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An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, moons, comets and galaxies – in either observational (by analyzing the data) or theoretical astronomy. Examples of topics or fi... | Astronomer | Wikipedia | 492 | 580 | https://en.wikipedia.org/wiki/Astronomer | Physical sciences | Astronomy basics | Astronomy |
Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device (CCD) camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photog... | Astronomer | Wikipedia | 468 | 580 | https://en.wikipedia.org/wiki/Astronomer | Physical sciences | Astronomy basics | Astronomy |
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. ASCII has just 128 code points, of which only 95 are , which severely limit its scope. Th... | ASCII | Wikipedia | 504 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Despite being an American standard, ASCII does not have a code point for the cent (¢). It also does not support English terms with diacritical marks such as résumé and jalapeño, or proper nouns with diacritical marks such as Beyoncé (although on certain devices characters could be combined with punctuation such as Tild... | ASCII | Wikipedia | 474 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
ASA X3.4-1963
ASA X3.4-1965 (approved, but not published, nevertheless used by IBM 2260 & 2265 Display Stations and IBM 2848 Display Control)
USAS X3.4-1967
USAS X3.4-1968
ANSI X3.4-1977
ANSI X3.4-1986
ANSI X3.4-1986 (R1992)
ANSI X3.4-1986 (R1997)
ANSI INCITS 4-1986 (R2002)
ANSI INCITS 4-1986 (R2007)
INCITS 4... | ASCII | Wikipedia | 422 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
The committee debated the possibility of a shift function (like in ITA2), which would allow more than 64 codes to be represented by a six-bit code. In a shifted code, some character codes determine choices between options for the following character codes. It allows compact encoding, but is less reliable for data trans... | ASCII | Wikipedia | 491 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Many of the non-alphanumeric characters were positioned to correspond to their shifted position on typewriters; an important subtlety is that these were based on mechanical typewriters, not electric typewriters. Mechanical typewriters followed the de facto standard set by the Remington No. 2 (1878), the first typewrite... | ASCII | Wikipedia | 445 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Some then-common typewriter characters were not included, notably ½ ¼ ¢, while ^ ` ~ were included as diacritics for international use, and < > for mathematical use, together with the simple line characters \ | (in addition to common /). The @ symbol was not used in continental Europe and the committee expected it wou... | ASCII | Wikipedia | 424 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
For example, character 0x0A represents the "line feed" function (which causes a printer to advance its paper), and character 8 represents "backspace". refers to control characters that do not include carriage return, line feed or white space as non-whitespace control characters. Except for the control characters that ... | ASCII | Wikipedia | 418 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
When a Teletype 33 ASR equipped with the automatic paper tape reader received a control-S (XOFF, an abbreviation for transmit off), it caused the tape reader to stop; receiving control-Q (XON, transmit on) caused the tape reader to resume. This so-called flow control technique became adopted by several early computer ... | ASCII | Wikipedia | 398 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
The early Unix tty drivers, unlike some modern implementations, allowed only one character to be set to erase the previous character in canonical input processing (where a very simple line editor is available); this could be set to BS or DEL, but not both, resulting in recurring situations of ambiguity where users had ... | ASCII | Wikipedia | 425 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
End of line
The inherent ambiguity of many control characters, combined with their historical usage, created problems when transferring "plain text" files between systems. The best example of this is the newline problem on various operating systems. Teletype machines required that a line of text be terminated with both... | ASCII | Wikipedia | 371 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Requiring two characters to mark the end of a line introduces unnecessary complexity and ambiguity as to how to interpret each character when encountered by itself. To simplify matters, plain text data streams, including files, on Multics used line feed (LF) alone as a line terminator. The tty driver would handle the L... | ASCII | Wikipedia | 440 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
End of file/stream
The PDP-6 monitor, and its PDP-10 successor TOPS-10, used control-Z (SUB) as an end-of-file indication for input from a terminal. Some operating systems such as CP/M tracked file length only in units of disk blocks, and used control-Z to mark the end of the actual text in the file. For these reasons... | ASCII | Wikipedia | 502 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Earlier versions of ASCII used the up arrow instead of the caret (5Ehex) and the left arrow instead of the underscore (5Fhex).
Usage
ASCII was first used commercially during 1963 as a seven-bit teleprinter code for American Telephone & Telegraph's TWX (TeletypeWriter eXchange) network. TWX originally used the earlier ... | ASCII | Wikipedia | 479 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
Other international standards bodies have ratified character encodings such as ISO 646 (1967) that are identical or nearly identical to ASCII, with extensions for characters outside the English alphabet and symbols used outside the United States, such as the symbol for the United Kingdom's pound sterling (£); e.g. with... | ASCII | Wikipedia | 155 | 586 | https://en.wikipedia.org/wiki/ASCII | Technology | Software development: General | null |
In mathematics and statistics, the arithmetic mean ( ), arithmetic average, or just the mean or average (when the context is clear) is the sum of a collection of numbers divided by the count of numbers in the collection. The collection is often a set of results from an experiment, an observational study, or a survey. T... | Arithmetic mean | Wikipedia | 487 | 612 | https://en.wikipedia.org/wiki/Arithmetic%20mean | Mathematics | Statistics | null |
History
The statistician Churchill Eisenhart, senior researcher fellow at the U. S. National Bureau of Standards, traced the history of the arithmetic mean in detail. In the modern age it started to be used as a way of combining various observations that should be identical, but were not such as estimates of the direct... | Arithmetic mean | Wikipedia | 457 | 612 | https://en.wikipedia.org/wiki/Arithmetic%20mean | Mathematics | Statistics | null |
The arithmetic mean may be contrasted with the median. The median is defined such that no more than half the values are larger, and no more than half are smaller than it. If elements in the data increase arithmetically when placed in some order, then the median and arithmetic average are equal. For example, consider th... | Arithmetic mean | Wikipedia | 352 | 612 | https://en.wikipedia.org/wiki/Arithmetic%20mean | Mathematics | Statistics | null |
If a numerical property, and any sample of data from it, can take on any value from a continuous range instead of, for example, just integers, then the probability of a number falling into some range of possible values can be described by integrating a continuous probability distribution across this range, even when th... | Arithmetic mean | Wikipedia | 509 | 612 | https://en.wikipedia.org/wiki/Arithmetic%20mean | Mathematics | Statistics | null |
In some document formats (such as PDF), the symbol may be replaced by a "¢" (cent) symbol when copied to a text processor such as Microsoft Word. | Arithmetic mean | Wikipedia | 35 | 612 | https://en.wikipedia.org/wiki/Arithmetic%20mean | Mathematics | Statistics | null |
Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals). All extant (living) amphibians... | Amphibian | Wikipedia | 339 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The earliest amphibians evolved in the Devonian period from tetrapodomorph sarcopterygians (lobe-finned fish with articulated limb-like fins) that evolved primitive lungs, which were helpful in adapting to dry land. They diversified and became ecologically dominant during the Carboniferous and Permian periods, but were... | Amphibian | Wikipedia | 433 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Subclass Lepospondyli† (A potentially polyphyletic Late Paleozoic group of small forms, likely more closely related to amniotes than Lissamphibia)
Subclass Temnospondyli† (diverse Late Paleozoic and early Mesozoic grade, some of which were large predators)
Subclass Lissamphibia (all modern amphibians, including frogs... | Amphibian | Wikipedia | 485 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based c... | Amphibian | Wikipedia | 509 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside... | Amphibian | Wikipedia | 306 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Many examples of species showing transitional features have been discovered. Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved ada... | Amphibian | Wikipedia | 234 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves ... | Amphibian | Wikipedia | 510 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three group... | Amphibian | Wikipedia | 474 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Characteristics
The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Lacking these membranes, amphibians re... | Amphibian | Wikipedia | 375 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. It has an average length of and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the Chinese giant salamander (Andr... | Amphibian | Wikipedia | 463 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are co... | Amphibian | Wikipedia | 431 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scale-free skins, either smooth o... | Amphibian | Wikipedia | 509 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca... | Amphibian | Wikipedia | 285 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians. These are long, cylindrical, limbless animals with a snake- or worm-like form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caeci... | Amphibian | Wikipedia | 485 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Amphibian skin is permeable to water. Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for their thin and delicate skin, amphibians have evolved mucous glands, pr... | Amphibian | Wikipedia | 506 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. T... | Amphibian | Wikipedia | 498 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the hear... | Amphibian | Wikipedia | 282 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Many aquatic salamanders and some caecilians possess electroreceptors called ampullary organs (completely absent in anurans), that allow them to locate objects around them when submerged in water. The ea... | Amphibian | Wikipedia | 502 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs... | Amphibian | Wikipedia | 415 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping. Most amphibians, however, are able to exchange gases with the wa... | Amphibian | Wikipedia | 468 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid... | Amphibian | Wikipedia | 421 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the egg... | Amphibian | Wikipedia | 451 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow f... | Amphibian | Wikipedia | 383 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In the egg, the embryo is suspended in perivitelline fluid and surrounded by semi-permeable gelatinous capsules, with the yolk mass providing nutrients. As the larvae hatch, the capsules are dissolved by enzymes secreted from gland at the tip of the snout. The eggs of some salamanders and frogs contain unicellular gree... | Amphibian | Wikipedia | 318 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing withi... | Amphibian | Wikipedia | 297 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Frogs
Unlike in other amphibians, frog tadpoles do not resemble adults. The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as Nannophrys ceylonensis) are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at fir... | Amphibian | Wikipedia | 371 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation. Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they atta... | Amphibian | Wikipedia | 339 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in ... | Amphibian | Wikipedia | 379 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do t... | Amphibian | Wikipedia | 442 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In the majority of species of caecilians, the young are produced by viviparity. Typhlonectes compressicauda, a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time. They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. At f... | Amphibian | Wikipedia | 508 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander (Desmognathus welteri) does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsul... | Amphibian | Wikipedia | 141 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad (... | Amphibian | Wikipedia | 385 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Genetics and genomics
Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ≈8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of dipl... | Amphibian | Wikipedia | 436 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response. Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caec... | Amphibian | Wikipedia | 473 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps betwee... | Amphibian | Wikipedia | 280 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air f... | Amphibian | Wikipedia | 386 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders (Plethodon cinereus) has been much studied. 91% of marked indivi... | Amphibian | Wikipedia | 447 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery... | Amphibian | Wikipedia | 439 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander (Salamandra salamandra) being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time ... | Amphibian | Wikipedia | 468 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Cognition
In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. Amphibians are widely considered to be sentient, able to feel emotions such as anxiety and fear.
In one experiment, when offered live fruit flies (Drosophila ... | Amphibian | Wikipedia | 487 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putt... | Amphibian | Wikipedia | 440 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Conservation and protection strategies
The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been work... | Amphibian | Wikipedia | 172 | 621 | https://en.wikipedia.org/wiki/Amphibian | Biology and health sciences | Biology | null |
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic eukaryotes, which include species from multiple distinct clades. Such organisms range from unicellular microalgae such as Chlorella, Prototheca and the diatoms, to multicellular macroalgae such as the giant kelp,... | Algae | Wikipedia | 344 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Algae lack the various structures that characterize plants (which evolved from freshwater green algae), such as the phyllids (leaf-like structures) and rhizoids of bryophytes (non-vascular plants), and the roots, leaves and other xylemic/phloemic organs found in tracheophytes (vascular plants). Most algae are autotroph... | Algae | Wikipedia | 500 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
The Ancient Greek word for 'seaweed' was (), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, , meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical (), 'paint' (if not that word i... | Algae | Wikipedia | 479 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves.
W. H. Harvey (1811–1866) and... | Algae | Wikipedia | 346 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g.,... | Algae | Wikipedia | 282 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis, while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red a... | Algae | Wikipedia | 494 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Recent genomic and phylogenomic approaches have significantly clarified plastid genome evolution, the horizontal movement of endosymbiont genes to the "host" nuclear genome, and plastid spread throughout the eukaryotic tree of life.
Relationship to land plants
Fossils of isolated spores suggest land plants may have be... | Algae | Wikipedia | 484 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage th... | Algae | Wikipedia | 508 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure". The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature, they do not occu... | Algae | Wikipedia | 505 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species.
Life cycle
Rhodophyta, Chlorophyta, a... | Algae | Wikipedia | 450 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Regional and group estimates have been made, as well:
5,000–5,500 species of red algae worldwide
"some 1,300 in Australian Seas"
400 seaweed species for the western coastline of South Africa, and 212 species from the coast of KwaZulu-Natal. Some of these are duplicates, as the range extends across both coasts, and t... | Algae | Wikipedia | 488 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies."
Ecology... | Algae | Wikipedia | 453 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Cultural associations
In classical Chinese, the word is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao (藻鑒堂島), which thus simultaneously means "Island of the Algae-... | Algae | Wikipedia | 477 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Algae are used as foods in many countries: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori; Ireland, dulse; Chile, cochayuyo. Laver is used to make laverbread in Wales, where it is known as . In Korea, green laver is used t... | Algae | Wikipedia | 389 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting wh... | Algae | Wikipedia | 433 | 633 | https://en.wikipedia.org/wiki/Algae | Biology and health sciences | Biology | null |
Analysis of variance (ANOVA) is a collection of statistical models and their associated estimation procedures (such as the "variation" among and between groups) used to analyze the differences between groups. It uses F-test by comparing variance between groups and taking noise, or assumed normal distribution of group, ... | Analysis of variance | Wikipedia | 401 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Ronald Fisher introduced the term variance and proposed its formal analysis in a 1918 article on theoretical population genetics, The Correlation Between Relatives on the Supposition of Mendelian Inheritance. His first application of the analysis of variance to data analysis was published in 1921, Studies in Crop Varia... | Analysis of variance | Wikipedia | 163 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Example
The analysis of variance can be used to describe otherwise complex relations among variables. A dog show provides an example. A dog show is not a random sampling of the breed: it is typically limited to dogs that are adult, pure-bred, and exemplary. A histogram of dog weights from a show is likely to be rather ... | Analysis of variance | Wikipedia | 507 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
An attempt to explain weight by breed is likely to produce a very good fit. All Chihuahuas are light and all St Bernards are heavy. The difference in weights between Setters and Pointers does not justify separate breeds. The analysis of variance provides the formal tools to justify these intuitive judgments. A common u... | Analysis of variance | Wikipedia | 471 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Textbook analysis using a normal distribution
The analysis of variance can be presented in terms of a linear model, which makes the following assumptions about the probability distribution of the responses:
Independence of observations – this is an assumption of the model that simplifies the statistical analysis.
Nor... | Analysis of variance | Wikipedia | 465 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Derived linear model
Kempthorne uses the randomization-distribution and the assumption of unit treatment additivity to produce a derived linear model, very similar to the textbook model discussed previously. The test statistics of this derived linear model are closely approximated by the test statistics of an appropria... | Analysis of variance | Wikipedia | 478 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Problems which do not satisfy the assumptions of ANOVA can often be transformed to satisfy the assumptions.
The property of unit-treatment additivity is not invariant under a "change of scale", so statisticians often use transformations to achieve unit-treatment additivity. If the response variable is expected to foll... | Analysis of variance | Wikipedia | 378 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
ANOVA uses traditional standardized terminology. The definitional equation of sample variance is , where the divisor is called the degrees of freedom (DF), the summation is called
the sum of squares (SS), the result is called the mean square (MS) and the squared terms are deviations from the sample mean. ANOVA estimat... | Analysis of variance | Wikipedia | 439 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
There are two methods of concluding the ANOVA hypothesis test, both of which produce the same result:
The textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and t... | Analysis of variance | Wikipedia | 456 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
The simplest experiment suitable for ANOVA analysis is the completely randomized experiment with a single factor. More complex experiments with a single factor involve constraints on randomization and include completely randomized blocks and Latin squares (and variants: Graeco-Latin squares, etc.). The more complex exp... | Analysis of variance | Wikipedia | 380 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
The use of ANOVA to study the effects of multiple factors has a complication. In a 3-way ANOVA with factors x, y and z, the ANOVA model includes terms for the main effects (x, y, z) and terms for interactions (xy, xz, yz, xyz).
All terms require hypothesis tests. The proliferation of interaction terms increases the ri... | Analysis of variance | Wikipedia | 488 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Reporting sample size analysis is generally required in psychology. "Provide information on sample size and the process that led to sample size decisions." The analysis, which is written in the experimental protocol before the experiment is conducted, is examined in grant applications and administrative review boards.
... | Analysis of variance | Wikipedia | 469 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
The follow-up tests may be "simple" pairwise comparisons of individual group means or may be "compound" comparisons (e.g., comparing the mean pooling across groups A, B and C to the mean of group D). Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable i... | Analysis of variance | Wikipedia | 248 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Some popular designs use the following types of ANOVA:
One-way ANOVA is used to test for differences among two or more independent groups (means), e.g. different levels of urea application in a crop, or different levels of antibiotic action on several different bacterial species, or different levels of effect of some m... | Analysis of variance | Wikipedia | 501 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
Generalizations
ANOVA is considered to be a special case of linear regression which in turn is a special case of the general linear model. All consider the observations to be the sum of a model (fit) and a residual (error) to be minimized.
The Kruskal-Wallis test and the Friedman test are nonparametric tests which do ... | Analysis of variance | Wikipedia | 409 | 634 | https://en.wikipedia.org/wiki/Analysis%20of%20variance | Mathematics | Statistics | null |
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single. Alkanes have the general chemical form... | Alkane | Wikipedia | 466 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
Methane is produced by methanogenic bacteria and some long-chain alkanes function as pheromones in certain animal species or as protective waxes in plants and fungi. Nevertheless, most alkanes do not have much biological activity. They can be viewed as molecular trees upon which can be hung the more active/reactive fu... | Alkane | Wikipedia | 218 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
Alkanes with more than three carbon atoms can be arranged in various ways, forming structural isomers. The simplest isomer of an alkane is the one in which the carbon atoms are arranged in a single chain with no branches. This isomer is sometimes called the n-isomer (n for "normal", although it is not necessarily the m... | Alkane | Wikipedia | 508 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
C12: 355 isomers
C32: 27,711,253,769 isomers
C60: 22,158,734,535,770,411,074,184 isomers, many of which are not stable | Alkane | Wikipedia | 50 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
Branched alkanes can be chiral. For example, 3-methylhexane and its higher homologues are chiral due to their stereogenic center at carbon atom number 3. The above list only includes differences of connectivity, not stereochemistry. In addition to the alkane isomers, the chain of carbon atoms may form one or more rings... | Alkane | Wikipedia | 403 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
Straight-chain alkanes are sometimes indicated by the prefix "n-" or "n-"(for "normal") where a non-linear isomer exists. Although this is not strictly necessary and is not part of the IUPAC naming system, the usage is still common in cases where one wishes to emphasize or distinguish between the straight-chain and bra... | Alkane | Wikipedia | 448 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
The key steps in the naming of more complicated branched alkanes are as follows:
Identify the longest continuous chain of carbon atoms
Name this longest root chain using standard naming rules
Name each side chain by changing the suffix of the name of the alkane from "-ane" to "-yl"
Number the longest continuous cha... | Alkane | Wikipedia | 470 | 639 | https://en.wikipedia.org/wiki/Alkane | Physical sciences | Hydrocarbons | null |
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