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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 We... | Irrigation | Wikipedia | 455 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null | vital_articles |
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... | Irrigation | Wikipedia | 426 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null | vital_articles |
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 Sov... | Irrigation | Wikipedia | 507 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null | vital_articles |
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... | Irrigation | Wikipedia | 383 | 42261 | https://en.wikipedia.org/wiki/Irrigation | Technology | Horticultural techniques | null | vital_articles |
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
... | Ichthyology | Wikipedia | 385 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology | vital_articles |
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 ... | Ichthyology | Wikipedia | 376 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology | vital_articles |
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... | Ichthyology | Wikipedia | 386 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology | vital_articles |
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-v... | Ichthyology | Wikipedia | 384 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology | vital_articles |
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 Ca... | Ichthyology | Wikipedia | 341 | 42405 | https://en.wikipedia.org/wiki/Ichthyology | Biology and health sciences | Basics_2 | Biology | vital_articles |
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, ... | Electrical cable | Wikipedia | 477 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null | vital_articles |
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 c... | Electrical cable | Wikipedia | 377 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null | vital_articles |
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,... | Electrical cable | Wikipedia | 375 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null | vital_articles |
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 b... | Electrical cable | Wikipedia | 348 | 42418 | https://en.wikipedia.org/wiki/Electrical%20cable | Technology | Components_2 | null | vital_articles |
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, gi... | Dalton (unit) | Wikipedia | 473 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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... | Dalton (unit) | Wikipedia | 459 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 am... | Dalton (unit) | Wikipedia | 482 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 uni... | Dalton (unit) | Wikipedia | 388 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 co... | Dalton (unit) | Wikipedia | 452 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 giv... | Dalton (unit) | Wikipedia | 493 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 ... | Dalton (unit) | Wikipedia | 127 | 42445 | https://en.wikipedia.org/wiki/Dalton%20%28unit%29 | Physical sciences | Mass | null | vital_articles |
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 ... | Polyp (zoology) | Wikipedia | 500 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals | vital_articles |
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 thei... | Polyp (zoology) | Wikipedia | 495 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals | vital_articles |
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 cal... | Polyp (zoology) | Wikipedia | 491 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals | vital_articles |
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,... | Polyp (zoology) | Wikipedia | 204 | 42563 | https://en.wikipedia.org/wiki/Polyp%20%28zoology%29 | Biology and health sciences | Cnidarians | Animals | vital_articles |
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 r... | Spleen | Wikipedia | 509 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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... | Spleen | Wikipedia | 458 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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 primar... | Spleen | Wikipedia | 453 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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... | Spleen | Wikipedia | 332 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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 platelet... | Spleen | Wikipedia | 504 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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 h... | Spleen | Wikipedia | 483 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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,... | Spleen | Wikipedia | 368 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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 mammal... | Spleen | Wikipedia | 321 | 42567 | https://en.wikipedia.org/wiki/Spleen | Biology and health sciences | Circulatory system | null | vital_articles |
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) b... | Upper and lower bounds | Wikipedia | 481 | 42693 | https://en.wikipedia.org/wiki/Upper%20and%20lower%20bounds | Mathematics | Order theory | null | vital_articles |
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 preo... | Upper and lower bounds | Wikipedia | 127 | 42693 | https://en.wikipedia.org/wiki/Upper%20and%20lower%20bounds | Mathematics | Order theory | null | vital_articles |
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 act... | Pendulum | Wikipedia | 456 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 ... | Pendulum | Wikipedia | 414 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 cent... | Pendulum | Wikipedia | 464 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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-shape... | Pendulum | Wikipedia | 466 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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.
... | Pendulum | Wikipedia | 344 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 perio... | Pendulum | Wikipedia | 431 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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... | Pendulum | Wikipedia | 497 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 i... | Pendulum | Wikipedia | 481 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 pe... | Pendulum | Wikipedia | 375 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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... | Pendulum | Wikipedia | 403 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 draw... | Pendulum | Wikipedia | 333 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 ... | Pendulum | Wikipedia | 199 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 th... | Pendulum | Wikipedia | 419 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 vi... | Pendulum | Wikipedia | 380 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 p... | Pendulum | Wikipedia | 469 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 ... | Pendulum | Wikipedia | 469 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 ... | Pendulum | Wikipedia | 396 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 pendu... | Pendulum | Wikipedia | 446 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 t... | Pendulum | Wikipedia | 419 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 pendulu... | Pendulum | Wikipedia | 153 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 sho... | Pendulum | Wikipedia | 477 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 apar... | Pendulum | Wikipedia | 433 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 a... | Pendulum | Wikipedia | 492 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 t... | Pendulum | Wikipedia | 428 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 accur... | Pendulum | Wikipedia | 499 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 ... | Pendulum | Wikipedia | 446 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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... | Pendulum | Wikipedia | 355 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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. T... | Pendulum | Wikipedia | 489 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 C... | Pendulum | Wikipedia | 505 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 S... | Pendulum | Wikipedia | 493 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 o... | Pendulum | Wikipedia | 488 | 42709 | https://en.wikipedia.org/wiki/Pendulum | Technology | Timekeeping | null | vital_articles |
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 | vital_articles |
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 primit... | Cephalopod | Wikipedia | 458 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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
Ne... | Cephalopod | Wikipedia | 455 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 constructi... | Cephalopod | Wikipedia | 470 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 accomm... | Cephalopod | Wikipedia | 443 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ch... | Cephalopod | Wikipedia | 305 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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. C... | Cephalopod | Wikipedia | 278 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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... | Cephalopod | Wikipedia | 462 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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,... | Cephalopod | Wikipedia | 461 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 int... | Cephalopod | Wikipedia | 355 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ... | Cephalopod | Wikipedia | 490 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 incre... | Cephalopod | Wikipedia | 460 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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... | Cephalopod | Wikipedia | 471 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 mai... | Cephalopod | Wikipedia | 356 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ... | Cephalopod | Wikipedia | 511 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 t... | Cephalopod | Wikipedia | 512 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 in... | Cephalopod | Wikipedia | 506 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 t... | Cephalopod | Wikipedia | 475 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 f... | Cephalopod | Wikipedia | 315 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 orga... | Cephalopod | Wikipedia | 243 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 go... | Cephalopod | Wikipedia | 270 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ... | Cephalopod | Wikipedia | 498 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ma... | Cephalopod | Wikipedia | 432 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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. T... | Cephalopod | Wikipedia | 472 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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... | Cephalopod | Wikipedia | 388 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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, wh... | Cephalopod | Wikipedia | 447 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ... | Cephalopod | Wikipedia | 355 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 devel... | Cephalopod | Wikipedia | 445 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 an... | Cephalopod | Wikipedia | 395 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ()
... | Cephalopod | Wikipedia | 510 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 Na... | Cephalopod | Wikipedia | 439 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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)
Or... | Cephalopod | Wikipedia | 460 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 ... | Cephalopod | Wikipedia | 284 | 42726 | https://en.wikipedia.org/wiki/Cephalopod | Biology and health sciences | Cephalopods | Animals | vital_articles |
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 representation... | Speech synthesis | Wikipedia | 454 | 42799 | https://en.wikipedia.org/wiki/Speech%20synthesis | Technology | Media and communication | null | vital_articles |
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-Danis... | Speech synthesis | Wikipedia | 395 | 42799 | https://en.wikipedia.org/wiki/Speech%20synthesis | Technology | Media and communication | null | vital_articles |
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