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Occlusion effect The occlusion effect occurs when an object fills the outer portion of a person's ear canal, and that person perceives "hollow" or "booming" echo-like sounds of their own voice. It is caused by bone-conducted sound vibrations reverberating off the object filling the ear canal. When talking or chewing, these vibrations normally escape through an open ear canal; most people are unaware of their existence. When the ear canal is blocked, the vibrations are reflected back toward the eardrum. Compared to a completely open ear canal, the occlusion effect can boost low frequency (usually below 500 Hz) sound pressure in the ear canal by 20 dB or more. This effect can be measured with a probe-tube microphone. A person with normal hearing can experience this by sticking their fingers into their ears and talking. Otherwise, this effect is often experienced by hearing aid users who only have a mild to moderate high-frequency hearing loss, but use hearing aids which block the entire ear canal. Active occlusion algorithms are needed to help people with severe hearing loss adequately. If a person suffers from "near-normal low-frequency hearing and mild to moderate hearing loss of up to 70 dB at mid and high frequencies," hearing aids with increased vent size or hollow ear-molds/domes are more suitable for them in lessening the extent of the occlusion effect. | https://en.wikipedia.org/wiki?curid=14429491 |
Kraków School of Mathematics and Astrology The () was an influential mid-to-late-15th-century group of mathematicians and astrologers at the University of Kraków (later "Jagiellonian University"). | https://en.wikipedia.org/wiki?curid=14439044 |
Nuclear detection The threat of radiological attacks has led several organizations to develop specially designed nuclear detection systems. These systems differ in design and abilities. | https://en.wikipedia.org/wiki?curid=14439210 |
Lajos Abafi or Ludwig Abafi-Aigner (11 February 1840 in Nagyjécsa, Kingdom of Hungary, Austrian Empire – 19 June 1909 in Budapest, Austria-Hungary) was a Hungarian editor, a librarian and entomologist. His family, of German origin, moved to Pozsony (today Bratislava) in 1858. There, he learned the Hungarian language. His family then moved to Pest in 1863. Ludwig part completed his studies in Cologne and part in Stuttgart. He was especially interested in Lepidoptera and he founded a popular library. In 1870, he became a freemason. He worked for twelve years on a history of freemasonry. He changed his first name Ludwig to its Hungarian form, Lajos, and he assumed his "nom de plume" Abafi. His enterprise declined during the years 1880 to 1890, when he closed it. From 1890, he was entirely devoted to entomology. He published his observations in the revue of the Budapest museum "Természetrajzi Füzetek" and participated as editor and author in the "Fauna Regni Hungariae". His book, "Magyarország lepkéi" (butterflies of Hungary) of 1907, was extremely popular and influenced many generations of entomologists of his country. | https://en.wikipedia.org/wiki?curid=14450665 |
Delta-v (physics) Delta comes as the 4th letter in the Greek alphabets which is spelled as 'D' in the English alphabets . In general physics, delta-"v" is simply a change in velocity. The Greek uppercase letter delta is the standard mathematical symbol to represent change in some quantity. Depending on the situation, delta-"v" can be either a spatial vector (Δv) or scalar (Δ"v"). In either case it is equal to the acceleration (vector or scalar) integrated over time: If acceleration is constant, the change in velocity can thus be expressed as: where: Change in velocity is useful in many cases, such as determining the change in momentum (impulse), where :formula_4, where formula_5 is momentum and m is mass. | https://en.wikipedia.org/wiki?curid=14454695 |
Pollakanth A pollakanth is a plant that reproduces, flowers and sets seed recurrently during its life. The term was first used by Frans R. Kjellman. Other terms with the same meaning are "polycarpic" and "iteroparous". Its antonym is hapaxanth. | https://en.wikipedia.org/wiki?curid=14456810 |
Coalescence (chemistry) In chemistry, coalescence is a process in which two phase domains of the same composition come together and form a larger phase domain. In other words, the process by which two or more separate masses of miscible substances seem to "pull" each other together should they make the slightest contact. | https://en.wikipedia.org/wiki?curid=14458653 |
Planetarium software is application software that allows a user to simulate the celestial sphere at any time of day, especially at night, on a computer. Such applications can be as rudimentary as displaying a star chart or sky map for a specific time and location, or as complex as rendering photorealistic views of the sky. While some planetarium software is meant to be used exclusively on a personal computer, some applications can be used to interface with and control telescopes or planetarium projectors. Optional features may include inserting the orbital elements of comets and other newly discovered bodies for display. | https://en.wikipedia.org/wiki?curid=14466034 |
Product-determining step The product-determining step is the step of a chemical reaction that determines the ratio of products formed via differing reaction mechanisms that start from the same reactants. The product determining step is not rate limiting if the rate limiting step of each mechanism is the same. | https://en.wikipedia.org/wiki?curid=14466384 |
Surface force denoted "f" is the force that acts across an internal or external surface element in a material body. can be decomposed into two perpendicular components: normal forces and shear forces. A normal force acts normally over an area and a shear force acts tangentially over an area. Since pressure is formula_2, and area is a formula_3, | https://en.wikipedia.org/wiki?curid=14467558 |
Sándor Szalay (physicist) Sándor Szalay, Sr. (October 4, 1909 – October 11, 1987) was a pioneer of Hungarian nuclear physics. He discovered a natural mechanism for uranium enrichment, which led to the discovery of several uranium deposits including an enriched deposit in the Mecsek Mountains of Hungary. In 1955 he collaborated with Gyula Csikai to discover the neutrino, a weakly interactive particle. In a photograph of a cloud chamber, they found a nucleus changing direction, which they interpreted as the emission of a neutrino. (The antineutrino was detected by Frederick Reines and Clyde Cowan in 1953, a discovery for which Reines was awarded the 1995 Nobel Prize in Physics.) Szalay also founded the Institute of Nuclear Research, a branch of the Hungarian Academy of Sciences. He is considered the father of Hungarian nuclear physics. | https://en.wikipedia.org/wiki?curid=14469689 |
Heng-O Corona is a corona in Guinevere Planitia on the planet Venus at Latitude 2° North, Longitude 355° East. It has a diameter of , and is the second largest corona on Venus. It is named for Heng O (also known as Chang'e), the Chinese goddess of the Moon. is located on the eastern Guinevere. Within the faulted ring system of lies several small impact craters and intricate fractures which trend to the north and to the northwest of the corona. | https://en.wikipedia.org/wiki?curid=14472512 |
Zisa Corona is a corona found on the planet Venus at Latitude 12° North, Longitude 221° East. It has a diameter of 850 kilometers, and is the 3rd largest corona on Venus. It is named for Zisa a German/Nordic harvest goddess and consort of Tyr. | https://en.wikipedia.org/wiki?curid=14473044 |
Quetzalpetlatl Corona is a corona in Lada Terra on the planet Venus. Latitude 68° South, Longitude 357° East. It has a diameter of 780 kilometers, and is the 4th largest corona on Venus. It lies in part on the Lada Rise, with part of the corona intersecting the Ammavuro-Quetzalpetlatl belt in the northwestern region of Lada Terra. It is named for Quetzalpetlatl an Aztec fertility goddess. | https://en.wikipedia.org/wiki?curid=14473293 |
Stephen Szára Stephen István Szára (born 21 March 1923) is a Hungarian chemist and psychiatrist who has made major contributions in the field of pharmacology. Szára was the first to scientifically study the psychotropic effects of "N,N"-Dimethyltryptamine (DMT), performing research with volunteers in the mid-1950s. Szára had turned his attention to DMT after his order for LSD from the Swiss company Sandoz Laboratories was rejected on the grounds that the powerful psychotropic could be dangerous in the hands of a communist country. Shortly after the Hungarian Revolution, Szára moved to the United States where he eventually became Chief of the Biomedical Branch of the U.S. National Institute on Drug Abuse. In the U.S., he worked with Julius Axelrod and others on the metabolism of DMT and related compounds in healthy and schizophrenic volunteers. Among other achievements, Szára and his colleagues characterized the biochemistry of the first three psychedelic cogeners of tryptamine: dimethyl-, diethyl-, and dipropyl-tryptamine (DMT, DET, and DPT), describing their pharmacokinetics and effects. Szára's research explored both the possibility that some tryptamines (DMT, in particular) might contribute to psychosis by forming in the brain as well as the possibility that some psychedelics might be useful in psychotherapy | https://en.wikipedia.org/wiki?curid=14477052 |
Stephen Szára In recent years, Szára has argued that psychedelic drugs should be studied in a heuristic manner and that learning the mechanisms by which they affect the brain may "serve as keys to unlock the mysteries of the brain/mind relationship". Szára is an Emeritus Fellow of the American College of Neuropsychopharmacology and Collegium Internationale Neuro-Psychopharmacologicum, and a member of the Scientific Advisory Board of the Heffter Research Institute. He was elected Honorary Member of the Hungarian Association of Psychopharmacology in 2007. He is also recipient of the Alcohol, Drug Abuse, and Mental Health Administration Administrator's Meritorious Achievement Award and the Kovats Medal of Freedom from the American Hungarian Federation (2005). | https://en.wikipedia.org/wiki?curid=14477052 |
Bernhard Eitel (born 31 August 1959) is a German earth scientist and geographer. Eitel was born in Baden. Since October 2007, he has been the Rector of Heidelberg University. | https://en.wikipedia.org/wiki?curid=14497677 |
Engin Arık (October 4, 1948 – November 30, 2007) was a Turkish particle physicist. She was a professor and head of the Experimental High Energy Physics group at the Boğaziçi University. Arık was born in Istanbul and received her BSc in 1969 in mathematics and physics from Istanbul University. Subsequently, she received her MSc in 1971 and PhD in 1976 in experimental high energy physics from the University of Pittsburgh, United States. She performed post doctoral studies at the Westfield College in University of London. Returning 1979 to Turkey, she became a member of faculty at Boğaziçi University. In 1983, she left the university to work with Control Data Corporation for two years. Arık subsequently became a professor at Boğaziçi University in 1988. Between 1997 and 2000, Arık was commissioned by the government to represent Turkey at the sessions of Comprehensive Nuclear-Test-Ban Treaty held at the International Atomic Energy Agency (IAEA) of the UN in Vienna, Austria. She was a member of the ATLAS and CAST collaborations at CERN in Switzerland. Arık died in the Atlasjet Flight 4203 crash on November 30, 2007. She was married to Metin Arık, also a professor in the same department at Boğaziçi University, and had two children. There is a street named after her in the İlkyerleşim neighborhood of the Yenimahalle district in Ankara, Turkey. | https://en.wikipedia.org/wiki?curid=14498641 |
Health Sciences Descriptors DeCS – is a structured and trilingual thesaurus created by BIREME – Latin American and Caribbean Center on Health Sciences Information – in 1987 for indexing scientific journal articles, books, proceedings of congresses, technical reports and other types of materials, as well as for searching and recovering scientific information in LILACS, MEDLINE and other databases. In the VHL, Virtual Health Library, DeCS is the tool that permits the navigation between records and sources of information through controlled concepts and organized in Portuguese, Spanish and English. It was developed from MeSH – Medical Subject Headings from the NLM – U.S. National Library of Medicine – in order to permit the use of common terminology for searching in three languages, providing a consistent and unique environment for information retrieval regardless of the language. In addition to the original MeSH terms, four specific areas were developed: Public Health (1987), Homeopathy (1991), Health Surveillance (2005), and Science and Health (2005). The concepts that compose the DeCS vocabulary are organized in a hierarchical structure permitting searches in broader or more specific terms or all the terms that belong to a single hierarchy | https://en.wikipedia.org/wiki?curid=14499993 |
Health Sciences Descriptors Its main purpose is to serve as a unique language for indexing and recovery of information among the components of the Latin American and Caribbean Health Sciences Information System, coordinated by BIREME and that encompasses 37 countries in Latin America and the Caribbean, permitting a uniform dialog between nearly 600 libraries. DeCS participates in the unified terminology development project, UMLS – Unified Medical Language System of the NLM, with the responsibility of contributing with the terms in Portuguese and Spanish. | https://en.wikipedia.org/wiki?curid=14499993 |
Physiographic regions of the world are a means of defining the Earth's landforms into distinct regions, based upon the classic three-tiered approach by Nevin M. Fenneman in 1916, that separates landforms into physiographic divisions, physiographic provinces, and physiographic sections. The model became the basis for similar classifications of other continents, and is still considered valid . During the early 1900s, the study of regional-scale geomorphology was termed "physiography". Unfortunately, physiography later was considered to be a contraction of "physical" and "geography", and therefore synonymous with physical geography, and the concept became embroiled in controversy surrounding the appropriate concerns of that discipline. Some geomorphologists held to a geological basis for physiography and emphasized a concept of physiographic regions while a conflicting trend among geographers was to equate physiography with "pure morphology," separated from its geological heritage. In the period following World War II, the emergence of process, climatic, and quantitative studies led to a preference by many Earth scientists for the term "geomorphology" in order to suggest an analytical approach to landscapes rather than a descriptive one. In current usage, physiography still lends itself to confusion as to which meaning is meant, the more specialized "geomorphological" definition or the more encompassing "physical geography" definition | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world For the remainder of this article, emphasis will remain on the more "geomorphological" usage, which is based upon geological landforms, not on climate, vegetation, or other non-geological criteria. For the purposes of physiographic mapping, landforms are classified according to both their geologic structures and histories. Distinctions based on geologic age also correspond to physiographic distinctions where the forms are so recent as to be in their first erosion cycle, as is generally the case with sheets of glacial drift. Generally, forms which result from similar histories are characterized by certain similar features, and differences in history result in corresponding differences of form, usually resulting in distinctive features which are obvious to the casual observer, but this is not always the case. A maturely dissected plateau may grade without a break from rugged mountains on the one hand to mildly rolling farm lands on the other. So also, forms which are not classified together may be superficially similar; for example, a young coastal plain and a peneplain. In a large number of cases, the boundary lines are also geologic lines, due to differences in the nature or structure of the underlying rocks. The history of "physiography" itself is at best a complicated effort. Much of the complications arise from how the term has evolved over time, both as its own 'science' and as a synonym for other branches of science | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world In 1848, Mary Somerville published her book "Physical Geography" which gave detailed descriptions of the topography of each continent, along with the distribution of plant, animals and humans. This work gave impetus to further works along the field. In Germany, Oscar Peschel in 1870, proposed that geographers should study the morphology of the Earth's surface, having an interest in the study of landforms for the development of human beings. As the chair of geography (and a geologist by training) in Bonn, Germany, Ferdinand von Richthofen made the study of landforms the main research field for himself and his students. Elsewhere, Thomas Henry Huxley's "Physiography" was published in 1877 in Britain. Shortly after, the field of "physical geography" itself was renamed as "physiography". Afterwards, physiography became a very popular school subject in Britain, accounting for roughly 10% of all examination papers in both English and Welsh schools, and physiography was now regarded as an integral, if not the most important aspect of geography. In conjunction with these 'advances' in physiography, physically and visually mapping these descriptive areas was underway as well. The early photographers and balloonists, Nadar and Triboulet, experimented with aerial photography and the view it provided of the landscape | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world In 1899, Albert Heim published his photographs and observations made during a balloon flight over the Alps; he is probably the first person to use aerial photography in geomorphological or physiographical research. The block diagrams of Fenneman, Raisz, Lobeck and many others were based in part upon both aerial photography and topographic maps, giving an oblique "birds-eye" view. By 1901, there were clear differences in the definition of the term physiography. "In England, physiography is regarded as the introduction to physical science in general. It is made to include the elements of physics, chemistry, astronomy, physical geography, and geology, and sometimes even certain phases of botany and zoology. In America, the term has a somewhat different meaning. It is sometimes used as a synonym for physical geography, and is sometimes as the science which describes and explains the physical features of the earth's surface". By 1911, the definition of physiography in "Encyclopædia Britannica" had evolved to be "In popular usage the words 'physical geography' have come to mean geography viewed from a particular standpoint rather than any special department of the subject. The popular meaning is better conveyed by the word physiography, a term which appears to have been introduced by Linnaeus, and was reinvented as a substitute for the cosmography of the Middle Ages by Professor Huxley | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world Although the term has since been limited by some writers to one particular part of the subject, it seems best to maintain the original and literal meaning. In the stricter sense, physical geography is that part of geography which involves the processes of contemporary change in the crust and the circulation of the fluid envelopes. It thus draws upon physics for the explanation of the phenomena with the space-relations of which it is specially concerned. Physical geography naturally falls into three divisions, dealing respectively with the surface of the lithosphere – geomorphology; the hydrosphere – oceanography; and the atmosphere – climatology. All these rest upon the facts of mathematical geography, and the three are so closely inter-related that they cannot be rigidly separated in any discussion". The 1919 edition of "The Encyclopedia Americana: A Library of Universal Knowledge" further adjusted the definition to be "Physiography (geomorphology), now generally recognized as a science distinct from geology, deals with the origins and development of land forms, traces out the topographic expression of structure, and embodies a logical history of oceanic basins, and continental elevations; of mountains, plateaus and plains; of hills and valleys. Physical geography is used loosely as a synonym, but the term is more properly applied to the borderland between geography and physiography; dealing, as it does, largely with the human element as influenced by its physiographic surroundings" | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world Even in the 21st century, some confusion remains as to exactly what "physiography" is. One source states "Geomorphology includes quaternary geology, physiography and most of physical geography", treating physiography as a separate field, but subservient to geomorphology. Another source states "Geomorphology (or physiography) refers to the study of the surface features of the earth. It involves looking at the distribution of land, water, soil and rock material that forms the land surface. Land is closely linked to the geomorphology of a particular landscape", regarding physiography as synonymous with geomorphology. Yet another source states "Physiography may be viewed from two distinct angles, the one dynamic, the other passive". The same source continues by stating "In a large fashion geodynamics is intimately associated with certain branches of geology, as sedimentation, while geomorphology connects physiography with geography. The dynamic interlude representing the active phase of physiography weaves the basic threads of geologic history." The U.S. Geological Survey defines physiography as a study of "Features and attributes of earth's land surface", while geomorphology is defined separately as "Branch of geology dealing with surface land features and the processes that create and change them" | https://en.wikipedia.org/wiki?curid=14500263 |
Physiographic regions of the world Partly due to this confusion over what "physiography" actually means, some scientists have refrained from using the term physiography (and instead use the similar term geomorphology) because the definitions vary from the American Geological Institute's "the study and classification of the surface features of Earth on the basis of similarities in geologic structure and the history of geologic changes" to descriptions that also include vegetation and/or land use. | https://en.wikipedia.org/wiki?curid=14500263 |
The Natural History and Antiquities of Selborne The Natural History and Antiquities of Selborne, or just The Natural History of Selborne is a book by English naturalist and ornithologist Gilbert White. It was first published in 1789 by his brother Benjamin. It has been continuously in print since then, with nearly 300 editions up to 2007. The book was published late in White's life, compiled from a mixture of his letters to other naturalists—Thomas Pennant and Daines Barrington; a 'Naturalist's Calendar' (in the second edition) comparing phenology observations made by White and William Markwick of the first appearances in the year of different animals and plants; and observations of natural history organized more or less systematically by species and group. A second volume, less often reprinted, covered the antiquities of Selborne. Some of the letters were never posted, and were written for the book. White's "Natural History" was at once well received by contemporary critics and the public, and continued to be admired by a diverse range of nineteenth and twentieth century literary figures. His work has been seen as an early contribution to ecology and in particular to phenology. The book has been enjoyed for its charm and apparent simplicity, and the way that it creates a vision of pre-industrial England. The original manuscript has been preserved and is displayed in the Gilbert White museum at The Wakes, Selborne | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne The main part of the book, the "Natural History", is presented as a compilation of 44 letters nominally to Thomas Pennant, a leading British zoologist of the day, and 66 letters to Daines Barrington, an English barrister and Fellow of the Royal Society. In these letters, White details the natural history of the area around his family home at the vicarage of Selborne in Hampshire. Many of the 'letters' were never posted, and were written especially for the book. Patrick Armstrong, in his book "The English Parson-Naturalist", notes that in particular, "an obvious example is the first, nominally to Thomas Pennant, but which is clearly contrived, as it introduces the parish, briefly summarizing its position, geography and principal physical features." White's biographer, Richard Mabey, estimates that up to 46 out of 66 'letters to Daines Barrington' "were probably never sent through the post"; Mabey explains that it is hard to be more precise, because of White's extensive editing. Some letters are dated although never sent. Some dates have been altered. Some letters have been cut down, split into shorter 'letters', merged, or distributed in small parts into other letters. A section about insect-eating birds in a letter sent to Barrington in 1770 appears in the book as letter 41 to Pennant. Personal remarks have been removed throughout. Thus, while the book is genuinely based on letters to Pennant and Barrington, the structure of the book is a literary device | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne As a compilation of letters and other materials, the book as a whole has an uneven structure. The first part is a diary-like sequence of 'letters', with the breaks and wanderings that naturally follow. The second is a calendar, organized by phenological event around the year. The third is a collection of observations, organised by animal or plant group and species, with a section on meteorology. The apparently rambling structure of the book is in fact bracketed by opening and closing sections, arranged like the rest as letters, which "give form and scale and even a semblance of narrative structure to what would otherwise have been a shapeless anthology." The unposted Letter 1 begins: "No novelist could have opened better", wrote Virginia Woolf; "Selborne is set solidly in the foreground." The first edition was illustrated with paintings by the Swiss artist Samuel Hieronymus Grimm, engraved by W. Angus and aquatinted. Grimm had lived in England since 1768, and was quite a famous artist, costing 2½ guineas per week. In the event, he stayed in Selborne for 28 days, and White recorded that he worked very hard on 24 of them. White also described Grimm's method, which was to sketch the landscape in lead pencil, then to put in the shading, and finally to add a light wash of watercolour. The illustrations were engraved (signed at lower right) by a variety of engravers including William Angus and Peter Mazell | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne There are 44 letters to White's friend Thomas Pennant (1726–1798), of which the first nine were never posted and are thus undated. Of those that were posted, the first, Letter 10 giving an overview of Selborne, is dated 4 August 1767; the last, Letter 44 on wood pigeons, is dated 30 November 1780. It is not known how the men became friends, or even if they ever met; White writes repeatedly that he would like to meet "to have a little conversation face to face after we have corresponded so freely for several years" so it is certain they did not meet for long periods, and possible they never met at all. The letters are edited from the form in which they were actually posted; for example, Letter 10 as posted had a cringing introductory paragraph of thanks to Pennant which White edited out of the published version. There are 66 letters to the lawyer Daines Barrington (1727–1800), occupying half the book. Letter 1, on summer birds of passage, is dated 30 June 1769; Letter 66, on thunderstorms, is dated 25 June 1787. The Barrington letters therefore largely overlap the time frame of those to Pennant, but began and ended somewhat later. It was Barrington who suggested to White that he should write a book from his observations; although Pennant had been corresponding with White for a while, he was relying on White for natural history information for his own books, and, suggests White's biographer Richard Mabey, must have wanted White as a continuing source of information, not as a rival author | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne Barrington, on the other hand, liked to theorize about the natural world, but had little interest in making observations himself, and tended to accept claimed facts uncritically. A character in some of the letters is a tortoise: Letter 65 describes the summer of 1783 as: This was caused by the eruption of the Laki volcano in Iceland between 8 June 1783 and February 1784, killing up to a quarter of the people of Iceland and spreading a haze as far as Egypt. This section, often omitted from later editions, consists like the "Natural History" of 26 "Letters", none of them posted, and without even the fiction of being addressed to Pennant or Barrington. Letter 1 begins "It is reasonable to suppose that in remote ages this woody and mountainous district was inhabited only by bears and wolves." Letter 2 discusses Selborne in Saxon times; Selborne was according to White a royal manor, belonging to Editha, queen to Edward the Confessor. Letter 3 describes the village's church, which "has no pretensions to antiquity, and is, as I suppose, of no earlier date than the beginning of the reign of Henry VII." Letter 5 describes the ancient Yew tree in the churchyard. Letter 7 describes the (ruined) priory. Letter 11 discusses the properties of the Knights Templar in and near the village. Letter 14 describes the visit of bishop William of Wykeham in 1373, to correct the scandalous "particular abuses" in the religious houses in the parish | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne He orders the canons of Selborne priory (Item 5th) "to take care that the doors of their church and priory be so attended to that no suspected and disorderly females, "suspectae at aliae inhonestae", pass through their choir and cloiser in the dark"; (Item 10th) to cease "living dissolutely after the flesh, and not after the spirit" as it has been proven that some of the canons "sleep naked in their beds without their breeches and shirts"; (Item 11th) to stop "keeping hounds, and publicly attending hunting-matches" and "noisy tumultuous huntings"; (Item 17th) to properly maintain their houses and the convent itself, since they have allowed "through neglect, notorious dilapidations to take place"; (Item 29th) to stop wearing "foppish ornaments, and the affectation of appearing like beaux with garments edged with costly furs, with fringed gloves, and silken girdles trimmed with gold and silver." Richard Mabey describes White's reaction to the "Priory saga" as "grave disapproval of the monks' sensuality and ... general delinquency". A sequence of Letters then relate the history of the priors of Selborne, until Letter 24 which relates the takeover of the priory by Magdalen College, Oxford under bishop William Waynflete in 1459. White describes this as a disastrous fall: "Thus fell the considerable and well-endowed priory of Selborne after it had subsisted about two hundred and fifty-four years; about seventy-four years after the suppression of priories alien by Henry V | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne , and about fifty years before the general dissolution of the monasteries by Henry VIII." The final letter records that "No sooner did the priory .. become an appendage to the college, but it must at once have tended to swift decay." White notes that since then, even "the very foundations have been torn up for the repair of the highways" so that nothing is left but a rough pasture "full of hillocks and pits, choaked with nettles, and dwarf-elder, and trampled by the feet of the ox and the heifer". White had reason to be bitter about the takeover by Magdalen College, as it had made them Lords of the Manor of Selborne, which in turn gave them the right to appoint the parish priest. White's biographer Richard Mabey casts doubt on the "frequent assumption" that White's "deepest regret was that he could never be vicar of Selborne", but it was true that he was ineligible, as only fellows of Magdalen could be granted the living. This section, compiled posthumously, contains a list of some 500 phenological observations in Selborne from White's manuscripts, organised by William Markwick (1739–1812), and supplemented by Markwick's own observations from Catsfield, near Battle, Sussex. The observations depend on the latitude of these places and on the (global) climate, forming a baseline for comparison with modern observations | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne For example, "Cuckoo "(Cuculus canorus)" heard" is recorded by White for 7—26 April, and by Markwick for 15 April and 3 May (presumably only once at the earlier date) and "last heard" by Markwick on 28 June. The table begins as follows: White's lifelong friend John Mulso wrote to him in 1776, correctly predicting that "Your work, upon the whole, will immortalize your Place of Abode as well as Yourself." Thomas White wrote "a long, appreciative, but.. properly restrained review" of his brother's book in "The Gentleman's Magazine" of January 1789, commenting that "Sagacity of observation runs through the work". An anonymous reviewer in "The Topographer" of April 1789 wrote that "A more delightful, or more original work than Mr. White's History of Selborne has seldom been published ... Natural History has evidently been the author's principal study, and, of that, ornithology is evidently the favourite. The book is not a compilation from former publications, but the result of many years' attentive observations to nature itself, which are told not only with the precision of a philosopher, but with that happy selection of circumstances, which mark the "poet"." In 1830, an anonymous critic, in what critic Tobias Menely called a description of Selborne "as a place that lingers beyond the spatio-temporal horizon of modern life", wrote having visited the village that: The book was widely admired by contemporary writers | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne Samuel Taylor Coleridge called it a "sweet, delightful book"; John Clare imitated its style of natural history letters. Thomas Carlyle wrote that "It is one of our most excellent books; White, a quiet country Parson, has preached a better sermon here than all the loud Bishops that then were". Charles Darwin is said to have been delighted by it. Circa 1862, the retired surgeon and zoologist Thomas Bell moved to "The Wakes". He devoted his tme to studying White's work, and editing new edition of the book. The 1907–1921 Cambridge History of English and American Literature begins its essay on White's "Selborne" with the words: White is sometimes treated as a pioneer of ecology. The British ornithologist James Fisher gives a more balanced view, writing in 1941: The medical historian Richard Barnett writes that Barnett notes, too, that: Yale nonfiction tutor Fred Strebeigh, writing in "Audubon magazine" in 1988, compared White with Henry Thoreau's Walden: Tobias Menely of Indiana University notes that the book "has garnered praise from Coleridge, Carlyle, Darwin, Ruskin, Woolf, and Auden" and that The naturalist Richard Mabey writes in his biography of White that Virginia Woolf liked the book enough to devote an essay in her "The Captain’s Death Bed and Other Essays", "White's Selborne" to it, stating that the start of the book is like a novel. The manuscript for the book stayed in the White family until 1895, when it was auctioned at Sotheby's. The purchaser was Stuart M | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne Samuel, who mounted the letters and bound the book in green Morocco leather. His library was sold in 1907. The manuscript was bought by the dealer A.S.W. Rosenbach in 1923, and passed into the collection of Arthur A. Houghton. The Houghton collection was auctioned by Christie's in 1980, where the manuscript was purchased by and for Gilbert White's museum at The Wakes, Selborne, where it is displayed. Thomas Bewick, in the first volume ("Land Birds") of his "A History of British Birds" (1797), presents a phenological list of 19 birds which are "chiefly selected from Mr. White's Natural History of Selborne, and are arranged nearly in the order of their appearing". The list begins with the wryneck ("Middle of March"), places the cuckoo in the middle of April, and ends with the flycatcher in the middle of May. Charles Darwin read the "Natural History" as a young man, inspiring him to take "much pleasure in watching the habits of birds" and to wonder "why every gentleman did not become an ornithologist". Sara Losh, too, read the "Natural History" as part of her "wonderful, varied and advanced [home] education for a young girl". White's "Natural History" has been continuously in print since its first publication. A paperback edition of "The Illustrated Natural History of Selborne" was reprinted by Thames & Hudson in 2007 | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne It was long held ("apocryphally", according to White's biographer, Richard Mabey) to be the fourth-most published book in the English language after the Bible, the works of Shakespeare, and John Bunyan's "The Pilgrim's Progress". White's frequent accounts in "The Natural History and Antiquities of Selborne" of his tortoise Timothy, inherited from his aunt, form the basis for a variety of literary mentions. Verlyn Klinkenborg's book, "Timothy; or, Notes of an Abject Reptile" (2006) is based wholly on that reptile, as is Sylvia Townsend Warner's "The Portrait of a Tortoise" (1946). The tortoise also finds its way into science, as its species, "Testudo whitei" (Bennett 1836), long thought to be a synonym of "Testudo graeca", has been rediscovered in Algeria. Various writers have commented on the book. The poet Samuel Taylor Coleridge called it "This sweet delightful book". The novelist Virginia Woolf observed that "By some apparently unconscious device .. a door [is] left open, through which we hear distant sounds." Among poets, Edward Thomas wrote that "In this present year, 1915, at least, it is hard to find a flaw in the life he led" while W. H. Auden stated that "Selfishly, I, too, would have plumbed to know you: I could have learned so much." The naturalist and broadcaster David Attenborough called White "A man in total harmony with his world." The novelist Roald Dahl has the main character in his short story "The Visitor" read the book | https://en.wikipedia.org/wiki?curid=14522051 |
The Natural History and Antiquities of Selborne The writer and zookeeper Gerald Durrell commented in "The Amateur Naturalist" that White "simply observed nature with a sharp eye and wrote about it lovingly." | https://en.wikipedia.org/wiki?curid=14522051 |
Budh Planitia is a large basin on Mercury located at 22.0° N, 150.9° W. It lies to the east of Odin Planitia. It falls within the Tolstoj quadrangle. It is named after the Hindu word for Mercury, Budha. | https://en.wikipedia.org/wiki?curid=14523900 |
Odin Planitia is a large basin on Mercury located in the Tolstoj quadrangle at 23.3° N, 171.6° W. It was named after the Norse god Odin in 1976 by the IAU. A large volcanic dome 7 km in diameter and 1.4 km high is situated near the center of Odin. | https://en.wikipedia.org/wiki?curid=14523957 |
SOFA (astronomy) The SOFA (Standards of Fundamental Astronomy) software libraries are a collection of subroutines that implement official International Astronomical Union algorithms for astronomical computations. As of February 2009 they are available in both Fortran and C source code format. The subroutines in the libraries cover the following areas: As of the February 2009 release, SOFA licensing changed to allow use for any purpose, provided certain requirements are met. Previously, commercial usage was specifically excluded and required written agreement of the SOFA board. | https://en.wikipedia.org/wiki?curid=14526771 |
Bris sextant The is not a sextant proper, but is a small angle-measuring device that can be used for navigation. The "Bris" is, however, a true reflecting instrument which derives its high accuracy from the same principle of double reflection which is fundamental to the octant, the true sextant, and other reflecting instruments. It differs from other sextants primarily in being a fixed angle sextant, capable of measuring a few specific angles. Sven Yrvind (Lundin) developed his as part of his quest for low-cost, low-technology equipment for ocean crossings. The "Bris" is a low-technology, high-precision, fixed-interval instrument. It is made of two narrow, flat pieces of glass (microscope slides) permanently and rigidly mounted in a V-shape to a third flat piece of #12 welding glass to make viewing the sun eye safe. When the sun or moon is viewed through the V, it is split into eight images. The instrument is small and rugged enough that it can be kept in a 35mm film canister (about 2 cm radius, 3 cm tall) on a lanyard around one's neck. The is calibrated at a known geographic position with a good clock and a nautical almanac. As the day passes, one works the sight reductions backwards to develop exact angles for each of the images' tops and bottoms. The Sun and Moon have approximately the same angular size from the surface of the Earth, and can use the same calibrations | https://en.wikipedia.org/wiki?curid=14528756 |
Bris sextant In use, one waits until an image's edge touches the horizon, and then records the time and reduces the sight using the recorded angle for that edge of the image. "Bris" is Swedish for "breeze". It would appear that the name "Bris" is used by Yrvind for a number of his sail boats and is a favourite of his. | https://en.wikipedia.org/wiki?curid=14528756 |
Sobkou Planitia is a large basin on the planet Mercury. It is named after the ancient Egyptian messenger deity Sobkou (whose name is more usually transliterated Sobek). He was associated by the Egyptians with the planet Mercury. was discovered after Sobkou, the basin, was recognized as a Pre-Tolstojan basin on images from "Mariner 10". The most prominent features within the plain itself are a pair of craters, similar in size to one another, known as Brontë (Mercurian crater) and Degas (crater). Brontë is the older of the two craters, and the impact that formed Degas has overlapped the edges of that older crater and spread a spray of rays across the southern regions of and beyond. According to Peter Grego's book, "Venus and Mercury and how to observe them", is free of scarps, ridges, fractures and valleys. Its southeastern edge is bordered by the scarp Heemskerck Rupes (26N, 125W) which is about 300 km long which along part of the line of a very broad, bright swathe which is 1,000 km long and terminating just to the east of Chong Ch'ol (45N, 116W). | https://en.wikipedia.org/wiki?curid=14529059 |
Suisei Planitia is a large basin on Mercury. Ghost craters are unusual forms that occur in the Suisei Planitia. They are buried and rounded in profile, with only their rim crests rising above the surrounding smooth plains. It has been suggested that the smooth plains that is part of (Caloris Planitia) might be ejecta from Caloris that were melted by the impact. The name for this Planitia was approved in 1976. The "MESSENGER" Mercury orbiter crashed into the plain in April 30, 2015, near the crater Janáček. | https://en.wikipedia.org/wiki?curid=14529154 |
Tir Planitia is a large basin on the planet Mercury. The name Tir (تیر) is the Persian word for "Mercury". | https://en.wikipedia.org/wiki?curid=14529260 |
Astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either observational (by analyzing the data) or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology, which studies the Universe as a whole. Astronomers usually fall under either of two main types: observational and theoretical. Observational astronomers make direct observations of celestial objects and analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed. Because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form, evolve, and die. They use these data to create models or simulations to theorize how different celestial objects work. Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology. Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws | https://en.wikipedia.org/wiki?curid=580 |
Astronomer Today, that distinction has mostly disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are highly educated individuals who typically have a PhD in physics or astronomy and are employed by research institutions or universities. They spend the majority of their time working on research, although they quite often have other duties such as teaching, building instruments, or aiding in the operation of an observatory. The number of professional astronomers in the United States is actually quite small. The American Astronomical Society, which is the major organization of professional astronomers in North America, has approximately 7,000 members. This number includes scientists from other fields such as physics, geology, and engineering, whose research interests are closely related to astronomy. The International Astronomical Union comprises almost 10,145 members from 70 different countries who are involved in astronomical research at the PhD level and beyond. Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device (CCD) camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend relatively little time at telescopes usually just a few weeks per year | https://en.wikipedia.org/wiki?curid=580 |
Astronomer Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities also have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field. Those who become astronomers usually have a broad background in maths, sciences and computing in high school. Taking courses that teach how to research, write and present papers are also invaluable. In college/university most astronomers get a PhD in astronomy or physics. While there is a relatively low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and often host star parties. The Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the very ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research. | https://en.wikipedia.org/wiki?curid=580 |
Atom An atom is the smallest constituent unit of ordinary matter that constitutes a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers (, a ten-millionth of a millimeter, or 1/254,000,000 of an inch). They are so small that accurately predicting their behavior using classical physics – as if they were billiard balls, for example – is not possible. This is due to quantum effects. Current atomic models now use quantum principles to better explain and predict this behavior. Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Protons and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge whereas the electrons have a negative electric charge. The neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively. These atoms are called ions. The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force | https://en.wikipedia.org/wiki?curid=902 |
Atom This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus shatters and leaves behind different elements. This is a kind of nuclear decay. All electrons, nucleons, and nuclei alike are subatomic particles. The behavior of electrons in atoms is closer to a wave than a particle. The number of protons in the nucleus, called the "atomic number", defines to which chemical element the atom belongs. For example, each copper atom contains 29 protons. The number of neutrons defines the isotope of the element. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature. Chemistry is the discipline that studies these changes. The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. The word "atomos", meaning "uncuttable", was coined by the ancient Greek philosophers Leucippus and his pupil Democritus (5th century BC). However, these ancient ideas were based on metaphysical reasoning rather than empirical evidence | https://en.wikipedia.org/wiki?curid=902 |
Atom In the early 1800s, John Dalton used the concept of atoms to explain why chemical elements seemed to combine in ratios of small whole numbers (the law of multiple proportions). For instance, there are two types of tin oxide: one is 88.1% tin and 11.9% oxygen, and the other is 78.7% tin and 21.3% oxygen. This means that 100g of tin will combine either with 13.5g or 27g of oxygen. 13.5 and 27 form a ratio of 1:2, a ratio of small whole numbers. Similarly, there are two common types of iron oxide: 112g of iron can combine with either 32g or 48g of oxygen, which gives a ratio of 2:3. This recurring pattern suggested that elements react in multiples of discrete units, which Dalton concluded were atoms. In the case of tin oxides, for every one tin atom, there are either one or two oxygen atoms (SnO and SnO). In the case of iron oxides, for every two iron atoms, there are either two or three oxygen atoms (FeO and FeO). Dalton also believed atomic theory could explain why some gases dissolve in water better than other gases. For example, he observed that water absorbs carbon dioxide far better than it absorbs nitrogen. Dalton hypothesized this was due to the differences in the mass and configuation of the particles. Indeed, carbon dioxide molecules (CO) are heavier and larger than nitrogen molecules (N). In 1827, botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically, a phenomenon that became known as "Brownian motion" | https://en.wikipedia.org/wiki?curid=902 |
Atom This was thought to be caused by water molecules knocking the grains about. In 1905, Albert Einstein proved the reality of these molecules and their motions by producing the first statistical physics analysis of Brownian motion. French physicist Jean Perrin used Einstein's work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton's atomic theory. In 1897, J.J. Thomson discovered that cathode rays are not electromagnetic waves but made of particles that are 1,800 times lighter than hydrogen (the lightest atom). Therefore, they were not atoms, but a new particle, the first "subatomic" particle to be discovered, which he originally called "corpuscles" but were later named "electrons", after particles postulated by George Johnstone Stoney in 1874. Thomson also showed they were identical to particles given off by photoelectric and radioactive materials. It was quickly recognized that they are the particles that carry electric currents in metal wires, and carry the negative electric charge within atoms. Thus Thomson overturned the belief that atoms are the indivisible, fundamental particles of matter. J.J. Thomson incorrectly postulated that the negatively-charged electrons were distributed throughout the atom in a uniform sea of positive charge. This was known as the plum pudding model. In 1909, Hans Geiger and Ernest Marsden, working under the direction of Ernest Rutherford, bombarded metal foil with alpha particles to observe how they scattered | https://en.wikipedia.org/wiki?curid=902 |
Atom They expected all the alpha particles to pass straight through with little deflection, because Thomson's model said that the charges in the atom are so diffuse that their electric fields could not affect the alpha particles much. However, Geiger and Marsden spotted alpha particles being deflected by angles greater than 90°, which was supposed to be impossible according to Thomson's model. To explain this, Rutherford proposed that the positive charge of the atom is concentrated in a tiny nucleus at the center of the atom. While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table. The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J.J. Thomson created a technique for isotope separation through his work on ionized gases, which subsequently led to the discovery of stable isotopes. In 1913 the physicist Niels Bohr proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon | https://en.wikipedia.org/wiki?curid=902 |
Atom This quantization was used to explain why the electrons' orbits are stable (given that normally, charges in acceleration, including circular motion, lose kinetic energy which is emitted as electromagnetic radiation, see "synchrotron radiation") and why elements absorb and emit electromagnetic radiation in discrete spectra. Later in the same year Henry Moseley provided additional experimental evidence in favor of Niels Bohr's theory. These results refined Ernest Rutherford's and Antonius Van den Broek's model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today. Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons. As the chemical properties of the elements were known to largely repeat themselves according to the periodic law, in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner. Groups of electrons were thought to occupy a set of electron shells about the nucleus. The Stern–Gerlach experiment of 1922 provided further evidence of the quantum nature of atomic properties | https://en.wikipedia.org/wiki?curid=902 |
Atom When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split in a way correlated with the direction of an atom's angular momentum, or spin. As this spin direction is initially random, the beam would be expected to deflect in a random direction. Instead, the beam was split into two directional components, corresponding to the atomic spin being oriented up or down with respect to the magnetic field. In 1925 Werner Heisenberg published the first consistent mathematical formulation of quantum mechanics (Matrix Mechanics). One year earlier, in 1924, Louis de Broglie had proposed that all particles behave to an extent like waves and, in 1926, Erwin Schrödinger used this idea to develop a mathematical model of the atom (Wave Mechanics) that described the electrons as three-dimensional waveforms rather than point particles. A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at a given point in time; this became known as the uncertainty principle, formulated by Werner Heisenberg in 1927. In this concept, for a given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa. This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen | https://en.wikipedia.org/wiki?curid=902 |
Atom Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed. The development of the mass spectrometer allowed the mass of atoms to be measured with increased accuracy. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule. The explanation for these different isotopes awaited the discovery of the neutron, an uncharged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus. In 1938, the German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product. A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental "nuclear fission". In 1944, Hahn received the Nobel prize in chemistry. Despite Hahn's efforts, the contributions of Meitner and Frisch were not recognized | https://en.wikipedia.org/wiki?curid=902 |
Atom In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies. Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. The standard model of particle physics was developed that so far has successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions. Though the word "atom" originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron; all three are fermions. However, the hydrogen-1 atom has no neutrons and the hydron ion has no electrons. The electron is by far the least massive of these particles at , with a negative electrical charge and a size that is too small to be measured using available techniques. It was the lightest particle with a positive rest mass measured, until the discovery of neutrino mass. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J | https://en.wikipedia.org/wiki?curid=902 |
Atom Thomson; see history of subatomic physics for details. Protons have a positive charge and a mass 1,836 times that of the electron, at . The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron, or . Neutrons are the heaviest of the three constituent particles, but their mass can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions—on the order of —although the 'surface' of these particles is not sharply defined. The neutron was discovered in 1932 by the English physicist James Chadwick. In the Standard Model of physics, electrons are truly elementary particles with no internal structure. However, both protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +) and one down quark (with a charge of −). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles | https://en.wikipedia.org/wiki?curid=902 |
Atom The quarks are held together by the strong interaction (or strong force), which is mediated by gluons. The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force, which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces. All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to 1.07 fm, where "A" is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 10 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other. Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay. The proton, the electron, and the neutron are classified as fermions | https://en.wikipedia.org/wiki?curid=902 |
Atom Fermions obey the Pauli exclusion principle which prohibits "identical" fermions, such as multiple protons, from occupying the same quantum state at the same time. Thus, every proton in the nucleus must occupy a quantum state different from all other protons, and the same applies to all neutrons of the nucleus and to all electrons of the electron cloud. A nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which slightly modifies this trend of equal numbers of protons to neutrons. The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay | https://en.wikipedia.org/wiki?curid=902 |
Atom The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element. If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (such as a gamma ray, or the kinetic energy of a beta particle), as described by Albert Einstein's mass–energy equivalence formula, formula_1, where formula_2 is the mass loss and formula_3 is the speed of light. This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate. The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel—a total nucleon number of about 60—is usually an exothermic process that releases more energy than is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process | https://en.wikipedia.org/wiki?curid=902 |
Atom These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star. The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations. Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured. Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form. Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation. Each atomic orbital corresponds to a particular energy level of the electron | https://en.wikipedia.org/wiki?curid=902 |
Atom The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines. The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23 "million" eV for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals. By definition, any two atoms with an identical number of "protons" in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of "neutrons" are different isotopes of the same element | https://en.wikipedia.org/wiki?curid=902 |
Atom For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The known elements form a set of atomic numbers, from the single proton element hydrogen up to the 118-proton element oganesson. All known isotopes of elements with atomic numbers greater than 82 are radioactive, although the radioactivity of element 83 (bismuth) is so slight as to be practically negligible. About 339 nuclides occur naturally on Earth, of which 252 (about 74%) have not been observed to decay, and are referred to as "stable isotopes". However, only 90 of these nuclides are stable to all decay, even in theory. Another 162 (bringing the total to 252) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 34 radioactive nuclides have half-lives longer than 100 million years, and are long-lived enough to be present from the birth of the solar system. This collection of 286 nuclides are known as primordial nuclides. Finally, an additional 53 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium), or else as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14). For 80 of the chemical elements, at least one stable isotope exists | https://en.wikipedia.org/wiki?curid=902 |
Atom As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.2 stable isotopes per element. Twenty-six elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes. Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 252 known stable nuclides, only four have both an odd number of protons "and" odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10 and nitrogen-14. Also, only four naturally occurring, radioactive odd–odd nuclides have a half-life over a billion years: potassium-40, vanadium-50, lanthanum-138 and tantalum-180m. Most odd–odd nuclei are highly unstable with respect to beta decay, because the decay products are even–even, and are therefore more strongly bound, due to nuclear pairing effects. The large majority of an atom's mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number | https://en.wikipedia.org/wiki?curid=902 |
Atom It is a positive integer and dimensionless (instead of having dimension of mass), because it expresses a count. An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons). The actual mass of an atom at rest is often expressed in daltons (Da), also called the unified atomic mass unit (u). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately . Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 Da. The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 Da). However, this number will not be exactly an integer except in the case of carbon-12 (see below). The heaviest stable atom is lead-208, with a mass of . As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about ). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg | https://en.wikipedia.org/wiki?curid=902 |
Atom Atoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius. This is a measure of the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin. On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right). Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm. When subjected to external forces, like electrical fields, the shape of an atom may deviate from spherical symmetry. The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystals, where large crystal-electrical fields may occur at low-symmetry lattice sites. Significant ellipsoidal deformations have been shown to occur for sulfur ions and chalcogen ions in pyrite-type compounds | https://en.wikipedia.org/wiki?curid=902 |
Atom Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they cannot be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width. A single drop of water contains about 2 sextillion () atoms of oxygen, and twice the number of hydrogen atoms. A single carat diamond with a mass of contains about 10 sextillion (10) atoms of carbon. If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple. Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm. The most common forms of radioactive decay are: Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle. An analog of gamma emission which allows excited nuclei to lose energy in a different way, is internal conversion—a process that produces high-speed electrons that are not beta rays, followed by production of high-energy photons that are not gamma rays | https://en.wikipedia.org/wiki?curid=902 |
Atom A few large nuclei explode into two or more charged fragments of varying masses plus several neutrons, in a decay called spontaneous nuclear fission. Each radioactive isotope has a characteristic decay time period—the half-life—that is determined by the amount of time needed for half of a sample to decay. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half-life. Hence after two half-lives have passed only 25% of the isotope is present, and so forth. Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin ½ ħ, or "spin-½". In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin. The magnetic field produced by an atom—its magnetic moment—is determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field. However, the most dominant contribution comes from electron spin | https://en.wikipedia.org/wiki?curid=902 |
Atom Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons. In ferromagnetic elements such as iron, cobalt and nickel, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a spontaneous process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field. The nucleus of an atom will have no spin when it has even numbers of both neutrons and protons, but for other cases of odd numbers, the nucleus may have a spin. Normally nuclei with spin are aligned in random directions because of thermal equilibrium | https://en.wikipedia.org/wiki?curid=902 |
Atom However, for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolarization. This has important applications in magnetic resonance imaging. The potential energy of an electron in an atom is negative, its dependence of its position reaches the minimum (the most absolute value) inside the nucleus, and vanishes when the distance from the nucleus goes to infinity, roughly in an inverse proportion to the distance. In the quantum-mechanical model, a bound electron can only occupy a set of states centered on the nucleus, and each state corresponds to a specific energy level; see time-independent Schrödinger equation for theoretical explanation. An energy level can be measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). The lowest energy state of a bound electron is called the ground state, i.e. stationary state, while an electron transition to a higher level results in an excited state. The electron's energy raises when "n" increases because the (average) distance to the nucleus increases. Dependence of the energy on is caused not by electrostatic potential of the nucleus, but by interaction between electrons. For an electron to transition between two different states, e.g | https://en.wikipedia.org/wiki?curid=902 |
Atom ground state to first excited state, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels, according to the Niels Bohr model, what can be precisely calculated by the Schrödinger equation. Electrons jump between orbitals in a particle-like fashion. For example, if a single photon strikes the electrons, only a single electron changes states in response to the photon; see Electron properties. The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum. Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors. When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a view that does not include the continuous spectrum in the background, instead sees a series of emission lines from the photons emitted by the atoms | https://en.wikipedia.org/wiki?curid=902 |
Atom ) Spectroscopic measurements of the strength and width of atomic spectral lines allow the composition and physical properties of a substance to be determined. Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spin–orbit coupling, which is an interaction between the spin and motion of the outermost electron. When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines. The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect. If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting photon. The emitted photon and the interacting photon then move off in parallel and with matching phases | https://en.wikipedia.org/wiki?curid=902 |
Atom That is, the wave patterns of the two photons are synchronized. This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band. Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds. The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in that shell are called valence electrons. The number of valence electrons determines the bonding behavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells. For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds. The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table | https://en.wikipedia.org/wiki?curid=902 |
Atom (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases. Quantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas. Within a state, a material can also exist in different allotropes. An example of this is solid carbon, which can exist as graphite or diamond. Gaseous allotropes exist as well, such as dioxygen and ozone. At temperatures close to absolute zero, atoms can form a Bose–Einstein condensate, at which point quantum mechanical effects, which are normally only observed at the atomic scale, become apparent on a macroscopic scale. This super-cooled collection of atoms then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior. The scanning tunneling microscope is a device for viewing surfaces at the atomic level. It uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would normally be insurmountable. Electrons tunnel through the vacuum between two planar metal electrodes, on each of which is an adsorbed atom, providing a tunneling-current density that can be measured | https://en.wikipedia.org/wiki?curid=902 |
Atom Scanning one atom (taken as the tip) as it moves past the other (the sample) permits plotting of tip displacement versus lateral separation for a constant current. The calculation shows the extent to which scanning-tunneling-microscope images of an individual atom are visible. It confirms that for low bias, the microscope images the space-averaged dimensions of the electron orbitals across closely packed energy levels—the Fermi level local density of states. An atom can be ionized by removing one of its electrons. The electric charge causes the trajectory of an atom to bend when it passes through a magnetic field. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis. A more area-selective method is electron energy loss spectroscopy, which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample | https://en.wikipedia.org/wiki?curid=902 |
Atom The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry. Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element. Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth. Baryonic matter forms about 4% of the total energy density of the observable Universe, with an average density of about 0.25 particles/m (mostly protons and electrons). Within a galaxy such as the Milky Way, particles have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 10 to 10 atoms/m. The Sun is believed to be inside the Local Bubble, so the density in the solar neighborhood is only about 10 atoms/m. Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium. Up to 95% of the Milky Way's baryonic matter are concentrated inside stars, where conditions are unfavorable for atomic matter. The total baryonic mass is about 10% of the mass of the galaxy; the remainder of the mass is an unknown dark matter | https://en.wikipedia.org/wiki?curid=902 |
Atom High temperature inside stars makes most "atoms" fully ionized, that is, separates "all" electrons from the nuclei. In stellar remnants—with exception of their surface layers—an immense pressure make electron shells impossible. Electrons are thought to exist in the Universe since early stages of the Big Bang. Atomic nuclei forms in nucleosynthesis reactions. In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of the beryllium and boron. Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang—an epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei. Since the Big Bang, which produced no carbon or heavier elements, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron; see stellar nucleosynthesis for details | https://en.wikipedia.org/wiki?curid=902 |
Atom Isotopes such as lithium-6, as well as some beryllium and boron are generated in space through cosmic ray spallation. This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected. Elements heavier than iron were produced in supernovae and colliding neutron stars through the r-process, and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei. Elements such as lead formed largely through the radioactive decay of heavier elements. Most of the atoms that make up the Earth and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating. Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay. There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere. Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions. Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth | https://en.wikipedia.org/wiki?curid=902 |
Atom Transuranic elements have radioactive lifetimes shorter than the current age of the Earth and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust. Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore. The Earth contains approximately atoms. Although small numbers of independent atoms of noble gases exist, such as argon, neon, and helium, 99% of the atmosphere is bound in the form of molecules, including carbon dioxide and diatomic oxygen and nitrogen. At the surface of the Earth, an overwhelming majority of atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals. This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter. All nuclides with atomic numbers higher than 82 (lead) are known to be radioactive. No nuclide with an atomic number exceeding 92 (uranium) exists on Earth as a primordial nuclide, and heavier elements generally have shorter half-lives. Nevertheless, an "island of stability" encompassing relatively long-lived isotopes of superheavy elements with atomic numbers 110–114 might exist. Predictions for the half-live of the most stable nuclide on the island range from a few minutes to millions of years | https://en.wikipedia.org/wiki?curid=902 |
Atom In any case, superheavy elements (with "Z" > 104) would not exist due to increasing Coulomb repulsion (which results in spontaneous fission with increasingly short half-lives) in the absence of any stabilizing effects. Each particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. The first causes of this imbalance are not yet fully understood, although theories of baryogenesis may offer an explanation. As a result, no antimatter atoms have been discovered in nature. However, in 1996 the antimatter counterpart of the hydrogen atom (antihydrogen) was synthesized at the CERN laboratory in Geneva. Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive muon, forming a muonic atom. These types of atoms can be used to test the fundamental predictions of physics. | https://en.wikipedia.org/wiki?curid=902 |
Alloy An alloy is a combination of metals or metals combined with one or more other elements. For example, combining the metallic elements gold and copper produces red gold, gold and silver becomes white gold, and silver combined with copper produces sterling silver. Elemental iron, combined with non-metallic carbon or silicon, produces alloys called steel or silicon steel. The resulting mixture forms a substance with properties that often differ from those of the pure metals, such as increased strength or hardness. Unlike other substances that may contain metallic bases but do not behave as metals, such as aluminium oxide (sapphire), beryllium aluminium silicate (emerald) or sodium chloride (salt), an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opaqueness, and luster. Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to automobiles to surgical tools, to exotic titanium-alloys used in the aerospace industry, to beryllium-copper alloys for non-sparking tools. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze and amalgams | https://en.wikipedia.org/wiki?curid=1187 |
Alloy An alloy may be a solid solution of metal elements (a single phase, where all metallic grains (crystals) are of the same composition) or a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal). Intermetallic compounds are alloys with a defined stoichiometry and crystal structure. Zintl phases are also sometimes considered alloys depending on bond types (see Van Arkel–Ketelaar triangle for information on classifying bonding in binary compounds). Alloys are defined by a metallic bonding character. The alloy constituents are usually measured by mass percentage for practical applications, and in atomic fraction for basic science studies. Alloys are usually classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy. They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic. An alloy is a mixture of chemical elements, which forms an impure substance (admixture) that retains the characteristics of a metal. An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are often considered useful. Alloys are made by mixing two or more elements, at least one of which is a metal | https://en.wikipedia.org/wiki?curid=1187 |
Alloy This is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture. The mechanical properties of alloys will often be quite different from those of its individual constituents. A metal that is normally very soft (malleable), such as aluminium, can be altered by alloying it with another soft metal, such as copper. Although both metals are very soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common alloys in modern use. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel. Like oil and water, a molten metal may not always mix with another element. For example, pure iron is almost completely insoluble with copper. Even when the constituents are soluble, each will usually have a saturation point, beyond which no more of the constituent can be added. Iron, for example, can hold a maximum of 6.67% carbon | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Although the elements of an alloy usually must be soluble in the liquid state, they may not always be soluble in the solid state. If the metals remain soluble when solid, the alloy forms a solid solution, becoming a homogeneous structure consisting of identical crystals, called a phase. If as the mixture cools the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases, some with more of one constituent than the other. However, in other alloys, the insoluble elements may not separate until after crystallization occurs. If cooled very quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents. As time passes, the atoms of these supersaturated alloys can separate from the crystal lattice, becoming more stable, and forming a second phase that serves to reinforce the crystals internally. Some alloys, such as electrum—an alloy of silver and gold—occur naturally. Meteorites are sometimes made of naturally occurring alloys of iron and nickel, but are not native to the Earth. One of the first alloys made by humans was bronze, which is a mixture of the metals tin and copper. Bronze was an extremely useful alloy to the ancients, because it is much stronger and harder than either of its components. Steel was another common alloy | https://en.wikipedia.org/wiki?curid=1187 |
Alloy However, in ancient times, it could only be created as an accidental byproduct from the heating of iron ore in fires (smelting) during the manufacture of iron. Other ancient alloys include pewter, brass and pig iron. In the modern age, steel can be created in many forms. Carbon steel can be made by varying only the carbon content, producing soft alloys like mild steel or hard alloys like spring steel. steels can be made by adding other elements, such as chromium, molybdenum, vanadium or nickel, resulting in alloys such as high-speed steel or tool steel. Small amounts of manganese are usually alloyed with most modern steels because of its ability to remove unwanted impurities, like phosphorus, sulfur and oxygen, which can have detrimental effects on the alloy. However, most alloys were not created until the 1900s, such as various aluminium, titanium, nickel, and magnesium alloys. Some modern superalloys, such as incoloy, inconel, and hastelloy, may consist of a multitude of different elements. As a noun, the term alloy is used to describe a mixture of atoms in which the primary constituent is a metal. When used as a verb, the term refers to the act of mixing a metal with other elements. The primary metal is called the "base", the "matrix", or the "solvent". The secondary constituents are often called "solutes". If there is a mixture of only two types of atoms (not counting impurities) such as a copper-nickel alloy, then it is called a "binary alloy | https://en.wikipedia.org/wiki?curid=1187 |
Alloy " If there are three types of atoms forming the mixture, such as iron, nickel and chromium, then it is called a "ternary alloy." An alloy with four constituents is a "quaternary alloy," while a five-part alloy is termed a "quinary alloy." Because the percentage of each constituent can be varied, with any mixture the entire range of possible variations is called a "system". In this respect, all of the various forms of an alloy containing only two constituents, like iron and carbon, is called a "binary system," while all of the alloy combinations possible with a ternary alloy, such as alloys of iron, carbon and chromium, is called a "ternary system". An alloy is technically an impure metal, but when referring to alloys, the term "impurities" usually denotes undesirable elements. Such impurities are introduced from the base metals and alloying elements, but are removed during processing. For instance, sulfur is a common impurity in steel. Sulfur combines readily with iron to form iron sulfide, which is very brittle, creating weak spots in the steel. Lithium, sodium and calcium are common impurities in aluminium alloys, which can have adverse effects on the structural integrity of castings. Conversely, otherwise pure-metals that simply contain unwanted impurities are often called "impure metals" and are not usually referred to as alloys. Oxygen, present in the air, readily combines with most metals to form metal oxides; especially at higher temperatures encountered during alloying | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Great care is often taken during the alloying process to remove excess impurities, using fluxes, chemical additives, or other methods of extractive metallurgy. In practice, some alloys are used so predominantly with respect to their base metals that the name of the primary constituent is also used as the name of the alloy. For example, 14 karat gold is an alloy of gold with other elements. Similarly, the silver used in jewelry and the aluminium used as a structural building material are also alloys. The term "alloy" is sometimes used in everyday speech as a synonym for a particular alloy. For example, automobile wheels made of an aluminium alloy are commonly referred to as simply "alloy wheels", although in point of fact steels and most other metals in practical use are also alloys. Steel is such a common alloy that many items made from it, like wheels, barrels, or girders, are simply referred to by the name of the item, assuming it is made of steel. When made from other materials, they are typically specified as such, (i.e.: "bronze wheel", "plastic barrel", or "wood girder"). Alloying a metal is done by combining it with one or more other elements. The most common and oldest alloying process is performed by heating the base metal beyond its melting point and then dissolving the solutes into the molten liquid, which may be possible even if the melting point of the solute is far greater than that of the base | https://en.wikipedia.org/wiki?curid=1187 |
Alloy For example, in its liquid state, titanium is a very strong solvent capable of dissolving most metals and elements. In addition, it readily absorbs gases like oxygen and burns in the presence of nitrogen. This increases the chance of contamination from any contacting surface, and so must be melted in vacuum induction-heating and special, water-cooled, copper crucibles. However, some metals and solutes, such as iron and carbon, have very high melting-points and were impossible for ancient people to melt. Thus, alloying (in particular, interstitial alloying) may also be performed with one or more constituents in a gaseous state, such as found in a blast furnace to make pig iron (liquid-gas), nitriding, carbonitriding or other forms of case hardening (solid-gas), or the cementation process used to make blister steel (solid-gas). It may also be done with one, more, or all of the constituents in the solid state, such as found in ancient methods of pattern welding (solid-solid), shear steel (solid-solid), or crucible steel production (solid-liquid), mixing the elements via solid-state diffusion. By adding another element to a metal, differences in the size of the atoms create internal stresses in the lattice of the metallic crystals; stresses that often enhance its properties. For example, the combination of carbon with iron produces steel, which is stronger than iron, its primary element. The electrical and thermal conductivity of alloys is usually lower than that of the pure metals | https://en.wikipedia.org/wiki?curid=1187 |
Alloy The physical properties, such as density, reactivity, Young's modulus of an alloy may not differ greatly from those of its base element, but engineering properties such as tensile strength, ductility, and shear strength may be substantially different from those of the constituent materials. This is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Sometimes alloys may exhibit marked differences in behavior even when small amounts of one element are present. For example, impurities in semiconducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura. Some alloys are made by melting and mixing two or more metals. Bronze, an alloy of copper and tin, was the first alloy discovered, during the prehistoric period now known as the Bronze Age. It was harder than pure copper and originally used to make tools and weapons, but was later superseded by metals and alloys with better properties. In later times bronze has been used for ornaments, bells, statues, and bearings. Brass is an alloy made from copper and zinc. Unlike pure metals, most alloys do not have a single melting point, but a melting range during which the material is a mixture of solid and liquid phases (a slush) | https://en.wikipedia.org/wiki?curid=1187 |
Alloy The temperature at which melting begins is called the solidus, and the temperature when melting is just complete is called the liquidus. For many alloys there is a particular alloy proportion (in some cases more than one), called either a eutectic mixture or a peritectic composition, which gives the alloy a unique and low melting point, and no liquid/solid slush transition. Alloying elements are added to a base metal, to induce hardness, toughness, ductility, or other desired properties. Most metals and alloys can be work hardened by creating defects in their crystal structure. These defects are created during plastic deformation by hammering, bending, extruding, et cetera, and are permanent unless the metal is recrystallized. Otherwise, some alloys can also have their properties altered by heat treatment. Nearly all metals can be softened by annealing, which recrystallizes the alloy and repairs the defects, but not as many can be hardened by controlled heating and cooling. Many alloys of aluminium, copper, magnesium, titanium, and nickel can be strengthened to some degree by some method of heat treatment, but few respond to this to the same degree as does steel. The base metal iron of the iron-carbon alloy known as steel, undergoes a change in the arrangement (allotropy) of the atoms of its crystal matrix at a certain temperature (usually between and , depending on carbon content). This allows the smaller carbon atoms to enter the interstices of the iron crystal | https://en.wikipedia.org/wiki?curid=1187 |
Alloy When this diffusion happens, the carbon atoms are said to be in "solution" in the iron, forming a particular single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly, the carbon can diffuse out of the iron and it will gradually revert to its low temperature allotrope. During slow cooling, the carbon atoms will no longer be as soluble with the iron, and will be forced to precipitate out of solution, nucleating into a more concentrated form of iron carbide (FeC) in the spaces between the pure iron crystals. The steel then becomes heterogeneous, as it is formed of two phases, the iron-carbon phase called cementite (or carbide), and pure iron ferrite. Such a heat treatment produces a steel that is rather soft. If the steel is cooled quickly, however, the carbon atoms will not have time to diffuse and precipitate out as carbide, but will be trapped within the iron crystals. When rapidly cooled, a diffusionless (martensite) transformation occurs, in which the carbon atoms become trapped in solution. This causes the iron crystals to deform as the crystal structure tries to change to its low temperature state, leaving those crystals very hard but much less ductile (more brittle). While the high strength of steel results when diffusion and precipitation is prevented (forming martensite), most heat-treatable alloys are precipitation hardening alloys, that depend on the diffusion of alloying elements to achieve their strength | https://en.wikipedia.org/wiki?curid=1187 |
Alloy When heated to form a solution and then cooled quickly, these alloys become much softer than normal, during the diffusionless transformation, but then harden as they age. The solutes in these alloys will precipitate over time, forming intermetallic phases, which are difficult to discern from the base metal. Unlike steel, in which the solid solution separates into different crystal phases (carbide and ferrite), precipitation hardening alloys form different phases within the same crystal. These intermetallic alloys appear homogeneous in crystal structure, but tend to behave heterogeneously, becoming hard and somewhat brittle. When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called "atom exchange" and the "interstitial mechanism". The relative size of each element in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent. This is called a "substitutional alloy". Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms respectively. In the case of the interstitial mechanism, one atom is usually much smaller than the other and can not successfully substitute for the other type of atom in the crystals of the base metal | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Instead, the smaller atoms become trapped in the spaces between the atoms of the crystal matrix, called the "interstices". This is referred to as an "interstitial alloy". Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are substituted by nickel and chromium atoms. The use of alloys by humans started with the use of meteoric iron, a naturally occurring alloy of nickel and iron. It is the main constituent of iron meteorites. As no metallurgic processes were used to separate iron from nickel, the alloy was used as it was. Meteoric iron could be forged from a red heat to make objects such as tools, weapons, and nails. In many cultures it was shaped by cold hammering into knives and arrowheads. They were often used as anvils. Meteoric iron was very rare and valuable, and difficult for ancient people to work. Iron is usually found as iron ore on Earth, except for one deposit of native iron in Greenland, which was used by the Inuit people. Native copper, however, was found worldwide, along with silver, gold, and platinum, which were also used to make tools, jewelry, and other objects since Neolithic times. Copper was the hardest of these metals, and the most widely distributed. It became one of the most important metals to the ancients | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Around 10,000 years ago in the highlands of Anatolia (Turkey), humans learned to smelt metals such as copper and tin from ore. Around 2500 BC, people began alloying the two metals to form bronze, which was much harder than its ingredients. Tin was rare, however, being found mostly in Great Britain. In the Middle East, people began alloying copper with zinc to form brass. Ancient civilizations took into account the mixture and the various properties it produced, such as hardness, toughness and melting point, under various conditions of temperature and work hardening, developing much of the information contained in modern alloy phase diagrams. For example, arrowheads from the Chinese Qin dynasty (around 200 BC) were often constructed with a hard bronze-head, but a softer bronze-tang, combining the alloys to prevent both dulling and breaking during use. Mercury has been smelted from cinnabar for thousands of years. Mercury dissolves many metals, such as gold, silver, and tin, to form amalgams (an alloy in a soft paste or liquid form at ambient temperature). Amalgams have been used since 200 BC in China for gilding objects such as armor and mirrors with precious metals. The ancient Romans often used mercury-tin amalgams for gilding their armor. The amalgam was applied as a paste and then heated until the mercury vaporized, leaving the gold, silver, or tin behind. Mercury was often used in mining, to extract precious metals like gold and silver from their ores | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Many ancient civilizations alloyed metals for purely aesthetic purposes. In ancient Egypt and Mycenae, gold was often alloyed with copper to produce red-gold, or iron to produce a bright burgundy-gold. Gold was often found alloyed with silver or other metals to produce various types of colored gold. These metals were also used to strengthen each other, for more practical purposes. Copper was often added to silver to make sterling silver, increasing its strength for use in dishes, silverware, and other practical items. Quite often, precious metals were alloyed with less valuable substances as a means to deceive buyers. Around 250 BC, Archimedes was commissioned by the King of Syracuse to find a way to check the purity of the gold in a crown, leading to the famous bath-house shouting of "Eureka!" upon the discovery of Archimedes' principle. The term pewter covers a variety of alloys consisting primarily of tin. As a pure metal, tin is much too soft to use for most practical purposes. However, during the Bronze Age, tin was a rare metal in many parts of Europe and the Mediterranean, so it was often valued higher than gold. To make jewellery, cutlery, or other objects from tin, workers usually alloyed it with other metals to increase strength and hardness. These metals were typically lead, antimony, bismuth or copper | https://en.wikipedia.org/wiki?curid=1187 |
Alloy These solutes were sometimes added individually in varying amounts, or added together, making a wide variety of objects, ranging from practical items such as dishes, surgical tools, candlesticks or funnels, to decorative items like ear rings and hair clips. The earliest examples of pewter come from ancient Egypt, around 1450 BC. The use of pewter was widespread across Europe, from France to Norway and Britain (where most of the ancient tin was mined) to the Near East. The alloy was also used in China and the Far East, arriving in Japan around 800 AD, where it was used for making objects like ceremonial vessels, tea canisters, or chalices used in shinto shrines. The first known smelting of iron began in Anatolia, around 1800 BC. Called the bloomery process, it produced very soft but ductile wrought iron. By 800 BC, iron-making technology had spread to Europe, arriving in Japan around 700 AD. Pig iron, a very hard but brittle alloy of iron and carbon, was being produced in China as early as 1200 BC, but did not arrive in Europe until the Middle Ages. Pig iron has a lower melting point than iron, and was used for making cast-iron. However, these metals found little practical use until the introduction of crucible steel around 300 BC. These steels were of poor quality, and the introduction of pattern welding, around the 1st century AD, sought to balance the extreme properties of the alloys by laminating them, to create a tougher metal | https://en.wikipedia.org/wiki?curid=1187 |
Alloy Around 700 AD, the Japanese began folding bloomery-steel and cast-iron in alternating layers to increase the strength of their swords, using clay fluxes to remove slag and impurities. This method of Japanese swordsmithing produced one of the purest steel-alloys of the ancient world. While the use of iron started to become more widespread around 1200 BC, mainly because of interruptions in the trade routes for tin, the metal was much softer than bronze. However, very small amounts of steel, (an alloy of iron and around 1% carbon), was always a byproduct of the bloomery process. The ability to modify the hardness of steel by heat treatment had been known since 1100 BC, and the rare material was valued for the manufacture of tools and weapons. Because the ancients could not produce temperatures high enough to melt iron fully, the production of steel in decent quantities did not occur until the introduction of blister steel during the Middle Ages. This method introduced carbon by heating wrought iron in charcoal for long periods of time, but the absorption of carbon in this manner is extremely slow thus the penetration was not very deep, so the alloy was not homogeneous. In 1740, Benjamin Huntsman began melting blister steel in a crucible to even out the carbon content, creating the first process for the mass production of tool steel. Huntsman's process was used for manufacturing tool steel until the early 1900s | https://en.wikipedia.org/wiki?curid=1187 |
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