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Tetrapod
Tetrapods (/ˈtɛtrəˌpɒdz/; from grc τετρα- (tetra-) 'four', and πούς (poús) 'foot') are four-limbed vertebrate animals constituting the superclass Tetrapoda (/tɛˈtrɒpədə/). It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including mammals). Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned (sarcopterygian) fish around 390 million years ago in the middle Devonian period; their forms were transitional between lobe-finned fishes and the four-limbed tetrapods. Limbed vertebrates (tetrapods in the broad sense of the word) are first known from Middle Devonian trackways, and body fossils became common near the end of the Late Devonian but these were all aquatic. The first crown-tetrapods (last common ancestors of extant tetrapods capable of terrestrial locomotion) appeared by the very early Carboniferous, 350 million years ago. The specific aquatic ancestors of the tetrapods and the process by which they colonized Earth's land after emerging from water remains unclear. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors. These include the structure of the head for feeding and breathing, limb girdles and digits for locomotion, eyes for seeing, ears for hearing, and the heart and lungs for gas circulation and exchange outside water. The first tetrapods (stem) or "fishapods" were primarily aquatic. Modern amphibians, which evolved from earlier groups, are generally semiaquatic; the first stage of their lives is as fish-like tadpoles, and later stages are partly terrestrial and partly aquatic. However, most tetrapod species today are amniotes, most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous. The key innovation in amniotes over amphibians is the amnion, which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water. (Some amniotes later evolved internal fertilization, although many aquatic species outside the tetrapod tree had evolved such before the tetrapods appeared, e.g. Materpiscis.) Some tetrapods, such as snakes and caecilians, have lost some or all of their limbs through further speciation and evolution; some have only concealed vestigial bones as a remnant of the limbs of their distant ancestors. Others returned to being amphibious or otherwise living partially or fully aquatic lives, the first during the Carboniferous period, others as recently as the Cenozoic. One group of amniotes diverged into the reptiles, which includes lepidosaurs, dinosaurs (which includes birds), crocodilians, turtles, and extinct relatives; while another group of amniotes diverged into the mammals and their extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, pterosaurs from the archosaurs, and bats from among the mammals.
  • 7.8K
  • 04 Nov 2022
Topic Review
Wearable Devices for Stroke Prediction
Stroke ranks as one of the top first leading causes of death and disability worldwide, particularly for the most populous countries in Asia, Europe, and North America. The emerging wearable devices intended to monitor the physiological parameters, and the growth of machine learning applied to predict diseases, are promising solutions to prevent stroke and eventually predict stroke risk.
  • 7.8K
  • 30 Sep 2021
Topic Review
List of Island Countries
This is a list of island countries. An island is a landmass (smaller than a continent) that is surrounded by water. Many island countries are spread over an archipelago, as is the case with the Federated States of Micronesia and Indonesia (both of which consist of thousands of islands). Others consist of a single island, such as Barbados or Nauru, or part of an island, such as the Dominican Republic or Brunei. Australia is a continent, although it has historically been referred to as an island, due to it having no land borders. The list also includes states with limited diplomatic recognition which have de facto control over territories entirely on the islands, such as Taiwan.[n 1] Indonesia is the world's largest island country by area (1,904,569 km2), and by total number of islands (more than 18,307), and is also the world's most populous island country, with a population of over 270 million (the fourth-largest population in the world, after China , India , and the United States ).
  • 7.8K
  • 14 Oct 2022
Topic Review
Social Integration
Social integration is the process during which newcomers or minorities are incorporated into the social structure of the host society. Social integration, together with economic integration and identity integration, are three main dimensions of a newcomers' experiences in the society that is receiving them. A higher extent of social integration contributes to a closer social distance between groups and more consistent values and practices. Bringing together various ethnic groups irrespective of language, caste, creed, etc., without losing one's identity. It gives access to all areas of community life and eliminates segregation. In a broader view, social integration is a dynamic and structured process in which all members participate in dialogue to achieve and maintain peaceful social relations. Social integration does not mean forced assimilation. Social integration is focused on the need to move toward a safe, stable and just society by mending conditions of social conflict, social disintegration, social exclusion, social fragmentation, exclusion and polarization, and by expanding and strengthening conditions of social integration towards peaceful social relations of coexistence, collaboration and cohesion.
  • 7.8K
  • 08 Nov 2022
Topic Review
History of Wind Power
Wind power has been used as long as humans have put sails into the wind. For more than two millennia wind-powered machines have ground grain and pumped water. Wind power was widely available and not confined to the banks of fast-flowing streams, or later, requiring sources of fuel. Wind-powered pumps drained the polders of the Netherlands, and in arid regions such as the American mid-west or the Australian outback, wind pumps provided water for livestock and steam engines. With the development of electric power, wind power found new applications in lighting buildings remote from centrally-generated power. Throughout the 20th century parallel paths developed small wind plants suitable for farms or residences, and larger utility-scale wind generators that could be connected to electricity grids for remote use of power. Today wind-powered generators operate in every size range between tiny plants for battery charging at isolated residences, up to near-gigawatt sized offshore wind farms that provide electricity to national electrical networks. By 2014, over 240,000 commercial-sized wind turbines were operating in the world, producing 4% of the world's electricity.
  • 7.8K
  • 02 Oct 2022
Topic Review
Neutral Country
A neutral country is a state that is neutral towards belligerents in a specific war or holds itself as permanently neutral in all future conflicts (including avoiding entering into military alliances such as NATO or CSTO). As a type of non-combatant status, nationals of neutral countries enjoy protection under the law of war from belligerent actions to a greater extent than other non-combatants such as enemy civilians and prisoners of war. Different countries interpret their neutrality differently: some, such as Costa Rica, have demilitarized, while Switzerland holds to "armed neutrality", to deter aggression with a sizeable military, while barring itself from foreign deployment. Not all neutral countries avoid any foreign deployment or alliances, as Austria, Ireland, Finland and Sweden have active UN peacekeeping forces and a political alliance within the European Union. Sweden's traditional policy is not to participate in military alliances, with the intention of staying neutral in the case of war. Immediately before World War II, the Nordic countries stated their neutrality, but Sweden changed its position to that of non-belligerent at the start of the Winter War. There have been considerable changes to the interpretation of neutral conduct over the past centuries. During the Cold War, Yugoslavia claimed military and ideological neutrality, and that is continued by its successor, Serbia.
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  • 01 Dec 2022
Topic Review
Armor-Piercing Shell
An armor-piercing shell, armour-piercing shell in Commonwealth English, AP for short, is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships and cause damage to the lightly-armored interior. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions. AP rounds smaller than 20 mm are typically known as "armor-piercing ammunition", and are intended for lightly-armored targets such as body armor, bulletproof glass and light armored vehicles. The AP shell is now seldom used in naval warfare, as modern warships have little or no armor protection. In the anti-tank role, as tank armor improved during World War II newer designs began to use a smaller but dense penetrating body within a larger shell. These lightweight shells were fired at very high muzzle velocity and retained that speed and the associated penetrating power over longer distances. An armor-piercing shell must withstand the shock of punching through armor plating. Shells designed for this purpose have a greatly strengthened body with a specially hardened and shaped nose. One common addition to later shells is the use of a softer ring or cap of metal on the nose known as a penetrating cap. This lowers the initial shock of impact to prevent the rigid shell from shattering, as well as aiding the contact between the target armor and the nose of the penetrator to prevent the shell from bouncing off in glancing shots. Ideally, these caps have a blunt profile, which led to the use of a further thin aerodynamic cap to improve long-range ballistics. AP shells may contain a small explosive charge known as a "bursting charge". Some smaller-caliber AP shells have an inert filling or an incendiary charge in place of the bursting charge. Designs using newer technologies no longer look like the classic artillery shell and have displaced it. Instead the penetrator is a long rod of dense material like tungsten or depleted uranium (DU) that further improves the terminal ballistics. Whether these modern designs are considered to be AP rounds depends on the definition. Accordingly reference sources vary in whether they include or exclude them.
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  • 02 Nov 2022
Topic Review
Clouding of Consciousness
Clouding of consciousness (also known as brain fog or mental fog) is when a person is slightly less wakeful or aware than normal. They are not as aware of time or their surroundings and find it difficult to pay attention. People describe this subjective sensation as their mind being "foggy".
  • 7.7K
  • 21 Nov 2022
Topic Review
Protection Motivation Theory
Protection motivation theory (PMT) was originally created to help understand individual human responses to fear appeals. Protection motivation theory proposes that people protect themselves based on two factors: threat appraisal and coping appraisal. Threat appraisal assesses the severity of the situation and examines how serious the situation is, while coping appraisal is how one responds to the situation. Threat appraisal consists of the perceived severity of a threatening event and the perceived probability of the occurrence, or vulnerability. Coping appraisal consists of perceived response efficacy, or an individual's expectation that carrying out the recommended action will remove the threat, and perceived self efficacy, or the belief in one's ability to execute the recommended courses of action successfully. PMT is one model that explains why people engage in unhealthy practices and offers suggestions for changing those behaviors. It is educational and motivational. Primary prevention: taking measures to combat the risk of developing a health problem. (e.g., controlling weight to prevent high blood pressure). Secondary prevention: taking steps to prevent a condition from becoming worse. (e.g., remembering to take daily medication to control blood pressure). Another psychological model that describes self-preservation and processing of fear is terror management theory.
  • 7.7K
  • 09 Oct 2022
Topic Review
Lignosulfonates
Lignosulfonates are biobased surfactants and specialty chemicals, which are usually produced as a byproduct during sulfite pulping of wood. They are the technical lignin that is, by far, the most commercially traded and are hence vital for replacing non‑renewable and fossil‑based chemicals. Due to their prominent use as plasticizers, dispersants, and stabilizers, the physicochemical properties of lignosulfonates play a key role in determining their end‑use and performance. Their chemical composition and structure are inherently linked to the characteristic behavior of lignosulfonates. This entry hence outlines the fundamental chemistry of lignosulfonates, while discussing the following physicochemical properties: · Solubility in different solvents · Conformation and shape in aqueous solution · Self-association and agglomeration in aqueous solution · Precipitation · Adsorption at surfaces and interfaces
  • 7.7K
  • 05 Jan 2021
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