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: the map shows the difference between the amount of sunlight Greenland reflected in the summer of 2011 versus the average percent it reflected between 2000 and 2006. Some areas reflect close to 20 percent less light than a decade ago. Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages. Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes visible spectrum Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global Climate change (general concept) Terrestrial albedo Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. White-sky, black-sky, and blue-sky albedo For land surfaces, it has been shown that the | Wikipedia:Albedo |
of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. White-sky, black-sky, and blue-sky albedo For land surfaces, it has been shown that the albedo at a particular solar zenith angle θi can be approximated by the proportionate sum of two terms: * the directional-hemispherical reflectance at that solar zenith angle, , sometimes referred to as black-sky albedo, and * the bi-hemispherical reflectance, , sometimes referred to as white-sky albedo. with 1-D being the proportion of direct radiation from a given solar angle, and D being the proportion of diffuse illumination, the actual albedo (also called blue-sky albedo) can then be given as: : (1 - D) (_i) + D . This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe. Human impact on the environment Urbanization generally decreases albedo (commonly being 0.01–0.02 lower than adjacent croplands), which contributes to global warming. Deliberately increasing albedo in urban areas can mitigate the urban heat island effect. An estimate in 2022 found that on a global scale, "an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing ~44 Gigatons Intentionally enhancing the albedo of the Earth'ssurface, along with its daytime thermal emittance, has been proposed as a Solar Radiation Management The tens of thousands of hectares of greenhouses in Province of Almería Examples of terrestrial albedo effects sunlight relative to various surface conditions Illumination Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth'ssurface at that | Wikipedia:Albedo |
Illumination Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth'ssurface at that location (e.g. through melting of reflective ice). However, albedo and illumination both vary by latitude. Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.Insolation effectsThe intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation (solar irradiance); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert, which also have a relatively high albedo, will be hotter due to high insolation. Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation. Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes. Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth. This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This Ice–albedo feedbackClimate and weatherssuch as the ice-albedo feedback) or inhibit (negative feedbacks) warming. Albedo affects climate by determining how much radiation a planet absorbs. The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather. The response of the climate system to an initial forcing is modified by feedbacks: increased by Positive feedbackAlbedo–temperature feedback When an area'salbedo changes due to snowfall, a snow–temperature | Wikipedia:Albedo |
albedo variations between land, ice, or ocean surfaces can drive weather. The response of the climate system to an initial forcing is modified by feedbacks: increased by Positive feedback Albedo–temperature feedback When an area'salbedo changes due to snowfall, a snow–temperature feedback results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g., a warm air mass), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local weather is dynamic due to the change of seasons, eventually warm air masses and a more direct angle of sunlight (higher insolation) cause melting. When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating. Snow Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow. Over Antarctica, snow albedo averages a little more than 0.8. If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (referred to as the Ice–albedo feedback In Switzerland, the citizens have been protecting their glaciers with large white tarpaulins to slow down the ice melt. These large white sheets are helping to reject the rays from the sun and defecting the heat. Although this method is very expensive, it has been shown to work, reducing snow and ice melt by 60%. Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would | Wikipedia:Albedo |
snow and ice melt by 60%. Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback. Both positive feedback loops have long been recognized as important for global warming. Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets. The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions. Small-scale effects Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing. Solar photovoltaic effects Albedo can affect the electrical energy output of solar photovoltaic system Trees Forests generally have a low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate | Wikipedia:Albedo |
have a low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease the reflection of sunlight (albedo). In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect. Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate. Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only a temporary mitigation benefit. In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15. The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy. Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming. Water Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the Fresnel equations. At the scale of the wavelength | Wikipedia:Albedo |
new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming. Water Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the Fresnel equations. At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular reflection Clouds Cloud albedo has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth." Albedo and climate in some areas are affected by artificial clouds, such as those created by the contrails of heavy commercial airliner traffic. A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as colder than temperatures several miles away under clear skies. Aerosol effects Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth'sradiative balance. The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain. Black carbon Another albedo-related effect on the climate is from black carbon particles. The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels is +0.2 W m−2, with a range +0.1 to +0.4 W m−2. Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo. Astronomical albedo is darker than Saturn even though they receive | Wikipedia:Albedo |
m−2. Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo. Astronomical albedo is darker than Saturn even though they receive the same amount of sunlight. This is due to a difference in albedo (0.22 versus 0.499 in geometric albedo).In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved. Optical or visual albedo The albedos of planets, Natural satellite Enceladus, a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is Eris (dwarf planet) The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non-Lambertian reflectance A ( 132910^ -H/5 D ) ^2, where A is the astronomical albedo, D is the diameter in kilometers, and H is the absolute magnitude. Radar albedo In planetary radar astronomy, a microwave (or radar) pulse is transmitted toward a planetary target (e.g. Moon, asteroid, etc.) and the echo from the target is measured. In most instances, the transmitted pulse is circular polarization The values reported for the Moon, Mercury, Mars, Venus, and Comet P/2005 JQ5 are derived from the total (OC+SC) radar albedo reported in those references. Relationship to surface bulk density In the event that most of the echo is from first surface reflections (_OC or so), the OC radar albedo is a first-order approximation of the Fresnel reflection coefficient (aka reflectivity) : cases 3.20 g cm^-3 ( 1 + 0.83 _ OC 1 - 0.83 _ OC ) & for _OC 0.07 \\ (6.944 _OC + 1.083) g cm^-3 & for _OC > 0.07 cases. History The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria. See also * Bio-geoengineering | Wikipedia:Albedo |
& for _OC 0.07 \\ (6.944 _OC + 1.083) g cm^-3 & for _OC > 0.07 cases. History The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria. See also * Bio-geoengineering * Cool roof * Daisyworld * Emissivity * Exitance * Global dimming * Ice–albedo feedback * Irradiance * Kirchhoff's law of thermal radiation * Opposition surge * Polar see-saw * Radar astronomy * Solar radiation management References External links * Albedo Project * Albedo – Encyclopedia of Earth * NASA MODIS BRDF/albedo product site * Ocean surface albedo look-up-table * Surface albedo derived from Meteosat observations * A discussion of Lunar albedos * reflectivity of metals (chart) Category:Land surface effects on climate Category:Climate change feedbacks Category:Climate forcing Category:Climatology Category:Electromagnetic radiation Category:Meteorological quantities Category:Radiometry Category:Scattering, absorption and radiative transfer (optics) Category:Radiation Category:1760s neologisms | Wikipedia:Albedo |
International Atomic Time (abbreviated TAI, from its French name '''') is a high-precision Atomic clock TAI may be reported using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth. Specifically, both Julian days and the Gregorian calendar are used. TAI in this form was synchronised with Universal Time at the beginning of 1958, and the two have drifted apart ever since, due primarily to the slowing rotation of the Earth. Operation TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories worldwide. The majority of the clocks involved are caesium clocks; the International System of Units (SI) definition of the second is based on caesium. The clocks are compared using GPS signals and two-way satellite time and frequency transfer. Due to the signal averaging TAI is an order of magnitude more stable than its best constituent clock. The participating institutions each broadcast, in real-time data The clocks at different institutions are regularly compared against each other. The International Bureau of Weights and Measures (BIPM, France), combines these measurements to retrospectively calculate the weighted average that forms the most stable time scale possible. and is the canonical form Errors in publication may be corrected by issuing a revision of the faulty Circular T or by errata in a subsequent Circular T. Aside from this, once published in Circular T, the TAI scale is not revised. In hindsight, it is possible to discover errors in TAI and to make better estimates of the true proper time scale. Since the published circulars are definitive, better estimates do not create another version of TAI; it is instead considered to be creating a better realisation of Terrestrial Time (TT). History Early atomic time scales consisted of quartz clocks with frequencies calibrated by a single atomic clock; the atomic clocks were not operated continuously. Atomic timekeeping | Wikipedia:International Atomic Time |
instead considered to be creating a better realisation of Terrestrial Time (TT). History Early atomic time scales consisted of quartz clocks with frequencies calibrated by a single atomic clock; the atomic clocks were not operated continuously. Atomic timekeeping services started experimentally in 1955, using the first caesium atomic clock at the National Physical Laboratory (United Kingdom) The International Time Bureau (BIH) began a time scale, Tm or AM, in July 1955, using both local caesium clocks and comparisons to distant clocks using the phase of VLF radio signals. The BIH scale, A.1, and NBS-A were defined by an epoch at the beginning of 1958 The procedures used by the BIH evolved, and the name for the time scale changed: A3 in 1964 and TA(BIH) in 1969. The SI second was defined in terms of the caesium atom in 1967. From 1971 to 1975 the General Conference on Weights and Measures and the International Committee for Weights and Measures made a series of decisions that designated the BIPM time scale International Atomic Time (TAI). In the 1970s, it became clear that the clocks participating in TAI were ticking at different rates due to gravitational time dilation, and the combined TAI scale, therefore, corresponded to an average of the altitudes of the various clocks. Starting from the Julian Date 2443144.5 (1 January 1977 00:00:00 TAI), corrections were applied to the output of all participating clocks, so that TAI would correspond to proper time at the geoid (mean sea level). Because the clocks were, on average, well above sea level, this meant that TAI slowed by about one part in a trillion. The former uncorrected time scale continues to be published under the name EAL (Échelle Atomique Libre, meaning Free Atomic Scale''). The instant that the gravitational correction started to be applied serves as the epoch for Barycentric Coordinate Time (TCB), Geocentric Coordinate Time (TCG), and Terrestrial Time (TT), which represent three fundamental | Wikipedia:International Atomic Time |
name EAL (Échelle Atomique Libre, meaning Free Atomic Scale''). The instant that the gravitational correction started to be applied serves as the epoch for Barycentric Coordinate Time (TCB), Geocentric Coordinate Time (TCG), and Terrestrial Time (TT), which represent three fundamental time scales in the Solar System. All three of these time scales were defined to read JD 2443144.5003725 (1 January 1977 00:00:32.184) exactly at that instant. TAI was henceforth a realisation of TT, with the equation TT(TAI) TAI + 32.184s. The continued existence of TAI was questioned in a 2007 letter from the BIPM to the ITU-R which stated, "In the case of a redefinition of UTC without leap seconds, the CCTF would consider discussing the possibility of suppressing TAI, as it would remain parallel to the continuous UTC." Relation to UTC Contrary to TAI, UTC is a discontinuous time scale. It is occasionally adjusted by leap seconds. Between these adjustments, it is composed of segments that are mapped to atomic time by a constant offset. From its beginning in 1961 through December 1971, the adjustments were made regularly in fractional leap seconds so that UTC approximated UT2. Afterwards, these adjustments were made only in whole seconds to approximate UT1. This was a compromise arrangement in order to enable a publicly broadcast time scale. The less frequent whole-second adjustments meant that the time scale would be more stable and easier to synchronize internationally. The fact that it continues to approximate UT1 means that tasks such as navigation which require a source of Universal Time continue to be well served by the public broadcast of UTC. See also * Clock synchronization * Time and frequency transfer Notes References * * Footnotes Bibliography * * External links * BIPM technical services: Time Metrology * Time and Frequency Section - National Physical Laboratory, UK * IERS website * NIST Web | Wikipedia:International Atomic Time |
References * * Footnotes Bibliography * * External links * BIPM technical services: Time Metrology * Time and Frequency Section - National Physical Laboratory, UK * IERS website * NIST Web Clock FAQs * History of time scales * NIST-F1 Cesium Fountain Atomic Clock * * Japan Standard Time Project, NICT, Japan * * Standard of time definition: UTC, GPS, LORAN and TAI Category:Time scales | Wikipedia:International Atomic Time |
Alain Connes (; born 1 April 1947) is a French mathematician, known for his contributions to the study of operator algebras and noncommutative geometry. He was a professor at the , , Ohio State University and Vanderbilt University. He was awarded the Fields Medal in 1982. Career Alain Connes attended high school at in Marseille, and was then a student of the Classe préparatoire aux grandes écoles In 1976 he returned to France and worked as professor at Pierre and Marie Curie University until 1980 and at French National Centre for Scientific Research In parallel, he was awarded a distinguished professorship at Vanderbilt University between 2003 and 2012, and at Ohio State University between 2012 and 2021. Research Connes' main research interests revolved around operator algebras. Besides noncommutative geometry, he has applied his works in various areas of mathematics and number theory, differential geometry. In his early work on von Neumann algebras in the 1970s, he succeeded in obtaining the almost complete classification of injective Von Neumann algebra#Factors Following this, he made contributions in K-theory He was a member of Nicolas Bourbaki. Over many years, he collaborated extensively with Henri Moscovici. the Ampère Prize in 1980, the Fields Medal in 1982, the Clay Research Award in 2000 and the Crafoord Prize in 2001. The CNRS He was an invited speaker at the International Congress of Mathematicians . He was awarded honorary degrees from Queen's University at Kingston in 1979, University of Rome Tor Vergata in 1997, University of Oslo in 1999, University of Southern Denmark in 2009, Université libre de Bruxelles in 2010 and Fudan University Since 1982 he is a member of the French Academy of Sciences. He was elected member of several foreign academies and societies, including the Royal Danish Academy of Sciences and Letters in 1980, the Norwegian Academy of Science and Letters in 1983, the American Academy of Arts and Sciences in 1989, the London | Wikipedia:Alain Connes |
was elected member of several foreign academies and societies, including the Royal Danish Academy of Sciences and Letters in 1980, the Norwegian Academy of Science and Letters in 1983, the American Academy of Arts and Sciences in 1989, the London Mathematical Society in 1994, the Canadian Academy of Sciences in 1995 (incorporated since 2002 in the Royal Society of Canada), the National Academy of Sciences In 2001 he received (together with his co-authors André Lichnerowicz and Marco Schutzenberger) the Peano Prize for his work Triangle of Thoughts. Family Alain Connes is the middle-born of three sons – born to parents both of whom lived to be 101 years old. He married in 1971. See also * Bost–Connes system * Cyclic category * Cyclic homology * Factor (functional analysis) * Higgs boson * C*-algebra * Noncommutative quantum field theory * M-theory * Groupoid * Spectral triple *Criticism of non-standard analysis * Riemann hypothesis References External links * Alain Connes Official Web Site containing downloadable papers, and his book Non-commutative geometry, . * * Alain Connes' Standard Model * An interview with Alain Connes and a discussion about it * * Category:1947 births Category:Living people Category:People from Draguignan Category:20th-century French mathematicians Category:21st-century French mathematicians Category:French mathematical analysts Category:Differential geometers Category:Fields Medalists Category:Clay Research Award recipients Category:École Normale Supérieure alumni Category:Academic staff of the Collège de France Category:Institute for Advanced Study visiting scholars Category:Foreign associates of the National Academy of Sciences Category:Vanderbilt University faculty Category:Foreign members of the Russian Academy of Sciences Category:Members of the French Academy of Sciences Category:Members of the Norwegian Academy of Science and Letters Category:Members of the Royal Danish Academy of Sciences and Letters Category:London Mathematical Society | Wikipedia:Alain Connes |
million The Afroasiatic languages (also known as Afro-Asiatic, Afrasian, Hamito-Semitic, or Semito-Hamitic) are a language family (or "phylum") of about 400 languages spoken predominantly in West Asia, North Africa, the Horn of Africa, and parts of the Sahara and Sahel. Over 500 million people are native speakers of an Afroasiatic language, constituting the fourth-largest language family after Indo-European languages Arabic is by far the most widely spoken within the family, with around 300 million native speakers concentrated primarily in the Middle East and North Africa. Other major Afroasiatic languages include the Cushitic Oromo language with 45 million native speakers, the Chadic Hausa language with over 34 million, the Semitic Amharic language with 25 million, and the Cushitic Somali language with 15 million. Other Afroasiatic languages with millions of native speakers include the Semitic Tigrinya language and Modern Hebrew, the Cushitic Sidama language, and the Omotic Wolaitta language, though most languages within the family are much smaller in size. There are many well-attested Afroasiatic languages from antiquity that have since Extinct language Comparative study of Afroasiatic is hindered by the massive disparities in textual attestation between its branches: while the Semitic and Egyptian branches are attested in writing as early as the fourth millennium BC, Berber, Cushitic, and Omotic languages were often not recorded until the 19th or 20th centuries. While systematic comparative method Name In current scholarship, the most common names for the family are Afroasiatic (or Afro-Asiatic), Hamito-Semitic, and Semito-Hamitic. Other proposed names that have yet to find widespread acceptance include Erythraic/Erythraean, Lisramic, Noahitic, and Lamekhite. Friedrich Müller (linguist) The term Hamito-Semitic has largely fallen out of favor among linguists writing in English, but is still | Wikipedia:Afroasiatic languages |
frequently used in the scholarship of various other languages, such as German. Several issues with the label Hamito-Semitic have led many scholars to abandon the term and criticize its continued use. One common objection is that the Hamitic component inaccurately suggests that a monophyletic | Wikipedia:Afroasiatic languages |
scholarship of various other languages, such as German. Several issues with the label Hamito-Semitic have led many scholars to abandon the term and criticize its continued use. One common objection is that the Hamitic component inaccurately suggests that a monophyletic "Hamitic" branch exists alongside Semitic. In addition, Joseph Greenberg has argued that Hamitic possesses Hamites While Greenberg ultimately popularized the name "Afroasiatic" in 1960, it appears to have been coined originally by Maurice Delafosse, as French , in 1914. The name refers to the fact that it is the only major language family with large populations in both Africa and Asia. Due to concerns that "Afroasiatic" could imply the inclusion of all languages spoken across Africa and Asia, the name "Afrasian" () was proposed by Igor Diakonoff in 1980. At present it predominantly sees use among Russian scholars. The names Lisramic based on the Afroasiastic root *lis- ("tongue") and the Egyptian word rmṯ ("person") and Erythraean referring to the core area around which the languages are spoken, the Red Sea have also been proposed. Distribution and branches Scholars generally consider Afroasiatic to have between five and eight branches. The five that are universally agreed upon are Berber languages M. Victoria Almansa-Villatoro and Silvia Štubňová Nigrelli write that there are about 400 languages in Afroasiatic; Ethnologue lists 375 languages. Many scholars estimate fewer languages; exact numbers vary depending on the definitions of "language" and "dialect". Berber The Berber (or Libyco-Berber) languages are spoken today by perhaps 16 million people. They are often considered to constitute a single language with multiple dialects. Other scholars, however, argue that they are a group of around twelve languages, about as different from each other as the Romance or Germanic languages. In the past, Berber languages were spoken throughout North Africa except in Egypt; since the 7th century CE, however, they have been heavily affected by Arabic and have been replaced by it in many places. There are two extinct languages potentially | Wikipedia:Afroasiatic languages |
the past, Berber languages were spoken throughout North Africa except in Egypt; since the 7th century CE, however, they have been heavily affected by Arabic and have been replaced by it in many places. There are two extinct languages potentially related to modern Berber. The first is the Numidian language, represented by over a thousand short inscriptions in the Libyco-Berber alphabet, found throughout North Africa and dating from the 2nd century BCE onward. The second is the Guanche language, which was formerly spoken on the Canary Islands and went extinct in the 17th century CE. The first longer written examples of modern Berber varieties only date from the 16th or 17th centuries CE. Chadic Chadic languages number between 150 and 190, making Chadic the largest family in Afroasiatic by number of extant languages. The Chadic languages are typically divided into three major branches, East Chadic, Central Chadic, and West Chadic. Most Chadic languages are located in the Chad Basin, with the exception of Hausa language Cushitic There are about 30 Cushitic languages, more if Omotic is included, spoken around the Horn of Africa and in Sudan and Tanzania. The Cushitic family is traditionally split into four branches: the single language of Beja (c. 3 million speakers), the Agaw languages, Eastern Cushitic, and Southern Cushitic. Only one Cushitic language, Oromo language Egyptian (c. 2690 BCE), containing the first complete sentence in Ancient Egyptian. The Egyptian branch consists of a single language, Egyptian language Omotic The c. 30 Omotic languages are still mostly undescribed by linguists. They are all spoken in southwest Ethiopia except for the Ganza language, spoken in Sudan. Omotic is typically split into North Omotic (or Damotic) and South Omotic (or Aroid), with the latter more influenced by the Nilotic languages; it is unclear whether the Dizoid group of Omotic languages belongs to the Northern or Southern group. The two Omotic languages with the most speakers are Wolaitta language A majority | Wikipedia:Afroasiatic languages |
Aroid), with the latter more influenced by the Nilotic languages; it is unclear whether the Dizoid group of Omotic languages belongs to the Northern or Southern group. The two Omotic languages with the most speakers are Wolaitta language A majority of specialists consider Omotic to constitute a sixth branch of Afroasiatic. Omotic was formerly considered part of the Cushitic branch; some scholars continue to consider it part of Cushitic. Other scholars have questioned whether it is Afroasiatic at all, due its lack of several typical aspects of Afroasiatic morphology. Semitic There are between 40 and 80 languages in the Semitic family. Today, Semitic languages are spoken across North Africa, West Asia, and the Horn of Africa, as well as on the island of Malta, making them the sole Afroasiatic branch with members originating outside Africa. Arabic, spoken in both Asia and Africa, is by far the most widely spoken Afroasiatic language today, with around 300 million native speakers, while the Ethiopian Amharic language has around 25 million; collectively, Semitic is the largest branch of Afroasiatic by number of current speakers. Most authorities divide Semitic into two branches: East Semitic, which includes the extinct Akkadian language, and West Semitic, which includes Arabic, Aramaic, the Canaanite languages (including Hebrew), as well as the Ethiopian Semitic languages such as Geʽez and Amharic. The classification within West Semitic remains contested. The only group with an African origin is Ethiopian Semitic. The oldest written attestations of Semitic languages come from Mesopotamia, Northern Syria, and Egypt and date as early as c. 3000 BCE. Other proposed branches There are also other proposed branches, but none has so far convinced a majority of scholars: * Linguist H. Fleming proposed that the near-extinct Ongota language is a separate branch of Afroasiatic; however, this is only one of several competing theories. About half of current scholarly hypotheses on Ongota'sorigins align it with Afroasiatic in some way. * Robert Hetzron proposed that | Wikipedia:Afroasiatic languages |
that the near-extinct Ongota language is a separate branch of Afroasiatic; however, this is only one of several competing theories. About half of current scholarly hypotheses on Ongota'sorigins align it with Afroasiatic in some way. * Robert Hetzron proposed that Beja language * The extinct Meroitic language has been proposed to represent a branch of Afroasiatic. Although an Afroasiatic connection is sometimes viewed as refuted, it continues to be defended by scholars such as Edward Lipiński. * The Kujarge language is usually considered part of the Chadic languages; however, Roger Blench has proposed that it may be a separate branch of Afroasiatic. Further subdivisions There is no agreement on the relationships between and subgrouping of the different Afroasiatic branches. Whereas Marcel Cohen (1947) claimed he saw no evidence for internal subgroupings, numerous other scholars have made proposals, with Carsten Peust counting 27 as of 2012. Common trends in proposals as of 2019 include using common or lacking grammatical features to argue that Omotic was the first language to branch off, often followed by Chadic. In contrast to scholars who argue for an early split of Chadic from Afroasiatic, scholars of the Russian school tend to argue that Chadic and Egyptian are closely related, and scholars who rely on percentage of shared lexicon often group Chadic with Berber. Three scholars who agree on an early split between Omotic and the other subbranches, but little else, are Harold Fleming (1983), Christopher Ehret (1995), and Lionel Bender (1997). In contrast, scholars relying on shared lexicon often produce a Cushitic-Omotic group. Additionally, the minority of scholars who favor an Asian origin of Afroasiatic tend to place Semitic as the first branch to split off. Disagreement on which features are innovative and which are inherited from Proto-Afroasiatic produces radically different trees, as can be seen by comparing the trees produced by Ehret and Igor Diakonoff. Responding to the above, Tom Güldemann criticizes attempts at finding subgroupings based | Wikipedia:Afroasiatic languages |
which features are innovative and which are inherited from Proto-Afroasiatic produces radically different trees, as can be seen by comparing the trees produced by Ehret and Igor Diakonoff. Responding to the above, Tom Güldemann criticizes attempts at finding subgroupings based on common or lacking morphology by arguing that the presence or absence of morphological features is not a useful way of discerning subgroupings in Afroasiatic, because it can not be excluded that families currently lacking certain features did not have them in the past; this also means that the presence of morphological features cannot be taken as defining a subgroup. Peust notes that other factors that can obscure genetic relationships between languages include the poor state of present documentation and understanding of particular language families (historically with Egyptian, presently with Omotic). Gene Gragg likewise argues that more needs to be known about Omotic still, and that Afroasiatic linguists have still not found convincing isoglosses on which to base genetic distinctions. One way of avoiding the problem of determining which features are original and which are inherited is to use a computational methodology such as lexicostatistics, with one of the earliest attempts being Fleming 1983. This is also the method used by Alexander Militarev and Sergei Starostin to create a family tree. Fleming (2006) was a more recent attempt by Fleming, with a different result from Militarev and Starostin. Hezekiah Bacovcin and David Wilson argue that this methodology is invalid for discerning linguistic sub-relationship. They note the method'sinability to detect various strong commonalities even between well-studied branches of AA. Official Status Classification history A relationship between Hebrew, Arabic, and Aramaic and the Berber languages was perceived as early as the 9th century CE by the Hebrew grammarian and physician Judah ibn Kuraish An important development in the history of Afroasiatic scholarship – and the history of African linguistics – was the creation of the "Hamites The first scholar to question the | Wikipedia:Afroasiatic languages |
century CE by the Hebrew grammarian and physician Judah ibn Kuraish An important development in the history of Afroasiatic scholarship – and the history of African linguistics – was the creation of the "Hamites The first scholar to question the existence of "Hamitic languages" was Marcel Cohen in 1924, with skepticism also expressed by A. Klingenheben and Dietrich Westermann during the 1920s and '30s. However, Meinhof's "Hamitic" classification remained prevalent throughout the early 20th century until it was definitively disproven by Joseph Greenberg in the 1940s, based on racial and anthropological data. Instead, Greenberg proposed an Afroasiatic family consisting of five branches: Berber, Chadic, Cushitic, Egyptian, and Semitic. Reluctance among some scholars to recognize Chadic as a branch of Afroasiatic persisted as late as the 1980s. In 1969, Harold C. Fleming Greenberg relied on his own method of mass comparison of vocabulary items rather than the comparative method of demonstrating regular sound correspondences to establish the family. An alternative classification, based on the pronominal and conjugation systems, was proposed by A.N. Tucker in 1967. As of 2023, widely accepted sound correspondences between the different branches have not yet been firmly established. Nevertheless, morphological traits attributable to the proto-language and the establishment of cognates throughout the family have confirmed its Genetic relationship (linguistics) Origin Timeline There is no consensus as to when Proto-Afroasiatic was spoken. The absolute latest date for when Proto-Afroasiatic could have been extant is , after which Egyptian and the Semitic languages are firmly attested. However, in all likelihood these languages began to diverge well before this hard boundary. The estimations offered by scholars as to when Proto-Afroasiatic was spoken vary widely, ranging from 18,000BCE to 8,000BCE. An estimate at the youngest end of this range still makes Afroasiatic the oldest proven language family. Contrasting proposals of an early emergence, Tom Güldemann has argued that less time may have been required for the divergence than is usually assumed, as it | Wikipedia:Afroasiatic languages |
the youngest end of this range still makes Afroasiatic the oldest proven language family. Contrasting proposals of an early emergence, Tom Güldemann has argued that less time may have been required for the divergence than is usually assumed, as it is possible for a language to rapidly restructure due to language contact Location Likewise, no consensus exists as to where proto-Afroasiatic originated. Scholars have proposed locations for the Afroasiatic homeland across Africa and West Asia. Roger Blench writes that the debate possesses "a strong ideological flavor", with associations between an Asian origin and "high civilization". An additional complicating factor is the lack of agreement on the subgroupings of Afroasiatic (see #Further subdivisions An origin somewhere on the African continent has broad scholarly support, and is seen as being well-supported by the linguistic data. Most scholars more narrowly place the homeland near the geographic center of its present distribution, "in the southeastern Sahara or adjacent Horn of Africa". The Afroasiatic languages spoken in Africa are not more closely related to each other than they are to Semitic, as one would expect if only Semitic had remained in a West Asian homeland while all other branches had spread from there. Likewise, all Semitic languages are fairly similar to each other, whereas the African branches of Afroasiatic are very diverse; this suggests the rapid spread of Semitic out of Africa. Proponents of an origin of Afroasiatic within Africa assume the proto-language to have been spoken by pre-Neolithic hunter-gatherers, arguing that there is no evidence of words in Proto-Afroasiatic related to agriculture or animal husbandry. Christopher Ehret, S.O. Y. Keita, and Paul Newman (linguist) A significant minority of scholars supports an Asian origin of Afroasiatic, most of whom are specialists in Semitic or Egyptian studies. The main proponent of an Asian origin is the linguist Alexander Militarev, who argues that Proto-Afroasiatic was spoken by early agriculturalists in the Levant and subsequently spread to Africa. Militarev associates | Wikipedia:Afroasiatic languages |
ly that this is inherited from proto-Afroasiatic. All Afroasiatic languages | Wikipedia:Afroasiatic languages |
important role in Afroasiatic, especially in Chadic; it can affect the form of affixes attached to a word. Consonant systems Several Afroasiatic languages have large consonant inventories, and it is likely that this is inherited from proto-Afroasiatic. All Afroasiatic languages contain stop consonant Most, if not all branches of Afroasiatic distinguish between voiceless, voiced, and "Emphatic consonant A form of long-distance consonant assimilation (linguistics) Consonant incompatibility Restrictions against the co-occurrence of certain, usually similar, consonants in verbal roots can be found in all Afroasiatic branches, though they are only weakly attested in Chadic and Omotic. The most widespread constraint is against two different labial consonants (other than w) occurring together in a root, a constraint which can be found in all branches but Omotic. Another widespread constraint is against two non-identical lateral consonant A set of constraints, developed originally by Joseph Greenberg on the basis of Arabic, has been claimed to be typical for Afroasiatic languages. Greenberg divided Semitic consonants into four types: "back consonants" (glottal consonant # velar consonants can occur with pharyngeals or laryngeals; # dental consonants can co-occur with sibilants; However, there are no Proto-Semitic verbal roots with ḍ and a sibilant, and roots with d and a sibilant are uncommon. In all attested cases of a dental and a sibilant, the sibilant occurs in first position and the dental in second. Similar exceptions can be demonstrated for the other Afroasiatic branches that have these restrictions to their root formation. James Peter Allen Vowel systems There is a large variety of vocalic systems in Afroasiatic, and attempts to reconstruct the vocalic system of Proto-Afroasiatic vary considerably. All branches of Afroasiatic have a limited number of underlying vowels (between two and seven), but the number of phonetic vowels can be much larger. The quality of the underlying vowels varies considerably by language; the most common vowel throughout Afroasiatic is schwa. In the different languages, central vowels are often inserted to | Wikipedia:Afroasiatic languages |
and seven), but the number of phonetic vowels can be much larger. The quality of the underlying vowels varies considerably by language; the most common vowel throughout Afroasiatic is schwa. In the different languages, central vowels are often inserted to break up consonant clusters (a form of epenthesis). Various Semitic, Cushitic, Berber, and Chadic languages, including Arabic, Amharic, Berber, Somali, and East Dangla, also exhibit various types of vowel harmony. Tones The majority of Afroasiatic languages are tonal languages: phonemic tonality is found in Omotic, Chadic, and Cushitic languages, but absent in Berber and Semitic. There is no information on whether Egyptian had tones. In contemporary Omotic, Chadic, and Cushitic languages, tone is primarily a grammatical feature: it encodes various grammatical functions, only differentiating lexical roots in a few cases. In some Chadic and some Omotic languages every syllable has to have a tone, whereas in most Cushitic languages this is not the case. Some scholars postulate that Proto-Afroasiatic may have had tone, while others believe it arose later from a pitch accent. Similarities in grammar, syntax, and morphology At present, there is no generally accepted reconstruction of Proto-Afroasiatic grammar, syntax, or morphology, nor one for any of the sub-branches besides Egyptian. This means that it is difficult to know which features in Afroasiatic languages are retentions, and which are innovations. Moreover, all Afroasiatic languages have long been in contact with other language families and with each other, leading to the possibility of widespread borrowing both within Afroasiatic and from unrelated languages. There are nevertheless a number of commonly observed features in Afroasiatic morphology and derivation, including the use of suffixes, infixes, vowel lengthening and Vowel reduction General features Consonantal root structures A widely attested feature in AA languages is a consonantal structure into which various vocalic "templates" are placed. This structure is particularly visible in the verbs, and is particularly noticeable in Semitic. Besides for Semitic, vocalic templates are well attested | Wikipedia:Afroasiatic languages |
A widely attested feature in AA languages is a consonantal structure into which various vocalic "templates" are placed. This structure is particularly visible in the verbs, and is particularly noticeable in Semitic. Besides for Semitic, vocalic templates are well attested for Cushitic and Berber, where, along with Chadic, it is less productive; it is absent in Omotic. For Egyptian, evidence for the root-and-template structure exists from Coptic. In Semitic, Egyptian, Berber, verbs have no inherent vowels at all; the vowels found in a given stem are dependent on the vocalic template. In Chadic, verb stems can include an inherent vowel as well. Most Semitic verbs are Semitic root As part of these templates, the alternation (apophony) between high vowels (e.g. i, u) and a low vowel (a) in verbal forms is usually described as one of the main characteristics of AA languages: this change codes a variety of different functions. It is unclear whether this system is a common AA trait; the Chadic examples, for instance, show signs of originally deriving from affixes, which could explain the origins of the alterations in other languages as well. Word order It remains unclear what word order Proto-Afroasiatic had. Berber, Egyptian, and most Semitic languages are Verb–subject–object word order Reduplication and gemination Afroasiatic Languages use the processes of reduplication and gemination (which often overlap in meaning) to derive nouns, verbs, adjectives, and adverbs throughout the AA language family. Gemination in particular is one of the typical features of AA. Full or partial reduplication of the verb is often used to derive forms showing repeated action (pluractionality), though it is unclear if this is an inherited feature or has been widely borrowed. Nouns Grammatical gender and number The assignment of nouns and pronouns to either masculine or feminine gender is present in all branches – but not all languages – of the Afroasiatic family. This sex-based gender system is widely agreed to derive from Proto-Afroasiatic. In | Wikipedia:Afroasiatic languages |
e, a "construct state", and a "pronominal state". The construct state is used when a noun becomes unstressed as the first element of a compound, whereas the pronominal state | Wikipedia:Afroasiatic languages |
and Egyptian grammar also refers to nouns having a "free" (absolute) state, a "construct state", and a "pronominal state". The construct state is used when a noun becomes unstressed as the first element of a compound, whereas the pronominal state is used when the noun has a suffixed possessive pronoun. Berber instead contrasts between the "free state" and the "annexed state", the latter of which is used for a variety of purposes, including for subjects placed after a verb and after certain prepositions. Modifiers and agreement There is no strict distinction between adjectives, nouns, and adverbs in Afroasiatic. All branches of Afroasiatic have a lexical category of adjectives except for Chadic; some Chadic languages do have adjectives, however. In Berber languages, adjectives are rare and are mostly replaced by nouns of quality and stative verbs. In different languages, adjectives (and other modifiers) must either precede or follow the noun. In most AA languages, numerals precede the noun. In those languages that have adjectives, they can take gender and number markings, which, in some cases, agree with the gender and number of the noun they are modifying. However, in Omotic, adjectives do not agree with nouns: sometimes, they only take gender and number marking when they are used as nouns, in other cases, they take gender and number marking only when they follow the noun (the noun then receives no marking). A widespread pattern of gender and number marking in Afroasiatic, found on demonstratives, articles, adjectives, and relative markers, is a consonant N for masculine, T for feminine, and N for plural. This can be found in Semitic, Egyptian, Beja, Berber, and Chadic. A system K (masculine), T (feminine), and H (plural) can be found in Cushitic, | Wikipedia:Afroasiatic languages |
Chadic, with masculine K also appearing in Omotic. The feminine marker T is one of the most consistent aspects across the different branches of AA. Verb forms Tenses, aspects, and moods (TAMs) There is no agreement | Wikipedia:Afroasiatic languages |
be found in Cushitic, Chadic, with masculine K also appearing in Omotic. The feminine marker T is one of the most consistent aspects across the different branches of AA. Verb forms Tenses, aspects, and moods (TAMs) There is no agreement about which tense-aspect-mood "Prefix conjugation" Conjugation of verbs using prefixes that mark person, number, and gender can be found in Semitic, Berber, and in Cushitic, where it is only found on a small set of frequent verbs. These prefixes are clearly cognate across the branches, although their use within the verbal systems of the individual languages varies. There is a general pattern in which n- is used for the first person plural, whereas t- is used for all forms of the second person regardless of plurality or gender, as well as feminine singular. Prefixes of ʔ- (glottal stop) for the first person singular and y- for the third person masculine can also be reconstructed. As there is no evidence for the "prefix conjugation" in Omotic, Chadic, or Egyptian, it is unclear whether this was a Proto-Afroasiatic feature that has been lost in those branches or is a shared innovation among Semitic, Berber, and Cushitic. "Suffix conjugation" Some AA branches have what is called a "suffix conjugation", formed by adding pronominal suffixes to indicate person, gender, and number to a verbal adjective. In Akkadian, Egyptian, Berber, and Cushitic this forms a "stative conjugation", used to express the state or result of an action; the same endings as in Akkadian and Egyptian are also present in the West Semitic perfective verb form. In Akkadian and Egyptian, the suffixes appear to be reduced forms of the independent pronouns (see #Pronouns Common derivational affixes M-prefix noun derivation A prefix in m- is the most widely attested affix in AA that is used to derive nouns, and is one of the features Joseph Greenberg used to diagnose membership in the family. It forms agent nouns, place nouns, | Wikipedia:Afroasiatic languages |
derivationA prefix in m- is the most widely attested affix in AA that is used to derive nouns, and is one of the features Joseph Greenberg used to diagnose membership in the family. It forms agent nouns, place nouns, and instrument nouns. In some branches, it can also derive abstract nouns and participles. Omotic, meanwhile, shows evidence for a non-productive prefix mV- associated with the feminine gender. Christopher Ehret has argued that this prefix is a later development that was not present in Proto-Afro-Asiatic, but rather derived from a PAA indefinite pronoun *m-. Such an etymology is rejected by A. Zaborski and Gábor Takács, the latter of whom argues for a PAA *ma- that unites all or some of the meanings in the modern languages.Verbal extensionsMany AA languages use prefixes or suffixes (verbal extensions) to encode various pieces of information about the verb. Three Derivation (linguistics)"Nisba" derivationThe so-called "Arabic nouns and adjectives#Nisba Due to its presence in the oldest attested and best-known AA branches, nisba derivation is often thought of as a "quintessentially Afroasiatic feature". Christopher Ehret argues for its presence in Proto-Afroasiatic and for its attestation in some form in all branches, with a shape -*ay in addition to -*iy in some cases.Vocabulary comparisonPronouns The forms of the pronouns are very stable throughout Afroasiatic (excluding Omotic), and they have been used as one of the chief tools for determining whether a language belongs to the family. However, there is no consensus on what the reconstructed set of Afroasiatic pronouns might have looked like. A common characteristic of AA languages is the existence of a special set of "independent" pronouns, which are distinct from subject pronouns. They can occur together with subject pronouns but cannot fulfill an object function. Also common are dependent/affix pronouns (used for direct objects and to mark possession). For most branches, the first person pronouns contain a nasal consonant (n, m), | Wikipedia:Afroasiatic languages |
pronouns. They can occur together with subject pronouns but cannot fulfill an object function. Also common are dependent/affix pronouns (used for direct objects and to mark possession). For most branches, the first person pronouns contain a nasal consonant (n, m), whereas the third person displays a sibilant consonant (s, sh). Other commonalities are masculine and feminine forms used in both the second and third persons, except in Cushitic and Omotic. These pronouns tend to show a masculine "u" and a feminine "i". The Omotic forms of the personal pronouns differ from the others, with only the plural forms in North Omotic appearing potentially to be cognate. Numerals Unlike in the Indo-European or Austronesian languages Another factor making comparisons of AA numeral systems difficult is the possibility of loanword Cognates Afroasiatic languages share a vocabulary of Proto-Afroasiatic origin to varying extents. Writing in 2004, John Huehnergard notes the great difficulty in establishing cognate sets across the family. Identifying cognates is difficult because the languages in question are often separated by thousands of years of development and many languages within the family have long been in contact with each other, raising the possibility of loanwords. Work is also hampered because of the poor state of documentation of many languages. There are two etymological dictionaries of Afroasiatic, one by Christopher Ehret, and one by Vladimir Orel and Olga Stolbova, both from 1995. Both works provide highly divergent reconstructions and have been heavily criticized by other scholars. Andrzej Zaborski refers to Orel and Stolbova'sreconstructions as "controversial", and Ehret's as "not acceptable to many scholars". Tom Güldemann argues that much comparative work in Afroasiatic suffers from not attempting first to reconstruct smaller units within the | Wikipedia:Afroasiatic languages |
individual branches, but instead comparing words in the individual languages. Nevertheless, both dictionaries agree on some items and some proposed cognates are uncontroversial. Such cognates tend to rely on relatively simple sound correspondences. (possibly) Hausa bùgaː 'to hit, strike Hausa halshe(háɽ.ʃè) 'tongue'; | Wikipedia:Afroasiatic languages |
Chicago: The Oriental Institute, 2007, p.139–145. * A comparison of Orel-Stolbova's and Ehret's Afro-Asiatic reconstructions * "Is Omotic Afro-Asiatic?" by Rolf Theil (2006) * Afro-Asiatic webpage of Roger Blench (with family tree). Category:Afroasiatic languages Category:Afroasiatic peoples Category:Language | Wikipedia:Afroasiatic languages |
Oriental Civilization 60. Chicago: The Oriental Institute, 2007, p.139–145. * A comparison of Orel-Stolbova's and Ehret's Afro-Asiatic reconstructions * "Is Omotic Afro-Asiatic?" by Rolf Theil (2006) * Afro-Asiatic webpage of Roger Blench (with family tree). Category:Afroasiatic languages Category:Afroasiatic peoples Category:Language families Category:Ethnic groups in Africa Category:Ethnic groups in Asia Category:Ethnic groups in Europe | Wikipedia:Afroasiatic languages |
In mathematics and statistics, the arithmetic mean ( ), arithmetic average, or just the mean or average (when the context is clear) is the sum of a collection of numbers divided by the count of numbers in the collection. The collection is often a set of results from an experiment, an observational study, or a Survey (statistics) In addition to mathematics and statistics, the arithmetic mean is frequently used in economics, anthropology, history, and almost every academic field to some extent. For example, per capita income is the arithmetic average income of a nation'spopulation. While the arithmetic mean is often used to report central tendency Definition The arithmetic mean of a set of observed data is equal to the sum of the numerical values of each observation, divided by the total number of observations. Symbolically, for a data set consisting of the values x_1,,x_n, the arithmetic mean is defined by the formula: :x 1n (_i 1^nx_i) x_1+x_2++x_nn (For an explanation of the summation operator, see summation.) In simpler terms, the formula for the arithmetic mean is: For example, if the monthly salaries of 10 employees are \2500,2700,2400,2300,2550,2650,2750,2450,2600,2400\, then the arithmetic mean is: :2500+2700+2400+2300+2550+2650+2750+2450+2600+240010 2530 If the data set is a statistical population (i.e., consists of every possible observation and not just a subset of them), then the mean of that population is called the population mean and denoted by the Greek alphabet The arithmetic mean can be similarly defined for Vector (mathematics and physics) History The statistician Churchill Eisenhart, senior researcher fellow at the National Institute of Standards and Technology In 1635 the mathematician Henry Gellibrand described | Wikipedia:Arithmetic mean |
as “meane” the midpoint of a lowest and highest number, not quite the arithmetic mean. In 1668, a person known as “DB” was quoted in the Transactions of the Royal Society describing “taking the mean” of five values: Motivating properties The arithmetic mean has several properties that make it interesting, especially as a measure of central tendency. | Wikipedia:Arithmetic mean |
a person known as “DB” was quoted in the Transactions of the Royal Society describing “taking the mean” of five values: Motivating properties The arithmetic mean has several properties that make it interesting, especially as a measure of central tendency. These include: *If numbers x_1,,x_n have mean x, then (x_1-x)++(x_n-x) 0. Since x_i-x is the distance from a given number to the mean, one way to interpret this property is by saying that the numbers to the left of the mean are balanced by the numbers to the right. The mean is the only number for which the Errors and residuals in statistics *If it is required to use a single number as a "typical" value for a set of known numbers x_1,,x_n, then the arithmetic mean of the numbers does this best since it minimizes the sum of squared deviations from the typical value: the sum of (x_i-x)^2. The sample mean is also the best single predictor because it has the lowest root mean squared error. If the arithmetic mean of a population of numbers is desired, then the estimate of it that is Unbiased estimate *The arithmetic mean is independent of scale of the units of measurement, in the sense that avg(ca_1,,ca_n) cavg(a_1,,a_n). So, for example, calculating a mean of liters and then converting to gallons is the same as converting to gallons first and then calculating the mean. This is also called Homogeneous function Additional properties * The arithmetic mean of a sample is always between the largest and smallest values in that sample. *The arithmetic mean of any amount of equal-sized number groups together is the arithmetic mean of the arithmetic means of each group. Contrast with median The arithmetic mean may be contrasted with the median. The median is defined such that no more than half the values are larger, and no more than half are smaller than it. If elements in the data arithmetic progression There are applications | Wikipedia:Arithmetic mean |
mean may be contrasted with the median. The median is defined such that no more than half the values are larger, and no more than half are smaller than it. If elements in the data arithmetic progression There are applications of this phenomenon in many fields. For example, since the 1980s, the median income in the United States has increased more slowly than the arithmetic average of income. Generalizations Weighted average A weighted average, or weighted mean, is an average in which some data points count more heavily than others in that they are given more weight in the calculation. For example, the arithmetic mean of 3 and 5 is 3+52 4, or equivalently 3 12+5 12 4. In contrast, a weighted mean in which the first number receives, for example, twice as much weight as the second (perhaps because it is assumed to appear twice as often in the general population from which these numbers were sampled) would be calculated as 3 23+5 13 113. Here the weights, which necessarily sum to one, are 23 and 13, the former being twice the latter. The arithmetic mean (sometimes called the "unweighted average" or "equally weighted average") can be interpreted as a special case of a weighted average in which all weights are equal to the same number (12 in the above example and 1n in a situation with nnumbers being averaged). Functions Continuous probability distributions swith equal median, but different skewness, resulting in various means and mode (statistics) If a numerical property, and any sample of data from it, can take on any value from a continuous range instead of, for example, just integers, then the probability of a number falling into some range of possible values can be described by integrating a continuous probability distribution across this range, even when the naive probability for a sample number taking one certain value from infinitely many is zero. In this context, the analog of a weighted | Wikipedia:Arithmetic mean |
possible values can be described by integrating a continuous probability distribution across this range, even when the naive probability for a sample number taking one certain value from infinitely many is zero. In this context, the analog of a weighted average, in which there are infinitely many possibilities for the precise value of the variable in each range, is called the mean of the probability distribution. The most widely encountered probability distribution is called the normal distribution; it has the property that all measures of its central tendency, including not just the mean but also the median mentioned above and the mode (the three Ms), are equal. This equality does not hold for other probability distributions, as illustrated for the log-normal distribution here. Angles Particular care is needed when using cyclic data, such as phases or angles. Taking the arithmetic mean of 1° and 359° yields a result of 180degree (angle) This is incorrect for two reasons: *Firstly, angle measurements are only defined up to an additive constant of 360° (2 or , if measuring in radians). Thus, these could easily be called 1° and -1°, or 361° and 719°, since each one of them produces a different average. *Secondly, in this situation, 0° (or 360°) is geometrically a better average value: there is lower Statistical dispersion In general application, such an oversight will lead to the average value artificially moving towards the middle of the numerical range. A solution to this problem is to use the optimization formulation (that is, define the mean as the central point: the point about which one has the lowest dispersion) and redefine the difference as a modular distance (i.e., the distance on the circle: so the modular distance between 1° and 359° is 2°, not 358°). Symbols and encoding The arithmetic mean is often denoted by a bar (Vinculum (symbol) In some document formats (such as PDF), the symbol may be replaced by a "¢" | Wikipedia:Arithmetic mean |
the modular distance between 1° and 359° is 2°, not 358°). Symbols and encoding The arithmetic mean is often denoted by a bar (Vinculum (symbol) In some document formats (such as PDF), the symbol may be replaced by a "¢" (Euro coins See also * Fréchet mean *Generalized mean *Inequality of arithmetic and geometric means * Sample mean and covariance * Standard deviation * Standard error of the mean * Summary statistics Notes References Further reading * External links *Calculations and comparisons between arithmetic mean and geometric mean of two numbers *Calculate the arithmetic mean of a series of numbers on MeanCalculator.com compare it with median and mode Category:Means | Wikipedia:Arithmetic mean |
Abacı -like abacus representing An abacus ( abaci or abacuses), also called a counting frame, is a hand-operated calculating tool which was used from ancient times in the ancient Near East, Europe, China, and Russia, until the adoption of the Hindu–Arabic numeral system. An abacus consists of a two-dimensional array of Sliding (motion) Each rod typically represents one Numerical digit Any particular abacus design supports multiple methods to perform calculations, including addition, subtraction, multiplication, Division (mathematics) In the ancient world, abacuses were a practical calculating tool. It was widely used in Europe as late as the 17th century, but fell out of use with the rise of Hindu–Arabic numeral system Etymology The word abacus dates to at least 1387AD when a Middle English work borrowed the word from Latin that described a sandboard abacus. The Latin word is derived from ancient Greek () which means something without a base, and colloquially, any piece of rectangular material. Alternatively, without reference to ancient texts on etymology, it has been suggested that it means "a square tablet strewn with dust", or "drawing-board covered with dust (for the use of mathematics)" (the exact shape of the Latin perhaps reflects the Genitive case Both abacuses and abaci History Mesopotamia The Sumerian abacus appeared between 2700 and 2300BC. It held a table of successive columns which delimited the successive orders of magnitude of their sexagesimal (base 60) number system. Some scholars point to a character in Akkadian language Egypt Greek historian Herodotus mentioned the abacus in Ancient Egypt. He wrote that the Egyptians manipulated the pebbles from right to left, opposite in direction to the Greek left-to-right method. Archaeologists have found ancient disks of various sizes that are thought to have been used as counters. However, wall depictions of this instrument are yet to be discovered. Persia At around 600BC, Persians first began to use the abacus, during the Achaemenid Empire. Under the Parthian Empire Greece | Wikipedia:Abacus |
are thought to have been used as counters. However, wall depictions of this instrument are yet to be discovered. Persia At around 600BC, Persians first began to use the abacus, during the Achaemenid Empire. Under the Parthian Empire Greece The earliest archaeological evidence for the use of the Greek abacus dates to the 5th century BC. Demosthenes (384–322 BC) complained that the need to use pebbles for calculations was too difficult. A play by Alexis (poet) One example of archaeological evidence of the Roman abacus, shown nearby in reconstruction, dates to the 1st century AD. It has eight long grooves containing up to five beads in each and eight shorter grooves having either one or no beads in each. The groove marked I indicates units, X tens, and so on up to millions. The beads in the shorter grooves denote fives (five units, five tens, etc.) resembling a bi-quinary coded decimal system related to the Roman numerals. The short grooves on the right may have been used for marking Roman "ounces" (i.e. fractions). Medieval Europe The Roman system of 'counter casting' was used widely in medieval Europe, and persisted in limited use into the nineteenth century. Wealthy abacists used decorative minted counters, called jetons. Due to Pope Sylvester II'sreintroduction of the abacus with modifications, it became widely used in Europe again during the 11th century It used beads on wires, unlike the traditional Roman counting boards, which meant the abacus could be used much faster and was more easily moved. China ) (the number represented in the picture is 6,302,715,408) The earliest known written documentation of the Chinese abacus dates to the 2nd century BC. The Chinese abacus, also known as the suanpan (算盤/算盘, lit. "calculating tray"), comes in various lengths and widths, depending on the operator. It usually has more than seven rods. There are two beads on each rod in the upper deck and five | Wikipedia:Abacus |
abacus, also known as the suanpan (算盤/算盘, lit. "calculating tray"), comes in various lengths and widths, depending on the operator. It usually has more than seven rods. There are two beads on each rod in the upper deck and five beads each in the bottom one, to represent numbers in a bi-quinary coded decimal-like system. The beads are usually rounded and made of hardwood. The beads are counted by moving them up or down towards the beam; beads moved toward the beam are counted, while those moved away from it are not. One of the top beads is 5, while one of the bottom beads is 1. Each rod has a number under it, showing the place value. The suanpan can be reset to the starting position instantly by a quick movement along the horizontal axis to spin all the beads away from the horizontal beam at the center. The prototype of the Chinese abacus appeared during the Han dynasty, and the beads are oval. The Song dynasty and earlier used the 1:4 type or four-beads abacus similar to the modern abacus including the shape of the beads commonly known as Japanese-style abacus. In the early Ming dynasty, the abacus began to appear in a 1:5 ratio. The upper deck had one bead and the bottom had five beads. In the late Ming dynasty, the abacus styles appeared in a 2:5 ratio. Hindu texts used the term śūnya (zero) to indicate the empty column on the abacus. Japan In Japan, the abacus is called soroban'' (, lit. "counting tray"). It was imported from China in the 14th century. It was probably in use by the working class a century or more before the ruling class adopted it, as the class structure obstructed such changes. The 1:4 abacus, which removes the seldom-used second and fifth bead, became popular in the 1940s. Today's Japanese abacus is a 1:4 type, four-bead abacus, introduced from | Wikipedia:Abacus |
in parts separated by a bar or intermediate cord. In the left part were four beads. Beads in the first row have unitary values (1, 2, 3, and 4), and on | Wikipedia:Abacus |
; and on the other hand 0, 1, 2, and 3 were used. Note the use of zero at | Wikipedia:Abacus |
Peninsula that also computed calendar data. This was a finger abacus, on one hand, 0, 1, 2, 3, and 4 were used; and on the other hand 0, 1, 2, and 3 were used. Note the use of zero at the beginning and end of the two cycles. The quipu of the Incas was a system of colored knotted cords used to record numerical data, like advanced tally sticks – but not used to perform calculations. Calculations were carried out using a yupana (Quechua languages Russia The Russian abacus, the schoty (, plural from , counting), usually has a single slanted deck, with ten beads on each wire (except one wire with four beads for quarter-ruble fractions). 4-bead wire was introduced for quarter-Russian ruble The Russian abacus was in use in shops and markets throughout the Commonwealth of Independent States The Russian abacus was brought to France around 1820 by mathematician Jean-Victor Poncelet, who had served in Napoleon'sarmy and had been a prisoner of war in Russia. To Poncelet's French contemporaries, it was something new. Poncelet used it, not for any applied purpose, but as a teaching and demonstration aid. The Turkic peoples School abacus Around the world, abacuses have been used in pre-schools and elementary schools as an aid in teaching the numeral system and arithmetic. In Western countries, a bead frame similar to the Russian abacus but with straight wires and a vertical frame is common (see image). Each bead represents one unit (e.g. 74 can be represented by shifting all beads on 7 wires and 4 beads on the 8th wire, so numbers up to 100 may be represented). In the bead frame shown, the gap between the 5th and 6th wire, corresponding to the color change between the 5th and the 6th bead on each wire, suggests the latter use. Teaching multiplication, e.g. 6 times 7, may be represented by shifting 7 beads on 6 wires. The red-and-white | Wikipedia:Abacus |
and 6th wire, corresponding to the color change between the 5th and the 6th bead on each wire, suggests the latter use. Teaching multiplication, e.g. 6 times 7, may be represented by shifting 7 beads on 6 wires. The red-and-white abacus is used in contemporary primary schools for a wide range of number-related lessons. The twenty bead version, referred to by its Dutch language Neurological analysis Learning how to calculate with the abacus may improve capacity for mental calculation. Mental abacus Visually impaired users An adapted abacus, invented by Tim Cranmer, and called a Cranmer abacus is commonly used by visually impaired users. A piece of soft fabric or rubber is placed behind the beads, keeping them in place while the users manipulate them. The device is then used to perform the mathematical functions of multiplication, division, addition, subtraction, square root, and cube root. Although blind students have benefited from talking calculators, the abacus is often taught to these students in early grades. Blind students can also complete mathematical assignments using a braille-writer and Nemeth Braille See also * Chinese Zhusuan * Chisanbop * Logical abacus * Napier'sbones * Sand table * Slide rule Notes Footnotes References * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Further reading * * * * * * External links * ** ** Tutorials * * Min Multimedia * History * * Curiosities * * Abacus in Various Number Systems at cut-the-knot * Java applet of Chinese, Japanese and Russian abaci * An atomic-scale abacus * Examples of Abaci * Aztex Abacus * Indian Abacus * Abacus Course Category:Abacus Category:Mathematical tools Category:Chinese mathematics Category:Egyptian mathematics Category:Greek mathematics Category:Indian mathematics Category:Japanese mathematics Category:Korean mathematics Category:Ancient Roman | Wikipedia:Abacus |
of Chinese, Japanese and Russian abaci * An atomic-scale abacus * Examples of Abaci * Aztex Abacus * Indian Abacus * Abacus Course Category:Abacus Category:Mathematical tools Category:Chinese mathematics Category:Egyptian mathematics Category:Greek mathematics Category:Indian mathematics Category:Japanese mathematics Category:Korean mathematics Category:Ancient Roman mathematics | Wikipedia:Abacus |
Acidity (novelette) , a typical metal, reacting with hydrochloric acid, a typical acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid–base theory The first category of acids are the proton donors, or Brønsted–Lowry acid–base theory Aqueous Arrhenius acids have characteristic properties that provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with Base (chemistry) Acid–base conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton (protonation and deprotonation, respectively). The acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as . In solution there exists an chemical equilibrium :K_a [H+] [A^ -] [HA] The stronger of two acids will have a higher Ka than the weaker acid; the ratio of hydrogen ions to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for Ka spans many orders of magnitude, a more manageable constant, pKa is more frequently used, where pKa log10 Ka. Stronger acids have a smaller pKa than weaker acids. Experimentally determined pKa at 25°C in aqueous solution are often quoted in textbooks and reference material. Nomenclature Arrhenius acids are named according to their anions. In the classical naming system, the ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro-" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as its anion, so the hydro- prefix is used, and the -ide suffix makes the name take the form hydrochloric acid. Classical naming system: In the IUPAC naming system, "aqueous" is simply added to the name | Wikipedia:Acid |
example, HCl has chloride as its anion, so the hydro- prefix is used, and the -ide suffix makes the name take the form hydrochloric acid. Classical naming system: In the IUPAC naming system, "aqueous" is simply added to the name of the ionic compound. Thus, for hydrogen chloride, as an acid solution, the IUPAC name is aqueous hydrogen chloride. Acid strength The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely dissociates in water; in other words, one mole (unit) Stronger acids have a larger acid dissociation constant, Ka and a lower pKa than weaker acids. Sulfonic acids, which are organic oxyacids, are a class of strong acids. A common example is toluenesulfonic acid (tosylic acid). Unlike sulfuric acid itself, sulfonic acids can be solids. In fact, polystyrene functionalized into polystyrene sulfonate is a solid strongly acidic plastic that is filterable. Superacids are acids stronger than 100% sulfuric acid. Examples of superacids are fluoroantimonic acid, magic acid and perchloric acid. The strongest known acid is helium hydride ion, with a proton affinity of 177.8kJ/mol. Superacids can permanently protonate water to give ionic, crystalline hydronium "salts". They can also quantitatively stabilize carbocations. While Ka measures the strength of an acid compound, the strength of an aqueous acid solution is measured by pH, which is an indication of the concentration of hydronium in the solution. The pH of a simple solution of an acid compound in water is determined by the dilution of the compound and the compound's Ka. Lewis acid strength in non-aqueous solutions Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by ECW model Chemical characteristics Monoprotic acids Monoprotic acids, also known as monobasic acids, are | Wikipedia:Acid |
) and lose a second to form carbonate anion (CO). Both Ka | Wikipedia:Acid |
large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid can lose one proton to form bicarbonate anion ) and lose a second to form carbonate anion (CO). Both Ka values are small, but Ka1 > Ka2 . A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 > Ka2 > Ka3. : Ka1 : Ka2 : Ka3 An inorganic example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid. All three protons can be successively lost to yield H2PO, then HPO, and finally PO, the orthophosphate ion, usually just called phosphate. Even though the positions of the three protons on the original phosphoric acid molecule are equivalent, the successive Ka values differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged. An organic compound Although the subsequent loss of each hydrogen ion is less favorable, all of the conjugate bases are present in solution. The fractional concentration, α (alpha), for each species can be calculated. For example, a generic diprotic acid will generate 3 species in solution: H2A, HA−, and A2−. The fractional concentrations can be calculated as below when given either the pH (which can be converted to the [H+]) or the concentrations of the acid with all its conjugate bases: :align _H2A & + [H+]K_1 + K_1 K_2 ] \\ _HA^- & [ H+]K_1 | Wikipedia:Acid |
+ [H+]K_1 + K_1 K_2 +[HA^-]+[A^ 2-] \\ _A^ 2- & K_1 K_2 + [H+]K_1 + K_1 K_2 ] +[A^ 2-] align A plot of these fractional concentrations against pH, for given K1 and K2, is known as a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general n -protic acid that has been deprotonated i -times: : _ A^i- [ H+]^n-i _j 0^iK_j _ i 0^n [ [H+]^n-i _j 0^iK_j ] where | Wikipedia:Acid |
a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general n -protic acid that has been deprotonated i -times: : _ A^i- [ H+]^n-i _j 0^iK_j _ i 0^n [ [H+]^n-i _j 0^iK_j ] where K0 1 and the other K-terms are the dissociation constants for the acid. Neutralization (in beaker (glassware) Neutralization (chemistry) :HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq) Neutralization is the basis of titration, where a pH indicator shows equivalence point when the equivalent number of moles of a base have been added to an acid. It is often wrongly assumed that neutralization should result in a solution with pH 7.0, which is only the case with similar acid and base strengths during a reaction. Neutralization with a base weaker than the acid results in a weakly acidic salt. An example is the weakly acidic ammonium chloride, which is produced from the strong acid hydrogen chloride and the weak base ammonia. Conversely, neutralizing a weak acid with a strong base gives a weakly basic salt (e.g., sodium fluoride from hydrogen fluoride and sodium hydroxide). Weak acid–weak base equilibrium In order for a protonated acid to lose a proton, the pH of the system must rise above the pKa of the acid. The decreased concentration of H+ in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) solutions, there is a high enough H+ concentration in the solution to cause the acid to remain in its protonated form. Solutions of weak acids and salts of their conjugate bases form buffer solutions. Titration To determine the concentration of an acid in an aqueous solution, an acid–base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of | Wikipedia:Acid |
an aqueous solution, an acid–base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added. The titration curve of an acid titrated by a base has two axes, with the base volume on the x-axis and the solution's pH value on the y-axis. The pH of the solution always goes up as the base is added to the solution. Example: Diprotic acid , a diprotic amino acid. Point 2 is the first equivalent point where the amount of NaOH added equals the amount of alanine in the original solution. For each diprotic acid titration curve, from left to right, there are two midpoints, two equivalence points, and two buffer regions. Equivalence points Due to the successive dissociation processes, there are two equivalence points in the titration curve of a diprotic acid. The first equivalence point occurs when all first hydrogen ions from the first ionization are titrated. In other words, the amount of OH− added equals the original amount of H2A at the first equivalence point. The second equivalence point occurs when all hydrogen ions are titrated. Therefore, the amount of OH− added equals twice the amount of H2A at this time. For a weak diprotic acid titrated by a strong base, the second equivalence point must occur at pH above 7 due to the hydrolysis of the resulted salts in the solution. Each segment of the curve that contains a midpoint at its center is called the buffer region. Because the buffer regions consist of the acid and its conjugate base, it can resist pH changes when base is added until the next equivalent points. Applications of acids In industry Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most | Wikipedia:Acid |
base, it can resist pH changes when base is added until the next equivalent points. Applications of acids In industry Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, and is also the most-produced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batteries and dyes, as well as used in processing many products such like removing impurities. According to the statistics data in 2011, the annual production of sulfuric acid was around 200 million tonnes in the world. For example, phosphate minerals react with sulfuric acid to produce phosphoric acid for the production of phosphate fertilizers, and zinc is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning. In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acid reacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can be Esterification Acids are often used to remove rust and other corrosion from metals in a process known as pickling (metal) In food Tartaric acid is an important component of some commonly used foods like unripened mangoes and tamarind. Natural fruits and vegetables also contain acids. Citric acid is present in oranges, lemon and other citrus fruits. Oxalic acid is present in tomatoes, spinach, and especially in carambola and rhubarb; rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid. Ascorbic acid (Vitamin C) is an essential vitamin for the human body and is present in such foods as amla (Phyllanthus emblica Many acids can be found in various kinds of food as additives, as they alter their taste and serve as preservatives. Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in day-to-day life as vinegar. Citric acid is used as a preservative in sauces and pickles. Carbonic acid is | Wikipedia:Acid |
alter their taste and serve as preservatives. Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in day-to-day life as vinegar. Citric acid is used as a preservative in sauces and pickles. Carbonic acid is one of the most common acid additives that are widely added in soft drinks. During the manufacturing process, CO2 is usually pressurized to dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO2 at room temperature and pressure. Therefore, when bottles or cans of these kinds of soft drinks are opened, the soft drinks fizz and effervesce as CO2 bubbles come out. Certain acids are used as drugs. Acetylsalicylic acid (Aspirin) is used as a pain killer and for bringing down fevers. In human bodies Acids play important roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for synthesis of proteins required for growth and repair of body tissues. Fatty acids are also required for growth and repair of body tissues. Nucleic acids are important for the manufacturing of DNA and RNA and transmitting of traits to offspring through genes. Carbonic acid is important for maintenance of pH equilibrium in the body. Human bodies contain a variety of organic and inorganic compounds, among those dicarboxylic acids play an essential role in many biological behaviors. Many of those acids are amino acids, which mainly serve as materials for the synthesis of proteins. Other weak acids serve as buffers with their conjugate bases to keep the body's pH from undergoing large scale changes that would be harmful to cells. The rest of the dicarboxylic acids also participate in the synthesis of various biologically important compounds in human bodies. Acid catalysis Acids are used as catalysts in industrial and organic chemistry; for example, sulfuric acid is used | Wikipedia:Acid |
acid (HFO), the only known oxoacid for fluorine. * Sulfuric acid (H2SO4) * Fluorosulfuric | Wikipedia:Acid |
t union of a carbonyl group and a hydroxyl group. In vinylogous carboxylic acids, a carbon-carbon double bond separates the carbonyl and hydroxyl groups. * Ascorbic acid Nucleic acids * DNA * RNA References * Listing of strengths of common acids and bases * * External links * Curtipot: Acid–Base equilibria diagrams, pH calculation and titration curves simulation and analysis – freeware Category:Acids Category:Acid–base chemistry | Wikipedia:Acid |
, demonstrating the viscosity of bitumen Bitumen ( , ) is an immensely viscosity About 70% of annual bitumen production is destined for road surface In material sciences and engineering, the terms asphalt and bitumen are often used interchangeably and refer both to natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term bitumen for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, bitumen is the prevalent term in much of the world; however, in American English, asphalt is more commonly used. To help avoid confusion, the terms "liquid asphalt", "asphalt binder", or "asphalt cement" are used in the U.S. to distinguish it from asphalt concrete. Colloquially, various forms of bitumen are sometimes referred to as "tar", as in the name of the La Brea Tar Pits. Naturally occurring bitumen is sometimes specified by the term crude bitumen. Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at is sometimes referred to as "refined bitumen". The Canadian province of Alberta has most of the world'sreserves of natural bitumen in the Athabasca oil sands, which cover , an area larger than England. Terminology Etymology The Latin word traces to the Proto-Indo-European root wikt:Reconstruction:Proto-Indo-European/gʷet- The word "asphalt" is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphaltum, which is the Latinisation (literature) The first use of asphalt by the ancients was as a cement to secure or join various objects, and it thus seems likely that the name itself was expressive of this application. Specifically, Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, and thence into | Wikipedia:Bitumen |
it thus seems likely that the name itself was expressive of this application. Specifically, Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, and thence into French (asphalte) and English ("asphaltum" and "asphalt"). In French, the term asphalte is used for naturally occurring asphalt-soaked limestone deposits, and for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads. Modern terminology Bitumen mixed with clay was usually called "asphaltum", but the term is less commonly used today. In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is also commonly used as a shortened form of "asphalt concrete" (therefore equivalent to the British "asphalt" or "Tarmacadam In Canadian English, the word "bitumen" is used to refer to the vast Canadian deposits of extremely heavy crude oil, while "asphalt" is used for the oil refinery product. Diluted bitumen (diluted with naphtha to make it flow in pipelines) is known as "dilbit" in the Canadian petroleum industry, while bitumen "Upgrader "Bitumen" is still the preferred geological term for naturally occurring deposits of the solid or semi-solid form of petroleum. "Bituminous rock" is a form of sandstone impregnated with bitumen. The oil sands of Alberta, Canada are a similar material. Neither of the terms "asphalt" or "bitumen" should be confused with tar or coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons primarily sourced from vegetation masses, whether fossilized as with coal, or freshly harvested. The majority of bitumen, on the other hand, was formed naturally when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenesis Composition Normal composition The components of bitumen include four main classes of compounds: * Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic | Wikipedia:Bitumen |
materials were deposited by water and buried hundreds of metres deep at the diagenesis Composition Normal composition The components of bitumen include four main classes of compounds: * Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic aromatic compounds * Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material * Saturated hydrocarbons; the percentage of saturated compounds in asphalt correlates with its softening point * Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes. Most natural bitumens also contain organosulfur compounds, nickel and vanadium are found at 3 over a 15-minute period. Bitumen is a largely inert material that must be heated or diluted to a point where it becomes workable for the production of materials for paving, roofing, and other applications. In examining the potential health hazards associated with bitumen, the International Agency for Research on Cancer (IARC) determined that it is the application parameters, predominantly temperature, that affect occupational exposure and the potential bioavailable carcinogenic hazard/risk of the bitumen emissions. In particular, temperatures greater than 199°C (390°F), were shown to produce a greater exposure risk than when bitumen was heated to lower temperatures, such as those typically used in asphalt pavement mix production and placement. IARC has classified paving asphalt fumes as a List of IARC Group 2B carcinogens A bitumen-like substance found in the Himalayas and known as shilajit'' is sometimes used as an Ayurveda medicine, but is not in fact a tar, resin or bitumen. See also * Asphalt plant * Asphaltene * Bioasphalt * Bitumen-based fuel * Bituminous coal * Bituminous rocks * Blacktop * Cariphalte * Duxit * Macadam * Oil sands * Pitch drop experiment * Pitch (resin) * | Wikipedia:Bitumen |
bitumen. See also * Asphalt plant * Asphaltene * Bioasphalt * Bitumen-based fuel * Bituminous coal * Bituminous rocks * Blacktop * Cariphalte * Duxit * Macadam * Oil sands * Pitch drop experiment * Pitch (resin) * Road surface * Tar * Tarmacadam * Sealcoat * Stamped asphalt Notes References Sources * . * * External links * * * * Pavement Interactive – Asphalt * CSU Sacramento, The World Famous Asphalt Museum * [https://www.cdc.gov/niosh/topics/asphalt/ National Institute for Occupational Safety and Health – Asphalt Fumes * Scientific American, "Asphalt", 20 August 1881, pp.121 Category:Asphalt Category:Amorphous solids Category:Building materials Category:Chemical mixtures Category:IARC Group 2B carcinogens Category:Pavements Category:Petroleum products Category:Road construction materials | Wikipedia:Bitumen |
astronaut Bruce McCandless II using a Manned Maneuvering Unit outside on shuttle mission STS-41-B in 1984 An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a List of human spaceflight programs "Astronaut" technically applies to all human space travelers regardless of nationality. However, astronauts fielded by Russia or the Soviet Union are typically known instead as cosmonauts (from the Russian "kosmos" (космос), meaning "space", also borrowed from Greek ). Comparatively recent developments in crewed spaceflight made by China have led to the rise of the term taikonaut (from the Standard Chinese Since 1961 and as of 2021, 600 astronauts have flown in space. Until 2002, astronauts were sponsored and trained exclusively by governments, either by the military or by civilian space agencies. With the suborbital flight of the privately funded SpaceShipOne in 2004, a new category of astronaut was created: the commercial astronaut. Definition aboard Mercury-Redstone 3 The criteria for what constitutes human spaceflight vary, with some focus on the point where the atmosphere becomes so thin that centrifugal force, rather than aerodynamic force, carries a significant portion of the weight of the flight object. The (FAI) Sporting Code for astronautics recognizes only flights that exceed the Kármán line, at an altitude of . In the United States, professional, military, and commercial astronauts who travel above an altitude of are awarded Astronaut Badge , 552 people from Timeline of space travel by nationality Of these, List of Apollo astronauts , under the U.S. definition, 558 people qualify as having reached space, above altitude. Of eight X-15 pilots who exceeded in altitude, only one, Joseph A. Walker, exceeded 100 kilometers (about 62.1 miles) and he did it two times, becoming the first person in space twice. , the man with the longest cumulative time in space is Oleg Kononenko, who has spent over 1100 days in space. Peggy Whitson | Wikipedia:Astronaut |
kilometers (about 62.1 miles) and he did it two times, becoming the first person in space twice. , the man with the longest cumulative time in space is Oleg Kononenko, who has spent over 1100 days in space. Peggy Whitson Terminology In 1959, when both the United States and Soviet Union were planning, but had yet to launch humans into space, NASA Administrator T. Keith Glennan and his Deputy Administrator, Hugh Latimer Dryden The first known formal use of the term astronautics in the scientific community was the establishment of the annual International Astronautical Congress in 1950, and the subsequent founding of the International Astronautical Federation the following year. NASA applies the term astronaut to any crew member aboard NASA spacecraft bound for Earth orbit or beyond. NASA also uses the term as a title for those selected to join its NASA Astronaut Corps Cosmonaut , Gherman Titov By convention, an astronaut employed by the Russian Federal Space Agency (or its predecessor, the Soviet space program) is called a cosmonaut in English texts. Other countries of the former Eastern Bloc use variations of the Russian kosmonavt, such as the (although Polish people Coinage of the term has been credited to Soviet aeronautics (or "cosmonautics") pioneer Mikhail Tikhonravov (1900–1974). The first cosmonaut was Soviet Air Force pilot Yuri Gagarin, also the first person in space. He was part of the first six Soviet citizens, with German Titov, Yevgeny Khrunov, Andriyan Nikolayev, Pavel Popovich, and Grigoriy Nelyubov, who were given the title of pilot-cosmonaut in January 1961. Valentina Tereshkova was the first female cosmonaut and the first and youngest Women in space Taikonaut In Chinese, the term (, "cosmos navigating personnel") is used for astronauts and cosmonauts in general, while (, "navigating celestial-heaven personnel") is used for Chinese astronauts. Here, (, literally "heaven-navigating", or spaceflight) is strictly defined as the navigation of outer space within the local star system, i.e. Solar System. The phrase | Wikipedia:Astronaut |
astronauts and cosmonauts in general, while (, "navigating celestial-heaven personnel") is used for Chinese astronauts. Here, (, literally "heaven-navigating", or spaceflight) is strictly defined as the navigation of outer space within the local star system, i.e. Solar System. The phrase (, "spaceman") is often used in Hong Kong and Taiwan. The term taikonaut is used by some English-language news media organizations for professional Chinese space program Other terms With the rise of space tourism, NASA and the Russian Federal Space Agency agreed to use the term "spaceflight participant" to distinguish those space travelers from professional astronauts on missions coordinated by those two agencies. astronaut Timothy Kopra While no nation other than Russia (and previously the Soviet Union), the United States, and China have launched a crewed spacecraft, several other nations have sent people into space in cooperation with one of these countries, e.g. the Soviet-led Interkosmos program. Inspired partly by these missions, other synonyms for astronaut have entered occasional English usage. For example, the term spationaut () is sometimes used to describe French space travelers, from the Latin word for "space"; the Malay language For its 2022 European Space Agency Astronaut Group As of 2021 in the United States, astronaut status is conferred on a person depending on the authorizing agency: * one who flies in a vehicle above for NASA or the military is considered an astronaut (with no qualifier) * one who flies in a vehicle to the International Space Station in a mission coordinated by NASA and Roscosmos is a spaceflight participant * one who flies above in a non-NASA vehicle as a crewmember and demonstrates activities during flight that are essential to public safety, or contribute to human space flight safety, is considered a commercial astronaut by the Federal Aviation Administration * one who flies to the International Space Station as part of a "privately funded, dedicated commercial spaceflight on a commercial launch vehicle dedicated to the mission | Wikipedia:Astronaut |
space flight safety, is considered a commercial astronaut by the Federal Aviation Administration * one who flies to the International Space Station as part of a "privately funded, dedicated commercial spaceflight on a commercial launch vehicle dedicated to the mission ... to conduct approved commercial and marketing activities on the space station (or in a commercial segment attached to the station)" is considered a private astronaut by NASA (as of 2020, nobody has yet qualified for this status) * a generally-accepted but unofficial term for a paying non-crew passenger who flies a private non-NASA or military vehicles above is a space tourist (as of 2020, nobody has yet qualified for this status) On July 20, 2021, the FAA issued an order redefining the eligibility criteria to be an astronaut in response to the private suborbital spaceflights of Jeff Bezos and Richard Branson. The new criteria states that one must have "[d]emonstrated activities during flight that were essential to public safety, or contributed to human space flight safety" to qualify as an astronaut. This new definition excludes Bezos and Branson. Space travel milestones , first human in space (1961) , first women in space , first human to walk on the Moon (1969) , a Czechoslovakia , first person sent into space by China (2003) The first human in space was Soviet Yuri Gagarin, who was launched on 12 April 1961, aboard Vostok 1 and orbited around the Earth for 108 minutes. The first woman in space was Soviet Valentina Tereshkova, who launched on 16 June 1963, aboard Vostok 6 and orbited Earth for almost three days. Alan Shepard became the first American and second person in space on 5 May 1961, on a 15-minute sub-orbital flight aboard ''Mercury-Redstone 3 Cosmonaut Alexei Leonov was the first person to conduct an extravehicular activity (EVA), (commonly called a "spacewalk"), on 18 March 1965, on the Soviet Union's Voskhod 2 mission. This was followed two and | Wikipedia:Astronaut |
a 15-minute sub-orbital flight aboard ''Mercury-Redstone 3 Cosmonaut Alexei Leonov was the first person to conduct an extravehicular activity (EVA), (commonly called a "spacewalk"), on 18 March 1965, on the Soviet Union's Voskhod 2 mission. This was followed two and a half months later by astronaut Ed White (astronaut) The first crewed mission to orbit the Moon, Apollo 8, included American William Anders who was born in Hong Kong, making him the first Asian-born astronaut in 1968. The Soviet Union, through its Intercosmos program, allowed people from multiple other countries, mostly Soviet-allied but also including from France and Austria, to participate in Soyuz TM-7 and Soyuz TM-13, respectively. This made the Czechoslovakia On 23 July 1980, Pham Tuan of Vietnam became the first Asian people With the increase of seats on the Space Shuttle, the U.S. also began taking international astronauts. In 1983, Ulf Merbold of West Germany became the first non-US citizen to fly in a US spacecraft. In 1984, Marc Garneau became the first of eight Canadian astronauts to fly in space (through 2010). The first person born in Africa to fly in space was Patrick Baudry of France, in 1985. In same NASA flight as the Frenchman was the Saudi Arabian Sultan Salman al-Saud In 1985, Rodolfo Neri Vela became the first Mexican-born person in space. In 1991, Helen Sharman became the first Briton to fly in space. In 2001, American Dennis Tito became the first space tourist, after paying a fee for a trip aboard Russian spacecraft Soyuz. In 2002, another private tourist, the South African Mark Shuttleworth, became the first citizen of an African country to fly into space. On 15 October 2003, Yang Liwei became China'sfirst astronaut on its own spacecraft, the Shenzhou 5. Age milestones The youngest person to reach space is Oliver Daemen, who was 18 years and 11 months old when he made a Sub-orbital spaceflight The oldest person to reach space is | Wikipedia:Astronaut |
astronaut on its own spacecraft, the Shenzhou 5. Age milestones The youngest person to reach space is Oliver Daemen, who was 18 years and 11 months old when he made a Sub-orbital spaceflight The oldest person to reach space is William Shatner, who was 90 years old when he made a suborbital spaceflight on Blue Origin NS-18. The oldest person to reach orbit is John Glenn, one of the Mercury 7, who was 77 when he flew on STS-95. Duration and distance milestones The longest time spent in space was by Russian Valeri Polyakov, who spent 438 days there. aboard Vostok 6 (she also became the first woman in space on that mission). Tereshkova was only honorarily inducted into the USSR's Air Force, which did not accept female pilots at that time. A month later, Joseph Albert Walker became the first American civilian in space when his X-15 Flight 90 crossed the line, qualifying him by the international definition of spaceflight. Walker had joined the US Army Air Force but was not a member during his flight. The first people in space who had never been a member of any country'sarmed forces were both Konstantin Feoktistov and Boris Yegorov aboard Voskhod 1. The first non-governmental space traveler was Byron K. Lichtenberg, a researcher from the Massachusetts Institute of Technology who flew on STS-9 in 1983. In December 1990, Toyohiro Akiyama became the first paying space traveler and the first journalist in space for Tokyo Broadcasting System, a visit to Mir as part of an estimated $12million (USD) deal with a Japanese TV station, although at the time, the term used to refer to Akiyama was "Research Cosmonaut". Akiyama suffered severe space adaptation syndrome # Dennis Tito (American): 28 April – 6 May 2001 # Mark Shuttleworth (South African): 25 April – 5 May 2002 # Gregory Olsen (American): 1–11 October 2005 # Anousheh Ansari (Iranian / American): 18–29 September 2006 # Charles | Wikipedia:Astronaut |
syndrome # Dennis Tito (American): 28 April – 6 May 2001 # Mark Shuttleworth (South African): 25 April – 5 May 2002 # Gregory Olsen (American): 1–11 October 2005 # Anousheh Ansari (Iranian / American): 18–29 September 2006 # Charles Simonyi (Hungarian / American): 7–21 April 2007, 26 March – 8 April 2009 # Richard Garriott (British / American): 12–24 October 2008 # Guy Laliberté (Canadian): 30 September 2009 – 11 October 2009 # Yusaku Maezawa and Yozo Hirano (both Japanese): 8 – 24 December 2021 Training during water egress training with NASA (1965) The first NASA astronauts were selected for training in 1959. Early in the space program, military jet test piloting and engineering training were often cited as prerequisites for selection as an astronaut at NASA, although neither John Glenn nor Scott Carpenter (of the Mercury Seven) had any university degree, in engineering or any other discipline at the time of their selection. Selection was initially limited to military pilots. The earliest astronauts for both the US and the USSR tended to be fighter aircraft Once selected, NASA astronauts go through twenty months of training in a variety of areas, including training for extravehicular activity in a facility such as NASA's Neutral Buoyancy Laboratory. NASA candidacy requirements * The candidate must be a citizen of the United States. * The candidate must complete a master'sdegree in a STEM field, including engineering, biological science, physical science, computer science or mathematics. * The candidate must have at least two years of related professional experience obtained after degree completion or at least 1,000 hours pilot-in-command time on jet aircraft. * The candidate must be able to pass the NASA long-duration flight astronaut physical. * The candidate must also have skills in leadership, teamwork and communications. The master'sdegree requirement can also be met by: * Two years of work toward a doctoral program in a related science, technology, engineering or math field. * A | Wikipedia:Astronaut |
* The candidate must also have skills in leadership, teamwork and communications. The master'sdegree requirement can also be met by: * Two years of work toward a doctoral program in a related science, technology, engineering or math field. * A completed Doctor of Medicine or Doctor of Osteopathic Medicine degree. * Completion of a nationally recognized test pilot school program. Mission Specialist Educator * Applicants must have a bachelor'sdegree with teaching experience, including work at the kindergarten through twelfth grade level. An advanced degree, such as a master'sdegree or a doctoral degree, is not required, but is strongly desired. Educator Astronaut Project Barbara Morgan, selected as back-up teacher to Christa McAuliffe in 1985, is considered to be the first Educator astronaut by the media, but she trained as a mission specialist. The Educator Astronaut program is a successor to the Teacher in Space program from the 1980s. Health risks of space travel performing ultrasound on Michael Fincke during ISS Expedition 9 Astronauts are susceptible to a variety of health risks including decompression sickness, barotrauma, immunodeficiencies, loss of bone and muscle, loss of eyesight, orthostatic intolerance, sleep disturbances, and radiation injury. A variety of large scale medical studies are being conducted in space via the National Space Biomedical Research Institute (NSBRI) to address these issues. Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity Study in which astronauts (including former ISS commanders Leroy Chiao and Gennady Padalka) perform ultrasound scans under the guidance of remote experts to diagnose and potentially treat hundreds of medical conditions in space. This study'stechniques are now being applied to cover professional and Olympic sports injuries as well as ultrasound performed by non-expert operators in medical and high school students. It is anticipated that remote guided ultrasound will have application on Earth in emergency and rural health A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated | Wikipedia:Astronaut |
school students. It is anticipated that remote guided ultrasound will have application on Earth in emergency and rural health A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated in space. More recently, in 2017, bacteria were found to be more resistant to antibiotics and to thrive in the near-weightlessness of space. Microorganisms have been observed to survive the vacuum of outer space. On 31 December 2012, a NASA-supported study reported that human spaceflight may harm the brain and accelerate the onset of Alzheimer'sdisease. In October 2015, the NASA Office of Inspector General issued a Effect of spaceflight on the human body Over the last decade, flight surgeons and scientists at NASA have seen a pattern of vision problems in astronauts on long-duration space missions. The syndrome, known as Visual impairment due to intracranial pressure On 2 November 2017, scientists reported that significant changes in the position and structure of the brain have been found in astronauts who have taken Human spaceflight Being in space can be physiologically deconditioning on the body. It can affect the otolith organs and adaptive capabilities of the central nervous system. Zero gravity and cosmic rays can cause many implications for astronauts. In October 2018, NASA-funded researchers found that lengthy journeys into outer space, including travel to the Mars Researchers in 2018 reported, after detecting the presence on the International Space Station (ISS) of five ''Enterobacter A study by Russian scientists published in April 2019 stated that astronauts facing space radiation could face temporary hindrance of their memory centers. While this does not affect their intellectual capabilities, it temporarily hinders formation of new cells in brain'smemory centers. The study conducted by Moscow Institute of Physics and Technology (MIPT) concluded this after they observed that mice exposed to neutron and gamma radiation did not impact the rodents' intellectual capabilities. A 2020 clinical trial Food and drink An | Wikipedia:Astronaut |
centers. The study conducted by Moscow Institute of Physics and Technology (MIPT) concluded this after they observed that mice exposed to neutron and gamma radiation did not impact the rodents' intellectual capabilities. A 2020 clinical trial Food and drink An astronaut on the International Space Station requires about mass of food per meal each day (inclusive of about packaging mass per meal). Space Shuttle astronauts worked with nutritionists to select menus that appealed to their individual tastes. Five months before flight, menus were selected and analyzed for nutritional content by the shuttle dietician. Foods are tested to see how they will react in a reduced gravity environment. Caloric requirements are determined using a basal energy expenditure (BEE) formula. On Earth, the average American uses about of water every day. On board the ISS astronauts limit water use to only about per day. Insignia In Russia, cosmonauts are awarded Pilot-Cosmonaut of the Russian Federation upon completion of their missions, often accompanied with the award of Hero of the Russian Federation. This follows the practice established in the USSR where cosmonauts were usually awarded the title Hero of the Soviet Union. At NASA, those who complete astronaut candidate training receive a silver Astronaut Badge#NASA Astronaut Pins Deaths , eighteen astronauts (fourteen men and four women) have died during four space flights. By nationality, thirteen were American, four were Russian (Soviet Union), and one was Israeli. , eleven people (all men) have died training for spaceflight: eight Americans and three Russians. Six of these were in crashes of training jet aircraft, one drowned during water recovery training, and four were due to fires in pure oxygen environments. Astronaut David Scott left a memorial consisting of a statuette titled Fallen Astronaut on the surface of the Moon during his 1971 Apollo 15 mission, along with a list of the names of eight of the astronauts and six cosmonauts known at the time to have | Wikipedia:Astronaut |
consisting of a statuette titled Fallen Astronaut on the surface of the Moon during his 1971 Apollo 15 mission, along with a list of the names of eight of the astronauts and six cosmonauts known at the time to have died in service. The Space Mirror Memorial, which stands on the grounds of the Kennedy Space Center Visitor Complex, is maintained by the Astronauts Memorial Foundation and commemorates the lives of the men and women who have died during spaceflight and during training in the space programs of the United States. In addition to twenty NASA career astronauts, the memorial includes the names of an X-15 test pilot, a U.S. Air Force officer who died while training for a then-classified military space program, and a civilian spaceflight participant. See also Explanatory notes References External links * * NASA: How to become an astronaut 101 * List of International partnership organizations * Encyclopedia Astronautica: Phantom cosmonauts * collectSPACE: Astronaut appearances calendar * spacefacts Spacefacts.de * Manned astronautics: facts and figures * Astronaut Candidate Brochure online Category:Astronauts Category:Science occupations Category:1959 introductions | Wikipedia:Astronaut |
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs),. The American Chemical Society (ACS) has used the spelling cesium since 1921, following ''Webster's Third New International Dictionary''. The alkali metals are all shiny, hardness All of the discovered alkali metals occur in nature as their compounds: in order of abundance of the chemical elements Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks form the basis of the second. A common application of the compounds of sodium is the sodium-vapour lamp, which emits light very efficiently. Table salt, or sodium chloride, has been used since antiquity. Lithium (medication) __TOC__ History , the lithium mineral from which lithium was first isolated Sodium compounds have been known since ancient times; salt (sodium chloride) has been an important commodity in human activities. While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence which led him to suggest the fundamental difference of sodium and potassium salts in 1702, and Henri-Louis Duhamel du Monceau was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789. Pure potassium was first isolated in 1807 in England by Humphry Davy, who derived it from caustic potash (KOH, potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented voltaic pile. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium'sextreme reactivity. Later that same year, Davy reported extraction of sodium | Wikipedia:Alkali metal |
potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented voltaic pile. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium'sextreme reactivity. Later that same year, Davy reported extraction of sodium from the similar substance caustic soda (NaOH, lye) by a similar technique, demonstrating the elements, and thus the salts, to be different. was among the first to notice similarities between what are now known as the alkali metals. Petalite () was discovered in 1800 by the Brazilian chemist José Bonifácio de Andrada in a mine on the island of Utö, Sweden. However, it was not until 1817 that Johan August Arfwedson, then working in the laboratory of the chemist Jöns Jacob Berzelius, discovery of the chemical elements Around 1865 John Alexander Reina Newlands : '''''' The next element below francium (Mendeleev'spredicted elements : + → * → no atoms It is highly unlikely to make a large enough target to increase the sensitivity of the experiment to the required level; einsteinium has not been found in nature and has only been produced in laboratories, and in quantities smaller than those needed for effective synthesis of superheavy elements. However, given that ununennium is only the first period 8 element on the extended periodic table, it may well be discovered in the near future through other reactions, and indeed an attempt to synthesise it is currently ongoing in Japan. Currently, none of the period 8 elements has been discovered yet, and it is also possible, due to nucleon drip line The Oddo–Harkins rule holds that elements with even atomic numbers are more common that those with odd atomic numbers, with the exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair | Wikipedia:Alkali metal |
This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability. All the alkali metals have odd atomic numbers and they are not as common as the elements with even atomic numbers adjacent to them (the noble gases and the alkaline earth metals) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in supernovae and not in stellar nucleosynthesis. Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both Big Bang nucleosynthesis and in stars: the Big Bang could only produce trace quantities of lithium, beryllium and boron due to the absence of a stable nucleus with 5 or 8 nucleons, and stellar nucleosynthesis could only pass this bottleneck by the triple-alpha process, fusing three helium nuclei to form carbon, and skipping over those three elements. The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are Goldschmidt classification Sodium and potassium are very abundant on Earth, both being among the ten abundance of elements in Earth'scrust Properties Physical and chemical The physical and chemical properties of the alkali metals can be readily explained by their having an ns1 valence electron configuration, which results in weak metallic bonding. Hence, all the alkali metals are soft and have low densities, The alkali metals are more similar to each other than the elements in any other group (periodic table) In aqueous solution, the alkali metal ions form metal ions in aqueous solution Lithium The chemistry of lithium shows several differences from that of the rest of the group | Wikipedia:Alkali metal |
than the elements in any other group (periodic table) In aqueous solution, the alkali metal ions form metal ions in aqueous solution Lithium The chemistry of lithium shows several differences from that of the rest of the group as the small Li+ cation chemical polarity Lithium fluoride is the only alkali metal halide that is poorly soluble in water, and the enthalpy of dissociation of the Fr2 molecule (42.1 kJ/mol). The CsFr molecule is polarised as Cs+Fr−, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. Due to the great rarity of odd–odd nuclei, almost all the primordial isotopes of the alkali metals are odd–even (the exceptions being the light stable isotope lithium-6 and the long-lived radioisotope potassium-40). For a given odd mass number, there can be only a single beta-decay stable isobars Periodic trends The alkali metals are more similar to each other than the elements in any other group (periodic table) Electronegativity of the periodic table from the period 2 element Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. If the bond between sodium and chlorine in sodium chloride were covalent, the pair of shared electrons would be attracted to the chlorine because the effective nuclear charge on the outer electrons is +7 in chlorine but is only +1 in sodium. The electron pair is attracted so close to the chlorine atom that they are practically transferred to the chlorine atom (an ionic bond). However, if the sodium atom was replaced by a lithium atom, the electrons will not be attracted as close to the chlorine atom as before because the lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms | Wikipedia:Alkali metal |
electrons will not be attracted as close to the chlorine atom as before because the lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms (further down the group) will be less electronegative as the bonding pair is less strongly attracted towards them. As mentioned previously, francium is expected to be an exception. and all the liquid changes state to gas. As a metal is heated to its melting point, the metallic bonds keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break completely at the metal'sboiling point. Therefore, the falling melting and boiling points of the alkali metals indicate that the strength of the metallic bonds of the alkali metals decreases down the group. All alkali metals melt as a part of the reaction with water. Water molecules ionise the bare metallic surface of the liquid metal, leaving a positively charged metal surface and negatively charged water ions. The attraction between the charged metal and water ions will rapidly increase the surface area, causing an exponential increase of ionisation. When the repulsive forces within the liquid metal surface exceeds the forces of the surface tension, it vigorously explodes. Some of these have ionic characteristics: taking the alloys with gold, the most electronegative of metals, as an example, NaAu and KAu are metallic, but RbAu and CsAu are semiconductors. An alloy of 41% caesium, 47% sodium, and 12% potassium has the lowest known melting point of any metal or alloy, −78°C. Nevertheless, while the elements in group 14 and beyond tend to form discrete anionic clusters, group 13 elements tend to form polymeric ions with the alkali metal cations located between the giant ionic lattice. For example, NaTl consists of a polymeric anion ( Tl− )nwith a covalent diamond cubic structure with Na+ ions located between the anionic lattice. The | Wikipedia:Alkali metal |
ely to the hydroxides when in contact with water. and several brightly | Wikipedia:Alkali metal |
the structure (RLi)xwhere R is the organic group. As the | Wikipedia:Alkali metal |
nd K can react with acetylene to give acetylides. :2 Li \ + \ 2 C \ \ Li2C2 :2 Na \ + \ 2 C2H2 \ ->[150 \ ^ oC ] \ 2 NaC2H \ + \ H2 :2 Na \ + \ 2 NaC2H \ ->[220 \ ^ oC ] \ 2 | Wikipedia:Alkali metal |
ave sometimes been called "pseudo-alkali metals". These substances include some elements and many more polyatomic ions; the polyatomic | Wikipedia:Alkali metal |
Many other substances are similar to the alkali metals in their tendency to form monopositive cations. Analogously to the pseudohalogens, they have sometimes been called "pseudo-alkali metals". These substances include some elements and many more polyatomic ions; the polyatomic ions are especially similar to the alkali metals in their large size and weak polarising power. Under typical conditions, pure hydrogen exists as a diatomic gas consisting of two atoms per molecule (H2); however, the alkali metals form diatomic molecules (such as dilithium, Li2) only at high temperatures, when they are in the gaseous state. Hydrogen, like the alkali metals, has one valence electron It is sometimes placed above fluorine due to their similar chemical properties, though the resemblance is likewise not absolute. The first ionisation energy of hydrogen (1312.0 kJ/mol) is much higher than that of the alkali metals. As only one additional electron is required to fill in the outermost shell of the hydrogen atom, hydrogen often behaves like a halogen, forming the negative hydride ion, and is very occasionally considered to be a halogen on that basis. (The alkali metals can also form negative ions, known as alkalides, but these are little more than laboratory curiosities, being unstable.) The electrical resistivity of liquid metallic hydrogen at 3000 K is approximately equal to that of liquid rubidium and caesium at 2000 K at the respective pressures when they undergo a nonmetal-to-metal transition. The 1s1 electron configuration of hydrogen, while analogous to that of the alkali metals (ns1), is unique because there is no 1p subshell. Hence it can lose an electron to form the hydron (chemistry) Ammonium and derivatives reacts with hydrochloric acid to form the salt ammonium chloride. The ammonium ion () has very similar properties to the heavier alkali metals, acting as an alkali metal intermediate between potassium and rubidium, and is often considered a close relative. Ammonium is expected to behave stably as a metal | Wikipedia:Alkali metal |
chloride. The ammonium ion () has very similar properties to the heavier alkali metals, acting as an alkali metal intermediate between potassium and rubidium, and is often considered a close relative. Ammonium is expected to behave stably as a metal ( ions in a sea of delocalised electrons) at very high pressures (though less than the typical pressure where transitions from insulating to metallic behaviour occur around, 100pascal (unit) Other "pseudo-alkali metals" include the alkylammonium cations, in which some of the hydrogen atoms in the ammonium cation are replaced by alkyl or aryl groups. In particular, the quaternary ammonium cations () are very useful since they are permanently charged, and they are often used as an alternative to the expensive Cs+ to stabilise very large and very easily polarisable anions such as . Cobalt may be substituted by its heavier congener rhodium to give rhodocene, an even stronger reducing agent. Iridocene (involving iridium) would presumably be still more potent, but is not very well-studied due to its instability. Thallium , stored under argon gas Thallium is the heaviest stable element in group 13 of the periodic table. At the bottom of the periodic table, the inert-pair effect is quite strong, because of the relativistic effects Copper, silver, and gold The group 11 element In Mendeleev's 1871 periodic table, copper, silver, and gold are listed twice, once under group VIII (with the iron triad and platinum group metals), and once under group IB. Group IB was nonetheless parenthesised to note that it was tentative. Mendeleev'smain criterion for group assignment was the maximum oxidation state of an element: on that basis, the group 11 elements could not be classified in group IB, due to the existence of copper(II) and gold(III) compounds being known at that time. Sodium occurs mostly in seawater and dried seabed, Extremely pure sodium can be produced through the thermal decomposition of sodium azide. Potassium occurs in | Wikipedia:Alkali metal |
idium and caesium also increased correspondingly. most francium is synthesised in | Wikipedia:Alkali metal |
methods: acid digestion, alkaline decomposition, and direct reduction. Both metals are produced as by-products of lithium production: after 1958, when interest in lithium'sthermonuclear properties increased sharply, the production of rubidium and caesium also increased correspondingly. most francium is synthesised in the nuclear reaction 197Gold Applications Lithium, sodium, and potassium have many useful applications, while rubidium and caesium are very notable in academic contexts but do not have many applications yet. In medicine, some Lithium (medication) Potassium compounds are often used as fertilisers as potassium is an important element for plant nutrition. Potassium hydroxide is a very strong base, and is used to control the pH of various substances. Potassium nitrate and potassium permanganate are often used as powerful oxidising agents. Caesium atomic clocks are extraordinarily accurate; if a clock had been made at the time of the dinosaurs, it would be off by less than four seconds (after 80 million years). For that reason, caesium atoms are used as the definition of the second. Rubidium ions are often used in purple fireworks, and caesium is often used in drilling fluids in the petroleum industry. Francium has no commercial applications, but because of francium'srelatively simple atomic structure, among other things, it has been used in spectroscopy experiments, leading to more information regarding energy levels and the coupling constants of the weak interaction. Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels, similar to those predicted by quantum mechanics Biological role and precautions Metals Pure alkali metals are dangerously reactive with air and water and must be kept away from heat, fire, oxidising agents, acids, most organic compounds, halocarbons, plastics, and moisture. They also react with carbon dioxide and carbon tetrachloride, so that normal fire extinguishers are counterproductive when used on alkali metal fires. Experiments are usually conducted using only small quantities of a few grams in a | Wikipedia:Alkali metal |
halocarbons, plastics, and moisture. They also react with carbon dioxide and carbon tetrachloride, so that normal fire extinguishers are counterproductive when used on alkali metal fires. Experiments are usually conducted using only small quantities of a few grams in a fume hood. Small quantities of lithium may be disposed of by reaction with cool water, but the heavier alkali metals should be dissolved in the less reactive isopropanol. The alkali metals must be stored under mineral oil or an inert atmosphere. The inert atmosphere used may be argon or nitrogen gas, except for lithium, which reacts with nitrogen. Rubidium and caesium must be kept away from air, even under oil, because even a small amount of air diffused into the oil may trigger formation of the dangerously explosive peroxide; for the same reason, potassium should not be stored under oil in an oxygen-containing atmosphere for longer than 6 months. Ions The bioinorganic chemistry of the alkali metal ions has been extensively reviewed. Solid state crystal structures have been determined for many complexes of alkali metal ions in small peptides, nucleic acid constituents, carbohydrates and ionophore complexes. Lithium naturally only occurs in traces in biological systems and has no known biological role, but does have effects on the body when ingested. Its biochemistry, the way it is handled by the human body and studies using rats and goats suggest that it is an essential element Sodium and potassium occur in all known biological systems, generally functioning as electrolytes inside and outside cell (biology) Potassium is the major cation (positive ion) inside cell (biology) Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic. Like rubidium, caesium tends to substitute potassium in the body, but is significantly larger and is therefore a poorer substitute. Excess caesium can lead to hypokalemia, arrhythmia, and acute cardiac arrest, but such amounts would not ordinarily be encountered in natural sources. | Wikipedia:Alkali metal |
caesium tends to substitute potassium in the body, but is significantly larger and is therefore a poorer substitute. Excess caesium can lead to hypokalemia, arrhythmia, and acute cardiac arrest, but such amounts would not ordinarily be encountered in natural sources. As such, caesium is not a major chemical environmental pollutant. Caesium chloride has been promoted as an alternative cancer therapy, but has been linked to the deaths of over 50 patients, on whom it was used as part of a scientifically unvalidated cancer treatment. Radioisotopes of caesium require special precautions: the improper handling of caesium-137 gamma ray sources can lead to release of this radioisotope and radiation injuries. Perhaps the best-known case is the Goiânia accident of 1987, in which an improperly-disposed-of radiation therapy system from an abandoned clinic in the city of Goiânia, Brazil, was scavenged from a junkyard, and the glowing caesium chloride Notes References Category:Chemical compounds by element Category:Alkali metals Category:Groups (periodic table) Category:Periodic table Category:Articles containing video clips | Wikipedia:Alkali metal |
The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number ('''np') or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary electric charge For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number Z and the neutron number N'' gives the atom'satomic mass number A. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the Binding energy#Mass change Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth determines the element'sstandard atomic weight. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century. The conventional symbol Z comes from the German word 'number', which, before the modern synthesis of ideas from chemistry and physics, merely denoted an element'snumerical place in the periodic table, whose order was then approximately, but not completely, consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge and a physical characteristic of atoms, did the word (and its English equivalent atomic number) come into common use in this context. The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons. Notation . | Wikipedia:Atomic number |
the word (and its English equivalent atomic number) come into common use in this context. The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons. Notation . Atomic number is the number of protons, and therefore also the total positive charge, in the atomic nucleus. The common pronunciation of the AZE notation is different from how it is written: is commonly pronounced as helium-four instead of four-two-helium, and as uranium two-thirty-five (American English) or uranium-two-three-five (British) instead of 235-92-uranium. Various notations appear in older sources were used, such as Ne(22) in 1934, Ne22 for neon-22 (1935) or Pb210 for lead-210 (1933) History In the 19th century, the term "atomic number" typically meant the number of atoms in a given volume. Modern chemists prefer to use the concept of molar concentration. In 1913, Antonius van den Broek proposed that the electric charge of an atomic nucleus, expressed as a multiplier of the elementary charge, was equal to the element'ssequential position on the periodic table. Ernest Rutherford, in various articles in which he discussed van den Broek'sidea, used the term "atomic number" to refer to an element'sposition on the periodic table. No writer before Rutherford is known to have used the term "atomic number" in this way, so it was probably he who established this definition. After Rutherford deduced the existence of the proton in 1920, "atomic number" customarily referred to the proton number of an atom. In 1921, the German Atomic Weight Commission based its new periodic table on the nuclear charge number and in 1923 the International Committee on Chemical Elements followed suit. The periodic table and a natural number for each element , creator of the periodic table. The periodic table of elements creates an ordering of the elements, and so they can be numbered in order. Dmitri Mendeleev arranged his first periodic tables | Wikipedia:Atomic number |
and a natural number for each element , creator of the periodic table. The periodic table of elements creates an ordering of the elements, and so they can be numbered in order. Dmitri Mendeleev arranged his first periodic tables (first published on March 6, 1869) in order of atomic weight ("Atomgewicht"). However, in consideration of the elements' observed chemical properties, he changed the order slightly and placed tellurium (atomic weight 127.6) ahead of iodine (atomic weight 126.9). This placement is consistent with the modern practice of ordering the elements by proton number, Z, but that number was not known or suspected at the time. A simple numbering based on atomic weight position was never entirely satisfactory. In addition to the case of iodine and tellurium, several other pairs of elements (such as argon and potassium, cobalt and nickel) were later shown to have nearly identical or reversed atomic weights, thus requiring their placement in the periodic table to be determined by their chemical properties. Moseley, after discussions with Bohr who was at the same lab (and who had used Van den Broek'shypothesis in his Bohr model of the atom), decided to test Van den Broek's and Bohr'shypothesis directly, by seeing if spectral lines emitted from excited atoms fitted the Bohr theory'spostulation that the frequency of the spectral lines be proportional to the square of Z. To do this, Moseley measured the wavelengths of the innermost photon transitions (K and L lines) produced by the elements from aluminium (Z 13) to gold (Z 79) used as a series of movable anodic targets inside an x-ray tube. The square root of the frequency of these photons increased from one target to the next in an arithmetic progression. This led to the conclusion (Moseley's law) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley'swork) to the calculated electric charge of the nucleus, i.e. the element number Z. Among | Wikipedia:Atomic number |
arithmetic progression. This led to the conclusion (Moseley's law) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley'swork) to the calculated electric charge of the nucleus, i.e. the element number Z. Among other things, Moseley demonstrated that the lanthanide series (from lanthanum to lutetium inclusive) must have 15 members no fewer and no more which was far from obvious from known chemistry at that time. Missing elements After Moseley'sdeath in 1915, the atomic numbers of all known elements from hydrogen to uranium (Z 92) were examined by his method. There were seven elements (with Z Category:Chemical properties Category:Nuclear physics Category:Atoms Category:Dimensionless numbers of chemistry Category:Numbers | Wikipedia:Atomic number |
'sillustration of the Caterpillar (Alice's Adventures in Wonderland) Ambiguity is the type of meaning (linguistics) The concept of ambiguity is generally contrasted with vagueness. In ambiguity, specific and distinct interpretations are permitted (although some may not be immediately obvious), whereas with vague information it is difficult to form any interpretation at the desired level of specificity. Linguistic forms Lexical ambiguity is contrasted with semantic ambiguity. The former represents a choice between a finite number of known and meaningful context (language use) Ambiguity in human language is argued to reflect principles of efficient communication. Languages that communicate efficiently will avoid sending information that is redundant with information provided in the context. This can be shown mathematically to result in a system that is ambiguous when context is neglected. In this way, ambiguity is viewed as a generally useful feature of a linguistic system. Linguistic ambiguity Ambiguity (law) Lexical ambiguity The Polysemy The context in which an ambiguous word is used often makes it clearer which of the meanings is intended. If, for instance, someone says "I put $100 in the bank", most people would not think someone used a shovel to dig in the mud. However, some linguistic contexts do not provide sufficient information to make a used word clearer. Lexical ambiguity can be addressed by algorithmic methods that automatically associate the appropriate meaning with a word in context, a task referred to as word-sense disambiguation. The use of multi-defined words requires the author or speaker to clarify their context, and sometimes elaborate on their specific intended meaning (in which case, a less ambiguous term should have been used). The goal of clear concise communication is that the receiver(s) have no misunderstanding about what was meant to be conveyed. An exception to this could include a politician whose "weasel words" and obfuscation are necessary to gain support from multiple Electoral district More problematic are words whose multiple meanings express | Wikipedia:Ambiguity |
have no misunderstanding about what was meant to be conveyed. An exception to this could include a politician whose "weasel words" and obfuscation are necessary to gain support from multiple Electoral district More problematic are words whose multiple meanings express closely related concepts. "Good", for example, can mean "useful" or "functional" (''That's a good hammer), "exemplary" (She's a good student), "pleasing" (This is good soup), "moral" (a good person versus the lesson to be learned from a story''), "righteous", etc. "I have a good daughter" is not clear about which sense is intended. The various ways to apply prefixes and suffixes can also create ambiguity ("unlockable" can mean "capable of being opened" or "impossible to lock"). Semantic and syntactic ambiguity Semantic ambiguity occurs when a word, phrase or sentence, taken out of context, has more than one interpretation. In "We saw her duck" (example due to Richard Nordquist), the words "her duck" can refer either # to the person'sbird (the noun "duck", modified by the possessive pronoun "her"), or # to a motion she made (the verb "duck", the subject of which is the objective pronoun "her", object of the verb "saw"). For the notion of, and theoretic results about, syntactic ambiguity in artificial, formal languages (such as computer programming languages), see Ambiguous grammar. Usually, semantic and syntactic ambiguity go hand in hand. The sentence "We saw her duck" is also syntactically ambiguous. Conversely, a sentence like "He ate the cookies on the couch" is also semantically ambiguous. Rarely, but occasionally, the different parsings of a syntactically ambiguous phrase result in the same meaning. For example, the command "Cook, cook Spoken language can contain many more types of ambiguities that are called phonological ambiguities, where there is more than one way to compose a set of sounds into words. For example, "ice cream" and "I scream". Such ambiguity is generally resolved according to the context. A mishearing of such, based | Wikipedia:Ambiguity |
are called phonological ambiguities, where there is more than one way to compose a set of sounds into words. For example, "ice cream" and "I scream". Such ambiguity is generally resolved according to the context. A mishearing of such, based on incorrectly resolved ambiguity, is called a mondegreen. Philosophy Philosophers (and other users of logic) spend a lot of time and effort searching for and removing (or intentionally adding) ambiguity in arguments because it can lead to incorrect conclusions and can be used to deliberately conceal bad arguments. For example, a politician might say, "I oppose taxes which hinder economic growth", an example of a glittering generality. Some will think they oppose taxes in general because they hinder economic growth. Others may think they oppose only those taxes that they believe will hinder economic growth. In writing, the sentence can be rewritten to reduce possible misinterpretation, either by adding a comma after "taxes" (to convey the first sense) or by changing "which" to "that" (to convey the second sense) or by rewriting it in other ways. The devious politician hopes that each constituent will interpret the statement in the most desirable way, and think the politician supports everyone'sopinion. However, the opposite can also be true an opponent can turn a positive statement into a bad one if the speaker uses ambiguity (intentionally or not). The logical fallacies of amphiboly and equivocation rely heavily on the use of ambiguous words and phrases. In continental philosophy (particularly phenomenology and existentialism), there is much greater tolerance of ambiguity, as it is generally seen as an integral part of the human condition. Martin Heidegger argued that the relation between the subject and object is ambiguous, as is the relation of mind and body, and part and whole. In Heidegger'sphenomenology, Dasein is always in a meaningful world, but there is always an underlying background for every instance of signification. Thus, although some things may be certain, | Wikipedia:Ambiguity |
as is the relation of mind and body, and part and whole. In Heidegger'sphenomenology, Dasein is always in a meaningful world, but there is always an underlying background for every instance of signification. Thus, although some things may be certain, they have little to do with Dasein'ssense of care and existential anxiety, e.g., in the face of death. In calling his work Being and Nothingness an "essay in phenomenological ontology" Jean-Paul Sartre follows Heidegger in defining the human essence as ambiguous, or relating fundamentally to such ambiguity. Simone de Beauvoir tries to base an ethics on Heidegger's and Sartre'swritings (The Ethics of Ambiguity), where she highlights the need to grapple with ambiguity: "as long as there have been philosophers and they have thought, most of them have tried to mask it... And the ethics which they have proposed to their disciples has always pursued the same goal. It has been a matter of eliminating the ambiguity by making oneself pure inwardness or pure externality, by escaping from the sensible world or being engulfed by it, by yielding to eternity or enclosing oneself in the pure moment." Ethics cannot be based on the authoritative certainty given by mathematics and logic, or prescribed directly from the empirical findings of science. She states: "Since we do not succeed in fleeing it, let us, therefore, try to look the truth in the face. Let us try to assume our fundamental ambiguity. It is in the knowledge of the genuine conditions of our life that we must draw our strength to live and our reason for acting". Other continental philosophers suggest that concepts such as life, nature, and sex are ambiguous. Corey Anton has argued that we cannot be certain what is separate from or unified with something else: language, he asserts, divides what is not, in fact, separate. Following Ernest Becker, he argues that the desire to 'authoritatively disambiguate' the world and existence has led to | Wikipedia:Ambiguity |
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"text": "Albedo is the fraction of sunlight that is reflected by a surface...",
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