have a methane/nitrogen atmosphere resembling that of Titan. It might host a subsurface oce... | TRAPPIST-1 | Wikipedia | 452 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
If the planets are tidally locked to TRAPPIST-1, surfaces that permanently face away from the star can cool sufficiently for any atmosphere to freeze out on the night side. This frozen-out atmosphere could be recycled through glacier-like flows to the day side with assistance from tidal or geothermal heating from below... | TRAPPIST-1 | Wikipedia | 143 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Numerical modelling and observations constrain the properties of hypothetical atmospheres around TRAPPIST-1 planets:
Theoretical calculations and observations have ruled out the possibility the TRAPPIST-1 planets have hydrogen-rich or helium-rich atmospheres. Hydrogen-rich exospheres may be detectable but have not bee... | TRAPPIST-1 | Wikipedia | 499 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
Theoretical modelling by Krissansen-Totton and Fortney (2022) suggests the inner planets most likely have oxygen-and-CO2-rich atmospheres, if any. If the planets have an atmosphere, the amount of precipitation, its form and location would be determined by the presence and position of mountains and oceans, and the rotat... | TRAPPIST-1 | Wikipedia | 372 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
TRAPPIST-1 has moderate to high stellar activity, and this may be another difficulty for the persistence of atmospheres and water on the planets:
Dwarfs of the spectral class M have intense flares; TRAPPIST-1 averages one flare every two days and about four to six superflares per year. Such flares would have only smal... | TRAPPIST-1 | Wikipedia | 453 | 50402274 | https://en.wikipedia.org/wiki/TRAPPIST-1 | Physical sciences | Notable stars | Astronomy |
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