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American West
Irrigated land in the United States increased from 300,000 acres in 1880 to 4.1 million in 1890 to 7.3 million in 1900. Two thirds of this irrigation sources from groundwater or small ponds and reservoirs, while the other one third comes from large dams. One of the main attractions of irrigation in the West was its increased dependability compared to rainfall-watered agriculture in the East. Proponents argued that farmers with a dependable water supply could more easily get loans from bankers interested in this more predictable farming model. Most irrigation in the Great Plains region derived from underground aquifers. Euro-American farmers who colonized the region in the 19th century tried to grow the commodity crops that they were used to, like wheat, corn, and alfalfa, but rainfall stifled their growing capacity. Between the late 1800s and the 1930s, farmers used wind-powered pumps to draw groundwater. These windpumps had limited power, but the development of gas-powered pumps in the mid-1930s pushed wells deep into the Ogallala Aquifer. Farmers irrigated fields by laying pipes across the field with sprinklers at intervals, a labor-intensive process, until the advent of the center-pivot sprinkler after WWII, which made irrigation significantly easier. By the 1970s farmers drained the aquifer ten times faster than it could recharge, and by 1993 they had removed half of the accessible water.
Large-scale federal funding and intervention pushed through the majority of irrigation projects in the West, especially in California, Colorado, Arizona, and Nevada. At first, plans to increase irrigated farmland, largely by giving land to farmers and asking them to find water, failed across the board. Congress passed the Desert Land Act in 1877 and the Carey Act in 1894, which only marginally increased irrigation. Only in 1902 did Congress pass the National Reclamation Act, which channeled money from the sale of western public lands, in parcels up to 160 acres large, into irrigation projects on public or private land in the arid West. The Congressmen who passed the law and their wealthy supporters supported Western irrigation because it would increase American exports, ‘reclaim’ the West, and push the Eastern poor out West for a better life. | Irrigation | Wikipedia | 455 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null |
While the National Reclamation Act was the most successful piece of federal irrigation legislation, the implementation of the act did not go as planned. The Reclamation Service chose to push most of the Act's money toward construction rather than settlement, so the Service overwhelmingly prioritized building large dams like the Hoover Dam. Over the 20th century, Congress and state governments grew more frustrated with the Reclamation Service and the irrigation schemes. Frederick Newell, head of the Reclamation Service, proving uncompromising and challenging to work with, falling crop prices, resistance to delay debt payments, and refusal to begin new projects until the completion of old ones all contributed. The Reclamation Extension Act of 1914, transferring a significant amount of irrigation decision-making power regarding irrigation projects from the Reclamation Service to Congress, was in many ways a result of increasing political unpopularity of the Reclamation Service.
In the lower Colorado Basin of Arizona, Colorado, and Nevada, the states derive irrigation water largely from rivers, especially the Colorado River, which irrigates more than 4.5 million acres of land, with a less significant amount coming from groundwater. In the 1952 case Arizona v. California, Arizona sued California for increased access to the Colorado River, under the grounds that their groundwater supply could not sustain their almost entirely irrigation-based agricultural economy, which they won. California, which began irrigating in earnest in the 1870s in San Joaquin Valley, had passed the Wright Act of 1887 permitting agricultural communities to construct and operate needed irrigation works. The Colorado River also irrigates large fields in California's Imperial Valley, fed by the National Reclamation Act-built All-American Canal.
Soviet Central Asia
When the Bolsheviks conquered Central Asia in 1917, the native Kazakhs, Uzbeks, and Turkmens used minimal irrigation. The Slavic immigrants pushed into the area by the Tsarist government brought their irrigation methods, including waterwheels, the use of rice paddies to restore salted land, and underground irrigation channels. Russians dismissed these techniques as crude and inefficient. Despite this, tsarist officials maintained these systems through the late 19th century without other solutions. | Irrigation | Wikipedia | 426 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null |
Before conquering the area, the Russian government accepted a 1911 American proposal to send hydraulic experts to Central Asia to investigate the potential for large-scale irrigation. A 1918 decree by Lenin then encouraged irrigation development in the region, which began in the 1930s. When it did, Stalin and other Soviet leaders prioritized large-scale, ambitious hydraulic projects, especially along the Volga River. The Soviet irrigation push stemmed mainly from their late 19th century fears of the American cotton monopoly and subsequent desire to achieve cotton self-sufficiency. They had built up their textile manufacturing industry in the 19th century, requiring increased cotton and irrigation, as the region did not receive enough rainfall to support cotton farming.
The Russians built dams on the Don and Kuban Rivers for irrigation, removing freshwater flow from the Sea of Azov and making it much saltier. Depletion and salinization scourged other areas of the Russian irrigation project. In the 1950s, Soviet officials began also diverting the Syr Darya and the Amu Darya, which fed the Aral Sea. Before diversion, the rivers delivered of water to the Aral Sea per year, but after, they only delivered . Because of its reduced inflow, the Aral Sea covered less than half of its original seabed, which made the regional climate more extreme and created airborne salinization, lowering nearby crop yields.
By 1975, the USSR used eight times as much water as they had in 1913, mostly for irrigation. Russia's expansion of irrigation began to decrease in the late 1980s, and irrigated hectares in Central Asia capped out at 7 million. Mikhail Gorbachev killed a proposed plan to reverse the Ob and Yenisei for irrigation in 1986, and the breakup of the USSR in 1991 ended Russian investment in Central Asian cotton irrigation.
Africa
Different irrigation schemes with various goals and success rates have been implemented across Africa in the 20th century but have all been influenced by colonial forces. The Tana River Irrigation Scheme in eastern Kenya, completed between 1948 and 1963, opened up new lands for agriculture. The Kenyan government attempted to resettle the area with detainees from the Mau Mau uprising. Italian oil drillers discovered Libya's underground water resources during the Italian colonization of Libya. This water lay dormant until 1969, when Muammar al-Gaddafi and American Armand Hammer built the Great Man-Made River to deliver the Saharan water to the coast. The water largely contributed to irrigation but cost four to ten times more than the crops it produced were worth. | Irrigation | Wikipedia | 507 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null |
In 1912, the Union of South Africa created an irrigation department and began investing in water storage infrastructure and irrigation. The government used irrigation and dam-building to further social goals like poverty relief by creating construction jobs for poor whites and by creating irrigation schemes to increase white farming. One of their first significant irrigation projects was the Hartbeespoort Dam, begun in 1916 to elevate the living conditions of the ‘poor whites’ in the region and eventually completed as a ‘whites only’ employment opportunity. The Pretoria irrigation scheme, Kammanassie project, and Buchuberg irrigation scheme on the Orange River all followed in the same vein in the 1920s and 30s.
In Egypt, modern irrigation began with Muhammad Ali Pasha in the mid-1800s, who sought to achieve Egyptian independence from the Ottomans through increased trade with Europe—specifically cotton exportation. His administration proposed replacing the traditional Nile basin irrigation, which took advantage of the annual ebb and flow of the Nile, with irrigation barrages in the lower Nile, which better suited cotton production. Egypt devoted 105,000 ha to cotton in 1861, which increased fivefold by 1865. Most of their exports were shipped to England, and the United-States-Civil-War-induced cotton scarcity in the 1860s cemented Egypt as England's cotton producer. As the Egyptian economy became more dependent on cotton in the 20th century, controlling even small Nile floods became more important. Cotton production was more at risk of destruction than more common crops like barley or wheat. After the British occupation of Egypt in 1882, the British intensified the conversion to perennial irrigation with the construction of the Delta Barrage, the Assiut Barrage, and the first Aswan Dam. Perennial irrigation decreased local control over water and made traditional subsistence farming or the farming of other crops incredibly difficult, eventually contributing to widespread peasant bankruptcy and the 1879-1882 ‘Urabi revolt.
Examples by country
Gallery | Irrigation | Wikipedia | 383 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null |
Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of October 2016, with approximately 250 new species described each year.
Etymology
The word is derived from the Greek words ἰχθύς, ikhthus, meaning "fish"; and λογία, logia, meaning "to study".
History
The study of fish dates from the Upper Paleolithic Revolution (with the advent of "high culture"). The science of ichthyology was developed in several interconnecting epochs, each with various significant advancements.
The study of fish receives its origins from humans' desire to feed, clothe, and equip themselves with useful implements. According to Michael Barton, a prominent ichthyologist and professor at Centre College, "the earliest ichthyologists were hunters and gatherers who had learned how to obtain the most useful fish, where to obtain them in abundance, and at what times they might be the most available". Early cultures manifested these insights in abstract and identifiable artistic expressions.
1500 BC–40 AD
Informal, scientific descriptions of fish are represented within the Judeo-Christian tradition. The Old Testament laws of kashrut forbade the consumption of fish without scales or appendages. Theologians and ichthyologists believe that the apostle Peter and his contemporaries harvested the fish that are today sold in modern industry along the Sea of Galilee, presently known as Lake Kinneret. These fish include cyprinids of the genera Barbus and Mirogrex, cichlids of the genus Sarotherodon, and Mugil cephalus of the family Mugilidae.
335 BC–80 AD | Ichthyology | Wikipedia | 385 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology |
Aristotle incorporated ichthyology into formal scientific study. Between 333 and 322 BC, he provided the earliest taxonomic classification of fish, accurately describing 117 species of Mediterranean fish. Furthermore, Aristotle documented anatomical and behavioral differences between fish and marine mammals. After his death, some of his pupils continued his ichthyological research. Theophrastus, for example, composed a treatise on amphibious fish. The Romans, although less devoted to science, wrote extensively about fish. Pliny the Elder, a notable Roman naturalist, compiled the ichthyological works of indigenous Greeks, including verifiable and ambiguous peculiarities such as the sawfish and mermaid, respectively. Pliny's documentation was the last significant contribution to ichthyology until the European Renaissance.
European Renaissance
The writings of three 16th-century scholars, Hippolito Salviani, Pierre Belon, and Guillaume Rondelet, signify the conception of modern ichthyology. The investigations of these individuals were based upon actual research in comparison to ancient recitations. This property popularized and emphasized these discoveries. Despite their prominence, Rondelet's De Piscibus Marinis is regarded as the most influential, identifying 244 species of fish.
16th–17th century
The incremental alterations in navigation and shipbuilding throughout the Renaissance marked the commencement of a new epoch in ichthyology. The Renaissance culminated with the era of exploration and colonization, and upon the cosmopolitan interest in navigation came the specialization in naturalism. Georg Marcgrave of Saxony composed the Naturalis Brasilae in 1648. This document contained a description of 100 species of fish indigenous to the Brazilian coastline. In 1686, John Ray and Francis Willughby collaboratively published Historia Piscium, a scientific manuscript containing 420 species of fish, 178 of these newly discovered. The fish contained within this informative literature were arranged in a provisional system of classification. | Ichthyology | Wikipedia | 376 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology |
The classification used within the Historia Piscium was further developed by Carl Linnaeus, the "father of modern taxonomy". His taxonomic approach became the systematic approach to the study of organisms, including fish. Linnaeus was a professor at the University of Uppsala and an eminent botanist; however, one of his colleagues, Peter Artedi, earned the title "father of ichthyology" through his indispensable advancements. Artedi contributed to Linnaeus's refinement of the principles of taxonomy. Furthermore, he recognized five additional orders of fish: Malacopterygii, Acanthopterygii, Branchiostegi, Chondropterygii, and Plagiuri. Artedi developed standard methods for making counts and measurements of anatomical features that are modernly exploited. Another associate of Linnaeus, Albertus Seba, was a prosperous pharmacist from Amsterdam. Seba assembled a cabinet, or collection, of fish. He invited Artedi to use this assortment of fish; in 1735, Artedi fell into an Amsterdam canal and drowned at the age of 30.
Linnaeus posthumously published Artedi's manuscripts as Ichthyologia, sive Opera Omnia de Piscibus (1738). His refinement of taxonomy culminated in the development of the binomial nomenclature, which is in use by contemporary ichthyologists. Furthermore, he revised the orders introduced by Artedi, placing significance on pelvic fins. Fish lacking this appendage were placed within the order Apodes; fish having abdominal, thoracic, or jugular pelvic fins were termed Abdominales, Thoracici, and Jugulares, respectively. However, these alterations were not grounded within evolutionary theory. Therefore, over a century was needed for Charles Darwin to provide the intellectual foundation needed to perceive that the degree of similarity in taxonomic features was a consequence of phylogenetic relationships.
Modern era | Ichthyology | Wikipedia | 386 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology |
Close to the dawn of the 19th century, Marcus Elieser Bloch of Berlin and Georges Cuvier of Paris made attempts to consolidate the knowledge of ichthyology. Cuvier summarized all of the available information in his monumental Histoire Naturelle des Poissons. This manuscript was published between 1828 and 1849 in a 22-volume series. This document describes 4,514 species of fish, 2,311 of these new to science. It remains one of the most ambitious treatises of the modern world. Scientific exploration of the Americas advanced knowledge of the remarkable diversity of fish. Charles Alexandre Lesueur was a student of Cuvier. He made a cabinet of fish dwelling within the Great Lakes and Saint Lawrence River regions.
Adventurous individuals such as John James Audubon and Constantine Samuel Rafinesque figure in the faunal documentation of North America. They often traveled with one another. Rafinesque wrote Ichthyologic Ohiensis in 1820. In addition, Louis Agassiz of Switzerland established his reputation through the study of freshwater fish and the first comprehensive treatment of palaeoichthyology, Poisson Fossil's. In the 1840s, Agassiz moved to the United States, where he taught at Harvard University until his death in 1873.
Albert Günther published his Catalogue of the Fish of the British Museum between 1859 and 1870, describing over 6,800 species and mentioning another 1,700. Generally considered one of the most influential ichthyologists, David Starr Jordan wrote 650 articles and books on the subject and served as president of Indiana University and Stanford University.
Modern publications
Organizations
Notable ichthyologists
Members of this list meet one or more of the following criteria: 1) Author of 50 or more fish taxon names, 2) Author of major reference work in ichthyology, 3) Founder of major journal or museum, 4) Person most notable for other reasons who has also worked in ichthyology. | Ichthyology | Wikipedia | 384 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology |
Alexander Emanuel Agassiz
Louis Agassiz
Emperor Akihito of Japan
Gerald R. Allen
Peter Artedi
Herbert R. Axelrod
William O. Ayres, California
Spencer Fullerton Baird
Tarleton Hoffman Bean
Lev Berg, Russia
Henry Bryant Bigelow
Pieter Bleeker, East Indies
Marcus Elieser Bloch
George Albert Boulenger
Jean Cadenat
Pierre Carbonnier
Eugenie Clark
Leonard Compagno
Edward Drinker Cope
Georges Cuvier
Francis Day, India
Francis Buchanan-Hamilton, Scottish
Carl H. Eigenmann
Rosa Smith Eigenmann
William N. Eschmeyer
Barton Warren Evermann
Henry Weed Fowler
Joseph Paul Gaimard
Samuel Garman
Charles Henry Gilbert
Theodore Nicholas Gill
Charles Frédéric Girard
George Brown Goode
Albert Günther
Albert William Herre
Carl L. Hubbs
David Starr Jordan
Maurice Kottelat, Swiss
Bernard Germain de Lacépède
Carl Linnaeus
Seth Eugene Meek
George S. Myers
Joseph S. Nelson, Fishes of the World
John Treadwell Nichols, China, founder of Copeia
John Roxborough Norman
Peter Simon Pallas
Wilhelm Peters
Felipe Poey
Jean René Constant Quoy
Constantine Samuel Rafinesque
John Ernest Randall
Charles Tate Regan
John Richardson
Raúl Adolfo Ringuelet
Eduard Rüppell
Johann Gottlob Schneider
H.M. Smith
J.L.B. Smith
Edwin Chapin Starks
Franz Steindachner
Royal D. Suttkus
Frank Talbot
Shigeho Tanaka
Ethelwynn Trewavas, English
Achille Valenciennes
Johann Julius Walbaum
Gilbert Percy Whitley
Francis Willughby
Stan Wood
William Yarrell
Paleoichthyologists
Hans C. Bjerring
Erik Jarvik
Erik Stensiö
Non-academic ichthyologists
Sakana-kun | Ichthyology | Wikipedia | 341 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology |
An electrical cable is an assembly of one or more wires running side by side or bundled, which is used as an electrical conductor to carry electric current.
Electrical cables are used to connect two or more devices, enabling the transfer of electrical signals, power, or both from one device to the other. Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective covering.
One or more electrical cables and their corresponding connectors may be formed into a cable assembly, which is not necessarily suitable for connecting two devices but can be a partial product (e.g. to be soldered onto a printed circuit board with a connector mounted to the housing). Cable assemblies can also take the form of a cable tree or cable harness, used to connect many terminals together.
Uses
Electrical cables are used to connect two or more devices, enabling the transfer of electrical signals or power from one device to the other. Long-distance communication takes place over undersea communication cables. Power cables are used for bulk transmission of alternating and direct current power, especially using high-voltage cable. Electrical cables are extensively used in building wiring for lighting, power and control circuits permanently installed in buildings. Since all the circuit conductors required can be installed in a cable at one time, installation labor is saved compared to certain other wiring methods.
Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective coverings. Electrical cables may be made more flexible by stranding the wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. Copper wires in a cable may be bare, or they may be plated with a thin layer of another metal, most often tin but sometimes gold, silver or some other material. Tin, gold, and silver are much less prone to oxidation than copper, which may lengthen wire life, and makes soldering easier. Tinning is also used to provide lubrication between strands. Tinning was used to help removal of rubber insulation. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords). | Electrical cable | Wikipedia | 477 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null |
In the 19th century and early 20th century, electrical cable was often insulated using cloth, rubber or paper. Plastic materials are generally used today, except for high-reliability power cables. The first thermoplastic used was gutta-percha (a natural latex) which was found useful for underwater cables in the 19th century. The first, and still very common, man-made plastic used for cable insulation was polyethylene. This was invented in 1930, but not available outside military use until after World War 2 during which a telegraph cable using it was laid across the English Channel to support troops following D-Day.
Cables can be securely fastened and organized, such as by using trunking, cable trays, cable ties or cable lacing. Continuous-flex or flexible cables used in moving applications within cable carriers can be secured using strain relief devices or cable ties.
Characteristics
Any current-carrying conductor, including a cable, radiates an electromagnetic field. Likewise, any conductor or cable will pick up energy from any existing electromagnetic field around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction.
The first solution to these problems is to keep cable lengths in buildings short since pick up and transmission are essentially proportional to the length of the cable. The second solution is to route cables away from trouble. Beyond this, there are particular cable designs that minimize electromagnetic pickup and transmission. Three of the principal design techniques are shielding, coaxial geometry, and twisted-pair geometry. | Electrical cable | Wikipedia | 377 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null |
Shielding makes use of the electrical principle of the Faraday cage. The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electrical fields, particularly if the shield is connected to a point of constant voltage, such as earth or ground. Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.
Coaxial design helps to further reduce low-frequency magnetic transmission and pickup. In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center. This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel each other.
A twisted pair has two wires of a cable twisted around each other. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line. Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.
Fire protection
Electrical cable jacket material is usually constructed of flexible plastic which will burn. The fire hazard of grouped cables can be significant. Cables jacketing materials can be formulated to prevent fire spread . Alternately, fire spread amongst combustible cables can be prevented by the application of fire retardant coatings directly on the cable exterior, or the fire threat can be isolated by the installation of boxes constructed of noncombustible materials around the bulk cable installation.
Types | Electrical cable | Wikipedia | 375 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null |
Coaxial cable – used for radio frequency signals, for example in cable television distribution systems.
Direct-buried cable
Flexible cables
Filled cable
Heliax cable
Non-metallic sheathed cable (or nonmetallic building wire, NM, NM-B)
Armored cable (or BX)
Multicore cable (consist of more than one wire and is covered by cable jacket)
Paired cable – Composed of two individually insulated conductors that are usually used in DC or low-frequency AC applications
Portable cord – Flexible cable for AC power in portable applications
Power cable – A cable used for transmission of power
Ribbon cable – Useful when many wires are required. This type of cable can easily flex, and it is designed to handle low-level voltages.
Shielded cable – Used for sensitive electronic circuits or to provide protection in high-voltage applications.
Single cable (from time to time this name is used for wire)
Structured cabling
Submersible cable
Twin and earth
Twinax cable
Twin-lead – This type of cable is a flat two-wire line. It is commonly called a 300 Ω line because the line has an impedance of 300 Ω. It is often used as a transmission line between an antenna and a receiver (e.g., TV and radio). These cables are stranded to lower skin effects.
Twisted pair – Consists of two interwound insulated wires. It resembles a paired cable, except that the paired wires are twisted
CENELEC HD 361 is a ratified standard published by CENELEC, which relates to wire and cable marking type, whose goal is to harmonize cables. Deutsches Institut für Normung (DIN, VDE) has released a similar standard (DIN VDE 0292). | Electrical cable | Wikipedia | 348 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null |
The dalton or unified atomic mass unit (symbols: Da or u, respectively) is a unit of mass defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. It is a non-SI unit accepted for use with SI. The atomic mass constant, denoted mu, is defined identically, giving .
This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles, both for discrete instances and multiple types of ensemble averages. For example, an atom of helium-4 has a mass of . This is an intrinsic property of the isotope and all helium-4 atoms have the same mass. Acetylsalicylic acid (aspirin), , has an average mass of about . However, there are no acetylsalicylic acid molecules with this mass. The two most common masses of individual acetylsalicylic acid molecules are , having the most common isotopes, and , in which one carbon is carbon-13.
The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the unit kilodalton (kDa) and megadalton (MDa). Titin, one of the largest known proteins, has a molecular mass of between 3 and 3.7 megadaltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about , or total.
The mole is a unit of amount of substance used in chemistry and physics, such that the mass of one mole of a substance expressed in grams is numerically equal to the average mass of one of its particles expressed in daltons. That is, the molar mass of a chemical compound expressed in g/mol or kg/kmol is numerically equal to its average molecular mass expressed in Da. For example, the average mass of one molecule of water is about 18.0153 Da, and the mass of one mole of water is about 18.0153 g. A protein whose molecule has an average mass of would have a molar mass of . However, while this equality can be assumed for practical purposes, it is only approximate, because of the 2019 redefinition of the mole. | Dalton (unit) | Wikipedia | 473 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
In general, the mass in daltons of an atom is numerically close but not exactly equal to the number of nucleons in its nucleus. It follows that the molar mass of a compound (grams per mole) is numerically close to the average number of nucleons contained in each molecule. By definition, the mass of an atom of carbon-12 is 12 daltons, which corresponds with the number of nucleons that it has (6 protons and 6 neutrons). However, the mass of an atomic-scale object is affected by the binding energy of the nucleons in its atomic nuclei, as well as the mass and binding energy of its electrons. Therefore, this equality holds only for the carbon-12 atom in the stated conditions, and will vary for other substances. For example, the mass of an unbound atom of the common hydrogen isotope (hydrogen-1, protium) is ,
the mass of a proton is the mass of a free neutron is and the mass of a hydrogen-2 (deuterium) atom is . In general, the difference (absolute mass excess) is less than 0.1%; exceptions include hydrogen-1 (about 0.8%), helium-3 (0.5%), lithium-6 (0.25%) and beryllium (0.14%).
The dalton differs from the unit of mass in the system of atomic units, which is the electron rest mass (m).
Energy equivalents
The atomic mass constant can also be expressed as its energy-equivalent, mc. The CODATA recommended values are:
The mass-equivalent is commonly used in place of a unit of mass in particle physics, and these values are also important for the practical determination of relative atomic masses.
History
Origin of the concept
The interpretation of the law of definite proportions in terms of the atomic theory of matter implied that the masses of atoms of various elements had definite ratios that depended on the elements. While the actual masses were unknown, the relative masses could be deduced from that law. In 1803 John Dalton proposed to use the (still unknown) atomic mass of the lightest atom, hydrogen, as the natural unit of atomic mass. This was the basis of the atomic weight scale. | Dalton (unit) | Wikipedia | 459 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
For technical reasons, in 1898, chemist Wilhelm Ostwald and others proposed to redefine the unit of atomic mass as the mass of an oxygen atom. That proposal was formally adopted by the International Committee on Atomic Weights (ICAW) in 1903. That was approximately the mass of one hydrogen atom, but oxygen was more amenable to experimental determination. This suggestion was made before the discovery of isotopes in 1912. Physicist Jean Perrin had adopted the same definition in 1909 during his experiments to determine the atomic masses and the Avogadro constant. This definition remained unchanged until 1961. Perrin also defined the "mole" as an amount of a compound that contained as many molecules as 32 grams of oxygen (). He called that number the Avogadro number in honor of physicist Amedeo Avogadro.
Isotopic variation
The discovery of isotopes of oxygen in 1929 required a more precise definition of the unit. Two distinct definitions came into use. Chemists choose to define the AMU as of the average mass of an oxygen atom as found in nature; that is, the average of the masses of the known isotopes, weighted by their natural abundance. Physicists, on the other hand, defined it as of the mass of an atom of the isotope oxygen-16 (16O).
Definition by IUPAC
The existence of two distinct units with the same name was confusing, and the difference (about in relative terms) was large enough to affect high-precision measurements. Moreover, it was discovered that the isotopes of oxygen had different natural abundances in water and in air. For these and other reasons, in 1961 the International Union of Pure and Applied Chemistry (IUPAC), which had absorbed the ICAW, adopted a new definition of the atomic mass unit for use in both physics and chemistry; namely, of the mass of a carbon-12 atom. This new value was intermediate between the two earlier definitions, but closer to the one used by chemists (who would be affected the most by the change).
The new unit was named the "unified atomic mass unit" and given a new symbol "u", to replace the old "amu" that had been used for the oxygen-based unit. However, the old symbol "amu" has sometimes been used, after 1961, to refer to the new unit, particularly in lay and preparatory contexts. | Dalton (unit) | Wikipedia | 482 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
With this new definition, the standard atomic weight of carbon is about , and that of oxygen is about . These values, generally used in chemistry, are based on averages of many samples from Earth's crust, its atmosphere, and organic materials.
Adoption by BIPM
The IUPAC 1961 definition of the unified atomic mass unit, with that name and symbol "u", was adopted by the International Bureau for Weights and Measures (BIPM) in 1971 as a non-SI unit accepted for use with the SI.
Unit name
In 1993, the IUPAC proposed the shorter name "dalton" (with symbol "Da") for the unified atomic mass unit. As with other unit names such as watt and newton, "dalton" is not capitalized in English, but its symbol, "Da", is capitalized. The name was endorsed by the International Union of Pure and Applied Physics (IUPAP) in 2005.
In 2003 the name was recommended to the BIPM by the Consultative Committee for Units, part of the CIPM, as it "is shorter and works better with [SI] prefixes". In 2006, the BIPM included the dalton in its 8th edition of the SI brochure of formal definitions as a non-SI unit accepted for use with the SI. The name was also listed as an alternative to "unified atomic mass unit" by the International Organization for Standardization in 2009. It is now recommended by several scientific publishers, and some of them consider "atomic mass unit" and "amu" deprecated. In 2019, the BIPM retained the dalton in its 9th edition of the SI brochure, while dropping the unified atomic mass unit from its table of non-SI units accepted for use with the SI, but secondarily notes that the dalton (Da) and the unified atomic mass unit (u) are alternative names (and symbols) for the same unit. | Dalton (unit) | Wikipedia | 388 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
2019 revision of the SI
The definition of the dalton was not affected by the 2019 revision of the SI, that is, 1 Da in the SI is still of the mass of a carbon-12 atom, a quantity that must be determined experimentally in terms of SI units. However, the definition of a mole was changed to be the amount of substance consisting of exactly entities and the definition of the kilogram was changed as well. As a consequence, the molar mass constant remains close to but no longer exactly 1 g/mol, meaning that the mass in grams of one mole of any substance remains nearly but no longer exactly numerically equal to its average molecular mass in daltons, although the relative standard uncertainty of at the time of the redefinition is insignificant for all practical purposes.
Measurement
Though relative atomic masses are defined for neutral atoms, they are measured (by mass spectrometry) for ions: hence, the measured values must be corrected for the mass of the electrons that were removed to form the ions, and also for the mass equivalent of the electron binding energy, E/mc. The total binding energy of the six electrons in a carbon-12 atom is = : Eb/muc2 = , or about one part in 10 million of the mass of the atom.
Before the 2019 revision of the SI, experiments were aimed to determine the value of the Avogadro constant for finding the value of the unified atomic mass unit.
Josef Loschmidt
A reasonably accurate value of the atomic mass unit was first obtained indirectly by Josef Loschmidt in 1865, by estimating the number of particles in a given volume of gas.
Jean Perrin
Perrin estimated the Avogadro number by a variety of methods, at the turn of the 20th century. He was awarded the 1926 Nobel Prize in Physics, largely for this work.
Coulometry
The electric charge per mole of elementary charges is a constant called the Faraday constant, F, whose value had been essentially known since 1834 when Michael Faraday published his works on electrolysis. In 1910, Robert Millikan obtained the first measurement of the charge on an electron, −e. The quotient F/e provided an estimate of the Avogadro constant. | Dalton (unit) | Wikipedia | 452 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
The classic experiment is that of Bower and Davis at NIST, and relies on dissolving silver metal away from the anode of an electrolysis cell, while passing a constant electric current I for a known time t. If m is the mass of silver lost from the anode and A the atomic weight of silver, then the Faraday constant is given by:
The NIST scientists devised a method to compensate for silver lost from the anode by mechanical causes, and conducted an isotope analysis of the silver used to determine its atomic weight. Their value for the conventional Faraday constant was F = , which corresponds to a value for the Avogadro constant of : both values have a relative standard uncertainty of .
Electron mass measurement
In practice, the atomic mass constant is determined from the electron rest mass m and the electron relative atomic mass A(e) (that is, the mass of electron divided by the atomic mass constant). The relative atomic mass of the electron can be measured in cyclotron experiments, while the rest mass of the electron can be derived from other physical constants.
where c is the speed of light, h is the Planck constant, α is the fine-structure constant, and R is the Rydberg constant.
As may be observed from the old values (2014 CODATA) in the table below, the main limiting factor in the precision of the Avogadro constant was the uncertainty in the value of the Planck constant, as all the other constants that contribute to the calculation were known more precisely.
The power of having defined values of universal constants as is presently the case can be understood from the table below (2018 CODATA).
X-ray crystal density methods
Silicon single crystals may be produced today in commercial facilities with extremely high purity and with few lattice defects. This method defined the Avogadro constant as the ratio of the molar volume, V, to the atomic volume V:
where and n is the number of atoms per unit cell of volume Vcell.
The unit cell of silicon has a cubic packing arrangement of 8 atoms, and the unit cell volume may be measured by determining a single unit cell parameter, the length a of one of the sides of the cube. The CODATA value of a for silicon is
In practice, measurements are carried out on a distance known as d(Si), which is the distance between the planes denoted by the Miller indices {220}, and is equal to . | Dalton (unit) | Wikipedia | 493 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
The isotope proportional composition of the sample used must be measured and taken into account. Silicon occurs in three stable isotopes (Si, Si, Si), and the natural variation in their proportions is greater than other uncertainties in the measurements. The atomic weight A for the sample crystal can be calculated, as the standard atomic weights of the three nuclides are known with great accuracy. This, together with the measured density ρ of the sample, allows the molar volume V to be determined:
where M is the molar mass constant. The CODATA value for the molar volume of silicon is , with a relative standard uncertainty of | Dalton (unit) | Wikipedia | 127 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null |
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end is attached to the substrate by means of a disc-like holdfast called a pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.
Classes
In the class Anthozoa, comprising the sea anemones and corals, the individual is always a polyp; in the class Hydrozoa, however, the individual may be either a polyp or a medusa, with most species undergoing a life cycle with both a polyp stage and a medusa stage.
In the class Scyphozoa, the medusa stage is dominant, and the polyp stage may or may not be present, depending on the family. In those scyphozoans that have the larval planula metamorphose into a polyp, the polyp, also called a "scyphistoma," grows until it develops a stack of plate-like medusae that pinch off and swim away in a process known as strobilation. Once strobilation is complete, the polyp may die, or regenerate itself to repeat the process again later. With cubozoans, the planula settles onto a suitable surface, and develops into a polyp. The cubozoan polyp then eventually metamorphoses directly into a medusa.
Anatomy
The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of cells. The outer layer is known technically as the ectoderm, with the inner layer as the endoderm (or gastroderm). Between ectoderm and endoderm is a supporting layer of structureless gelatinous substance termed mesoglea, secreted by the cell layers of the body wall. The mesoglea can be thinner than the endoderm or ectoderm or comprise the bulk of the body as in larger jellyfish. The mesoglea can contain skeletal elements derived from cells migrated from ectoderm. | Polyp (zoology) | Wikipedia | 500 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals |
The sac-like body built up in this way is attached usually to some firm object by its blind end, and bears at the upper end the mouth which is surrounded by a circle of tentacles which resemble glove fingers. The tentacles are organs which serve both for the tactile sense and for the capture of food. Polyps extend their tentacles, particularly at night, containing coiled stinging nettle-like cells, or nematocysts, which pierce, poison, and firmly hold living prey paralysing or killing them. Polyp prey includes copepods and fish larvae. Longitudinal muscular fibrils formed from the cells of the ectoderm allow tentacles to contract when conveying the food to the mouth. Similarly, circularly disposed muscular fibrils formed from the endoderm permit tentacles to be protract or thrust out once they are contracted. These muscle fibres belong to the same two systems, allowing the whole body to retract or protrude outwards.
We can distinguish therefore in the body of a polyp the column, circular or oval in section, forming the trunk, resting on a base or foot and surmounted by the crown of tentacles, which enclose an area termed the peristome, in the centre of which again is the mouth. Generally, there is no other opening to the body except the mouth, but in some cases excretory pores are known to occur in the foot, and pores may occur at the tips of the tentacles. A polyp is an animal of very simple structure, a living fossil that has not changed significantly for about half a billion years (per generally accepted dating of Cambrian sedimentary rock).
The external form of the polyp varies greatly in different cases. The column may be long and slender, or may be so short in the vertical direction that the body becomes disk-like. The tentacles may number many hundreds or may be very few, in rare cases only one or two. They may be long and filamentous, or short and reduced to mere knobs or warts. They may be simple and unbranched, or they may be feathery in pattern. The mouth may be level with the surface of the peristome, or may be projecting and trumpet-shaped. As regards internal structure, polyps exhibit two well-marked types of organization, each characteristic of one of the two classes, Hydrozoa and Anthozoa. | Polyp (zoology) | Wikipedia | 495 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals |
In the class Hydrozoa, the polyps are indeed often very simple, like the common little fresh water species of the genus Hydra. Anthozoan polyps, including the corals and sea anemones, are much more complex due to the development of a tubular stomodaeum leading inward from the mouth and a series of radial partitions called mesenteries. Many of the mesenteries project into the enteric cavity but some extend from the body wall to the central stomodaeum.
Reproduction
It is an almost universal attribute of polyps to reproduce asexually by the method of budding. This mode of reproduction may be combined with sexual reproduction, or may be the sole method by which the polyp produces offspring, in which case the polyp is entirely without sexual organs.
Asexual reproduction
In many cases the buds formed do not separate from the parent but remain in continuity with it, thus forming colonies or stocks, which may reach a great size and contain a vast number of individuals. Slight differences in the method of budding produce great variations in the form of the colonies. The reef-building corals are polyp-colonies, strengthened by the formation of a firm skeleton.
Sexual reproduction
Among sea anemones, sexual plasticity may occur. That is, asexually produced clones derived from a single founder individual can contain both male and female individuals (ramets). When eggs and sperm (gametes) are formed, they can produce zygotes derived from "selfing" (within the founding clone) or out-crossing, that then develop into swimming planula larvae.
The overwhelming majority of stony coral (Scleractinia) taxa are hermaphroditic in their adult colonies. In these species, there is ordinarily synchronized release of eggs and sperm into the water during brief spawning events. Although some species are capable of self-fertilization to varying extents, cross-fertilization appears to be the dominant mating pattern.
Etymology
The name polyp was given by René Antoine Ferchault de Réaumur to these organisms from their superficial resemblance to an octopus (, ultimately from Ancient Greek adverb (, "much") + noun (, "foot")), with its circle of writhing arms round the mouth. This comparison contrasts to the common name "coral-insects", applied to the polyps which form coral. | Polyp (zoology) | Wikipedia | 491 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals |
Threats
75% of the world's corals are threatened due to overfishing, destructive fishing, coastal development, pollution, thermal stress, ocean acidification, crown-of-thorns starfish, and introduced invasive species.
In recent decades the conditions that corals and polyps have found themselves in have been changing, leading to new diseases being observed in corals in many parts of the world, posing even greater risk to an already pressured animal. Aquatic life has been put under a substantial amount of stress because of the pollutants caused by land-based agriculture. Particularly, exposure to the insecticide profenofos and the fungicide MEMC have played a major part in polyp retraction and biomass decrease.
There have been many experiments supporting the hypothesis that heat stress in Acropora tenuis juvenile polyps provokes an up-regulation of protein in the endoplasmic reticulum. The results vary based on the polyp characteristics such as age, type, and growth stage. | Polyp (zoology) | Wikipedia | 204 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals |
The spleen (, from Ancient Greek σπλήν, splḗn) is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter.
The spleen plays important roles in regard to red blood cells (erythrocytes) and the immune system. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. As a part of the mononuclear phagocyte system, it metabolizes hemoglobin removed from senescent red blood cells. The globin portion of hemoglobin is degraded to its constitutive amino acids, and the heme portion is metabolized to bilirubin, which is removed in the liver.
The spleen houses antibody-producing lymphocytes in its white pulp and monocytes which remove antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. These monocytes, upon moving to injured tissue (such as the heart after myocardial infarction), turn into dendritic cells and macrophages while promoting tissue healing. The spleen is a center of activity of the mononuclear phagocyte system and is analogous to a large lymph node, as its absence causes a predisposition to certain infections.
In humans, the spleen is purple in color and is in the left upper quadrant of the abdomen. The surgical process to remove the spleen is known as a splenectomy.
Structure
In humans, the spleen is underneath the left part of the diaphragm, and has a smooth, convex surface that faces the diaphragm. It is underneath the ninth, tenth, and eleventh ribs. The other side of the spleen is divided by a ridge into two regions: an anterior gastric portion, and a posterior renal portion. The gastric surface is directed forward, upward, and toward the middle, is broad and concave, and is in contact with the posterior wall of the stomach. Below this it is in contact with the tail of the pancreas. The renal surface is directed medialward and downward. It is somewhat flattened, considerably narrower than the gastric surface, and is in relation with the upper part of the anterior surface of the left kidney and occasionally with the left adrenal gland. | Spleen | Wikipedia | 509 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
There are four ligaments attached to the spleen: gastrosplenic ligament, splenorenal ligament, colicosplenic ligament, and phrenocolic ligament.
Measurements
The spleen, in healthy adult humans, is approximately in length.
An easy way to remember the anatomy of the spleen is the 1×3×5×7×9×10×11 rule. The spleen is , weighs approximately , and lies between the ninth and eleventh ribs on the left-hand side and along the axis of the tenth rib. The weight varies between and (standard reference range), correlating mainly to height, body weight and degree of acute congestion but not to sex or age.
Blood supply
Near the middle of the spleen is a long fissure, the hilum, which is the point of attachment for the gastrosplenic ligament and the point of insertion for the splenic artery and splenic vein. There are other openings present for lymphatic vessels and nerves. In addition to the splenic artery, collateral blood supply is provided by the adjacent short gastric arteries.
Like the thymus, the spleen possesses only efferent lymphatic vessels. The spleen is part of the lymphatic system. Both the short gastric arteries and the splenic artery supply it with blood.
The germinal centers are supplied by arterioles called penicilliary radicles.
Nerve supply
The spleen is innervated by the splenic plexus, which connects a branch of the celiac ganglia to the vagus nerve.
The underlying central nervous processes coordinating the spleen's function seem to be embedded into the hypothalamic-pituitary-adrenal-axis, and the brainstem, especially the subfornical organ.
Development
The spleen is unique in respect to its development within the gut. While most of the gut organs are endodermally derived, the spleen is derived from mesenchymal tissue. Specifically, the spleen forms within, and from, the dorsal mesentery. However, it still shares the same blood supply—the celiac trunk—as the foregut organs.
Function
Pulp | Spleen | Wikipedia | 458 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
Other
Other functions of the spleen are less prominent, especially in the healthy adult:
Spleen produces all types of blood cells during fetal life
Production of opsonins, properdin, and tuftsin.
Release of neutrophils following myocardial infarction.
Creation of red blood cells. While the bone marrow is the primary site of hematopoiesis in the adult, the spleen has important hematopoietic functions up until the fifth month of gestation. After birth, erythropoietic functions cease, except in some hematologic disorders. As a major lymphoid organ and a central player in the reticuloendothelial system, the spleen retains the ability to produce lymphocytes and, as such, remains a hematopoietic organ.
Storage of red blood cells, lymphocytes and other formed elements. The spleen of horses stores roughly 30 percent of the red blood cells and can release them when needed. In humans, up to a cup (240 ml) of red blood cells is held within the spleen and released in cases of hypovolemia and hypoxia. It can store platelets in case of an emergency and also clears old platelets from the circulation. Up to a quarter of lymphocytes are stored in the spleen at any one time.
Clinical significance
Enlarged spleen
Enlargement of the spleen is known as splenomegaly. It may be caused by sickle cell anemia, sarcoidosis, malaria, bacterial endocarditis, leukemia, polycythemia vera, pernicious anemia, Gaucher's disease, leishmaniasis, Hodgkin's disease, Banti's disease, hereditary spherocytosis, cysts, glandular fever (including mononucleosis or 'Mono' caused by the Epstein–Barr virus and infection from cytomegalovirus), and tumours. Primary tumors of the spleen include hemangiomas and hemangiosarcomas. Marked splenomegaly may result in the spleen occupying a large portion of the left side of the abdomen. | Spleen | Wikipedia | 453 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
The spleen is the largest collection of lymphoid tissue in the body. It is normally palpable in preterm infants, in 30% of normal, full-term neonates, and in 5% to 10% of infants and toddlers. A spleen easily palpable below the costal margin in any child over the age of three to four years should be considered abnormal until proven otherwise.
Splenomegaly can result from antigenic stimulation (e.g., infection), obstruction of blood flow (e.g., portal vein obstruction), underlying functional abnormality (e.g., hemolytic anemia), or infiltration (e.g., leukemia or storage disease, such as Gaucher's disease). The most common cause of acute splenomegaly in children is viral infection, which is transient and usually moderate. Basic work-up for acute splenomegaly includes a complete blood count with differential, platelet count, and reticulocyte and atypical lymphocyte counts to exclude hemolytic anemia and leukemia. Assessment of IgM antibodies to viral capsid antigen (a rising titer) is indicated to confirm Epstein–Barr virus or cytomegalovirus. Other infections should be excluded if these tests are negative.
Calculators have been developed for measurements of spleen size based on CT, US, and MRI findings.
Splenic injury
Trauma, such as a road traffic collision, can cause rupture of the spleen, which is a situation requiring immediate medical attention.
Asplenia | Spleen | Wikipedia | 332 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
Asplenia refers to a non-functioning spleen, which may be congenital, or caused by traumatic injury, surgical resection (splenectomy) or a disease such as sickle cell anaemia. Hyposplenia refers to a partially functioning spleen. These conditions may cause a modest increase in circulating white blood cells and platelets, a diminished response to some vaccines, and an increased susceptibility to infection. In particular, there is an increased risk of sepsis from polysaccharide encapsulated bacteria. Encapsulated bacteria inhibit binding of complement or prevent complement assembled on the capsule from interacting with macrophage receptors. Phagocytosis needs natural antibodies, which are immunoglobulins that facilitate phagocytosis either directly or by complement deposition on the capsule. They are produced by IgM memory B cells (a subtype of B cells) in the marginal zone of the spleen.
A splenectomy (removal of the spleen) results in a greatly diminished frequency of memory B cells. A 28-year follow-up of 740 World War II veterans whose spleens were removed on the battlefield showed a significant increase in the usual death rate from pneumonia (6 rather than the expected 1.3) and an increase in the death rate from ischemic heart disease (41 rather than the expected 30), but not from other conditions.
Accessory spleen
An accessory spleen is a small splenic nodule extra to the spleen usually formed in early embryogenesis. Accessory spleens are found in approximately 10 percent of the population and are typically around 1 centimeter in diameter. Splenosis is a condition where displaced pieces of splenic tissue (often following trauma or splenectomy) autotransplant in the abdominal cavity as accessory spleens.
Polysplenia is a congenital disease manifested by multiple small accessory spleens, rather than a single, full-sized, normal spleen. Polysplenia sometimes occurs alone, but it is often accompanied by other developmental abnormalities such as intestinal malrotation or biliary atresia, or cardiac abnormalities, such as dextrocardia. These accessory spleens are non-functional.
Infarction
Splenic infarction is a condition in which blood flow supply to the spleen is compromised, leading to partial or complete infarction (tissue death due to oxygen shortage) in the organ. | Spleen | Wikipedia | 504 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
Splenic infarction occurs when the splenic artery or one of its branches are occluded, for example by a blood clot. Although it can occur asymptomatically, the typical symptom is severe pain in the left upper quadrant of the abdomen, sometimes radiating to the left shoulder. Fever and chills develop in some cases. It has to be differentiated from other causes of acute abdomen.
Hyaloserositis
The spleen may be affected by hyaloserositis, in which it is coated with fibrous hyaline.
Society and culture
There has been a long and varied history of misconceptions regarding the physiological role of the spleen, and it has often been seen as a reservoir for juices closely linked to digestion. In various cultures, the organ has been linked to melancholia, due to the influence of ancient Greek medicine and the associated doctrine of humourism, in which the spleen was believed to be a reservoir for an elusive fluid known as "black bile" (one of the four humours). The spleen also plays an important role in traditional Chinese medicine, where it is considered to be a key organ that displays the Yin aspect of the Earth element (its Yang counterpart is the stomach). In contrast, the Talmud (tractate Berachoth 61b) refers to the spleen as the organ of laughter while possibly suggesting a link with the humoral view of the organ.
Etymologically, spleen comes from the Ancient Greek (splḗn), where it was the idiomatic equivalent of the heart in modern English. Persius, in his satires, associated spleen with immoderate laughter. The native Old English word for it is , now primarily used for animals; a loanword from Latin is .
In English, William Shakespeare frequently used the word spleen to signify melancholy, but also caprice and merriment. In Julius Caesar, he uses the spleen to describe Cassius's irritable nature:
Must I observe you? must I stand and crouch
Under your testy humour? By the gods
You shall digest the venom of your spleen,
Though it do split you; for, from this day forth,
I'll use you for my mirth, yea, for my laughter,
When you are waspish. | Spleen | Wikipedia | 483 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
The spleen, as a byword for melancholy, has also been considered an actual disease. In the early 18th century, the physician Richard Blackmore considered it to be one of the two most prevalent diseases in England (along with consumption). In 1701, Anne Finch (later, Countess of Winchilsea) had published a Pindaric ode, The Spleen, drawing on her first-hand experiences of an affliction which, at the time, also had a reputation of being a fashionably upper-class disease of the English. Both Blackmore and George Cheyne treated this malady as the male equivalent of "the vapours", while preferring the more learned terms "hypochondriasis" and "hysteria". In the late 18th century, the German word Spleen came to denote eccentric and hypochondriac tendencies that were thought to be characteristic of English people.
In French, "splénétique" refers to a state of pensive sadness or melancholy. This usage was popularised by the poems of Charles Baudelaire (1821–1867) and his collection Le Spleen de Paris, but it was also present in earlier 19th-century Romantic literature.
Food
The spleen is one of the many organs that may be included in offal. It is not widely eaten as a principal ingredient, but cow spleen sandwiches are eaten in Sicilian cuisine. Chicken spleen is one of the main ingredients of Jerusalem mixed grill.
Other animals
In cartilaginous and ray-finned fish, the spleen consists primarily of red pulp and is normally somewhat elongated, as it lies inside the serosal lining of the intestine. In many amphibians, especially frogs, it has the more rounded form and there is often a greater quantity of white pulp. | Spleen | Wikipedia | 368 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
In reptiles, birds, and mammals, white pulp is always relatively plentiful, and in birds and some mammals the spleen is typically rounded, but it adjusts its shape somewhat to the arrangement of the surrounding organs. In most vertebrates, the spleen continues to produce red blood cells throughout life; only in mammals this function is lost in middle-aged adults. Many mammals have tiny spleen-like structures known as haemal nodes throughout the body that are presumed to have the same function as the spleen. The spleens of aquatic mammals differ in some ways from those of fully land-dwelling mammals; in general they are bluish in colour. In cetaceans and manatees, they tend to be quite small, but in deep diving pinnipeds, they can be massive, due to their function of storing red blood cells.
Marsupials have y-shaped spleens, and it develops postnatally.
The only vertebrates lacking a spleen are the lampreys and hagfishes (the early-branching Cyclostomata, or jawless fishes). Even in these animals, there is a diffuse layer of haematopoeitic tissue within the gut wall, which has a similar structure to red pulp and is presumed homologous with the spleen of higher vertebrates.
In mice, the spleen stores half the body's monocytes so that, upon injury, they can migrate to the injured tissue and transform into dendritic cells and macrophages to assist wound healing.
Additional images | Spleen | Wikipedia | 321 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null |
In mathematics, particularly in order theory, an upper bound or majorant of a subset of some preordered set is an element of that is every element of .
Dually, a lower bound or minorant of is defined to be an element of that is less than or equal to every element of .
A set with an upper (respectively, lower) bound is said to be bounded from above or majorized (respectively bounded from below or minorized) by that bound.
The terms bounded above (bounded below) are also used in the mathematical literature for sets that have upper (respectively lower) bounds.
Examples
For example, is a lower bound for the set (as a subset of the integers or of the real numbers, etc.), and so is . On the other hand, is not a lower bound for since it is not smaller than every element in . and other numbers x such that would be an upper bound for S.
The set has as both an upper bound and a lower bound; all other numbers are either an upper bound or a lower bound for that .
Every subset of the natural numbers has a lower bound since the natural numbers have a least element (0 or 1, depending on convention). An infinite subset of the natural numbers cannot be bounded from above. An infinite subset of the integers may be bounded from below or bounded from above, but not both. An infinite subset of the rational numbers may or may not be bounded from below, and may or may not be bounded from above.
Every finite subset of a non-empty totally ordered set has both upper and lower bounds.
Bounds of functions
The definitions can be generalized to functions and even to sets of functions.
Given a function with domain and a preordered set as codomain, an element of is an upper bound of if for each in . The upper bound is called sharp if equality holds for at least one value of . It indicates that the constraint is optimal, and thus cannot be further reduced without invalidating the inequality.
Similarly, a function defined on domain and having the same codomain is an upper bound of , if for each in . The function is further said to be an upper bound of a set of functions, if it is an upper bound of each function in that set.
The notion of lower bound for (sets of) functions is defined analogously, by replacing ≥ with ≤.
Tight bounds | Upper and lower bounds | Wikipedia | 481 | 42693 | https://en.wikipedia.org/wiki/Upper%20and%20lower%20bounds | Mathematics | Order theory | null |
An upper bound is said to be a tight upper bound, a least upper bound, or a supremum, if no smaller value is an upper bound. Similarly, a lower bound is said to be a tight lower bound, a greatest lower bound, or an infimum, if no greater value is a lower bound.
Exact upper bounds
An upper bound of a subset of a preordered set is said to be an exact upper bound for if every element of that is strictly majorized by is also majorized by some element of . Exact upper bounds of reduced products of linear orders play an important role in PCF theory. | Upper and lower bounds | Wikipedia | 127 | 42693 | https://en.wikipedia.org/wiki/Upper%20and%20lower%20bounds | Mathematics | Order theory | null |
A pendulum is a device made of a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force acting on the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum and also to a slight degree on the amplitude, the width of the pendulum's swing.
The regular motion of pendulums was used for timekeeping and was the world's most accurate timekeeping technology until the 1930s. The pendulum clock invented by Christiaan Huygens in 1656 became the world's standard timekeeper, used in homes and offices for 270 years, and achieved accuracy of about one second per year before it was superseded as a time standard by the quartz clock in the 1930s. Pendulums are also used in scientific instruments such as accelerometers and seismometers. Historically they were used as gravimeters to measure the acceleration of gravity in geo-physical surveys, and even as a standard of length. The word pendulum is Neo-Latin, from the Latin , meaning .
Mechanics
Simple gravity pendulum
The simple gravity pendulum is an idealized mathematical model of a pendulum. This is a weight (or bob) on the end of a massless cord suspended from a pivot, without friction. When given an initial push, it will swing back and forth at a constant amplitude. Real pendulums are subject to friction and air drag, so the amplitude of their swings declines.
Period of oscillation
The period of swing of a simple gravity pendulum depends on its length, the local strength of gravity, and to a small extent on the maximum angle that the pendulum swings away from vertical, θ0, called the amplitude. It is independent of the mass of the bob. If the amplitude is limited to small swings, the period of a simple pendulum, the time taken for a complete cycle, is:
where is the length of the pendulum and is the local acceleration of gravity. | Pendulum | Wikipedia | 456 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
For small swings the period of swing is approximately the same for different size swings: that is, the period is independent of amplitude. This property, called isochronism, is the reason pendulums are so useful for timekeeping. Successive swings of the pendulum, even if changing in amplitude, take the same amount of time.
For larger amplitudes, the period increases gradually with amplitude so it is longer than given by equation (1). For example, at an amplitude of θ0 = 0.4 radians (23°) it is 1% larger than given by (1). The period increases asymptotically (to infinity) as θ0 approaches π radians (180°), because the value θ0 = π is an unstable equilibrium point for the pendulum. The true period of an ideal simple gravity pendulum can be written in several different forms (see pendulum (mechanics)), one example being the infinite series:
where is in radians.
The difference between this true period and the period for small swings (1) above is called the circular error. In the case of a typical grandfather clock whose pendulum has a swing of 6° and thus an amplitude of 3° (0.05 radians), the difference between the true period and the small angle approximation (1) amounts to about 15 seconds per day.
For small swings the pendulum approximates a harmonic oscillator, and its motion as a function of time, t, is approximately simple harmonic motion:
where is a constant value, dependent on initial conditions.
For real pendulums, the period varies slightly with factors such as the buoyancy and viscous resistance of the air, the mass of the string or rod, the size and shape of the bob and how it is attached to the string, and flexibility and stretching of the string. In precision applications, corrections for these factors may need to be applied to eq. (1) to give the period accurately.
A damped, driven pendulum is a chaotic system.
Compound pendulum | Pendulum | Wikipedia | 414 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Any swinging rigid body free to rotate about a fixed horizontal axis is called a compound pendulum or physical pendulum. A compound pendulum has the same period as a simple gravity pendulum of length , called the equivalent length or radius of oscillation, equal to the distance from the pivot to a point called the center of oscillation. This point is located under the center of mass of the pendulum, at a distance which depends on the mass distribution of the pendulum. If most of the mass is concentrated in a relatively small bob compared to the pendulum length, the center of oscillation is close to the center of mass.
The radius of oscillation or equivalent length of any physical pendulum can be shown to be
where is the moment of inertia of the pendulum about the pivot point , is the total mass of the pendulum, and is the distance between the pivot point and the center of mass.
Substituting this expression in (1) above, the period of a compound pendulum is given by
for sufficiently small oscillations.
For example, a rigid uniform rod of length pivoted about one end has moment of inertia . The center of mass is located at the center of the rod, so Substituting these values into the above equation gives . This shows that a rigid rod pendulum has the same period as a simple pendulum of two-thirds its length.
Christiaan Huygens proved in 1673 that the pivot point and the center of oscillation are interchangeable. This means if any pendulum is turned upside down and swung from a pivot located at its previous center of oscillation, it will have the same period as before and the new center of oscillation will be at the old pivot point. In 1817 Henry Kater used this idea to produce a type of reversible pendulum, now known as a Kater pendulum, for improved measurements of the acceleration due to gravity.
Double pendulum
In physics and mathematics, in the area of dynamical systems, a double pendulum, also known as a chaotic pendulum, is a pendulum with another pendulum attached to its end, forming a simple physical system that exhibits rich dynamic behavior with a strong sensitivity to initial conditions. The motion of a double pendulum is governed by a set of coupled ordinary differential equations and is chaotic.
History | Pendulum | Wikipedia | 464 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
One of the earliest known uses of a pendulum was a 1st-century seismometer device of Han dynasty Chinese scientist Zhang Heng. Its function was to sway and activate one of a series of levers after being disturbed by the tremor of an earthquake far away. Released by a lever, a small ball would fall out of the urn-shaped device into one of eight metal toads' mouths below, at the eight points of the compass, signifying the direction the earthquake was located.
Many sources claim that the 10th-century Egyptian astronomer Ibn Yunus used a pendulum for time measurement, but this was an error that originated in 1684 with the British historian Edward Bernard.
During the Renaissance, large hand-pumped pendulums were used as sources of power for manual reciprocating machines such as saws, bellows, and pumps.
1602: Galileo's research
Italian scientist Galileo Galilei was the first to study the properties of pendulums, beginning around 1602. The first recorded interest in pendulums made by Galileo was around 1588 in his posthumously published notes titled On Motion, in which he noted that heavier objects would continue to oscillate for a greater amount of time than lighter objects. The earliest extant report of his experimental research is contained in a letter to Guido Ubaldo dal Monte, from Padua, dated November 29, 1602. His biographer and student, Vincenzo Viviani, claimed his interest had been sparked around 1582 by the swinging motion of a chandelier in Pisa Cathedral. Galileo discovered the crucial property that makes pendulums useful as timekeepers, called isochronism; the period of the pendulum is approximately independent of the amplitude or width of the swing. He also found that the period is independent of the mass of the bob, and proportional to the square root of the length of the pendulum. He first employed freeswinging pendulums in simple timing applications. Santorio Santori in 1602 invented a device which measured a patient's pulse by the length of a pendulum; the pulsilogium. In 1641 Galileo dictated to his son Vincenzo a design for a mechanism to keep a pendulum swinging, which has been described as the first pendulum clock; Vincenzo began construction, but had not completed it when he died in 1649.
1656: The pendulum clock | Pendulum | Wikipedia | 466 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
In 1656 the Dutch scientist Christiaan Huygens built the first pendulum clock. This was a great improvement over existing mechanical clocks; their best accuracy was improved from around 15 minutes deviation a day to around 15 seconds a day. Pendulums spread over Europe as existing clocks were retrofitted with them.
The English scientist Robert Hooke studied the conical pendulum around 1666, consisting of a pendulum that is free to swing in two dimensions, with the bob rotating in a circle or ellipse. He used the motions of this device as a model to analyze the orbital motions of the planets. Hooke suggested to Isaac Newton in 1679 that the components of orbital motion consisted of inertial motion along a tangent direction plus an attractive motion in the radial direction. This played a part in Newton's formulation of the law of universal gravitation. Robert Hooke was also responsible for suggesting as early as 1666 that the pendulum could be used to measure the force of gravity.
During his expedition to Cayenne, French Guiana in 1671, Jean Richer found that a pendulum clock was minutes per day slower at Cayenne than at Paris. From this he deduced that the force of gravity was lower at Cayenne. In 1687, Isaac Newton in Principia Mathematica showed that this was because the Earth was not a true sphere but slightly oblate (flattened at the poles) from the effect of centrifugal force due to its rotation, causing gravity to increase with latitude. Portable pendulums began to be taken on voyages to distant lands, as precision gravimeters to measure the acceleration of gravity at different points on Earth, eventually resulting in accurate models of the shape of the Earth. | Pendulum | Wikipedia | 344 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
1673: Huygens' Horologium Oscillatorium
In 1673, 17 years after he invented the pendulum clock, Christiaan Huygens published his theory of the pendulum, Horologium Oscillatorium sive de motu pendulorum. Marin Mersenne and René Descartes had discovered around 1636 that the pendulum was not quite isochronous; its period increased somewhat with its amplitude. Huygens analyzed this problem by determining what curve an object must follow to descend by gravity to the same point in the same time interval, regardless of starting point; the so-called tautochrone curve. By a complicated method that was an early use of calculus, he showed this curve was a cycloid, rather than the circular arc of a pendulum, confirming that the pendulum was not isochronous and Galileo's observation of isochronism was accurate only for small swings. Huygens also solved the problem of how to calculate the period of an arbitrarily shaped pendulum (called a compound pendulum), discovering the center of oscillation, and its interchangeability with the pivot point.
The existing clock movement, the verge escapement, made pendulums swing in very wide arcs of about 100°. Huygens showed this was a source of inaccuracy, causing the period to vary with amplitude changes caused by small unavoidable variations in the clock's drive force. To make its period isochronous, Huygens mounted cycloidal-shaped metal guides next to the pivots in his clocks, that constrained the suspension cord and forced the pendulum to follow a cycloid arc (see cycloidal pendulum). This solution didn't prove as practical as simply limiting the pendulum's swing to small angles of a few degrees. The realization that only small swings were isochronous motivated the development of the anchor escapement around 1670, which reduced the pendulum swing in clocks to 4°–6°. This became the standard escapement used in pendulum clocks.
1721: Temperature compensated pendulums | Pendulum | Wikipedia | 431 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
During the 18th and 19th century, the pendulum clock's role as the most accurate timekeeper motivated much practical research into improving pendulums. It was found that a major source of error was that the pendulum rod expanded and contracted with changes in ambient temperature, changing the period of swing. This was solved with the invention of temperature compensated pendulums, the mercury pendulum in 1721 and the gridiron pendulum in 1726, reducing errors in precision pendulum clocks to a few seconds per week.
The accuracy of gravity measurements made with pendulums was limited by the difficulty of finding the location of their center of oscillation. Huygens had discovered in 1673 that a pendulum has the same period when hung from its center of oscillation as when hung from its pivot, and the distance between the two points was equal to the length of a simple gravity pendulum of the same period. In 1818 British Captain Henry Kater invented the reversible Kater's pendulum which used this principle, making possible very accurate measurements of gravity. For the next century the reversible pendulum was the standard method of measuring absolute gravitational acceleration.
1851: Foucault pendulum
In 1851, Jean Bernard Léon Foucault showed that the plane of oscillation of a pendulum, like a gyroscope, tends to stay constant regardless of the motion of the pivot, and that this could be used to demonstrate the rotation of the Earth. He suspended a pendulum free to swing in two dimensions (later named the Foucault pendulum) from the dome of the Panthéon in Paris. The length of the cord was . Once the pendulum was set in motion, the plane of swing was observed to precess or rotate 360° clockwise in about 32 hours.
This was the first demonstration of the Earth's rotation that did not depend on celestial observations, and a "pendulum mania" broke out, as Foucault pendulums were displayed in many cities and attracted large crowds.
1930: Decline in use
Around 1900 low-thermal-expansion materials began to be used for pendulum rods in the highest precision clocks and other instruments, first invar, a nickel steel alloy, and later fused quartz, which made temperature compensation trivial. Precision pendulums were housed in low pressure tanks, which kept the air pressure constant to prevent changes in the period due to changes in buoyancy of the pendulum due to changing atmospheric pressure. The best pendulum clocks achieved accuracy of around a second per year. | Pendulum | Wikipedia | 497 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The timekeeping accuracy of the pendulum was exceeded by the quartz crystal oscillator, invented in 1921, and quartz clocks, invented in 1927, replaced pendulum clocks as the world's best timekeepers. Pendulum clocks were used as time standards until World War 2, although the French Time Service continued using them in their official time standard ensemble until 1954. Pendulum gravimeters were superseded by "free fall" gravimeters in the 1950s, but pendulum instruments continued to be used into the 1970s.
Use for time measurement
For 300 years, from its discovery around 1582 until development of the quartz clock in the 1930s, the pendulum was the world's standard for accurate timekeeping. In addition to clock pendulums, freeswinging seconds pendulums were widely used as precision timers in scientific experiments in the 17th and 18th centuries. Pendulums require great mechanical stability: a length change of only 0.02%, 0.2 mm in a grandfather clock pendulum, will cause an error of a minute per week.
Clock pendulums
Pendulums in clocks (see example at right) are usually made of a weight or bob (b) suspended by a rod of wood or metal (a). To reduce air resistance (which accounts for most of the energy loss in precision clocks) the bob is traditionally a smooth disk with a lens-shaped cross section, although in antique clocks it often had carvings or decorations specific to the type of clock. In quality clocks the bob is made as heavy as the suspension can support and the movement can drive, since this improves the regulation of the clock (see Accuracy below). A common weight for seconds pendulum bobs is . Instead of hanging from a pivot, clock pendulums are usually supported by a short straight spring (d) of flexible metal ribbon. This avoids the friction and 'play' caused by a pivot, and the slight bending force of the spring merely adds to the pendulum's restoring force. The highest precision clocks have pivots of 'knife' blades resting on agate plates. The impulses to keep the pendulum swinging are provided by an arm hanging behind the pendulum called the crutch, (e), which ends in a fork, (f) whose prongs embrace the pendulum rod. The crutch is pushed back and forth by the clock's escapement, (g,h). | Pendulum | Wikipedia | 481 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Each time the pendulum swings through its centre position, it releases one tooth of the escape wheel (g). The force of the clock's mainspring or a driving weight hanging from a pulley, transmitted through the clock's gear train, causes the wheel to turn, and a tooth presses against one of the pallets (h), giving the pendulum a short push. The clock's wheels, geared to the escape wheel, move forward a fixed amount with each pendulum swing, advancing the clock's hands at a steady rate.
The pendulum always has a means of adjusting the period, usually by an adjustment nut (c) under the bob which moves it up or down on the rod. Moving the bob up decreases the pendulum's length, causing the pendulum to swing faster and the clock to gain time. Some precision clocks have a small auxiliary adjustment weight on a threaded shaft on the bob, to allow finer adjustment. Some tower clocks and precision clocks use a tray attached near to the midpoint of the pendulum rod, to which small weights can be added or removed. This effectively shifts the centre of oscillation and allows the rate to be adjusted without stopping the clock.
The pendulum must be suspended from a rigid support. During operation, any elasticity will allow tiny imperceptible swaying motions of the support, which disturbs the clock's period, resulting in error. Pendulum clocks should be attached firmly to a sturdy wall.
The most common pendulum length in quality clocks, which is always used in grandfather clocks, is the seconds pendulum, about long. In mantel clocks, half-second pendulums, long, or shorter, are used. Only a few large tower clocks use longer pendulums, the 1.5 second pendulum, long, or occasionally the two-second pendulum, which is used in Big Ben.
Temperature compensation | Pendulum | Wikipedia | 375 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The largest source of error in early pendulums was slight changes in length due to thermal expansion and contraction of the pendulum rod with changes in ambient temperature. This was discovered when people noticed that pendulum clocks ran slower in summer, by as much as a minute per week (one of the first was Godefroy Wendelin, as reported by Huygens in 1658). Thermal expansion of pendulum rods was first studied by Jean Picard in 1669. A pendulum with a steel rod will expand by about 11.3 parts per million (ppm) with each degree Celsius increase, causing it to lose about 0.27 seconds per day for every degree Celsius increase in temperature, or 9 seconds per day for a change. Wood rods expand less, losing only about 6 seconds per day for a change, which is why quality clocks often had wooden pendulum rods. The wood had to be varnished to prevent water vapor from getting in, because changes in humidity also affected the length.
Mercury pendulum
The first device to compensate for this error was the mercury pendulum, invented by George Graham in 1721. The liquid metal mercury expands in volume with temperature. In a mercury pendulum, the pendulum's weight (bob) is a container of mercury. With a temperature rise, the pendulum rod gets longer, but the mercury also expands and its surface level rises slightly in the container, moving its centre of mass closer to the pendulum pivot. By using the correct height of mercury in the container these two effects will cancel, leaving the pendulum's centre of mass, and its period, unchanged with temperature. Its main disadvantage was that when the temperature changed, the rod would come to the new temperature quickly but the mass of mercury might take a day or two to reach the new temperature, causing the rate to deviate during that time. To improve thermal accommodation several thin containers were often used, made of metal. Mercury pendulums were the standard used in precision regulator clocks into the 20th century.
Gridiron pendulum | Pendulum | Wikipedia | 403 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The most widely used compensated pendulum was the gridiron pendulum, invented in 1726 by John Harrison. This consists of alternating rods of two different metals, one with lower thermal expansion (CTE), steel, and one with higher thermal expansion, zinc or brass. The rods are connected by a frame, as shown in the drawing at the right, so that an increase in length of the zinc rods pushes the bob up, shortening the pendulum. With a temperature increase, the low expansion steel rods make the pendulum longer, while the high expansion zinc rods make it shorter. By making the rods of the correct lengths, the greater expansion of the zinc cancels out the expansion of the steel rods which have a greater combined length, and the pendulum stays the same length with temperature.
Zinc-steel gridiron pendulums are made with 5 rods, but the thermal expansion of brass is closer to steel, so brass-steel gridirons usually require 9 rods. Gridiron pendulums adjust to temperature changes faster than mercury pendulums, but scientists found that friction of the rods sliding in their holes in the frame caused gridiron pendulums to adjust in a series of tiny jumps. In high precision clocks this caused the clock's rate to change suddenly with each jump. Later it was found that zinc is subject to creep. For these reasons mercury pendulums were used in the highest precision clocks, but gridirons were used in quality regulator clocks.
Gridiron pendulums became so associated with good quality that, to this day, many ordinary clock pendulums have decorative 'fake' gridirons that don't actually have any temperature compensation function. | Pendulum | Wikipedia | 333 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Invar and fused quartz
Around 1900, low thermal expansion materials were developed which could be used as pendulum rods in order to make elaborate temperature compensation unnecessary. These were only used in a few of the highest precision clocks before the pendulum became obsolete as a time standard. In 1896 Charles Édouard Guillaume invented the nickel steel alloy Invar. This has a CTE of around (), resulting in pendulum temperature errors over of only 1.3 seconds per day, and this residual error could be compensated to zero with a few centimeters of aluminium under the pendulum bob (this can be seen in the Riefler clock image above). Invar pendulums were first used in 1898 in the Riefler regulator clock which achieved accuracy of 15 milliseconds per day. Suspension springs of Elinvar were used to eliminate temperature variation of the spring's restoring force on the pendulum. Later fused quartz was used which had even lower CTE. These materials are the choice for modern high accuracy pendulums. | Pendulum | Wikipedia | 199 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Atmospheric pressure
The effect of the surrounding air on a moving pendulum is complex and requires fluid mechanics to calculate precisely, but for most purposes its influence on the period can be accounted for by three effects:
By Archimedes' principle the effective weight of the bob is reduced by the buoyancy of the air it displaces, while the mass (inertia) remains the same, reducing the pendulum's acceleration during its swing and increasing the period. This depends on the air pressure and the density of the pendulum, but not its shape.
The pendulum carries an amount of air with it as it swings, and the mass of this air increases the inertia of the pendulum, again reducing the acceleration and increasing the period. This depends on both its density and shape.
Viscous air resistance slows the pendulum's velocity. This has a negligible effect on the period, but dissipates energy, reducing the amplitude. This reduces the pendulum's Q factor, requiring a stronger drive force from the clock's mechanism to keep it moving, which causes increased disturbance to the period.
Increases in barometric pressure increase a pendulum's period slightly due to the first two effects, by about . Researchers using pendulums to measure the acceleration of gravity had to correct the period for the air pressure at the altitude of measurement, computing the equivalent period of a pendulum swinging in vacuum. A pendulum clock was first operated in a constant-pressure tank by Friedrich Tiede in 1865 at the Berlin Observatory, and by 1900 the highest precision clocks were mounted in tanks that were kept at a constant pressure to eliminate changes in atmospheric pressure. Alternatively, in some a small aneroid barometer mechanism attached to the pendulum compensated for this effect.
Gravity
Pendulums are affected by changes in gravitational acceleration, which varies by as much as 0.5% at different locations on Earth, so precision pendulum clocks have to be recalibrated after a move. Even moving a pendulum clock to the top of a tall building can cause it to lose measurable time from the reduction in gravity. | Pendulum | Wikipedia | 419 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Accuracy of pendulums as timekeepers
The timekeeping elements in all clocks, which include pendulums, balance wheels, the quartz crystals used in quartz watches, and even the vibrating atoms in atomic clocks, are in physics called harmonic oscillators. The reason harmonic oscillators are used in clocks is that they vibrate or oscillate at a specific resonant frequency or period and resist oscillating at other rates. However, the resonant frequency is not infinitely 'sharp'. Around the resonant frequency there is a narrow natural band of frequencies (or periods), called the resonance width or bandwidth, where the harmonic oscillator will oscillate. In a clock, the actual frequency of the pendulum may vary randomly within this resonance width in response to disturbances, but at frequencies outside this band, the clock will not function at all. The resonance width is determined by the damping, the frictional energy loss per swing of the pendulum.
Q factor
The measure of a harmonic oscillator's resistance to disturbances to its oscillation period is a dimensionless parameter called the Q factor equal to the resonant frequency divided by the resonance width. The higher the Q, the smaller the resonance width, and the more constant the frequency or period of the oscillator for a given disturbance. The reciprocal of the Q is roughly proportional to the limiting accuracy achievable by a harmonic oscillator as a time standard.
The Q is related to how long it takes for the oscillations of an oscillator to die out. The Q of a pendulum can be measured by counting the number of oscillations it takes for the amplitude of the pendulum's swing to decay to 1/e = 36.8% of its initial swing, and multiplying by 'π. | Pendulum | Wikipedia | 380 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
In a clock, the pendulum must receive pushes from the clock's movement to keep it swinging, to replace the energy the pendulum loses to friction. These pushes, applied by a mechanism called the escapement, are the main source of disturbance to the pendulum's motion. The Q is equal to 2π times the energy stored in the pendulum, divided by the energy lost to friction during each oscillation period, which is the same as the energy added by the escapement each period. It can be seen that the smaller the fraction of the pendulum's energy that is lost to friction, the less energy needs to be added, the less the disturbance from the escapement, the more 'independent' the pendulum is of the clock's mechanism, and the more constant its period is. The Q of a pendulum is given by:
where M is the mass of the bob, is the pendulum's radian frequency of oscillation, and Γ is the frictional damping force on the pendulum per unit velocity.ω is fixed by the pendulum's period, and M is limited by the load capacity and rigidity of the suspension. So the Q of clock pendulums is increased by minimizing frictional losses (Γ). Precision pendulums are suspended on low friction pivots consisting of triangular shaped 'knife' edges resting on agate plates. Around 99% of the energy loss in a freeswinging pendulum is due to air friction, so mounting a pendulum in a vacuum tank can increase the Q, and thus the accuracy, by a factor of 100.
The Q of pendulums ranges from several thousand in an ordinary clock to several hundred thousand for precision regulator pendulums swinging in vacuum. A quality home pendulum clock might have a Q of 10,000 and an accuracy of 10 seconds per month. The most accurate commercially produced pendulum clock was the Shortt-Synchronome free pendulum clock, invented in 1921. Its Invar master pendulum swinging in a vacuum tank had a Q of 110,000 and an error rate of around a second per year.
Their Q of 103–105 is one reason why pendulums are more accurate timekeepers than the balance wheels in watches, with Q around 100–300, but less accurate than the quartz crystals in quartz clocks, with Q of 105–106. | Pendulum | Wikipedia | 469 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Escapement
Pendulums (unlike, for example, quartz crystals) have a low enough Q that the disturbance caused by the impulses to keep them moving is generally the limiting factor on their timekeeping accuracy. Therefore, the design of the escapement, the mechanism that provides these impulses, has a large effect on the accuracy of a clock pendulum. If the impulses given to the pendulum by the escapement each swing could be exactly identical, the response of the pendulum would be identical, and its period would be constant. However, this is not achievable; unavoidable random fluctuations in the force due to friction of the clock's pallets, lubrication variations, and changes in the torque provided by the clock's power source as it runs down, mean that the force of the impulse applied by the escapement varies.
If these variations in the escapement's force cause changes in the pendulum's width of swing (amplitude), this will cause corresponding slight changes in the period, since (as discussed at top) a pendulum with a finite swing is not quite isochronous. Therefore, the goal of traditional escapement design is to apply the force with the proper profile, and at the correct point in the pendulum's cycle, so force variations have no effect on the pendulum's amplitude. This is called an isochronous escapement.
The Airy condition
Clockmakers had known for centuries that the disturbing effect of the escapement's drive force on the period of a pendulum is smallest if given as a short impulse as the pendulum passes through its bottom equilibrium position. If the impulse occurs before the pendulum reaches bottom, during the downward swing, it will have the effect of shortening the pendulum's natural period, so an increase in drive force will decrease the period. If the impulse occurs after the pendulum reaches bottom, during the upswing, it will lengthen the period, so an increase in drive force will increase the pendulum's period. In 1826 British astronomer George Airy proved this; specifically, he proved that if a pendulum is driven by an impulse that is symmetrical about its bottom equilibrium position, the pendulum's period will be unaffected by changes in the drive force. The most accurate escapements, such as the deadbeat, approximately satisfy this condition. | Pendulum | Wikipedia | 469 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Gravity measurement
The presence of the acceleration of gravity g in the periodicity equation (1) for a pendulum means that the local gravitational acceleration of the Earth can be calculated from the period of a pendulum. A pendulum can therefore be used as a gravimeter to measure the local gravity, which varies by over 0.5% across the surface of the Earth.The value of "g" (acceleration due to gravity) at the equator is 9.780 m/s2 and at the poles is 9.832 m/s2, a difference of 0.53%. The pendulum in a clock is disturbed by the pushes it receives from the clock movement, so freeswinging pendulums were used, and were the standard instruments of gravimetry up to the 1930s.
The difference between clock pendulums and gravimeter pendulums is that to measure gravity, the pendulum's length as well as its period has to be measured. The period of freeswinging pendulums could be found to great precision by comparing their swing with a precision clock that had been adjusted to keep correct time by the passage of stars overhead. In the early measurements, a weight on a cord was suspended in front of the clock pendulum, and its length adjusted until the two pendulums swung in exact synchronism. Then the length of the cord was measured. From the length and the period, g could be calculated from equation (1).
The seconds pendulum
The seconds pendulum, a pendulum with a period of two seconds so each swing takes one second, was widely used to measure gravity, because its period could be easily measured by comparing it to precision regulator clocks, which all had seconds pendulums. By the late 17th century, the length of the seconds pendulum became the standard measure of the strength of gravitational acceleration at a location. By 1700 its length had been measured with submillimeter accuracy at several cities in Europe. For a seconds pendulum, g is proportional to its length: | Pendulum | Wikipedia | 396 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Early observations
1620: British scientist Francis Bacon was one of the first to propose using a pendulum to measure gravity, suggesting taking one up a mountain to see if gravity varies with altitude.
1644: Even before the pendulum clock, French priest Marin Mersenne first determined the length of the seconds pendulum was , by comparing the swing of a pendulum to the time it took a weight to fall a measured distance. He also was first to discover the dependence of the period on amplitude of swing.
1669: Jean Picard determined the length of the seconds pendulum at Paris, using a copper ball suspended by an aloe fiber, obtaining . He also did the first experiments on thermal expansion and contraction of pendulum rods with temperature.
1672: The first observation that gravity varied at different points on Earth was made in 1672 by Jean Richer, who took a pendulum clock to Cayenne, French Guiana and found that it lost minutes per day; its seconds pendulum had to be shortened by lignes (2.6 mm) shorter than at Paris, to keep correct time. In 1687 Isaac Newton in Principia Mathematica showed this was because the Earth had a slightly oblate shape (flattened at the poles) caused by the centrifugal force of its rotation. At higher latitudes the surface was closer to the center of the Earth, so gravity increased with latitude. From this time on, pendulums began to be taken to distant lands to measure gravity, and tables were compiled of the length of the seconds pendulum at different locations on Earth. In 1743 Alexis Claude Clairaut created the first hydrostatic model of the Earth, Clairaut's theorem, which allowed the ellipticity of the Earth to be calculated from gravity measurements. Progressively more accurate models of the shape of the Earth followed.
1687: Newton experimented with pendulums (described in Principia) and found that equal length pendulums with bobs made of different materials had the same period, proving that the gravitational force on different substances was exactly proportional to their mass (inertia). This principle, called the equivalence principle, confirmed to greater accuracy in later experiments, became the foundation on which Albert Einstein based his general theory of relativity. | Pendulum | Wikipedia | 446 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
1737: French mathematician Pierre Bouguer made a sophisticated series of pendulum observations in the Andes mountains, Peru. He used a copper pendulum bob in the shape of a double pointed cone suspended by a thread; the bob could be reversed to eliminate the effects of nonuniform density. He calculated the length to the center of oscillation of thread and bob combined, instead of using the center of the bob. He corrected for thermal expansion of the measuring rod and barometric pressure, giving his results for a pendulum swinging in vacuum. Bouguer swung the same pendulum at three different elevations, from sea level to the top of the high Peruvian altiplano. Gravity should fall with the inverse square of the distance from the center of the Earth. Bouguer found that it fell off slower, and correctly attributed the 'extra' gravity to the gravitational field of the huge Peruvian plateau. From the density of rock samples he calculated an estimate of the effect of the altiplano on the pendulum, and comparing this with the gravity of the Earth was able to make the first rough estimate of the density of the Earth.
1747: Daniel Bernoulli showed how to correct for the lengthening of the period due to a finite angle of swing θ0 by using the first order correction θ02/16, giving the period of a pendulum with an extremely small swing.
1792: To define a pendulum standard of length for use with the new metric system, in 1792 Jean-Charles de Borda and Jean-Dominique Cassini made a precise measurement of the seconds pendulum at Paris. They used a -inch (14 mm) platinum ball suspended by a iron wire. Their main innovation was a technique called the "method of coincidences" which allowed the period of pendulums to be compared with great precision. (Bouguer had also used this method). The time interval Δt between the recurring instants when the two pendulums swung in synchronism was timed. From this the difference between the periods of the pendulums, T1 and T2, could be calculated: | Pendulum | Wikipedia | 419 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
1821: Francesco Carlini made pendulum observations on top of Mount Cenis, Italy, from which, using methods similar to Bouguer's, he calculated the density of the Earth. He compared his measurements to an estimate of the gravity at his location assuming the mountain wasn't there, calculated from previous nearby pendulum measurements at sea level. His measurements showed 'excess' gravity, which he allocated to the effect of the mountain. Modeling the mountain as a segment of a sphere in diameter and high, from rock samples he calculated its gravitational field, and estimated the density of the Earth at 4.39 times that of water. Later recalculations by others gave values of 4.77 and 4.95, illustrating the uncertainties in these geographical methods. | Pendulum | Wikipedia | 153 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Kater's pendulum
The precision of the early gravity measurements above was limited by the difficulty of measuring the length of the pendulum, L . L was the length of an idealized simple gravity pendulum (described at top), which has all its mass concentrated in a point at the end of the cord. In 1673 Huygens had shown that the period of a rigid bar pendulum (called a compound pendulum) was equal to the period of a simple pendulum with a length equal to the distance between the pivot point and a point called the center of oscillation, located under the center of gravity, that depends on the mass distribution along the pendulum. But there was no accurate way of determining the center of oscillation in a real pendulum. Huygens' discovery is sometimes referred to as Huygens' law of the (cycloidal) pendulum.
To get around this problem, the early researchers above approximated an ideal simple pendulum as closely as possible by using a metal sphere suspended by a light wire or cord. If the wire was light enough, the center of oscillation was close to the center of gravity of the ball, at its geometric center. This "ball and wire" type of pendulum wasn't very accurate, because it didn't swing as a rigid body, and the elasticity of the wire caused its length to change slightly as the pendulum swung.
However Huygens had also proved that in any pendulum, the pivot point and the center of oscillation were interchangeable. That is, if a pendulum were turned upside down and hung from its center of oscillation, it would have the same period as it did in the previous position, and the old pivot point would be the new center of oscillation.
British physicist and army captain Henry Kater in 1817 realized that Huygens' principle could be used to find the length of a simple pendulum with the same period as a real pendulum. If a pendulum was built with a second adjustable pivot point near the bottom so it could be hung upside down, and the second pivot was adjusted until the periods when hung from both pivots were the same, the second pivot would be at the center of oscillation, and the distance between the two pivots would be the length L of a simple pendulum with the same period. | Pendulum | Wikipedia | 477 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Kater built a reversible pendulum (see drawing) consisting of a brass bar with two opposing pivots made of short triangular "knife" blades (a) near either end. It could be swung from either pivot, with the knife blades supported on agate plates. Rather than make one pivot adjustable, he attached the pivots a meter apart and instead adjusted the periods with a moveable weight on the pendulum rod (b,c). In operation, the pendulum is hung in front of a precision clock, and the period timed, then turned upside down and the period timed again. The weight is adjusted with the adjustment screw until the periods are equal. Then putting this period and the distance between the pivots into equation (1) gives the gravitational acceleration g very accurately.
Kater timed the swing of his pendulum using the "method of coincidences" and measured the distance between the two pivots with a micrometer. After applying corrections for the finite amplitude of swing, the buoyancy of the bob, the barometric pressure and altitude, and temperature, he obtained a value of 39.13929 inches for the seconds pendulum at London, in vacuum, at sea level, at 62 °F. The largest variation from the mean of his 12 observations was 0.00028 in. representing a precision of gravity measurement of 7×10−6 (7 mGal or 70 μm/s2). Kater's measurement was used as Britain's official standard of length (see below) from 1824 to 1855.
Reversible pendulums (known technically as "convertible" pendulums) employing Kater's principle were used for absolute gravity measurements into the 1930s.
Later pendulum gravimeters
The increased accuracy made possible by Kater's pendulum helped make gravimetry a standard part of geodesy. Since the exact location (latitude and longitude) of the 'station' where the gravity measurement was made was necessary, gravity measurements became part of surveying, and pendulums were taken on the great geodetic surveys of the 18th century, particularly the Great Trigonometric Survey of India. | Pendulum | Wikipedia | 433 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Invariable pendulums: Kater introduced the idea of relative gravity measurements, to supplement the absolute measurements made by a Kater's pendulum. Comparing the gravity at two different points was an easier process than measuring it absolutely by the Kater method. All that was necessary was to time the period of an ordinary (single pivot) pendulum at the first point, then transport the pendulum to the other point and time its period there. Since the pendulum's length was constant, from (1) the ratio of the gravitational accelerations was equal to the inverse of the ratio of the periods squared, and no precision length measurements were necessary. So once the gravity had been measured absolutely at some central station, by the Kater or other accurate method, the gravity at other points could be found by swinging pendulums at the central station and then taking them to the other location and timing their swing there. Kater made up a set of "invariable" pendulums, with only one knife edge pivot, which were taken to many countries after first being swung at a central station at Kew Observatory, UK.
Airy's coal pit experiments: Starting in 1826, using methods similar to Bouguer, British astronomer George Airy attempted to determine the density of the Earth by pendulum gravity measurements at the top and bottom of a coal mine. The gravitational force below the surface of the Earth decreases rather than increasing with depth, because by Gauss's law the mass of the spherical shell of crust above the subsurface point does not contribute to the gravity. The 1826 experiment was aborted by the flooding of the mine, but in 1854 he conducted an improved experiment at the Harton coal mine, using seconds pendulums swinging on agate plates, timed by precision chronometers synchronized by an electrical circuit. He found the lower pendulum was slower by 2.24 seconds per day. This meant that the gravitational acceleration at the bottom of the mine, 1250 ft below the surface, was 1/14,000 less than it should have been from the inverse square law; that is the attraction of the spherical shell was 1/14,000 of the attraction of the Earth. From samples of surface rock he estimated the mass of the spherical shell of crust, and from this estimated that the density of the Earth was 6.565 times that of water. Von Sterneck attempted to repeat the experiment in 1882 but found inconsistent results. | Pendulum | Wikipedia | 492 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Repsold-Bessel pendulum: It was time-consuming and error-prone to repeatedly swing the Kater's pendulum and adjust the weights until the periods were equal. Friedrich Bessel showed in 1835 that this was unnecessary. As long as the periods were close together, the gravity could be calculated from the two periods and the center of gravity of the pendulum. So the reversible pendulum didn't need to be adjustable, it could just be a bar with two pivots. Bessel also showed that if the pendulum was made symmetrical in form about its center, but was weighted internally at one end, the errors due to air drag would cancel out. Further, another error due to the finite diameter of the knife edges could be made to cancel out if they were interchanged between measurements. Bessel didn't construct such a pendulum, but in 1864 Adolf Repsold, under contract by the Swiss Geodetic Commission made a pendulum along these lines. The Repsold pendulum was about 56 cm long and had a period of about second. It was used extensively by European geodetic agencies, and with the Kater pendulum in the Survey of India. Similar pendulums of this type were designed by Charles Pierce and C. Defforges.
Von Sterneck and Mendenhall gravimeters: In 1887 Austro-Hungarian scientist Robert von Sterneck developed a small gravimeter pendulum mounted in a temperature-controlled vacuum tank to eliminate the effects of temperature and air pressure. It used a "half-second pendulum," having a period close to one second, about 25 cm long. The pendulum was nonreversible, so the instrument was used for relative gravity measurements, but their small size made them small and portable. The period of the pendulum was picked off by reflecting the image of an electric spark created by a precision chronometer off a mirror mounted at the top of the pendulum rod. The Von Sterneck instrument, and a similar instrument developed by Thomas C. Mendenhall of the United States Coast and Geodetic Survey in 1890, were used extensively for surveys into the 1920s. | Pendulum | Wikipedia | 428 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The Mendenhall pendulum was actually a more accurate timekeeper than the highest precision clocks of the time, and as the 'world's best clock' it was used by Albert A. Michelson in his 1924 measurements of the speed of light on Mt. Wilson, California.
Double pendulum gravimeters: Starting in 1875, the increasing accuracy of pendulum measurements revealed another source of error in existing instruments: the swing of the pendulum caused a slight swaying of the tripod stand used to support portable pendulums, introducing error. In 1875 Charles S Peirce calculated that measurements of the length of the seconds pendulum made with the Repsold instrument required a correction of 0.2 mm due to this error. In 1880 C. Defforges used a Michelson interferometer to measure the sway of the stand dynamically, and interferometers were added to the standard Mendenhall apparatus to calculate sway corrections. A method of preventing this error was first suggested in 1877 by Hervé Faye and advocated by Peirce, Cellérier and Furtwangler: mount two identical pendulums on the same support, swinging with the same amplitude, 180° out of phase. The opposite motion of the pendulums would cancel out any sideways forces on the support. The idea was opposed due to its complexity, but by the start of the 20th century the Von Sterneck device and other instruments were modified to swing multiple pendulums simultaneously.
Gulf gravimeter: One of the last and most accurate pendulum gravimeters was the apparatus developed in 1929 by the Gulf Research and Development Co.Lenzen & Multauf 1964, p.336, fig.28 It used two pendulums made of fused quartz, each in length with a period of 0.89 second, swinging on pyrex knife edge pivots, 180° out of phase. They were mounted in a permanently sealed temperature and humidity controlled vacuum chamber. Stray electrostatic charges on the quartz pendulums had to be discharged by exposing them to a radioactive salt before use. The period was detected by reflecting a light beam from a mirror at the top of the pendulum, recorded by a chart recorder and compared to a precision crystal oscillator calibrated against the WWV radio time signal. This instrument was accurate to within (0.3–0.5)×10−7 (30–50 microgals or 3–5 nm/s2). It was used into the 1960s. | Pendulum | Wikipedia | 499 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Relative pendulum gravimeters were superseded by the simpler LaCoste zero-length spring gravimeter, invented in 1934 by Lucien LaCoste. Absolute (reversible) pendulum gravimeters were replaced in the 1950s by free fall gravimeters, in which a weight is allowed to fall in a vacuum tank and its acceleration is measured by an optical interferometer.
Standard of length
Because the acceleration of gravity is constant at a given point on Earth, the period of a simple pendulum at a given location depends only on its length. Additionally, gravity varies only slightly at different locations. Almost from the pendulum's discovery until the early 19th century, this property led scientists to suggest using a pendulum of a given period as a standard of length.
Until the 19th century, countries based their systems of length measurement on prototypes, metal bar primary standards, such as the standard yard in Britain kept at the Houses of Parliament, and the standard toise in France, kept at Paris. These were vulnerable to damage or destruction over the years, and because of the difficulty of comparing prototypes, the same unit often had different lengths in distant towns, creating opportunities for fraud. During the Enlightenment scientists argued for a length standard that was based on some property of nature that could be determined by measurement, creating an indestructible, universal standard. The period of pendulums could be measured very precisely by timing them with clocks that were set by the stars. A pendulum standard amounted to defining the unit of length by the gravitational force of the Earth, for all intents constant, and the second, which was defined by the rotation rate of the Earth, also constant. The idea was that anyone, anywhere on Earth, could recreate the standard by constructing a pendulum that swung with the defined period and measuring its length.
Virtually all proposals were based on the seconds pendulum, in which each swing (a half period) takes one second, which is about a meter (39 inches) long, because by the late 17th century it had become a standard for measuring gravity (see previous section). By the 18th century its length had been measured with sub-millimeter accuracy at a number of cities in Europe and around the world. | Pendulum | Wikipedia | 446 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The initial attraction of the pendulum length standard was that it was believed (by early scientists such as Huygens and Wren) that gravity was constant over the Earth's surface, so a given pendulum had the same period at any point on Earth. So the length of the standard pendulum could be measured at any location, and would not be tied to any given nation or region; it would be a truly democratic, worldwide standard. Although Richer found in 1672 that gravity varies at different points on the globe, the idea of a pendulum length standard remained popular, because it was found that gravity only varies with latitude. Gravitational acceleration increases smoothly from the equator to the poles, due to the oblate shape of the Earth, so at any given latitude (east–west line), gravity was constant enough that the length of a seconds pendulum was the same within the measurement capability of the 18th century. Thus the unit of length could be defined at a given latitude and measured at any point along that latitude. For example, a pendulum standard defined at 45° north latitude, a popular choice, could be measured in parts of France, Italy, Croatia, Serbia, Romania, Russia, Kazakhstan, China, Mongolia, the United States and Canada. In addition, it could be recreated at any location at which the gravitational acceleration had been accurately measured.
By the mid 19th century, increasingly accurate pendulum measurements by Edward Sabine and Thomas Young revealed that gravity, and thus the length of any pendulum standard, varied measurably with local geologic features such as mountains and dense subsurface rocks. So a pendulum length standard had to be defined at a single point on Earth and could only be measured there. This took much of the appeal from the concept, and efforts to adopt pendulum standards were abandoned. | Pendulum | Wikipedia | 355 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Early proposals
One of the first to suggest defining length with a pendulum was Flemish scientist Isaac Beeckman who in 1631 recommended making the seconds pendulum "the invariable measure for all people at all times in all places". Marin Mersenne, who first measured the seconds pendulum in 1644, also suggested it. The first official proposal for a pendulum standard was made by the British Royal Society in 1660, advocated by Christiaan Huygens and Ole Rømer, basing it on Mersenne's work, and Huygens in Horologium Oscillatorium proposed a "horary foot" defined as 1/3 of the seconds pendulum. Christopher Wren was another early supporter. The idea of a pendulum standard of length must have been familiar to people as early as 1663, because Samuel Butler satirizes it in Hudibras:
Upon the bench I will so handle ‘em
That the vibration of this pendulum
Shall make all taylors’ yards of one
Unanimous opinion
In 1671 Jean Picard proposed a pendulum-defined 'universal foot' in his influential Mesure de la Terre. Gabriel Mouton around 1670 suggested defining the toise either by a seconds pendulum or a minute of terrestrial degree. A plan for a complete system of units based on the pendulum was advanced in 1675 by Italian polymath Tito Livio Burratini. In France in 1747, geographer Charles Marie de la Condamine proposed defining length by a seconds pendulum at the equator; since at this location a pendulum's swing wouldn't be distorted by the Earth's rotation. James Steuart (1780) and George Skene Keith were also supporters.
By the end of the 18th century, when many nations were reforming their weight and measure systems, the seconds pendulum was the leading choice for a new definition of length, advocated by prominent scientists in several major nations. In 1790, then US Secretary of State Thomas Jefferson proposed to Congress a comprehensive decimalized US 'metric system' based on the seconds pendulum at 38° North latitude, the mean latitude of the United States. No action was taken on this proposal. In Britain the leading advocate of the pendulum was politician John Riggs Miller. When his efforts to promote a joint British–French–American metric system fell through in 1790, he proposed a British system based on the length of the seconds pendulum at London. This standard was adopted in 1824 (below). | Pendulum | Wikipedia | 489 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
The metre
In the discussions leading up to the French adoption of the metric system in 1791, the leading candidate for the definition of the new unit of length, the metre, was the seconds pendulum at 45° North latitude. It was advocated by a group led by French politician Talleyrand and mathematician Antoine Nicolas Caritat de Condorcet. This was one of the three final options considered by the French Academy of Sciences committee. However, on March 19, 1791, the committee instead chose to base the metre on the length of the meridian through Paris. A pendulum definition was rejected because of its variability at different locations, and because it defined length by a unit of time. (However, since 1983 the metre has been officially defined in terms of the length of the second and the speed of light.) A possible additional reason is that the radical French Academy didn't want to base their new system on the second, a traditional and nondecimal unit from the ancien regime.
Although not defined by the pendulum, the final length chosen for the metre, 10−7 of the pole-to-equator meridian arc, was very close to the length of the seconds pendulum (0.9937 m), within 0.63%. Although no reason for this particular choice was given at the time, it was probably to facilitate the use of the seconds pendulum as a secondary standard, as was proposed in the official document. So the modern world's standard unit of length is certainly closely linked historically with the seconds pendulum.
Britain and Denmark
Britain and Denmark appear to be the only nations that (for a short time) based their units of length on the pendulum. In 1821 the Danish inch was defined as 1/38 of the length of the mean solar seconds pendulum at 45° latitude at the meridian of Skagen, at sea level, in vacuum. The British parliament passed the Imperial Weights and Measures Act in 1824, a reform of the British standard system which declared that if the prototype standard yard was destroyed, it would be recovered by defining the inch so that the length of the solar seconds pendulum at London, at sea level, in a vacuum, at 62 °F was 39.1393 inches. This also became the US standard, since at the time the US used British measures. However, when the prototype yard was lost in the 1834 Houses of Parliament fire, it proved impossible to recreate it accurately from the pendulum definition, and in 1855 Britain repealed the pendulum standard and returned to prototype standards.
Other uses | Pendulum | Wikipedia | 505 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Seismometers
A pendulum in which the rod is not vertical but almost horizontal was used in early seismometers for measuring Earth tremors. The bob of the pendulum does not move when its mounting does, and the difference in the movements is recorded on a drum chart.
Schuler tuning
As first explained by Maximilian Schuler in a 1923 paper, a pendulum whose period exactly equals the orbital period of a hypothetical satellite orbiting just above the surface of the Earth (about 84 minutes) will tend to remain pointing at the center of the Earth when its support is suddenly displaced. This principle, called Schuler tuning, is used in inertial guidance systems in ships and aircraft that operate on the surface of the Earth. No physical pendulum is used, but the control system that keeps the inertial platform containing the gyroscopes stable is modified so the device acts as though it is attached to such a pendulum, keeping the platform always facing down as the vehicle moves on the curved surface of the Earth.
Coupled pendulums
In 1665 Huygens made a curious observation about pendulum clocks. Two clocks had been placed on his mantlepiece, and he noted that they had acquired an opposing motion. That is, their pendulums were beating in unison but in the opposite direction; 180° out of phase. Regardless of how the two clocks were started, he found that they would eventually return to this state, thus making the first recorded observation of a coupled oscillator.
The cause of this behavior was that the two pendulums were affecting each other through slight motions of the supporting mantlepiece. This process is called entrainment or mode locking in physics and is observed in other coupled oscillators. Synchronized pendulums have been used in clocks and were widely used in gravimeters in the early 20th century. Although Huygens only observed out-of-phase synchronization, recent investigations have shown the existence of in-phase synchronization, as well as "death" states wherein one or both clocks stops.
Religious practice
Pendulum motion appears in religious ceremonies as well. The swinging incense burner called a censer, also known as a thurible, is an example of a pendulum. Pendulums are also seen at many gatherings in eastern Mexico where they mark the turning of the tides on the day which the tides are at their highest point. Pendulums may also be used for dowsing.
Education | Pendulum | Wikipedia | 493 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
Pendulums are widely used in science education as an example of a harmonic oscillator, to teach dynamics and oscillatory motion. One use is to demonstrate the law of conservation of energy. A heavy object such as a bowling ball or wrecking ball is attached to a string. The weight is then moved to within a few inches of a volunteer's face, then released and allowed to swing and come back. In most instances, the weight reverses direction and then returns to (almost) the same position as the original release location — i.e. a small distance from the volunteer's face — thus leaving the volunteer unharmed. On occasion the volunteer is injured if either the volunteer does not stand still or the pendulum is initially released with a push (so that when it returns it surpasses the release position).
Torture device
It is claimed that the pendulum was used as an instrument of torture and execution by the Spanish Inquisition in the 18th century. The allegation is contained in the 1826 book The history of the Inquisition of Spain by the Spanish priest, historian and liberal activist Juan Antonio Llorente. A swinging pendulum whose edge is a knife blade slowly descends toward a bound prisoner until it cuts into his body. This method of torture came to popular consciousness through the 1842 short story "The Pit and the Pendulum" by American author Edgar Allan Poe.
Most knowledgeable sources are skeptical that this torture was ever actually used. The only evidence of its use is one paragraph in the preface to Llorente's 1826 History, relating a second-hand account by a single prisoner released from the Inquisition's Madrid dungeon in 1820, who purportedly described the pendulum torture method. Modern sources point out that due to Jesus' admonition against bloodshed, Inquisitors were only allowed to use torture methods which did not spill blood, and the pendulum method would have violated this stricture. One theory is that Llorente misunderstood the account he heard; the prisoner was actually referring to another common Inquisition torture, the strappado (garrucha), in which the prisoner has his hands tied behind his back and is hoisted off the floor by a rope tied to his hands. This method was also known as the "pendulum". Poe's popular horror tale, and public awareness of the Inquisition's other brutal methods, has kept the myth of this elaborate torture method alive.
Pendulum wave | Pendulum | Wikipedia | 488 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
A pendulum wave is a physics demonstration and kinetic art comprising several uncoupled pendulums with different lengths. As the pendulums oscillate, they appear to produce travelling and standing waves, beating, and random motion. | Pendulum | Wikipedia | 46 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null |
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.
Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites). Extant cephalopods range in size from the 10 mm (0.3 in) Idiosepius thailandicus to the 700 kilograms (1,500 lb) heavy colossal squid, the largest extant invertebrate.
Distribution
There are over 800 extant species of cephalopod, although new species continue to be described. An estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not easily fossilised.
Cephalopods are found in all the oceans of Earth. None of them can tolerate fresh water, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water. Cephalopods are thought to be unable to live in fresh water due to multiple biochemical constraints, and in their >400 million year existence have never ventured into fully freshwater habitats. | Cephalopod | Wikipedia | 458 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Cephalopods occupy most of the depth of the ocean, from the abyssal plains to the sea surface, and have also been found in the hadal zone. Their diversity is greatest near the equator (~40 species retrieved in nets at 11°N by a diversity study) and decreases towards the poles (~5 species captured at 60°N).
Biology
Nervous system and behavior
Cephalopods are widely regarded as the most intelligent of the invertebrates and have well-developed senses and large brains (larger than those of gastropods). The nervous system of cephalopods is the most complex of the invertebrates and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates. Captive cephalopods have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on captive crabs, and return to their own aquarium.
The brain is protected in a cartilaginous cranium. The giant nerve fibers of the cephalopod mantle have been widely used for many years as experimental material in neurophysiology; their large diameter (due to lack of myelination) makes them relatively easy to study compared with other animals.
Many cephalopods are social creatures; when isolated from their own kind, some species have been observed shoaling with fish.
Some cephalopods are able to fly through the air for distances of up to . While cephalopods are not particularly aerodynamic, they achieve these impressive ranges by jet-propulsion; water continues to be expelled from the funnel while the organism is in the air. The animals spread their fins and tentacles to form wings and actively control lift force with body posture. One species, Todarodes pacificus, has been observed spreading tentacles in a flat fan shape with a mucus film between the individual tentacles, while another, Sepioteuthis sepioidea, has been observed putting the tentacles in a circular arrangement.
Senses
Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of chemical sense organs. Octopuses use their arms to explore their environment and can use them for depth perception.
Vision | Cephalopod | Wikipedia | 455 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Most cephalopods rely on vision to detect predators and prey and to communicate with one another. Consequently, cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. The morphological construction gives cephalopod eyes the same performance as shark eyes; however, their construction differs, as cephalopods lack a cornea and have an everted retina. Cephalopods' eyes are also sensitive to the plane of polarization of light. Unlike many other cephalopods, nautiluses do not have good vision; their eye structure is highly developed, but lacks a solid lens. They have a simple "pinhole" eye through which water can pass. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates.
All octopuses and most cephalopods are considered to be color blind. Coleoid cephalopods (octopus, squid, cuttlefish) have a single photoreceptor type and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels. When camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment. They also produce visual pigments throughout their body and may sense light levels directly from their body. Evidence of color vision has been found in the sparkling enope squid (Watasenia scintillans). It achieves color vision with three photoreceptors, which are based on the same opsin, but use distinct retinal molecules as chromophores: A1 (retinal), A3 (3-dehydroretinal), and A4 (4-hydroxyretinal). The A1-photoreceptor is most sensitive to green-blue (484 nm), the A2-photoreceptor to blue-green (500 nm), and the A4-photoreceptor to blue (470 nm) light. | Cephalopod | Wikipedia | 470 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
In 2015, a novel mechanism for spectral discrimination in cephalopods was described. This relies on the exploitation of chromatic aberration (wavelength-dependence of focal length). Numerical modeling shows that chromatic aberration can yield useful chromatic information through the dependence of image acuity on accommodation. The unusual off-axis slit and annular pupil shapes in cephalopods enhance this ability by acting as prisms which are scattering white light in all directions.
Photoreception
In 2015, molecular evidence was published indicating that cephalopod chromatophores are photosensitive; reverse transcription polymerase chain reactions (RT-PCR) revealed transcripts encoding rhodopsin and retinochrome within the retinas and skin of the longfin inshore squid (Doryteuthis pealeii), and the common cuttlefish (Sepia officinalis) and broadclub cuttlefish (Sepia latimanus). The authors claim this is the first evidence that cephalopod dermal tissues may possess the required combination of molecules to respond to light.
Hearing
Some squids have been shown to detect sound using their statocysts, but, in general, cephalopods are deaf.
Use of light
Most cephalopods possess an assemblage of skin components that interact with light. These may include iridophores, leucophores, chromatophores and (in some species) photophores. Chromatophores are colored pigment cells that expand and contract in accordance to produce color and pattern which they can use in a startling array of fashions. As well as providing camouflage with their background, some cephalopods bioluminesce, shining light downwards to disguise their shadows from any predators that may lurk below. The bioluminescence is produced by bacterial symbionts; the host cephalopod is able to detect the light produced by these organisms. Bioluminescence may also be used to entice prey, and some species use colorful displays to impress mates, startle predators, or even communicate with one another.
Coloration | Cephalopod | Wikipedia | 443 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Cephalopods can change their colors and patterns in milliseconds, whether for signalling (both within the species and for warning) or active camouflage, as their chromatophores are expanded or contracted. Although color changes appear to rely primarily on vision input, there is evidence that skin cells, specifically chromatophores, can detect light and adjust to light conditions independently of the eyes. The octopus changes skin color and texture during quiet and active sleep cycles.
Cephalopods can use chromatophores like a muscle, which is why they can change their skin hue as rapidly as they do.
Coloration is typically stronger in near-shore species than those living in the open ocean, whose functions tend to be restricted to disruptive camouflage. These chromatophores are found throughout the body of the octopus, however, they are controlled by the same part of the brain that controls elongation during jet propulsion to reduce drag. As such, jetting octopuses can turn pale because the brain is unable to achieve both controlling elongation and controlling the chromatophores. Most octopuses mimic select structures in their field of view rather than becoming a composite color of their full background.
Evidence of original coloration has been detected in cephalopod fossils dating as far back as the Silurian; these orthoconic individuals bore concentric stripes, which are thought to have served as camouflage. Devonian cephalopods bear more complex color patterns, of unknown function. | Cephalopod | Wikipedia | 305 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Chromatophores
Coleoids, a shell-less subclass of cephalopods (squid, cuttlefish, and octopuses), have complex pigment containing cells called chromatophores which are capable of producing rapidly changing color patterns. These cells store pigment within an elastic sac which produces the color seen from these cells. Coleoids can change the shape of this sac, called the cytoelastic sacculus, which then causes changes in the translucency and opacity of the cell. By rapidly changing multiple chromatophores of different colors, cephalopods are able to change the color of their skin at astonishing speeds, an adaptation that is especially notable in an organism that sees in black and white. Chromatophores are known to only contain three pigments, red, yellow, and brown, which cannot create the full color spectrum. However, cephalopods also have cells called iridophores, thin, layered protein cells that reflect light in ways that can produce colors chromatophores cannot. The mechanism of iridophore control is unknown, but chromatophores are under the control of neural pathways, allowing the cephalopod to coordinate elaborate displays. Together, chromatophores and iridophores are able to produce a large range of colors and pattern displays. | Cephalopod | Wikipedia | 278 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Adaptive value
Cephalopods utilize chromatophores' color changing ability in order to camouflage themselves. Chromatophores allow coleoids to blend into many different environments, from coral reefs to the sandy sea floor. The color change of chromatophores works in concert with papillae, epithelial tissue which grows and deforms through hydrostatic motion to change skin texture. Chromatophores are able to perform two types of camouflage, mimicry and color matching. Mimicry is when an organism changes its appearance to appear like a different organism. The squid Sepioteuthis sepioidea has been documented changing its appearance to appear as the non threatening herbivorous parrotfish to approach unaware prey. The octopus Thaumoctopus mimicus is known to mimic a number of different venomous organisms it cohabitates with to deter predators. While background matching, a cephalopod changes its appearance to resemble its surroundings, hiding from its predators or concealing itself from prey. The ability to both mimic other organisms and match the appearance of their surroundings is notable given that cephalopods' vision is monochromatic.
Cephalopods also use their fine control of body coloration and patterning to perform complex signaling displays for both conspecific and intraspecific communication. Coloration is used in concert with locomotion and texture to send signals to other organisms. Intraspecifically this can serve as a warning display to potential predators. For example, when the octopus Callistoctopus macropus is threatened, it will turn a bright red brown color speckled with white dots as a high contrast display to startle predators. Conspecifically, color change is used for both mating displays and social communication. Cuttlefish have intricate mating displays from males to females. There is also male to male signaling that occurs during competition over mates, all of which are the product of chromatophore coloration displays.
Origin
There are two hypotheses about the evolution of color change in cephalopods. One hypothesis is that the ability to change color may have evolved for social, sexual, and signaling functions. Another explanation is that it first evolved because of selective pressures encouraging predator avoidance and stealth hunting. | Cephalopod | Wikipedia | 462 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
For color change to have evolved as the result of social selection the environment of cephalopods' ancestors would have to fit a number of criteria. One, there would need to be some kind of mating ritual that involved signaling. Two, they would have to experience demonstrably high levels of sexual selection. And three, the ancestor would need to communicate using sexual signals that are visible to a conspecific receiver. For color change to have evolved as the result of natural selection different parameters would have to be met. For one, one would need some phenotypic diversity in body patterning among the population. The species would also need to cohabitate with predators which rely on vision for prey identification. These predators should have a high range of visual sensitivity, detecting not just motion or contrast but also colors. The habitats they occupy would also need to display a diversity of backgrounds. Experiments done in dwarf chameleons testing these hypotheses showed that chameleon taxa with greater capacity for color change had more visually conspicuous social signals but did not come from more visually diverse habitats, suggesting that color change ability likely evolved to facilitate social signaling, while camouflage is a useful byproduct. Because camouflage is used for multiple adaptive purposes in cephalopods, color change could have evolved for one use and the other developed later, or it evolved to regulate trade offs within both.
Convergent evolution
Color change is widespread in ectotherms including anoles, frogs, mollusks, many fish, insects, and spiders. The mechanism behind this color change can be either morphological or physiological. Morphological change is the result of a change in the density of pigment containing cells and tends to change over longer periods of time. Physiological change, the kind observed in cephalopod lineages, is typically the result of the movement of pigment within the chromatophore, changing where different pigments are localized within the cell. This physiological change typically occurs on much shorter timescales compared to morphological change. Cephalopods have a rare form of physiological color change which utilizes neural control of muscles to change the morphology of their chromatophores. This neural control of chromatophores has evolved convergently in both cephalopods and teleosts fishes.
Ink | Cephalopod | Wikipedia | 461 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
With the exception of the Nautilidae and the species of octopus belonging to the suborder Cirrina, all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse predators. This sac is a muscular bag which originated as an extension of the hindgut. It lies beneath the gut and opens into the anus, into which its contents – almost pure melanin – can be squirted; its proximity to the base of the funnel means the ink can be distributed by ejected water as the cephalopod uses its jet propulsion. The ejected cloud of melanin is usually mixed, upon expulsion, with mucus, produced elsewhere in the mantle, and therefore forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator, like a smokescreen. However, a more sophisticated behavior has been observed, in which the cephalopod releases a cloud, with a greater mucus content, that approximately resembles the cephalopod that released it (this decoy is referred to as a pseudomorph). This strategy often results in the predator attacking the pseudomorph, rather than its rapidly departing prey. For more information, see Inking behaviors.
The ink sac of cephalopods has led to a common name of "inkfish", formerly the pen-and-ink fish.
Circulatory system
Cephalopods are the only molluscs with a closed circulatory system. Coleoids have two gill hearts (also known as branchial hearts) that move blood through the capillaries of the gills. A single systemic heart then pumps the oxygenated blood through the rest of the body. | Cephalopod | Wikipedia | 355 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Like most molluscs, cephalopods use hemocyanin, a copper-containing protein, rather than hemoglobin, to transport oxygen. As a result, their blood is colorless when deoxygenated and turns blue when bonded to oxygen. In oxygen-rich environments and in acidic water, hemoglobin is more efficient, but in environments with little oxygen and in low temperatures, hemocyanin has the upper hand. The hemocyanin molecule is much larger than the hemoglobin molecule, allowing it to bond with 96 or molecules, instead of the hemoglobin's just four. But unlike hemoglobin, which are attached in millions on the surface of a single red blood cell, hemocyanin molecules float freely in the bloodstream.
Respiration
Cephalopods exchange gases with the seawater by forcing water through their gills, which are attached to the roof of the organism. Water enters the mantle cavity on the outside of the gills, and the entrance of the mantle cavity closes. When the mantle contracts, water is forced through the gills, which lie between the mantle cavity and the funnel. The water's expulsion through the funnel can be used to power jet propulsion. If respiration is used concurrently with jet propulsion, large losses in speed or oxygen generation can be expected. The gills, which are much more efficient than those of other mollusks, are attached to the ventral surface of the mantle cavity. There is a trade-off with gill size regarding lifestyle. To achieve fast speeds, gills need to be small – water will be passed through them quickly when energy is needed, compensating for their small size. However, organisms which spend most of their time moving slowly along the bottom do not naturally pass much water through their cavity for locomotion; thus they have larger gills, along with complex systems to ensure that water is constantly washing through their gills, even when the organism is stationary. The water flow is controlled by contractions of the radial and circular mantle cavity muscles.
The gills of cephalopods are supported by a skeleton of robust fibrous proteins; the lack of mucopolysaccharides distinguishes this matrix from cartilage. The gills are also thought to be involved in excretion, with NH4+ being swapped with K+ from the seawater.
Locomotion and buoyancy | Cephalopod | Wikipedia | 490 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
While most cephalopods can move by jet propulsion, this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The efficiency of a propeller-driven waterjet (i.e. Froude efficiency) is greater than a rocket. The relative efficiency of jet propulsion decreases further as animal size increases; paralarvae are far more efficient than juvenile and adult individuals. Since the Paleozoic era, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity. Whilst jet propulsion is never the sole mode of locomotion, the stop-start motion provided by the jets continues to be useful for providing bursts of high speed – not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates, and they can out-accelerate most fish. The jet is supplemented with fin motion; in the squid, the fins flap each time that a jet is released, amplifying the thrust; they are then extended between jets (presumably to avoid sinking). Oxygenated water is taken into the mantle cavity to the gills and through muscular contraction of this cavity, the spent water is expelled through the hyponome, created by a fold in the mantle. The size difference between the posterior and anterior ends of this organ control the speed of the jet the organism can produce. The velocity of the organism can be accurately predicted for a given mass and morphology of animal. Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions. Some cephalopods accompany this expulsion of water with a gunshot-like popping noise, thought to function to frighten away potential predators.
Cephalopods employ a similar method of propulsion despite their increasing size (as they grow) changing the dynamics of the water in which they find themselves. Thus their paralarvae do not extensively use their fins (which are less efficient at low Reynolds numbers) and primarily use their jets to propel themselves upwards, whereas large adult cephalopods tend to swim less efficiently and with more reliance on their fins. | Cephalopod | Wikipedia | 460 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Early cephalopods are thought to have produced jets by drawing their body into their shells, as Nautilus does today. Nautilus is also capable of creating a jet by undulations of its funnel; this slower flow of water is more suited to the extraction of oxygen from the water. When motionless, Nautilus can only extract 20% of oxygen from the water. The jet velocity in Nautilus is much slower than in coleoids, but less musculature and energy is involved in its production. Jet thrust in cephalopods is controlled primarily by the maximum diameter of the funnel orifice (or, perhaps, the average diameter of the funnel) and the diameter of the mantle cavity. Changes in the size of the orifice are used most at intermediate velocities. The absolute velocity achieved is limited by the cephalopod's requirement to inhale water for expulsion; this intake limits the maximum velocity to eight body-lengths per second, a speed which most cephalopods can attain after two funnel-blows. Water refills the cavity by entering not only through the orifices, but also through the funnel. Squid can expel up to 94% of the fluid within their cavity in a single jet thrust. To accommodate the rapid changes in water intake and expulsion, the orifices are highly flexible and can change their size by a factor of 20; the funnel radius, conversely, changes only by a factor of around 1.5.
Some octopus species are also able to walk along the seabed. Squids and cuttlefish can move short distances in any direction by rippling of a flap of muscle around the mantle.
While most cephalopods float (i.e. are neutrally buoyant or nearly so; in fact most cephalopods are about 2–3% denser than seawater), they achieve this in different ways.
Some, such as Nautilus, allow gas to diffuse into the gap between the mantle and the shell; others allow purer water to ooze from their kidneys, forcing out denser salt water from the body cavity; others, like some fish, accumulate oils in the liver; and some octopuses have a gelatinous body with lighter chloride ions replacing sulfate in the body chemistry. | Cephalopod | Wikipedia | 471 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Squids are the primary sufferers of negative buoyancy in cephalopods. The negative buoyancy means that some squids, especially those whose habitat depths are rather shallow, have to actively regulate their vertical positions. This means that they must expend energy, often through jetting or undulations, in order to maintain the same depth. As such, the cost of transport of many squids are quite high. That being said, squid and other cephalopod that dwell in deep waters tend to be more neutrally buoyant which removes the need to regulate depth and increases their locomotory efficiency.
The Macrotritopus defilippi, or the sand-dwelling octopus, was seen mimicking both the coloration and the swimming movements of the sand-dwelling flounder Bothus lunatus to avoid predators. The octopuses were able to flatten their bodies and put their arms back to appear the same as the flounders as well as move with the same speed and movements.
Females of two species, Ocythoe tuberculata and Haliphron atlanticus, have evolved a true swim bladder.
Octopus vs. squid locomotion
Two of the categories of cephalopods, octopus and squid, are vastly different in their movements despite being of the same class. Octopuses are generally not seen as active swimmers; they are often found scavenging the sea floor instead of swimming long distances through the water. Squid, on the other hand, can be found to travel vast distances, with some moving as much as 2,000 km in 2.5 months at an average pace of 0.9 body lengths per second. There is a major reason for the difference in movement type and efficiency: anatomy. | Cephalopod | Wikipedia | 356 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Both octopuses and squids have mantles (referenced above) which function towards respiration and locomotion in the form of jetting. The composition of these mantles differs between the two families, however. In octopuses, the mantle is made up of three muscle types: longitudinal, radial, and circular. The longitudinal muscles run parallel to the length of the octopus and they are used in order to keep the mantle the same length throughout the jetting process. Given that they are muscles, it can be noted that this means the octopus must actively flex the longitudinal muscles during jetting in order to keep the mantle at a constant length. The radial muscles run perpendicular to the longitudinal muscles and are used to thicken and thin the wall of the mantle. Finally, the circular muscles are used as the main activators in jetting. They are muscle bands that surround the mantle and expand/contract the cavity. All three muscle types work in unison to produce a jet as a propulsion mechanism.
Squids do not have the longitudinal muscles that octopus do. Instead, they have a tunic. This tunic is made of layers of collagen and it surrounds the top and the bottom of the mantle. Because they are made of collagen and not muscle, the tunics are rigid bodies that are much stronger than the muscle counterparts. This provides the squids some advantages for jet propulsion swimming. The stiffness means that there is no necessary muscle flexing to keep the mantle the same size. In addition, tunics take up only 1% of the squid mantle's wall thickness, whereas the longitudinal muscle fibers take up to 20% of the mantle wall thickness in octopuses. Also because of the rigidity of the tunic, the radial muscles in squid can contract more forcefully.
The mantle is not the only place where squids have collagen. Collagen fibers are located throughout the other muscle fibers in the mantle. These collagen fibers act as elastics and are sometimes named "collagen springs". As the name implies, these fibers act as springs. When the radial and circular muscles in the mantle contract, they reach a point where the contraction is no longer efficient to the forward motion of the creature. In such cases, the excess contraction is stored in the collagen which then efficiently begins or aids in the expansion of the mantle at the end of the jet. In some tests, the collagen has been shown to be able to begin raising mantle pressure up to 50ms before muscle activity is initiated. | Cephalopod | Wikipedia | 511 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
These anatomical differences between squid and octopuses can help explain why squid can be found swimming comparably to fish while octopuses usually rely on other forms of locomotion on the sea floor such as bipedal walking, crawling, and non-jetting swimming.
Shell
Nautiluses are the only extant cephalopods with a true external shell. However, all molluscan shells are formed from the ectoderm (outer layer of the embryo); in cuttlefish (Sepia spp.), for example, an invagination of the ectoderm forms during the embryonic period, resulting in a shell (cuttlebone) that is internal in the adult. The same is true of the chitinous gladius of squid and octopuses. Cirrate octopods have arch-shaped cartilaginous fin supports, which are sometimes referred to as a "shell vestige" or "gladius". The Incirrina have either a pair of rod-shaped stylets or no vestige of an internal shell, and some squid also lack a gladius. The shelled coleoids do not form a clade or even a paraphyletic group. The Spirula shell begins as an organic structure, and is then very rapidly mineralized. Shells that are "lost" may be lost by resorption of the calcium carbonate component.
Females of the octopus genus Argonauta secrete a specialized paper-thin egg case in which they reside, and this is popularly regarded as a "shell", although it is not attached to the body of the animal and has a separate evolutionary origin.
The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common as fossils.
The deposition of carbonate, leading to a mineralized shell, appears to be related to the acidity of the organic shell matrix (see Mollusc shell); shell-forming cephalopods have an acidic matrix, whereas the gladius of squid has a basic matrix. The basic arrangement of the cephalopod outer wall is: an outer (spherulitic) prismatic layer, a laminar (nacreous) layer and an inner prismatic layer. The thickness of every layer depends on the taxa. In modern cephalopods, the Ca carbonate is aragonite. As for other mollusc shells or coral skeletons, the smallest visible units are irregular rounded granules.
Head appendages | Cephalopod | Wikipedia | 512 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Cephalopods, as the name implies, have muscular appendages extending from their heads and surrounding their mouths. These are used in feeding, mobility, and even reproduction. In coleoids they number eight or ten. Decapods such as cuttlefish and squid have five pairs. The longer two, termed "tentacles", are actively involved in capturing prey; they can lengthen rapidly (in as little as 15 milliseconds). In giant squid, they may reach a length of 8 metres. They may terminate in a broadened, sucker-coated club. The shorter four pairs are termed arms, and are involved in holding and manipulating the captured organism. They too have suckers, on the side closest to the mouth; these help to hold onto the prey. Octopods only have four pairs of sucker-coated arms, as the name suggests, though developmental abnormalities can modify the number of arms expressed.
The tentacle consists of a thick central nerve cord (which must be thick to allow each sucker to be controlled independently) surrounded by circular and radial muscles. Because the volume of the tentacle remains constant, contracting the circular muscles decreases the radius and permits the rapid increase in length. Typically, a 70% lengthening is achieved by decreasing the width by 23%. The shorter arms lack this capability.
The size of the tentacle is related to the size of the buccal cavity; larger, stronger tentacles can hold prey as small bites are taken from it; with more numerous, smaller tentacles, prey is swallowed whole, so the mouth cavity must be larger.
Externally shelled nautilids (Nautilus and Allonautilus) have on the order of 90 finger-like appendages, termed tentacles, which lack suckers but are sticky instead, and are partly retractable.
Feeding
All living cephalopods have a two-part beak; most have a radula, although it is reduced in most octopus and absent altogether in Spirula. They feed by capturing prey with their tentacles, drawing it into their mouth and taking bites from it. They have a mixture of toxic digestive juices, some of which are manufactured by symbiotic algae, which they eject from their salivary glands onto their captured prey held in their mouths. These juices separate the flesh of their prey from the bone or shell. The salivary gland has a small tooth at its end which can be poked into an organism to digest it from within. | Cephalopod | Wikipedia | 506 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
The digestive gland itself is rather short. It has four elements, with food passing through the crop, stomach and caecum before entering the intestine. Most digestion, as well as the absorption of nutrients, occurs in the digestive gland, sometimes called the liver. Nutrients and waste materials are exchanged between the gut and the digestive gland through a pair of connections linking the gland to the junction of the stomach and caecum. Cells in the digestive gland directly release pigmented excretory chemicals into the lumen of the gut, which are then bound with mucus passed through the anus as long dark strings, ejected with the aid of exhaled water from the funnel. Cephalopods tend to concentrate ingested heavy metals in their body tissue. However, octopus arms use a family of cephalopod-specific chemotactile receptors (CRs) to be their "taste by touch" system.
Radula
The cephalopod radula consists of multiple symmetrical rows of up to nine teeth – thirteen in fossil classes. The organ is reduced or even vestigial in certain octopus species and is absent in Spirula. The teeth may be homodont (i.e. similar in form across a row), heterodont (otherwise), or ctenodont (comb-like). Their height, width and number of cusps is variable between species. The pattern of teeth repeats, but each row may not be identical to the last; in the octopus, for instance, the sequence repeats every five rows.
Cephalopod radulae are known from fossil deposits dating back to the Ordovician. They are usually preserved within the cephalopod's body chamber, commonly in conjunction with the mandibles; but this need not always be the case; many radulae are preserved in a range of settings in the Mason Creek. Radulae are usually difficult to detect, even when they are preserved in fossils, as the rock must weather and crack in exactly the right fashion to expose them; for instance, radulae have only been found in nine of the 43 ammonite genera, and they are rarer still in non-ammonoid forms: only three pre-Mesozoic species possess one. | Cephalopod | Wikipedia | 475 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Excretory system
Most cephalopods possess a single pair of large nephridia. Filtered nitrogenous waste is produced in the pericardial cavity of the branchial hearts, each of which is connected to a nephridium by a narrow canal. The canal delivers the excreta to a bladder-like renal sac, and also resorbs excess water from the filtrate. Several outgrowths of the lateral vena cava project into the renal sac, continuously inflating and deflating as the branchial hearts beat. This action helps to pump the secreted waste into the sacs, to be released into the mantle cavity through a pore.
Nautilus, unusually, possesses four nephridia, none of which are connected to the pericardial cavities.
The incorporation of ammonia is important for shell formation in terrestrial molluscs and other non-molluscan lineages. Because protein (i.e., flesh) is a major constituent of the cephalopod diet, large amounts of ammonium ions are produced as waste. The main organs involved with the release of this excess ammonium are the gills. The rate of release is lowest in the shelled cephalopods Nautilus and Sepia as a result of their using nitrogen to fill their shells with gas to increase buoyancy. Other cephalopods use ammonium in a similar way, storing the ions (as ammonium chloride) to reduce their overall density and increase buoyancy.
Reproduction and life cycle | Cephalopod | Wikipedia | 315 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Cephalopods are a diverse group of species, but share common life history traits, for example, they have a rapid growth rate and short life spans. Stearns (1992) suggested that in order to produce the largest possible number of viable offspring, spawning events depend on the ecological environmental factors of the organism. The majority of cephalopods do not provide parental care to their offspring, except, for example, octopus, which helps this organism increase the survival rate of their offspring. Marine species' life cycles are affected by various environmental conditions. The development of a cephalopod embryo can be greatly affected by temperature, oxygen saturation, pollution, light intensity, and salinity. These factors are important to the rate of embryonic development and the success of hatching of the embryos. Food availability also plays an important role in the reproductive cycle of cephalopods. A limitation of food influences the timing of spawning along with their function and growth. Spawning time and spawning vary among marine species; it's correlated with temperature, though cephalopods in shallow water spawn in cold months so that the offspring would hatch at warmer temperatures. Breeding can last from several days to a month. | Cephalopod | Wikipedia | 243 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Sexual maturity
Cephalopods that are sexually mature and of adult size begin spawning and reproducing. After the transfer of genetic material to the following generation, the adult cephalopods in most species then die. Sexual maturation in male and female cephalopods can be observed internally by the enlargement of gonads and accessory glands. Mating would be a poor indicator of sexual maturation in females; they can receive sperm when not fully reproductively mature and store them until they are ready to fertilize the eggs. Males are more aggressive in their pre-mating competition when in the presence of immature females than when competing for a sexually mature female. Most cephalopod males develop a hectocotylus, an arm tip which is capable of transferring their spermatozoa into the female mantle cavity. Though not all species use a hectocotylus; for example, the adult nautilus releases a spadix. Some male squids, mainly deep-water species, have instead evolved a penis longer than their own body length, the longest penis in any free-living animals. It is assumed these males simply attach a spermatophore anywhere on a female's body. An indication of sexual maturity of females is the development of brachial photophores to attract mates. | Cephalopod | Wikipedia | 270 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Fertilization
Cephalopods are not broadcast spawners. During the process of fertilization, the females use sperm provided by the male via external fertilization. Internal fertilization is seen only in octopuses. The initiation of copulation begins when the male catches a female and wraps his arm around her, either in a "male to female neck" position or mouth to mouth position, depending on the species. The males then initiate the process of fertilization by contracting their mantle several times to release the spermatozoa. Cephalopods often mate several times, which influences males to mate longer with females that have previously, nearly tripling the number of contractions of the mantle. To ensure the fertilization of the eggs, female cephalopods release a sperm-attracting peptide through the gelatinous layers of the egg to direct the spermatozoa. Female cephalopods lay eggs in clutches; each egg is composed of a protective coat to ensure the safety of the developing embryo when released into the water column. Reproductive strategies differ between cephalopod species. In the giant Pacific octopus, large eggs are laid in a den; it will often take several days to lay all of them. Once the eggs are released and normally attached to a sheltered substrate, the female usually die shortly after, but octopuses and a few squids will look after their eggs afterwards. Others, like the Japanese flying squid, will spawn neutrally buoyant egg masses which will float at the interface between water layers of slightly different densities, or the female will swim around while carrying the eggs with her. Most species are semelparous (only reproduce once before dying), the only known exceptions are the vampire squid, the lesser Pacific striped octopus and the nautilus, which are iteroparous. In some species of cephalopods, egg clutches are anchored to substrates by a mucilaginous adhesive substance. These eggs are swelled with perivitelline fluid (PVF), a hypertonic fluid that prevents premature hatching. Fertilized egg clusters are neutrally buoyant depending on the depth that they were laid, but can also be found in substrates such as sand, a matrix of corals, or seaweed. Because these species do not provide parental care for their offspring, egg capsules can be injected with ink by the female in order to camouflage the embryos from predators. | Cephalopod | Wikipedia | 498 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Male–male competition
Most cephalopods engage in aggressive sex: a protein in the male capsule sheath stimulates this behavior. They also engage in male–male aggression, where larger males tend to win the interactions. When a female is near, the males charge one another continuously and flail their arms. If neither male backs away, the arms extend to the back, exposing the mouth, followed by the biting of arm tips. During mate competition males also participate in a technique called flushing. This technique is used by the second male attempting to mate with a female. Flushing removes spermatophores in the buccal cavity that was placed there by the first mate by forcing water into the cavity. Another behavior that males engage in is sneaker mating or mimicry – smaller males adjust their behavior to that of a female in order to reduce aggression. By using this technique, they are able to fertilize the eggs while the larger male is distracted by a different male. During this process, the sneaker males quickly insert drop-like sperm into the seminal receptacle.
Mate choice
Mate choice is seen in cuttlefish species, where females prefer some males over others, though characteristics of the preferred males are unknown. A hypothesis states that females reject males by olfactory cues rather than visual cues. Several cephalopod species are polyandrous – accepting and storing multiple male spermatophores, which has been identified by DNA fingerprinting. Females are no longer receptive to mating attempts when holding their eggs in their arms. Females can store sperm in two places (1) the buccal cavity where recently mated males place their spermatophores, and (2) the internal sperm-storage receptacles where sperm packages from previous males are stored. Spermatophore storage results in sperm competition; which states that the female controls which mate fertilizes the eggs. In order to reduce this sort of competition, males develop agonistic behaviors like mate guarding and flushing. The Hapalochlaena lunulata, or the blue-ringed octopus, readily mates with both males and females. | Cephalopod | Wikipedia | 432 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Sexual dimorphism
In a variety of marine organisms, it is seen that females are larger in size compared to the males in some closely related species. In some lineages, such as the blanket octopus, males become structurally smaller and smaller resembling a term, "dwarfism" dwarf males usually occurs at low densities. The blanket octopus male is an example of sexual-evolutionary dwarfism; females grow 10,000 to 40,000 times larger than the males and the sex ratio between males and females can be distinguished right after hatching of the eggs.
Embryology
Cephalopod eggs span a large range of sizes, from 1 to 30 mm in diameter. The fertilised ovum initially divides to produce a disc of germinal cells at one pole, with the yolk remaining at the opposite pole. The germinal disc grows to envelop and eventually absorb the yolk, forming the embryo. The tentacles and arms first appear at the hind part of the body, where the foot would be in other molluscs, and only later migrate towards the head.
The funnel of cephalopods develops on the top of their head, whereas the mouth develops on the opposite surface. The early embryological stages are reminiscent of ancestral gastropods and extant Monoplacophora.
The shells develop from the ectoderm as an organic framework which is subsequently mineralized. In Sepia, which has an internal shell, the ectoderm forms an invagination whose pore is sealed off before this organic framework is deposited.
Development
The length of time before hatching is highly variable; smaller eggs in warmer waters are the fastest to hatch, and newborns can emerge after as little as a few days. Larger eggs in colder waters can develop for over a year before hatching.
The process from spawning to hatching follows a similar trajectory in all species, the main variable being the amount of yolk available to the young and when it is absorbed by the embryo.
Unlike most other molluscs, cephalopods do not have a morphologically distinct larval stage. Instead, the juveniles are known as paralarvae. They quickly learn how to hunt, using encounters with prey to refine their strategies.
Growth in juveniles is usually allometric, whilst adult growth is isometric.
Evolution | Cephalopod | Wikipedia | 472 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
The traditional view of cephalopod evolution holds that they evolved in the Late Cambrian from a monoplacophoran-like ancestor with a curved, tapering shell, which was closely related to the gastropods (snails). The similarity of the early shelled cephalopod Plectronoceras to some gastropods was used in support of this view. The development of a siphuncle would have allowed the shells of these early forms to become gas-filled (thus buoyant) in order to support them and keep the shells upright while the animal crawled along the floor, and separated the true cephalopods from putative ancestors such as Knightoconus, which lacked a siphuncle. Neutral or positive buoyancy (i.e. the ability to float) would have come later, followed by swimming in the Plectronocerida and eventually jet propulsion in more derived cephalopods.
Possible early Cambrian remains have been found in the Avalon Peninsula, matching genetic data for a pre-Cambrian origin. However, this specimen is later shown that is a chimerical fossil.
In 2010, some researchers proposed that Nectocaris pteryx is the early cephalopod, which did not have a shell and appeared to possess jet propulsion in the manner of "derived" cephalopods, complicated the question of the order in which cephalopod features developed. However, most of other researchers do not agree that Nectocaris actually being a cephalopod or even mollusk.
Early cephalopods were likely predators near the top of the food chain. After the late Cambrian extinction led to the disappearance of many radiodonts, predatory niches became available for other animals. During the Ordovician period, the primitive cephalopods underwent pulses of diversification to become diverse and dominant in the Paleozoic and Mesozoic seas. | Cephalopod | Wikipedia | 388 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
In the Early Palaeozoic, their range was far more restricted than today; they were mainly constrained to sublittoral regions of shallow shelves of the low latitudes, and usually occurred in association with thrombolites. A more pelagic habit was gradually adopted as the Ordovician progressed. Deep-water cephalopods, whilst rare, have been found in the Lower Ordovician – but only in high-latitude waters.
The mid-Ordovician saw the first cephalopods with septa strong enough to cope with the pressures associated with deeper water, and could inhabit depths greater than 100–200 m. The direction of shell coiling would prove to be crucial to the future success of the lineages; endogastric coiling would only permit large size to be attained with a straight shell, whereas exogastric coiling – initially rather rare – permitted the spirals familiar from the fossil record to develop, with their corresponding large size and diversity. (Endogastric means the shell is curved so as the ventral or lower side is longitudinally concave (abdomen in); exogastric means the shell is curved so as the ventral side is longitudinally convex (abdomen out) allowing the funnel to be pointed backward beneath the shell.)
The ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago. The Bactritida, a Devonian–Triassic group of orthocones, are widely held to be paraphyletic without the coleoids and ammonoids, that is, the latter groups arose from within the Bactritida. An increase in the diversity of the coleoids and ammonoids is observed around the start of the Devonian period and corresponds with a profound increase in fish diversity. This could represent the origin of the two derived groups.
Unlike most modern cephalopods, most ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. | Cephalopod | Wikipedia | 447 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Competitive pressure from fish is thought to have forced the shelled forms into deeper water, which provided an evolutionary pressure towards shell loss and gave rise to the modern coleoids, a change which led to greater metabolic costs associated with the loss of buoyancy, but which allowed them to recolonize shallow waters. However, some of the straight-shelled nautiloids evolved into belemnites. The loss of the shell may also have resulted from evolutionary pressure to increase maneuverability, resulting in a more fish-like habit.
There has been debate on the embryological origin of cephalopod appendages. Until the mid-20th century, the "Arms as Head" hypothesis was widely recognized. In this theory, the arms and tentacles of cephalopods look similar to the head appendages of gastropods, suggesting that they might be homologous structures. Cephalopod appendages surround the mouth, so logically they could be derived from embryonic head tissues. However, the "Arms as Foot" hypothesis, proposed by Adolf Naef in 1928, has increasingly been favoured; for example, fate mapping of limb buds in the chambered nautilus indicates that limb buds originate from "foot" embryonic tissues.
Genetics
The sequencing of a full cephalopod genome has remained challenging to researchers due to the length and repetition of their DNA. The characteristics of cephalopod genomes were initially hypothesized to be the result of entire genome duplications. Following the full sequencing of a California two-spot octopus, the genome showed similar patterns to other marine invertebrates with significant additions to the genome assumed to be unique to cephalopods. No evidence of full genome duplication was found. | Cephalopod | Wikipedia | 355 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Within the California two-spot octopus genome there are substantial replications of two gene families. Significantly, the expanded gene families were only previously known to exhibit replicative behaviour within vertebrates. The first gene family was identified as the protocadherins which are attributed to neuron development. Protocadherins function as cell adhesion molecules, essential for synaptic specificity. The mechanism for protocadherin gene family replication in vertebrates is attributed to complex splicing, or cutting and pasting, from a locus. Following the sequencing of the California two-spot octopus, researchers found that the protocadherin gene family in cephalopods has expanded in the genome due to tandem gene duplication. The different replication mechanisms for protocadherin genes indicate an independent evolution of protocadherin gene expansion in vertebrates and invertebrates. Analysis of individual cephalopod protocadherin genes indicate independent evolution between species of cephalopod. A species of shore squid Doryteuthis pealeii with expanded protocadherin gene families differ significantly from those of the California two-spot octopus suggesting gene expansion did not occur before speciation within cephalopods. Despite different mechanisms for gene expansion, the two-spot octopus protocadherin genes were more similar to vertebrates than squid, suggesting a convergent evolution mechanism. The second gene family known as are small proteins that function as zinc transcription factors. are understood to moderate DNA, RNA and protein functions within the cell.
The sequenced California two spot octopus genome also showed a significant presence of transposable elements as well as transposon expression. Although the role of transposable elements in marine vertebrates is still relatively unknown, significant expression of transposons in nervous system tissues have been observed. In a study conducted on vertebrates, the expression of transposons during development in the fruitfly Drosophila melanogaster activated genomic diversity between neurons. This diversity has been linked to increased memory and learning in mammals. The connection between transposons and increased neuron capability may provide insight into the observed intelligence, memory and function of cephalopods. | Cephalopod | Wikipedia | 445 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Using long-read sequencing, researchers have decoded the cephalopod genomes and discovered they have been churned and scrambled. The genes were compared to those of thousands of other species and while blocks of three or more genes co-occurred between squid and octopus, the blocks of genes were not found together in any other animals'. Many of the groupings were in the nervous tissue, suggesting the course they adapted their intelligence.
Phylogeny
The approximate consensus of extant cephalopod phylogeny, after Whalen & Landman (2022), is shown in the cladogram. Mineralized taxa are in bold.
The internal phylogeny of the cephalopods is difficult to constrain; many molecular techniques have been adopted, but the results produced are conflicting. Nautilus tends to be considered an outgroup, with Vampyroteuthis forming an outgroup to other squid; however in one analysis the nautiloids, octopus and teuthids plot as a polytomy. Some molecular phylogenies do not recover the mineralized coleoids (Spirula, Sepia, and Metasepia) as a clade; however, others do recover this more parsimonious-seeming clade, with Spirula as a sister group to Sepia and Metasepia in a clade that had probably diverged before the end of the Triassic.
Molecular estimates for clade divergence vary. One 'statistically robust' estimate has Nautilus diverging from Octopus at .
Taxonomy
The classification presented here, for recent cephalopods, follows largely from Current Classification of Recent Cephalopoda (May 2001), for fossil cephalopods takes from Arkell et al. 1957, Teichert and Moore 1964, Teichert 1988, and others. The three subclasses are traditional, corresponding to the three orders of cephalopods recognized by Bather. | Cephalopod | Wikipedia | 395 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Class Cephalopoda († indicates extinct groups)
Subclass Nautiloidea: Fundamental ectocochliate cephalopods that provided the source for the Ammonoidea and Coleoidea.
Order † Plectronocerida: the ancestral cephalopods from the Cambrian Period
Order † Ellesmerocerida ()
Order † Endocerida ()
Order † Actinocerida ()
Order † Discosorida ()
Order † Pseudorthocerida ()
Order † Tarphycerida ()
Order † Oncocerida ()
Order Nautilida (extant; 410.5 Ma to present)
Order † Orthocerida ()
Order † Ascocerida ()
Order † Bactritida ()
Subclass † Ammonoidea: ammonites ()
Order † Goniatitida ()
Order † Ceratitida ()
Order † Ammonitida ()
Subclass Coleoidea (410.0 Ma-Rec)
Cohort † Belemnoidea: Belemnites and kin
Genus † Jeletzkya
Order † Aulacocerida ()
Order † Phragmoteuthida ()
Order † Hematitida ()
Order † Belemnitida ()
Genus † Belemnoteuthis ()
Cohort Neocoleoidea
Superorder Decapodiformes (also known as Decabrachia or Decembranchiata)
Order Spirulida: ram's horn squid
Order Sepiida: cuttlefish
Order Sepiolida: pygmy, bobtail and bottletail squid
Order Idiosepida
Order Oegopsida: neritic squid
Order Myopsida: coastal squid
Order Bathyteuthida
Superorder Octopodiformes (also known as Vampyropoda)
Family † Trachyteuthididae
Order Vampyromorphida: vampire squid
Order Octopoda: octopus
Superorder † Palaeoteuthomorpha
Order † Boletzkyida
Other classifications differ, primarily in how the various decapod orders are related, and whether they should be orders or families.
Suprafamilial classification of the Treatise
This is the older classification that combines those found in parts K and L of the Treatise on Invertebrate Paleontology, which forms the basis for and is retained in large part by classifications that have come later. | Cephalopod | Wikipedia | 510 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Nautiloids in general (Teichert and Moore, 1964) sequence as given.
Subclass † Endoceratoidea. Not used by Flower, e.g. Flower and Kummel 1950, interjocerids included in the Endocerida.
Order † Endocerida
Order † Intejocerida
Subclass † Actinoceratoidea Not used by Flower, ibid
Order † Actinocerida
Subclass Nautiloidea Nautiloidea in the restricted sense.
Order † Ellesmerocerida Plectronocerida subsequently split off as separate order.
Order † Orthocerida Includes orthocerids and pseudorthocerids
Order † Ascocerida
Order † Oncocerida
Order † Discosorida
Order † Tarphycerida
Order † Barrandeocerida A polyphyletic group now included in the Tarphycerida
Order Nautilida
Subclass † Bactritoidea
Order † Bactritida
Paleozoic Ammonoidea (Miller, Furnish and Schindewolf, 1957)
Suborder † Anarcestina
Suborder † Clymeniina
Suborder † Goniatitina
Suborder † Prolecanitina
Mesozoic Ammonoidea (Arkel et al., 1957)
Suborder † Ceratitina
Suborder † Phylloceratina
Suborder † Lytoceratina
Suborder † Ammonitina
Subsequent revisions include the establishment of three Upper Cambrian orders, the Plectronocerida, Protactinocerida, and Yanhecerida; separation of the pseudorthocerids as the Pseudorthocerida, and elevating orthoceratid as the Subclass Orthoceratoidea.
Shevyrev classification
Shevyrev (2005) suggested a division into eight subclasses, mostly comprising the more diverse and numerous fossil forms, although this classification has been criticized as arbitrary, lacking evidence, and based on misinterpretations of other papers. | Cephalopod | Wikipedia | 439 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Class Cephalopoda
Subclass † Ellesmeroceratoidea
Order † Plectronocerida ()
Order † Protactinocerida
Order † Yanhecerida
Order † Ellesmerocerida ()
Subclass † Endoceratoidea ()
Order † Endocerida ()
Order † Intejocerida ()
Subclass † Actinoceratoidea
Order † Actinocerida ()
Subclass Nautiloidea (490.0 Ma- Rec)
Order † Basslerocerida ()
Order † Tarphycerida ()
Order † Lituitida ()
Order † Discosorida ()
Order † Oncocerida ()
Order Nautilida (410.5 Ma-Rec)
Subclass † Orthoceratoidea ()
Order † Orthocerida ()
Order † Ascocerida ()
Order † Dissidocerida ()
Order † Bajkalocerida
Subclass † Bactritoidea ()
Subclass † Ammonoidea ()
Subclass Coleoidea (410.0 Ma-rec)
Cladistic classification
Another recent system divides all cephalopods into two clades. One includes nautilus and most fossil nautiloids. The other clade (Neocephalopoda or Angusteradulata) is closer to modern coleoids, and includes belemnoids, ammonoids, and many orthocerid families. There are also stem group cephalopods of the traditional Ellesmerocerida that belong to neither clade.
The coleoids, despite some doubts, appear from molecular data to be monophyletic.
In culture
Ancient seafaring people were aware of cephalopods, as evidenced by such artworks as a stone carving found in the archaeological recovery from Bronze Age Minoan Crete at Knossos (1900 – 1100 BC), which has a depiction of a fisherman carrying an octopus. The terrifyingly powerful Gorgon of Greek mythology may have been inspired by the octopus or squid, the octopus's body representing the severed head of Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes. | Cephalopod | Wikipedia | 460 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
The kraken is a legendary sea monster of giant proportions said to dwell off the coasts of Norway and Greenland, usually portrayed in art as a giant cephalopod attacking ships. Linnaeus included it in the first edition of his 1735 Systema Naturae. In a Hawaiian creation myth that says the present cosmos is the last of a series which arose in stages from the ruins of the previous universe, the octopus is the lone survivor of the previous, alien universe. The Akkorokamui is a gigantic tentacled monster from Ainu folklore.
A battle with an octopus plays a significant role in Victor Hugo's book Travailleurs de la mer (Toilers of the Sea), relating to his time in exile on Guernsey.
Ian Fleming's 1966 short story collection Octopussy and The Living Daylights, and the 1983 James Bond film were partly inspired by Hugo's book.
Japanese erotic art, shunga, includes ukiyo-e woodblock prints such as Katsushika Hokusai's 1814 print Tako to ama (The Dream of the Fisherman's Wife), in which an ama diver is sexually intertwined with a large and a small octopus. The print is a forerunner of tentacle erotica.
Its many arms that emanate from a common center means that the octopus is sometimes used to symbolize a powerful and manipulative organization. | Cephalopod | Wikipedia | 284 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals |
Speech synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware products. A text-to-speech (TTS) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech. The reverse process is speech recognition.
Synthesized speech can be created by concatenating pieces of recorded speech that are stored in a database. Systems differ in the size of the stored speech units; a system that stores phones or diphones provides the largest output range, but may lack clarity. For specific usage domains, the storage of entire words or sentences allows for high-quality output. Alternatively, a synthesizer can incorporate a model of the vocal tract and other human voice characteristics to create a completely "synthetic" voice output.
The quality of a speech synthesizer is judged by its similarity to the human voice and by its ability to be understood clearly. An intelligible text-to-speech program allows people with visual impairments or reading disabilities to listen to written words on a home computer. Many computer operating systems have included speech synthesizers since the early 1990s.
A text-to-speech system (or "engine") is composed of two parts: a front-end and a back-end. The front-end has two major tasks. First, it converts raw text containing symbols like numbers and abbreviations into the equivalent of written-out words. This process is often called text normalization, pre-processing, or tokenization. The front-end then assigns phonetic transcriptions to each word, and divides and marks the text into prosodic units, like phrases, clauses, and sentences. The process of assigning phonetic transcriptions to words is called text-to-phoneme or grapheme-to-phoneme conversion. Phonetic transcriptions and prosody information together make up the symbolic linguistic representation that is output by the front-end. The back-end—often referred to as the synthesizer—then converts the symbolic linguistic representation into sound. In certain systems, this part includes the computation of the target prosody (pitch contour, phoneme durations), which is then imposed on the output speech.
History | Speech synthesis | Wikipedia | 454 | 42799 | https://en.wikipedia.org/wiki/Speech%20synthesis | Technology | Media and communication | null |
Long before the invention of electronic signal processing, some people tried to build machines to emulate human speech. There were also legends of the existence of "Brazen Heads", such as those involving Pope Silvester II (d. 1003 AD), Albertus Magnus (1198–1280), and Roger Bacon (1214–1294).
In 1779, the German-Danish scientist Christian Gottlieb Kratzenstein won the first prize in a competition announced by the Russian Imperial Academy of Sciences and Arts for models he built of the human vocal tract that could produce the five long vowel sounds (in International Phonetic Alphabet notation: , , , and ). There followed the bellows-operated "acoustic-mechanical speech machine" of Wolfgang von Kempelen of Pressburg, Hungary, described in a 1791 paper. This machine added models of the tongue and lips, enabling it to produce consonants as well as vowels. In 1837, Charles Wheatstone produced a "speaking machine" based on von Kempelen's design, and in 1846, Joseph Faber exhibited the "Euphonia". In 1923, Paget resurrected Wheatstone's design.
In the 1930s, Bell Labs developed the vocoder, which automatically analyzed speech into its fundamental tones and resonances. From his work on the vocoder, Homer Dudley developed a keyboard-operated voice-synthesizer called The Voder (Voice Demonstrator), which he exhibited at the 1939 New York World's Fair.
Dr. Franklin S. Cooper and his colleagues at Haskins Laboratories built the Pattern playback in the late 1940s and completed it in 1950. There were several different versions of this hardware device; only one currently survives. The machine converts pictures of the acoustic patterns of speech in the form of a spectrogram back into sound. Using this device, Alvin Liberman and colleagues discovered acoustic cues for the perception of phonetic segments (consonants and vowels).
Electronic devices | Speech synthesis | Wikipedia | 395 | 42799 | https://en.wikipedia.org/wiki/Speech%20synthesis | Technology | Media and communication | null |
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