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In Europe, there are two varieties of chrain. "Red" chrain is mixed with red beetroot and "white" chrain contains no beetroot. Chrain is a part of Christian Easter and Jewish Passover tradition (as maror) in Eastern and Central Europe. In the Christian tradition, horseradish is eaten during Eastertide (Paschaltide) as "is a reminder of the bitterness of Jesus' suffering" on Good Friday.
In parts of Southern Germany "kren" is a component of the traditional wedding dinner. It is served with cooked beef and a dip made from lingonberry to balance the slight hotness of the Kren.
In Poland, a variety with red beetroot is called or simply ćwikła.
In Russia, a very popular ingredient for pickles (cucumbers, tomatoes, mushrooms).
In Ashkenazi European Jewish cooking, beetroot horseradish is commonly served with gefilte fish.
In Transylvania and other Romanian regions, red beetroot with horseradish is used as a salad served with lamb dishes at Easter called sfecla cu hrean.
In Serbia, ren is an essential condiment with cooked meat and freshly roasted suckling pig.
In Croatia, freshly grated horseradish (Croatian: Hren) is often eaten with boiled ham or beef.
In Hungary, Slovenia, and in the adjacent Italian regions of Friuli-Venezia Giulia and nearby Italian region of Veneto, horseradish (often grated and mixed with sour cream, vinegar, hard-boiled eggs, or apples) is also a traditional Easter dish.
In the Italian regions of Lombardy, Emilia-Romagna, and Piedmont, it is called barbaforte (strong beard) and is a traditional accompaniment to bollito misto; while in northeastern regions like Trentino-Alto Adige/Südtirol, Veneto and Friuli-Venezia Giulia, it is still called kren or cren. In the southern region of Basilicata it is known as rafano and used for the preparation of rafanata, a main course made of horseradish, eggs, cheese and sausage.
Horseradish is also used as a main ingredient for soups. In Poland, horseradish soup is a common Easter Day dish. | Horseradish | Wikipedia | 482 | 45714 | https://en.wikipedia.org/wiki/Horseradish | Biology and health sciences | Brassicales | null |
Relation to wasabi
Outside Japan, the Japanese condiment wasabi, although traditionally prepared from the true wasabi plant (Wasabia japonica), is now usually made with horseradish due to the scarcity of the wasabi plant. The Japanese botanical name for horseradish is , or "Western wasabi". Both plants are members of the family Brassicaceae.
Nutritional content
In a 100-gram amount, prepared horseradish provides 48 calories and has high content of vitamin C with moderate content of sodium, folate and dietary fiber, while other essential nutrients are negligible in content. In a typical serving of one tablespoon (15 grams), horseradish supplies no significant nutrient content.
Horseradish contains volatile oils, notably mustard oil.
Biomedical uses
The enzyme horseradish peroxidase (HRP), found in the plant, is used extensively in molecular biology and biochemistry primarily for its ability to amplify a weak signal and increase detectability of a target molecule. HRP has been used in decades of research to visualize under microscopy and assess non-quantitatively the permeability of capillaries, particularly those of the brain. | Horseradish | Wikipedia | 243 | 45714 | https://en.wikipedia.org/wiki/Horseradish | Biology and health sciences | Brassicales | null |
The Arecaceae () is a family of perennial, flowering plants in the monocot order Arecales. Their growth form can be climbers, shrubs, tree-like and stemless plants, all commonly known as palms. Those having a tree-like form are colloquially called palm trees. Currently, 181 genera with around 2,600 species are known, most of which are restricted to tropical and subtropical climates. Most palms are distinguished by their large, compound, evergreen leaves, known as fronds, arranged at the top of an unbranched stem, except for the Hyphaene genus, who has branched palms. However, palms exhibit an enormous diversity in physical characteristics and inhabit nearly every type of habitat within their range, from rainforests to deserts.
Palms are among the best known and most extensively cultivated plant families. They have been important to humans throughout much of history, especially in regions like the Middle East and North Africa. A wide range of common products and foods are derived from palms. In contemporary times, palms are also widely used in landscaping. In many historical cultures, because of their importance as food, palms were symbols for such ideas as victory, peace, and fertility.
Etymology
The word Arecaceae is derived from the word areca with the suffix "-aceae". Areca is derived from Portuguese, via Malayalam അടയ്ക്ക (aṭaykka), which is from Dravidian *aṭ-ay-kkāy ("areca nut"). The suffix -aceae is the feminine plural of the Latin -āceus ("resembling").
Palm originates from Latin palma semantically overlapping with sense of "hand front" (due to similar splayed shape) ultimately from Proto-Indo-European *pl̥h₂meh₂, a direct descendant once existed in Old English. | Arecaceae | Wikipedia | 371 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Morphology
Whether as shrubs, tree-like, or vines, palms have two methods of growth: solitary or clustered. The common representation is that of a solitary shoot ending in a crown of leaves. This monopodial character may be exhibited by prostrate, trunkless, and trunk-forming members. Some common palms restricted to solitary growth include Washingtonia and Roystonea. Palms may instead grow in sparse though dense clusters. The trunk develops an axillary bud at a leaf node, usually near the base, from which a new shoot emerges. The new shoot, in turn, produces an axillary bud and a clustering habit results. Exclusively sympodial genera include many of the rattans, Guihaia, and Rhapis. Several palm genera have both solitary and clustering members. Palms which are usually solitary may grow in clusters and vice versa.
Palms have large, evergreen leaves that are either palmately ('fan-leaved') or pinnately ('feather-leaved') compound and spirally arranged at the top of the stem. The leaves have a tubular sheath at the base that usually splits open on one side at maturity. The inflorescence is a spadix or spike surrounded by one or more bracts or spathes that become woody at maturity. The flowers are generally small and white, radially symmetric, and can be either uni- or bisexual. The sepals and petals usually number three each and may be distinct or joined at the base. The stamens generally number six, with filaments that may be separate, attached to each other, or attached to the pistil at the base. The fruit is usually a single-seeded drupe (sometimes berry-like) but some genera (e.g., Salacca) may contain two or more seeds in each fruit.
Like all monocots, palms do not have the ability to increase the width of a stem (secondary growth) via the same kind of vascular cambium found in non-monocot woody plants. This explains the cylindrical shape of the trunk (almost constant diameter) that is often seen in palms, unlike in ring-forming trees. However, many palms, like some other monocots, do have secondary growth, although because it does not arise from a single vascular cambium producing xylem inwards and phloem outwards, it is often called "anomalous secondary growth". | Arecaceae | Wikipedia | 505 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
The Arecaceae are notable among monocots for their height and for the size of their seeds, leaves, and inflorescences. Ceroxylon quindiuense, Colombia's national "tree", is the tallest monocot in the world, reaching up to tall. The coco de mer (Lodoicea maldivica) has the largest seeds of any plant, in diameter and weighing each (coconuts are the second largest). Raffia palms (Raphia spp.) have the largest leaves of any plant, up to long and wide. The Corypha species have the largest inflorescence of any plant, up to tall and containing millions of small flowers. Calamus stems can reach in length.
Range and habitat
Most palms are native to tropical and subtropical climates. Palms thrive in moist and hot climates but can be found in a variety of different habitats. Their diversity is highest in wet, lowland forests. South America, the Caribbean, and areas of the South Pacific and southern Asia are regions of concentration. Colombia may have the highest number of palm species in one country. There are some palms that are also native to desert areas such as the Arabian Peninsula and parts of northwestern Mexico. Only about 130 palm species naturally grow entirely beyond the tropics, mostly in humid lowland subtropical climates, in highlands in southern Asia, and along the rim lands of the Mediterranean Sea. The northernmost native palm is Chamaerops humilis, which reaches 44°N latitude along the coast of Liguria, Italy. In the southern hemisphere, the southernmost palm is the Rhopalostylis sapida, which reaches 44°S on the Chatham Islands where an oceanic climate prevails. Cultivation of palms is possible north of subtropical climates, and some higher latitude locales such as Ireland, Scotland, England, and the Pacific Northwest feature a few palms in protected locations and microclimates. In the United States, there are at least 12 native palm species, mostly occurring in the states of the Deep South and Florida. | Arecaceae | Wikipedia | 415 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Palms inhabit a variety of ecosystems. More than two-thirds of palm species live in humid moist forests, where some species grow tall enough to form part of the canopy and shorter ones form part of the understory. Some species form pure stands in areas with poor drainage or regular flooding, including Raphia hookeri which is common in coastal freshwater swamps in West Africa. Other palms live in tropical mountain habitats above , such as those in the genus Ceroxylon native to the Andes. Palms may also live in grasslands and scrublands, usually associated with a water source, and in desert oases such as the date palm. A few palms are adapted to extremely basic lime soils, while others are similarly adapted to extreme potassium deficiency and toxicity of heavy metals in serpentine soils.
Taxonomy
Palms are a monophyletic group of plants, meaning the group consists of a common ancestor and all its descendants. Extensive taxonomic research on palms began with botanist H.E. Moore, who organized palms into 15 major groups based mostly on general morphological characteristics. The following classification, proposed by N.W. Uhl and J. Dransfield in 1987, is a revision of Moore's classification that organizes palms into 6 subfamilies. A few general traits of each subfamily are listed below.
Subfamily are the largest subfamily with 14 tribes and containing over 100 genera. All tribes have pinnate or bipinnate leaves and flowers arranged in groups of three, with a central pistillate and two staminate flowers.
Subfamily includes the climbing palms, such as rattans. The leaves are usually pinnate; derived characters (synapomorphies) include spines on various organs, organs specialized for climbing, an extension of the main stem of the leaf-bearing reflexed spines, and overlapping scales covering the fruit and ovary.
Subfamily has small to medium-sized flowers, spirally arranged, with a gynoecium of three joined carpels.
Subfamily are the second-largest subfamily with 8 tribes. Most palms in this subfamily have palmately lobed leaves and solitary flowers with three, or sometimes four carpels. The fruit normally develops from only one carpel.
Subfamily contains only one species, Nypa fruticans, which has large, pinnate leaves. The fruit is unusual in that it floats, and the stem is underground and dichotomously branched, also unusual in palms. | Arecaceae | Wikipedia | 488 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
The is the sixth subfamily of Arecaceae in N.W. Uhl and J. Dransfield's 1987 classification. Members of this group have distinct monopodial flower clusters. Other distinct features include a gynoecium with five to 10 joined carpels, and flowers with more than three parts per whorl. Fruits are multiple-seeded and have multiple parts. From the modern phylogenomic data, the Phytelephantoideae are tribe in the Ceroxyloideae subfamily.
Currently, few extensive phylogenetic studies of the Arecaceae exist. In 1997, Baker et al. explored subfamily and tribe relationships using chloroplast DNA from 60 genera from all subfamilies and tribes. The results strongly showed the Calamoideae are monophyletic, and Ceroxyloideae and Coryphoideae are paraphyletic. The relationships of Arecoideae are uncertain, but they are possibly related to the Ceroxyloideae and Phytelephantoideae. Studies have suggested the lack of a fully resolved hypothesis for the relationships within the family is due to a variety of factors, including difficulties in selecting appropriate outgroups, homoplasy in morphological character states, slow rates of molecular evolution important for the use of standard DNA markers, and character polarization. However, hybridization has been observed among Orbignya and Phoenix species, and using chloroplast DNA in cladistic studies may produce inaccurate results due to maternal inheritance of the chloroplast DNA. Chemical and molecular data from non-organelle DNA, for example, could be more effective for studying palm phylogeny.
Recently, nuclear genomes and transcriptomes have been used to reconstruct the phylogeny of palms. This has revealed, for example, that a whole-genome duplication event occurred early in the evolution of the Arecaceae lineage, that was not experienced by its sister clade, the Dasypogonaceae.
For a phylogenetic tree of the family, see the list of Arecaceae genera.
Selected genera | Arecaceae | Wikipedia | 435 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Archontophoenix—Bangalow palm
Areca—Betel palm
Astrocaryum
Attalea
Bactris—Pupunha
Beccariophoenix—Beccariophoenix alfredii
Bismarckia—Bismarck palm
Borassus—Palmyra palm, sugar palm, toddy palm
Butia
Calamus—Rattan palm
Ceroxylon
Cocos—Coconut
Coccothrinax
Copernicia—Carnauba wax palm
Corypha—Gebang palm, Buri palm or Talipot palm
Elaeis—Oil palm
Euterpe—Cabbage heart palm, açaí palm
Hyphaene—Doum palm
Jubaea—Chilean wine palm, Coquito palm
Latania—Latan palm
Licuala
Livistona—Cabbage palm
Mauritia—Moriche palm
Metroxylon—Sago palm
Nypa—Nipa palm
Parajubaea—Bolivian coconut palms
Phoenix—Date palm
Pritchardia
Raphia—Raffia palm
Rhapidophyllum
Rhapis
Roystonea—Royal palm
Sabal—Palmettos
Salacca—Salak
Syagrus—Queen palm
Thrinax
Trachycarpus—Windmill palm, Kumaon palm
Trithrinax
Veitchia—Manila palm, Joannis palm
Washingtonia—Fan palm
Evolution
The Arecaceae were the first modern family of monocots to appear in the fossil record around 80 million years ago (Mya), during the late Cretaceous period. The first modern species, such as Nypa fruticans and Acrocomia aculeata, appeared 69 Mya, as evidenced by fossil Nypa pollen. Palms appear to have undergone an early period of adaptive radiation. By 60 Mya, many of the modern, specialized genera of palms appeared and became widespread and common, much more widespread than their range today. Because palms separated from the monocots earlier than other families, they developed more intrafamilial specialization and diversity. By tracing back these diverse characteristics of palms to the basic structures of monocots, palms may be valuable in studying monocot evolution. Several species of palms have been identified from flowers preserved in amber, including Palaeoraphe dominicana and Roystonea palaea. Fossil evidence of them can also be found in samples of petrified palmwood.
The relationship between the subfamilies is shown in the following cladogram:
Uses | Arecaceae | Wikipedia | 497 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Evidence for cultivation of the date palm by Mesopotamians and other Middle Eastern peoples exists from more than 5,000 years ago, in the form of date wood, pits for storing dates, and other remains of the date palm in Mesopotamian sites. The date palm had a significant effect on the history of the Middle East and North Africa. In the text "Date Palm Products" (1993), W.H. Barreveld wrote:
An indication of the importance of palms in ancient times is that they are mentioned more than 30 times in the Bible, and at least 22 times in the Quran. The Torah also references the "70 date palm trees", which symbolize the 70 aspects of Torah that are revealed to those who "eat of its fruit."
Arecaceae have great economic importance, including coconut products, oils, dates, palm syrup, ivory nuts, carnauba wax, rattan cane, raffia, and palm wood. This family supplies a large amount of the human diet and several other human uses, both by absolute amount produced and by number of species domesticated. This is far higher than almost any other plant family, sixth out of domesticated crops in the human diet, and first in total economic value produced sharing the top spot with the Poaceae and Fabaceae. These human uses have also spread many Arecaceae species around the world. | Arecaceae | Wikipedia | 277 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Along with dates mentioned above, members of the palm family with human uses are numerous:
The type member of Arecaceae is the areca palm (Areca catechu), the fruit of which, the areca nut, is chewed with the betel leaf for intoxicating effects.
Carnauba wax is harvested from the leaves of South American palms of the genus Copernicia.
Rattans, whose stems are used extensively in furniture and baskets, are in the genus Calamus.
Palm oil is an edible vegetable oil produced by the oil palms in the genus Elaeis.
Several species are harvested for heart of palm, a vegetable eaten in salads.
Sap of the nipa palm, Nypa fruticans, is used to make vinegar.
Palm sap is sometimes fermented to produce palm wine or toddy, an alcoholic beverage common in parts of Africa, India, and the Philippines. The sap may be drunk fresh, but fermentation is rapid, reaching up to 4% alcohol content within an hour, and turning vinegary in a day.
Palmyra and date palm sap is harvested in Bengal, India, to process into gur and jaggery.
Coconut is the partially edible seed of the fruit of the coconut palm (Cocos nucifera).
Coir is a coarse, water-resistant fiber extracted from the outer shell of coconuts, used in doormats, brushes, mattresses, and ropes.
Some indigenous groups living in palm-rich areas use palms to make many of their necessary items and food. Sago, for example, a starch made from the pith of the trunk of the sago palm Metroxylon sagu, is a major staple food for lowland peoples of New Guinea and the Moluccas.
Palm wine is made from Jubaea also called Chilean wine palm, or coquito palm.
Recently, the fruit of the açaí palm Euterpe has been used for its reputed health benefits.
Saw palmetto (Serenoa repens) is being investigated as a drug for treating enlarged prostates.
Palm leaves are also valuable to some peoples as a material for thatching, basketry, clothing, and in religious ceremonies (see "Symbolism" below). | Arecaceae | Wikipedia | 457 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Ornamental uses: Today, palms are valuable as ornamental plants and are often grown along streets in tropical and subtropical cities. Chamaedorea elegans is a popular houseplant and is grown indoors for its low maintenance. Farther north, palms are a common feature in botanical gardens or as indoor plants. Few palms tolerate severe cold and the majority of the species are tropical or subtropical. The three most cold-tolerant species are Trachycarpus fortunei, native to eastern Asia, and Rhapidophyllum hystrix and Sabal minor, both native to the southeastern United States.
The southeastern U.S. state of South Carolina is nicknamed the Palmetto State after the sabal palmetto (cabbage palmetto), logs from which were used to build the fort at Fort Moultrie. During the American Revolutionary War, they were invaluable to those defending the fort, because their spongy wood absorbed or deflected the British cannonballs.
Singaporean politician Tan Cheng Bock uses a palm tree-like symbol similar to a Ravenala to represent him in the 2011 Singaporean presidential election. The symbol of a party he founded, Progress Singapore Party, was also based on a palm tree.
On Ash Wednesday, Catholics receive a cross on their forehead made of palm ashes as a reminder of the Catholic belief that everyone and everything eventually returns to where it came from, commonly expressed by the saying "ashes to ashes and dust to dust."
Lately the Fujairah Research Centre reported the use of date palm leaves to help restore coral reefs as it merged ancient Emerati techniques with modern science. | Arecaceae | Wikipedia | 328 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Endangered species
Like many other plants, palms have been threatened by human intervention and exploitation. The greatest risk to palms is destruction of habitat, especially in the tropical forests, due to urbanization, wood-chipping, mining, and conversion to farmland. Palms rarely reproduce after such great changes in the habitat, and those with small habitat ranges are most vulnerable to them. The harvesting of heart of palm, a delicacy in salads, also poses a threat because it is derived from the palm's apical meristem, a vital part of the palm that cannot be regrown (except in domesticated varieties, e.g. of peach palm). The use of rattan palms in furniture has caused a major population decrease in these species that has negatively affected local and international markets, as well as biodiversity in the area. The sale of seeds to nurseries and collectors is another threat, as the seeds of popular palms are sometimes harvested directly from the wild. In 2006, at least 100 palm species were considered endangered, and nine species have been reported as recently extinct.
However, several factors make palm conservation more difficult. Palms live in almost every type of warm habitat and have tremendous morphological diversity. Most palm seeds lose viability quickly, and they cannot be preserved in low temperatures because the cold kills the embryo. Using botanical gardens for conservation also presents problems, since they can rarely house more than a few plants of any species or truly imitate the natural setting. There is also the risk that cross-pollination can lead to hybrid species.
The Palm Specialist Group of the World Conservation Union (IUCN) began in 1984, and has performed a series of three studies to find basic information on the status of palms in the wild, use of wild palms, and palms under cultivation. Two projects on palm conservation and use supported by the World Wildlife Fund took place from 1985 to 1990 and 1986–1991, in the American tropics and southeast Asia, respectively. Both studies produced copious new data and publications on palms. Preparation of a global action plan for palm conservation began in 1991, supported by the IUCN, and was published in 1996.
The rarest palm known is Hyophorbe amaricaulis. The only living individual remains at the Botanic Gardens of Curepipe in Mauritius.
Arthropod pests
Some pests are specialists to particular taxa. Pests that attack a variety of species of palms include: | Arecaceae | Wikipedia | 488 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Raoiella indica, the red palm mite
Caryobruchus gleditsiae, the palm seed beetle or palm seed weevil
Rhynchophorus ferrugineus, the red palm weevil, recently introduced to Europe
Symbolism
The palm branch was a symbol of triumph and victory in classical antiquity. The Romans rewarded champions of the games and celebrated military successes with palm branches. Early Christians used the palm branch to symbolize the victory of the faithful over enemies of the soul, as in the Palm Sunday festival celebrating the triumphal entry of Jesus Christ into Jerusalem. In Judaism, the palm represents peace and plenty, and is one of the Four Species of Sukkot; the palm may also symbolize the Tree of Life in Kabbalah.
The canopies of the Rathayatra carts which carry the deities of Krishna and his family members in the cart festival of Jagganath Puri in India are marked with the emblem of a palm tree. Specifically it is the symbol of Krishna's brother, Baladeva.
In 1840, the American geologist Edward Hitchcock (1793–1864) published the first tree-like paleontology chart in his Elementary Geology, with two separate trees of life for the plants and the animals. These are crowned (graphically) with the Palms and with Man.
Today, the palm, especially the coconut palm, remains a symbol of the tropical island paradise.
Palms appear on the flags and seals of several places where they are native, including those of Haiti, Guam, Saudi Arabia, Florida, and South Carolina.
Other plants
Some species commonly called palms, though they are not true palms, include: | Arecaceae | Wikipedia | 334 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Ailanthus altissima (Ghetto palm), a tree in the flowering plant family Simaroubaceae
Alocasia odora x gageana 'Calidora' (Persian palm), a flowering plant in the family Araceae
Aloe thraskii (Palm aloe), a flowering plant in the family Asphodelaceae
Amorphophallus konjac (Snake palm), a flowering plant in the family Araceae
Beaucarnea recurvata (Ponytail palm), a flowering plant in the family Asparagaceae
Begonia luxurians (Palm leaf begonia), a flowering plant in the family Begoniaceae
Biophytum umbraculum (South Pacific palm), a flowering plant in the family Oxalidaceae
Blechnum appendiculatum (Palm fern), a fern in the family Aspleniaceae
Brassica oleracea 'Lacinato kale' (Black Tuscan palm), a flowering plant in the family Brassicaceae
Brighamia insignis (Vulcan palm), a flowering plant in the family Campanulaceae
Carludovica palmata (Panama hat palm) and perhaps other members in the family Cyclanthaceae.
Cordyline australis (Cabbage palm, Torbay palm, ti palm) or palm lily (family Asparagaceae) and other representatives in the genus Cordyline.
Cyathea cunninghamii (Palm fern) and other tree ferns (families Cyatheaceae and Dicksoniaceae) that may be confused with palms.
Cycas revoluta (Sago palm) and the rest of the order Cycadales.
Cyperus alternifolius (Umbrella palm), a sedge in the family Cyperaceae
Dasylirion longissimum (Grass palm), a flowering plant in the family Asparagaceae and other plants in the genus Dasylirion
Dioon spinulosum (Gum palm), a cycad in the family Zamiaceae
Dracaena marginata (Dragon palm) a flowering plant in the family Asparagaceae
Eisenia arborea (Southern sea palm), a species of brown alga in the family Lessoniaceae
Fatsia japonica (Figleaf palm), a flowering plant in the family Araliaceae
Hypnodendron comosum (Palm tree moss or palm moss), a moss in the family Hypnodendraceae | Arecaceae | Wikipedia | 503 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Musa species (Banana palm), a flowering plant in the family Musaceae
Pachypodium lamerei (Madagascar palm), a flowering plant in the family Apocynaceae
Pandanus spiralis (Screw palm), a flowering plant in the family Pandanaceae and perhaps other Pandanus spp.
Ravenala (Traveller's palm), a flowering plant in the family Strelitziaceae
Setaria palmifolia (Palm grass), a grass in the family Poaceae
Yucca brevifolia (Yucca palm or palm tree yucca)
Yucca filamentosa (Needle palm) and Yucca filifera (St. Peter's palm), flowering plants in the family Asparagaceae
Zamia furfuracea (Cardboard palm), a cycad in the family Zamiaceae
Zamioculcas zamiifolia (Emerald palm or aroid palm), a flowering plant in the family Araceae | Arecaceae | Wikipedia | 193 | 45715 | https://en.wikipedia.org/wiki/Arecaceae | Biology and health sciences | Monocots | null |
Panthera is a genus within the family Felidae, and one of two extant genera in the subfamily Pantherinae. It contains the largest living members of the cat family. There are five living species: the jaguar, leopard, lion, snow leopard and tiger. Numerous extinct species are also named, including the cave lion and American lion.
Etymology
The word panther derives from classical Latin panthēra, itself from the ancient Greek pánthēr (πάνθηρ).
Characteristics
In Panthera species, the dorsal profile of the skull is flattish or evenly convex. The frontal interorbital area is not noticeably elevated, and the area behind the elevation is less steeply sloped. The basic cranial axis is nearly horizontal. The inner chamber of the bullae is large, the outer small. The partition between them is close to the external auditory meatus. The convexly rounded chin is sloping.
All Panthera species have an incompletely ossified hyoid bone and a specially adapted larynx with large vocal folds covered in a fibro-elastic pad; these characteristics enable them to roar. Only the snow leopard cannot roar, as it has shorter vocal folds of that provide a lower resistance to airflow; it was therefore proposed to be retained in the genus Uncia.
Panthera species can prusten, which is a short, soft, snorting sound; it is used during contact between friendly individuals. The roar is an especially loud call with a distinctive pattern that depends on the species. | Panthera | Wikipedia | 304 | 45729 | https://en.wikipedia.org/wiki/Panthera | Biology and health sciences | Felines | Animals |
Evolution
The geographic origin of the genus Panthera is uncertain, though the earliest known definitive species Panthera principialis is from Tanzania. P. blytheae from northern Central Asia, originally described as the oldest known Panthera species, is suggested to be similar in skull features to the snow leopard, but subsequent studies have since agreed that it is not a member of or a related species of the snow leopard lineage and that it belongs to a different genus Palaeopanthera. The tiger, snow leopard, and clouded leopard genetic lineages likely dispersed in Southeast Asia during the Late Miocene.
Genetic studies indicate that the pantherine cats diverged from the subfamily Felinae between six and ten million years ago.
The genus Neofelis is sister to Panthera.
The clouded leopard appears to have diverged about . Panthera diverged from other cat species about and then evolved into the species tiger about , snow leopard about and leopard about . Mitochondrial sequence data from fossils suggest that the American lion (P. atrox) is a sister lineage to Panthera spelaea (the Eurasian cave or steppe lion) that diverged about , and that both P. atrox and P. spelaea are most closely related to lions among living Panthera species. The snow leopard is nested within Panthera and is the sister species of the tiger.
Results of a 2016 study based on analysis of biparental nuclear genomes suggest the following relationships of living Panthera species:
The extinct species Panthera gombaszoegensis, was probably closely related to the modern jaguar. The first fossil remains were excavated in Olivola, in Italy, and date to .
Fossil remains found in South Africa that appear to belong within the Panthera lineage date to about . | Panthera | Wikipedia | 359 | 45729 | https://en.wikipedia.org/wiki/Panthera | Biology and health sciences | Felines | Animals |
Classification
Panthera was named and described by Lorenz Oken in 1816 who placed all the spotted cats in this group. During the 19th and 20th centuries, various explorers and staff of natural history museums suggested numerous subspecies, or at times called "races", for all Panthera species. The taxonomist Reginald Innes Pocock reviewed skins and skulls in the zoological collection of the Natural History Museum, London, and grouped subspecies described, thus shortening the lists considerably. Reginald Innes Pocock revised the classification of this genus in 1916 as comprising the tiger (P. tigris), lion (P. leo), jaguar (P. onca), and leopard (P. pardus) on the basis of common features of their skulls. Since the mid-1980s, several Panthera species became subjects of genetic research, mostly using blood samples of captive individuals. Study results indicate that many of the lion and leopard subspecies are questionable because of insufficient genetic distinction between them. Subsequently, it was proposed to group all African leopard populations to P. p. pardus and retain eight subspecific names for Asian leopard populations. Results of genetic analysis indicate that the snow leopard (formerly Uncia uncia) also belongs to the genus Panthera (P. uncia), a classification that was accepted by IUCN Red List assessors in 2008.
Based on genetic research, it was suggested to group all living sub-Saharan lion populations into P. l. leo.
Results of phylogeographic studies indicate that the Western and Central African lion populations are more closely related to those in India and form a different clade than lion populations in Southern and East Africa; southeastern Ethiopia is an admixture region between North African and East African lion populations.
Black panthers do not form a distinct species, but are melanistic specimens of the genus, most often encountered in the leopard and jaguar.
Contemporary species
The following list of the genus Panthera is based on the taxonomic assessment in Mammal Species of the World and reflects the taxonomy revised in 2017 by the Cat Classification Task Force of the Cat Specialist Group:
Extinct species and subspecies
Other, now invalid, species have also been described, such as Panthera crassidens from South Africa, which was later found to be based on a mixture of leopard and cheetah fossils.
Phylogeny
In 2018, results of a phylogenetic study on living and fossil cats were published. This study was based on the morphological diversity of the mandibles of saber-toothed cats, their speciation and extinction rates. | Panthera | Wikipedia | 512 | 45729 | https://en.wikipedia.org/wiki/Panthera | Biology and health sciences | Felines | Animals |
The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. The color has also led to the nicknames brass, brazzle, and brazil, primarily used to refer to pyrite found in coal.
The name pyrite is derived from the Greek (), 'stone or mineral which strikes fire', in turn from (), 'fire'. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what is now called pyrite.
By Georgius Agricola's time, , the term had become a generic term for all of the sulfide minerals.
Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has also been identified in the sclerites of scaly-foot gastropods. Despite being nicknamed "fool's gold", pyrite is sometimes found in association with small quantities of gold. A substantial proportion of the gold is "invisible gold" incorporated into the pyrite (see Carlin-type gold deposit). It has been suggested that the presence of both gold and arsenic is a case of coupled substitution but as of 1997 the chemical state of the gold remained controversial.
Uses
Pyrite gained a brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun.
Pyrite is used with flintstone and a form of tinder made of stringybark by the Kaurna people of South Australia, as a traditional method of starting fires. | Pyrite | Wikipedia | 456 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
Pyrite has been used since classical times to manufacture copperas (ferrous sulfate). Iron pyrite was heaped up and allowed to weather (an example of an early form of heap leaching). The acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of sulfuric acid. By the 19th century, it had become the dominant method.
Pyrite remains in commercial use for the production of sulfur dioxide, for use in such applications as the paper industry, and in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS (iron(II) sulfide) and elemental sulfur starts at ; at around , pS2 is about .
A newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium metal batteries (Energizer Ultimate Lithium™) .
Pyrite is a semiconductor material with a band gap of 0.95 eV. Pure pyrite is naturally n-type, in both crystal and thin-film forms, potentially due to sulfur vacancies in the pyrite crystal structure acting as n-dopants.
During the early years of the 20th century, pyrite was used as a mineral detector in radio receivers, and is still used by crystal radio hobbyists. Until the vacuum tube matured, the crystal detector was the most sensitive and dependable detector available—with considerable variation between mineral types and even individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector.
Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost photovoltaic solar panels. Synthetic iron sulfide was used with copper sulfide to create the photovoltaic material. More recent efforts are working toward thin-film solar cells made entirely of pyrite. | Pyrite | Wikipedia | 437 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
Pyrite is used to make marcasite jewelry. Marcasite jewelry, using small faceted pieces of pyrite, often set in silver, has been made since ancient times and was popular in the Victorian era. At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, and not to the orthorhombic FeS2 mineral marcasite which is lighter in color, brittle and chemically unstable, and thus not suitable for jewelry making. Marcasite jewelry does not actually contain the mineral marcasite. The specimens of pyrite, when it appears as good quality crystals, are used in decoration. They are also very popular in mineral collecting. Among the sites that provide the best specimens are Soria and La Rioja provinces (Spain).
In value terms, China ($47 million) constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. China is also the fastest growing in terms of the unroasted iron pyrites imports, with a CAGR of +27.8% from 2007 to 2016.
Research
In July 2020 scientists reported that they have observed a voltage-induced transformation of normally diamagnetic pyrite into a ferromagnetic material, which may lead to applications in devices such as solar cells or magnetic data storage.
Researchers at Trinity College Dublin, Ireland have demonstrated that FeS2 can be exfoliated into few-layers just like other two-dimensional layered materials such as graphene by a simple liquid-phase exfoliation route. This is the first study to demonstrate the production of non-layered 2D-platelets from 3D bulk FeS2. Furthermore, they have used these 2D-platelets with 20% single walled carbon-nanotube as an anode material in lithium-ion batteries, reaching a capacity of 1000 mAh/g close to the theoretical capacity of FeS2.
In 2021, a natural pyrite stone has been crushed and pre-treated followed by liquid-phase exfoliation into two-dimensional nanosheets, which has shown capacities of 1200 mAh/g as an anode in lithium-ion batteries.
Formal oxidation states for pyrite, marcasite, molybdenite and arsenopyrite | Pyrite | Wikipedia | 485 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite and marcasite are probably best described as Fe2+[S2]2−. This formalism recognizes that the sulfur atoms in pyrite occur in pairs with clear S–S bonds. These persulfide [–S–S–] units can be viewed as derived from hydrogen disulfide, H2S2. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast, molybdenite, MoS2, features isolated sulfide S2− centers and the oxidation state of molybdenum is Mo4+. The mineral arsenopyrite has the formula FeAsS. Whereas pyrite has [S2]2– units, arsenopyrite has [AsS]3– units, formally derived from deprotonation of arsenothiol (H2AsSH). Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+[AsS]3−.
Crystallography
Iron-pyrite FeS2 represents the prototype compound of the crystallographic pyrite structure. The structure is cubic and was among the first crystal structures solved by X-ray diffraction. It belongs to the crystallographic space group Pa and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant of stoichiometric iron pyrite FeS2 amounts to . The unit cell is composed of a Fe face-centered cubic sublattice into which the ions are embedded. (Note though that the iron atoms in the faces are not equivalent by translation alone to the iron atoms at the corners.) The pyrite structure is also seen in other MX2 compounds of transition metals M and chalcogens X = O, S, Se and Te. Certain dipnictides with X standing for P, As and Sb etc. are also known to adopt the pyrite structure.
The Fe atoms are bonded to six S atoms, giving a distorted octahedron. The material is a semiconductor. The Fe ions are usually considered to be low spin divalent state (as shown by Mössbauer spectroscopy as well as XPS). The material as a whole behaves as a Van Vleck paramagnet, despite its low-spin divalency. | Pyrite | Wikipedia | 507 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
The sulfur centers occur in pairs, described as S22−. Reduction of pyrite with potassium gives potassium dithioferrate, KFeS2. This material features ferric ions and isolated sulfide (S2-) centers.
The S atoms are tetrahedral, being bonded to three Fe centers and one other S atom. The site symmetry at Fe and S positions is accounted for by point symmetry groups C3i and C3, respectively. The missing center of inversion at S lattice sites has important consequences for the crystallographic and physical properties of iron pyrite. These consequences derive from the crystal electric field active at the sulfur lattice site, which causes a polarization of S ions in the pyrite lattice. The polarisation can be calculated on the basis of higher-order Madelung constants and has to be included in the calculation of the lattice energy by using a generalised Born–Haber cycle. This reflects the fact that the covalent bond in the sulfur pair is inadequately accounted for by a strictly ionic treatment.
Arsenopyrite has a related structure with heteroatomic As–S pairs rather than S-S pairs. Marcasite also possesses homoatomic anion pairs, but the arrangement of the metal and diatomic anions differs from that of pyrite. Despite its name, chalcopyrite () does not contain dianion pairs, but single S2− sulfide anions.
Crystal habit
Pyrite usually forms cuboid crystals, sometimes forming in close association to form raspberry-shaped masses called framboids. However, under certain circumstances, it can form anastomosing filaments or T-shaped crystals.
Pyrite can also form shapes almost the same as a regular dodecahedron, known as pyritohedra, and this suggests an explanation for the artificial geometrical models found in Europe as early as the 5th century BC.
Varieties
Cattierite (CoS2), vaesite (NiS2) and hauerite (MnS2), as well as sperrylite (PtAs2) are similar in their structure and belong also to the pyrite group.
is a nickel-cobalt bearing variety of pyrite, with > 50% substitution of Ni2+ for Fe2+ within pyrite. Bravoite is not a formally recognised mineral, and is named after the Peruvian scientist Jose J. Bravo (1874–1928). | Pyrite | Wikipedia | 508 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
Distinguishing similar minerals
Pyrite is distinguishable from native gold by its hardness, brittleness and crystal form. Pyrite fractures are very uneven, sometimes conchoidal because it does not cleave along a preferential plane. Native gold nuggets, or glitters, do not break but deform in a ductile way. Pyrite is brittle, gold is malleable.
Natural gold tends to be anhedral (irregularly shaped without well defined faces), whereas pyrite comes as either cubes or multifaceted crystals with well developed and sharp faces easy to recognise. Well crystallised pyrite crystals are euhedral (i.e., with nice faces). Pyrite can often be distinguished by the striations which, in many cases, can be seen on its surface. Chalcopyrite () is brighter yellow with a greenish hue when wet and is softer (3.5–4 on Mohs' scale). Arsenopyrite (FeAsS) is silver white and does not become more yellow when wet.
Hazards
Iron pyrite is unstable when exposed to the oxidizing conditions prevailing at the Earth's surface: iron pyrite in contact with atmospheric oxygen and water, or damp, ultimately decomposes into iron oxyhydroxides (ferrihydrite, FeO(OH)) and sulfuric acid (). This process is accelerated by the action of Acidithiobacillus bacteria which oxidize pyrite to first produce ferrous ions (), sulfate ions (), and release protons (, or ). In a second step, the ferrous ions () are oxidized by into ferric ions () which hydrolyze also releasing ions and producing FeO(OH). These oxidation reactions occur more rapidly when pyrite is finely dispersed (framboidal crystals initially formed by sulfate reducing bacteria (SRB) in argillaceous sediments or dust from mining operations).
Pyrite oxidation and acid mine drainage
Pyrite oxidation by atmospheric in the presence of moisture () initially produces ferrous ions () and sulfuric acid which dissociates into sulfate ions and protons, leading to acid mine drainage (AMD). An example of acid rock drainage caused by pyrite is the 2015 Gold King Mine waste water spill. | Pyrite | Wikipedia | 492 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
2FeS2{\scriptstyle (s)} + 7O2{\scriptstyle (g)} + 2H2O{\scriptstyle (l)} -> 2Fe^{2+}{\scriptstyle (aq)} + 4SO4^{2-}{\scriptstyle (aq)} + 4H+{\scriptstyle (aq)}.
Dust explosions
Pyrite oxidation is sufficiently exothermic that underground coal mines in high-sulfur coal seams have occasionally had serious problems with spontaneous combustion. The solution is the use of buffer blasting and the use of various sealing or cladding agents to hermetically seal the mined-out areas to exclude oxygen.
In modern coal mines, limestone dust is sprayed onto the exposed coal surfaces to reduce the hazard of dust explosions. This has the secondary benefit of neutralizing the acid released by pyrite oxidation and therefore slowing the oxidation cycle described above, thus reducing the likelihood of spontaneous combustion. In the long term, however, oxidation continues, and the hydrated sulfates formed may exert crystallization pressure that can expand cracks in the rock and lead eventually to roof fall.
Weakened building materials
Building stone containing pyrite tends to stain brown as pyrite oxidizes. This problem appears to be significantly worse if any marcasite is present. The presence of pyrite in the aggregate used to make concrete can lead to severe deterioration as pyrite oxidizes. In early 2009, problems with Chinese drywall imported into the United States after Hurricane Katrina were attributed to pyrite oxidation, followed by microbial sulfate reduction which released hydrogen sulfide gas (). These problems included a foul odor and corrosion of copper wiring. In the United States, in Canada, and more recently in Ireland, where it was used as underfloor infill, pyrite contamination has caused major structural damage. Concrete exposed to sulfate ions, or sulfuric acid, degrades by sulfate attack: the formation of expansive mineral phases, such as ettringite (small needle crystals exerting a huge crystallization pressure inside the concrete pores) and gypsum creates inner tensile forces in the concrete matrix which destroy the hardened cement paste, form cracks and fissures in concrete, and can lead to the ultimate ruin of the structure. Normalized tests for construction aggregate certify such materials as free of pyrite or marcasite. | Pyrite | Wikipedia | 504 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
Occurrence
Pyrite is the most common of sulfide minerals and is widespread in igneous, metamorphic, and sedimentary rocks. It is a common accessory mineral in igneous rocks, where it also occasionally occurs as larger masses arising from an immiscible sulfide phase in the original magma. It is found in metamorphic rocks as a product of contact metamorphism. It also forms as a high-temperature hydrothermal mineral, though it occasionally forms at lower temperatures.
Pyrite occurs both as a primary mineral, present in the original sediments, and as a secondary mineral, deposited during diagenesis. Pyrite and marcasite commonly occur as replacement pseudomorphs after fossils in black shale and other sedimentary rocks formed under reducing environmental conditions. Pyrite is common as an accessory mineral in shale, where it is formed by precipitation from anoxic seawater, and coal beds often contain significant pyrite.
Notable deposits are found as lenticular masses in Virginia, U.S., and in smaller quantities in many other locations. Large deposits are mined at Rio Tinto in Spain and elsewhere in the Iberian Peninsula.
Cultural beliefs
In the beliefs of the Thai people (especially those in the south), pyrite is known as Khao tok Phra Ruang, Khao khon bat Phra Ruang (ข้าวตอกพระร่วง, ข้าวก้นบาตรพระร่วง) or Phet na tang, Hin na tang (เพชรหน้าทั่ง, หินหน้าทั่ง). It is believed to be a sacred item that has the power to prevent evil, black magic or demons.
Images | Pyrite | Wikipedia | 315 | 45756 | https://en.wikipedia.org/wiki/Pyrite | Physical sciences | Minerals | Earth science |
Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from (bios), life, and μίμησις (mīmēsis), imitation, from μιμεῖσθαι (mīmeisthai), to imitate, from μῖμος (mimos), actor. A closely related field is bionics.
Nature has gone through evolution over the 3.8 billion years since life is estimated to have appeared on the Earth. It has evolved species with high performance using commonly found materials. Surfaces of solids interact with other surfaces and the environment and derive the properties of materials. Biological materials are highly organized from the molecular to the nano-, micro-, and macroscales, often in a hierarchical manner with intricate nanoarchitecture that ultimately makes up a myriad of different functional elements. Properties of materials and surfaces result from a complex interplay between surface structure and morphology and physical and chemical properties. Many materials, surfaces, and objects in general provide multifunctionality.
Various materials, structures, and devices have been fabricated for commercial interest by engineers, material scientists, chemists, and biologists, and for beauty, structure, and design by artists and architects. Nature has solved engineering problems such as self-healing abilities, environmental exposure tolerance and resistance, hydrophobicity, self-assembly, and harnessing solar energy. Economic impact of bioinspired materials and surfaces is significant, on the order of several hundred billion dollars per year worldwide.
History
One of the early examples of biomimicry was the study of birds to enable human flight. Although never successful in creating a "flying machine", Leonardo da Vinci (1452–1519) was a keen observer of the anatomy and flight of birds, and made numerous notes and sketches on his observations as well as sketches of "flying machines". The Wright Brothers, who succeeded in flying the first heavier-than-air aircraft in 1903, allegedly derived inspiration from observations of pigeons in flight. | Biomimetics | Wikipedia | 445 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
During the 1950s the American biophysicist and polymath Otto Schmitt developed the concept of "biomimetics". During his doctoral research he developed the Schmitt trigger by studying the nerves in squid, attempting to engineer a device that replicated the biological system of nerve propagation. He continued to focus on devices that mimic natural systems and by 1957 he had perceived a converse to the standard view of biophysics at that time, a view he would come to call biomimetics.
In 1960 Jack E. Steele coined a similar term, bionics, at Wright-Patterson Air Force Base in Dayton, Ohio, where Otto Schmitt also worked. Steele defined bionics as "the science of systems which have some function copied from nature, or which represent characteristics of natural systems or their analogues". During a later meeting in 1963 Schmitt stated,
In 1969, Schmitt used the term "biomimetic" in the title one of his papers, and by 1974 it had found its way into Webster's Dictionary. Bionics entered the same dictionary earlier in 1960 as "a science concerned with the application of data about the functioning of biological systems to the solution of engineering problems". Bionic took on a different connotation when Martin Caidin referenced Jack Steele and his work in the novel Cyborg which later resulted in the 1974 television series The Six Million Dollar Man and its spin-offs. The term bionic then became associated with "the use of electronically operated artificial body parts" and "having ordinary human powers increased by or as if by the aid of such devices". Because the term bionic took on the implication of supernatural strength, the scientific community in English speaking countries largely abandoned it.
The term biomimicry appeared as early as 1982. Biomimicry was popularized by scientist and author Janine Benyus in her 1997 book Biomimicry: Innovation Inspired by Nature. Biomimicry is defined in the book as a "new science that studies nature's models and then imitates or takes inspiration from these designs and processes to solve human problems". Benyus suggests looking to Nature as a "Model, Measure, and Mentor" and emphasizes sustainability as an objective of biomimicry. | Biomimetics | Wikipedia | 464 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
One of the latest examples of biomimicry has been created by Johannes-Paul Fladerer and Ernst Kurzmann by the description of "managemANT". This term (a combination of the words "management" and "ant"), describes the usage of behavioural strategies of ants in economic and management strategies. The potential long-term impacts of biomimicry were quantified in a 2013 Fermanian Business & Economic Institute Report commissioned by the San Diego Zoo. The findings demonstrated the potential economic and environmental benefits of biomimicry, which can be further seen in Johannes-Paul Fladerer and Ernst Kurzmann's "managemANT" approach. This approach utilizes the behavioral strategies of ants in economic and management strategies.
Bio-inspired technologies
Biomimetics could in principle be applied in many fields. Because of the diversity and complexity of biological systems, the number of features that might be imitated is large. Biomimetic applications are at various stages of development from technologies that might become commercially usable to prototypes. Murray's law, which in conventional form determined the optimum diameter of blood vessels, has been re-derived to provide simple equations for the pipe or tube diameter which gives a minimum mass engineering system.
Locomotion
Aircraft wing design and flight techniques are being inspired by birds and bats. The aerodynamics of streamlined design of improved Japanese high speed train Shinkansen 500 Series were modelled after the beak of Kingfisher bird.
Biorobots based on the physiology and methods of locomotion of animals include BionicKangaroo which moves like a kangaroo, saving energy from one jump and transferring it to its next jump; Kamigami Robots, a children's toy, mimic cockroach locomotion to run quickly and efficiently over indoor and outdoor surfaces, and Pleobot, a shrimp-inspired robot to study metachronal swimming and the ecological impacts of this propulsive gait on the environment.
Biomimetic flying robots (BFRs) | Biomimetics | Wikipedia | 411 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
BFRs take inspiration from flying mammals, birds, or insects. BFRs can have flapping wings, which generate the lift and thrust, or they can be propeller actuated. BFRs with flapping wings have increased stroke efficiencies, increased maneuverability, and reduced energy consumption in comparison to propeller actuated BFRs. Mammal and bird inspired BFRs share similar flight characteristics and design considerations. For instance, both mammal and bird inspired BFRs minimize edge fluttering and pressure-induced wingtip curl by increasing the rigidity of the wing edge and wingtips. Mammal and insect inspired BFRs can be impact resistant, making them useful in cluttered environments.
Mammal inspired BFRs typically take inspiration from bats, but the flying squirrel has also inspired a prototype. Examples of bat inspired BFRs include Bat Bot and the DALER. Mammal inspired BFRs can be designed to be multi-modal; therefore, they're capable of both flight and terrestrial movement. To reduce the impact of landing, shock absorbers can be implemented along the wings. Alternatively, the BFR can pitch up and increase the amount of drag it experiences. By increasing the drag force, the BFR will decelerate and minimize the impact upon grounding. Different land gait patterns can also be implemented.
Bird inspired BFRs can take inspiration from raptors, gulls, and everything in-between. Bird inspired BFRs can be feathered to increase the angle of attack range over which the prototype can operate before stalling. The wings of bird inspired BFRs allow for in-plane deformation, and the in-plane wing deformation can be adjusted to maximize flight efficiency depending on the flight gait. An example of a raptor inspired BFR is the prototype by Savastano et al. The prototype has fully deformable flapping wings and is capable of carrying a payload of up to 0.8 kg while performing a parabolic climb, steep descent, and rapid recovery. The gull inspired prototype by Grant et al. accurately mimics the elbow and wrist rotation of gulls, and they find that lift generation is maximized when the elbow and wrist deformations are opposite but equal. | Biomimetics | Wikipedia | 440 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Insect inspired BFRs typically take inspiration from beetles or dragonflies. An example of a beetle inspired BFR is the prototype by Phan and Park, and a dragonfly inspired BFR is the prototype by Hu et al. The flapping frequency of insect inspired BFRs are much higher than those of other BFRs; this is because of the aerodynamics of insect flight. Insect inspired BFRs are much smaller than those inspired by mammals or birds, so they are more suitable for dense environments. The prototype by Phan and Park took inspiration from the rhinoceros beetle, so it can successfully continue flight even after a collision by deforming its hindwings.
Biomimetic architecture
Living beings have adapted to a constantly changing environment during evolution through mutation, recombination, and selection. The core idea of the biomimetic philosophy is that nature's inhabitants including animals, plants, and microbes have the most experience in solving problems and have already found the most appropriate ways to last on planet Earth. Similarly, biomimetic architecture seeks solutions for building sustainability present in nature. While nature serves as a model, there are few examples of biomimetic architecture that aim to be nature positive.
The 21st century has seen a ubiquitous waste of energy due to inefficient building designs, in addition to the over-utilization of energy during the operational phase of its life cycle. In parallel, recent advancements in fabrication techniques, computational imaging, and simulation tools have opened up new possibilities to mimic nature across different architectural scales. As a result, there has been a rapid growth in devising innovative design approaches and solutions to counter energy problems. Biomimetic architecture is one of these multi-disciplinary approaches to sustainable design that follows a set of principles rather than stylistic codes, going beyond using nature as inspiration for the aesthetic components of built form but instead seeking to use nature to solve problems of the building's functioning and saving energy.
Characteristics
The term biomimetic architecture refers to the study and application of construction principles which are found in natural environments and species, and are translated into the design of sustainable solutions for architecture. Biomimetic architecture uses nature as a model, measure and mentor for providing architectural solutions across scales, which are inspired by natural organisms that have solved similar problems in nature. Using nature as a measure refers to using an ecological standard of measuring sustainability, and efficiency of man-made innovations, while the term mentor refers to learning from natural principles and using biology as an inspirational source. | Biomimetics | Wikipedia | 507 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Biomorphic architecture, also referred to as bio-decoration, on the other hand, refers to the use of formal and geometric elements found in nature, as a source of inspiration for aesthetic properties in designed architecture, and may not necessarily have non-physical, or economic functions. A historic example of biomorphic architecture dates back to Egyptian, Greek and Roman cultures, using tree and plant forms in the ornamentation of structural columns.
Procedures
Within biomimetic architecture, two basic procedures can be identified, namely, the bottom-up approach (biology push) and top-down approach (technology pull). The boundary between the two approaches is blurry with the possibility of transition between the two, depending on each individual case. Biomimetic architecture is typically carried out in interdisciplinary teams in which biologists and other natural scientists work in collaboration with engineers, material scientists, architects, designers, mathematicians and computer scientists.
In the bottom-up approach, the starting point is a new result from basic biological research promising for biomimetic implementation. For example, developing a biomimetic material system after the quantitative analysis of the mechanical, physical, and chemical properties of a biological system.
In the top-down approach, biomimetic innovations are sought for already existing developments that have been successfully established on the market. The cooperation focuses on the improvement or further development of an existing product.
Examples
Researchers studied the termite's ability to maintain virtually constant temperature and humidity in their termite mounds in Africa despite outside temperatures that vary from . Researchers initially scanned a termite mound and created 3-D images of the mound structure, which revealed construction that could influence human building design. The Eastgate Centre, a mid-rise office complex in Harare, Zimbabwe, stays cool via a passive cooling architecture that uses only 10% of the energy of a conventional building of the same size.
Researchers in the Sapienza University of Rome were inspired by the natural ventilation in termite mounds and designed a double façade that significantly cuts down over lit areas in a building. Scientists have imitated the porous nature of mound walls by designing a facade with double panels that was able to reduce heat gained by radiation and increase heat loss by convection in cavity between the two panels. The overall cooling load on the building's energy consumption was reduced by 15%. | Biomimetics | Wikipedia | 471 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
A similar inspiration was drawn from the porous walls of termite mounds to design a naturally ventilated façade with a small ventilation gap. This design of façade is able to induce air flow due to the Venturi effect and continuously circulates rising air in the ventilation slot. Significant transfer of heat between the building's external wall surface and the air flowing over it was observed. The design is coupled with greening of the façade. Green wall facilitates additional natural cooling via evaporation, respiration and transpiration in plants. The damp plant substrate further support the cooling effect.
Scientists in Shanghai University were able to replicate the complex microstructure of clay-made conduit network in the mound to mimic the excellent humidity control in mounds. They proposed a porous humidity control material (HCM) using sepiolite and calcium chloride with water vapor adsorption-desorption content at 550 grams per meter squared. Calcium chloride is a desiccant and improves the water vapor adsorption-desorption property of the Bio-HCM. The proposed bio-HCM has a regime of interfiber mesopores which acts as a mini reservoir. The flexural strength of the proposed material was estimated to be 10.3 MPa using computational simulations.
In structural engineering, the Swiss Federal Institute of Technology (EPFL) has incorporated biomimetic characteristics in an adaptive deployable "tensegrity" bridge. The bridge can carry out self-diagnosis and self-repair. The arrangement of leaves on a plant has been adapted for better solar power collection.
Analysis of the elastic deformation happening when a pollinator lands on the sheath-like perch part of the flower Strelitzia reginae (known as bird-of-paradise flower) has inspired architects and scientists from the University of Freiburg and University of Stuttgart to create hingeless shading systems that can react to their environment. These bio-inspired products are sold under the name Flectofin.
Other hingeless bioinspired systems include Flectofold. Flectofold has been inspired from the trapping system developed by the carnivorous plant Aldrovanda vesiculosa.
Structural materials
There is a great need for new structural materials that are light weight but offer exceptional combinations of stiffness, strength, and toughness. | Biomimetics | Wikipedia | 472 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Such materials would need to be manufactured into bulk materials with complex shapes at high volume and low cost and would serve a variety of fields such as construction, transportation, energy storage and conversion. In a classic design problem, strength and toughness are more likely to be mutually exclusive, i.e., strong materials are brittle and tough materials are weak. However, natural materials with complex and hierarchical material gradients that span from nano- to macro-scales are both strong and tough. Generally, most natural materials utilize limited chemical components but complex material architectures that give rise to exceptional mechanical properties. Understanding the highly diverse and multi functional biological materials and discovering approaches to replicate such structures will lead to advanced and more efficient technologies. Bone, nacre (abalone shell), teeth, the dactyl clubs of stomatopod shrimps and bamboo are great examples of damage tolerant materials. The exceptional resistance to fracture of bone is due to complex deformation and toughening mechanisms that operate at spanning different size scales — nanoscale structure of protein molecules to macroscopic physiological scale. Nacre exhibits similar mechanical properties however with rather simpler structure. Nacre shows a brick and mortar like structure with thick mineral layer (0.2–0.9 μm) of closely packed aragonite structures and thin organic matrix (~20 nm). While thin films and micrometer sized samples that mimic these structures are already produced, successful production of bulk biomimetic structural materials is yet to be realized. However, numerous processing techniques have been proposed for producing nacre like materials. Pavement cells, epidermal cells on the surface of plant leaves and petals, often form wavy interlocking patterns resembling jigsaw puzzle pieces and are shown to enhance the fracture toughness of leaves, key to plant survival. Their pattern, replicated in laser-engraved Poly(methyl methacrylate) samples, was also demonstrated to lead to increased fracture toughness. It is suggested that the arrangement and patterning of cells play a role in managing crack propagation in tissues.
Biomorphic mineralization is a technique that produces materials with morphologies and structures resembling those of natural living organisms by using bio-structures as templates for mineralization. Compared to other methods of material production, biomorphic mineralization is facile, environmentally benign and economic. | Biomimetics | Wikipedia | 467 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Freeze casting (ice templating), an inexpensive method to mimic natural layered structures, was employed by researchers at Lawrence Berkeley National Laboratory to create alumina-Al-Si and IT HAP-epoxy layered composites that match the mechanical properties of bone with an equivalent mineral/organic content. Various further studies also employed similar methods to produce high strength and high toughness composites involving a variety of constituent phases.
Recent studies demonstrated production of cohesive and self supporting macroscopic tissue constructs that mimic living tissues by printing tens of thousands of heterologous picoliter droplets in software-defined, 3D millimeter-scale geometries. Efforts are also taken up to mimic the design of nacre in artificial composite materials using fused deposition modelling and the helicoidal structures of stomatopod clubs in the fabrication of high performance carbon fiber-epoxy composites.
Various established and novel additive manufacturing technologies like PolyJet printing, direct ink writing, 3D magnetic printing, multi-material magnetically assisted 3D printing and magnetically assisted slip casting have also been utilized to mimic the complex micro-scale architectures of natural materials and provide huge scope for future research.
Spider silk is tougher than Kevlar used in bulletproof vests. Engineers could in principle use such a material, if it could be reengineered to have a long enough life, for parachute lines, suspension bridge cables, artificial ligaments for medicine, and other purposes. The self-sharpening teeth of many animals have been copied to make better cutting tools.
New ceramics that exhibit giant electret hysteresis have also been realized.
Neuronal computers
Neuromorphic computers and sensors are electrical devices that copy the structure and function of biological neurons in order to compute. One example of this is the event camera in which only the
pixels that receive a new signal update to a new state. All other pixels do not update until a signal is received. | Biomimetics | Wikipedia | 394 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Self healing-materials
In some biological systems, self-healing occurs via chemical releases at the site of fracture, which initiate a systemic response to transport repairing agents to the fracture site. This promotes autonomic healing. To demonstrate the use of micro-vascular networks for autonomic healing, researchers developed a microvascular coating–substrate architecture that mimics human skin. Bio-inspired self-healing structural color hydrogels that maintain the stability of an inverse opal structure and its resultant structural colors were developed. A self-repairing membrane inspired by rapid self-sealing processes in plants was developed for inflatable lightweight structures such as rubber boats or Tensairity constructions. The researchers applied a thin soft cellular polyurethane foam coating on the inside of a fabric substrate, which closes the crack if the membrane is punctured with a spike. Self-healing materials, polymers and composite materials capable of mending cracks have been produced based on biological materials.
The self-healing properties may also be achieved by the breaking and reforming of hydrogen bonds upon cyclical stress of the material.
Surfaces
Surfaces that recreate the properties of shark skin are intended to enable more efficient movement through water. Efforts have been made to produce fabric that emulates shark skin.
Surface tension biomimetics are being researched for technologies such as hydrophobic or hydrophilic coatings and microactuators.
Adhesion
Wet adhesion
Some amphibians, such as tree and torrent frogs and arboreal salamanders, are able to attach to and move over wet or even flooded environments without falling. This kind of organisms have toe pads which are permanently wetted by mucus secreted from glands that open into the channels between epidermal cells. They attach to mating surfaces by wet adhesion and they are capable of climbing on wet rocks even when water is flowing over the surface. Tire treads have also been inspired by the toe pads of tree frogs. 3D printed hierarchical surface models, inspired from tree and torrent frogs toe pad design, have been observed to produce better wet traction than conventional tire design. | Biomimetics | Wikipedia | 420 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Marine mussels can stick easily and efficiently to surfaces underwater under the harsh conditions of the ocean. Mussels use strong filaments to adhere to rocks in the inter-tidal zones of wave-swept beaches, preventing them from being swept away in strong sea currents. Mussel foot proteins attach the filaments to rocks, boats and practically any surface in nature including other mussels. These proteins contain a mix of amino acid residues which has been adapted specifically for adhesive purposes. Researchers from the University of California Santa Barbara borrowed and simplified chemistries that the mussel foot uses to overcome this engineering challenge of wet adhesion to create copolyampholytes, and one-component adhesive systems with potential for employment in nanofabrication protocols. Other research has proposed adhesive glue from mussels.
Dry adhesion
Leg attachment pads of several animals, including many insects (e.g., beetles and flies), spiders and lizards (e.g., geckos), are capable of attaching to a variety of surfaces and are used for locomotion, even on vertical walls or across ceilings. Attachment systems in these organisms have similar structures at their terminal elements of contact, known as setae. Such biological examples have offered inspiration in order to produce climbing robots, boots and tape. Synthetic setae have also been developed for the production of dry adhesives.
Liquid repellency
Superliquiphobicity refers to a remarkable surface property where a solid surface exhibits an extreme aversion to liquids, causing droplets to bead up and roll off almost instantaneously upon contact. This behavior arises from intricate surface textures and interactions at the nanoscale, effectively preventing liquids from wetting or adhering to the surface. The term "superliquiphobic" is derived from "superhydrophobic," which describes surfaces highly resistant to water. Superliquiphobic surfaces go beyond water repellency and display repellent characteristics towards a wide range of liquids, including those with very low surface tension or containing surfactants. | Biomimetics | Wikipedia | 420 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Superliquiphobicity emerges when a solid surface possesses minute roughness, forming interfaces with droplets through wetting while altering contact angles. This behavior hinges on the roughness factor (Rf), defining the ratio of solid-liquid area to its projection, influencing contact angles. On rough surfaces, non-wetting liquids give rise to composite solid-liquid-air interfaces, their contact angles determined by the distribution of wet and air-pocket areas. The achievement of superliquiphobicity involves increasing the fractional flat geometrical area (fLA) and Rf, leading to surfaces that actively repel liquids.
The inspiration for crafting such surfaces draws from nature's ingenuity, illustrated by the "lotus effect". Leaves of water-repellent plants, like the lotus, exhibit inherent hierarchical structures featuring nanoscale wax-coated formations. Other natural surfaces with these capabilities can include Beetle carapaces and cacti spines, which may exhibit rough features at multiple size scales. These structures lead to superhydrophobicity, where water droplets perch on trapped air bubbles, resulting in high contact angles and minimal contact angle hysteresis. This natural example guides the development of superliquiphobic surfaces, capitalizing on re-entrant geometries that can repel low surface tension liquids and achieve near-zero contact angles.
Creating superliquiphobic surfaces involves pairing re-entrant geometries with low surface energy materials, such as fluorinated substances or liquid-like silocones . These geometries include overhangs that widen beneath the surface, enabling repellency even for minimal contact angles. These surfaces find utility in self-cleaning, anti-icing, anti-fogging, antifouling, enhanced condensation, and more, presenting innovative solutions to challenges in biomedicine, desalination, atmospheric water harvesting, and energy conversion.
In essence, superliquiphobicity, inspired by natural models like the lotus leaf, capitalizes on re-entrant geometries and surface properties to create interfaces that actively repel liquids. These surfaces hold immense promise across a range of applications, promising enhanced functionality and performance in various technological and industrial contexts.
Optics | Biomimetics | Wikipedia | 456 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Biomimetic materials are gaining increasing attention in the field of optics and photonics. There are still little known bioinspired or biomimetic products involving the photonic properties of plants or animals. However, understanding how nature designed such optical materials from biological resources is a current field of research.
Inspiration from fruits and plants
One source of biomimetic inspiration is from plants. Plants have proven to be concept generations for the following functions; re(action)-coupling, self (adaptability), self-repair, and energy-autonomy. As plants do not have a centralized decision making unit (i.e. a brain), most plants have a decentralized autonomous system in various organs and tissues of the plant. Therefore, they react to multiple stimulus such as light, heat, and humidity.
One example is the carnivorous plant species Dionaea muscipula (Venus flytrap). For the last 25 years, there has been research focus on the motion principles of the plant to develop AVFT (artificial Venus flytrap robots). Through the movement during prey capture, the plant inspired soft robotic motion systems. The fast snap buckling (within 100–300 ms) of the trap closure movement is initiated when prey triggers the hairs of the plant within a certain time (twice within 20 s). AVFT systems exist, in which the trap closure movements are actuated via magnetism, electricity, pressurized air, and temperature changes. | Biomimetics | Wikipedia | 298 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Another example of mimicking plants, is the Pollia condensata, also known as the marble berry. The chiral self-assembly of cellulose inspired by the Pollia condensata berry has been exploited to make optically active films. Such films are made from cellulose which is a biodegradable and biobased resource obtained from wood or cotton. The structural colours can potentially be everlasting and have more vibrant colour than the ones obtained from chemical absorption of light. Pollia condensata is not the only fruit showing a structural coloured skin; iridescence is also found in berries of other species such as Margaritaria nobilis. These fruits show iridescent colors in the blue-green region of the visible spectrum which gives the fruit a strong metallic and shiny visual appearance. The structural colours come from the organisation of cellulose chains in the fruit's epicarp, a part of the fruit skin. Each cell of the epicarp is made of a multilayered envelope that behaves like a Bragg reflector. However, the light which is reflected from the skin of these fruits is not polarised unlike the one arising from man-made replicates obtained from the self-assembly of cellulose nanocrystals into helicoids, which only reflect left-handed circularly polarised light.
The fruit of Elaeocarpus angustifolius also show structural colour that come arises from the presence of specialised cells called iridosomes which have layered structures. Similar iridosomes have also been found in Delarbrea michieana fruits.
In plants, multi layer structures can be found either at the surface of the leaves (on top of the epidermis), such as in Selaginella willdenowii or within specialized intra-cellular organelles, the so-called iridoplasts, which are located inside the cells of the upper epidermis. For instance, the rain forest plants Begonia pavonina have iridoplasts located inside the epidermal cells.
Structural colours have also been found in several algae, such as in the red alga Chondrus crispus (Irish Moss).
Inspiration from animals | Biomimetics | Wikipedia | 454 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Structural coloration produces the rainbow colours of soap bubbles, butterfly wings and many beetle scales. Phase-separation has been used to fabricate ultra-white scattering membranes from polymethylmethacrylate, mimicking the beetle Cyphochilus. LED lights can be designed to mimic the patterns of scales on fireflies' abdomens, improving their efficiency.
Morpho butterfly wings are structurally coloured to produce a vibrant blue that does not vary with angle. This effect can be mimicked by a variety of technologies. Lotus Cars claim to have developed a paint that mimics the Morpho butterfly's structural blue colour. In 2007, Qualcomm commercialised an interferometric modulator display technology, "Mirasol", using Morpho-like optical interference. In 2010, the dressmaker Donna Sgro made a dress from Teijin Fibers' Morphotex, an undyed fabric woven from structurally coloured fibres, mimicking the microstructure of Morpho butterfly wing scales.
Canon Inc.'s SubWavelength structure Coating uses wedge-shaped structures the size of the wavelength of visible light. The wedge-shaped structures cause a continuously changing refractive index as light travels through the coating, significantly reducing lens flare. This imitates the structure of a moth's eye. Notable figures such as the Wright Brothers and Leonardo da Vinci attempted to replicate the flight observed in birds. In an effort to reduce aircraft noise researchers have looked to the leading edge of owl feathers, which have an array of small finlets or rachis adapted to disperse aerodynamic pressure and provide nearly silent flight to the bird.
Agricultural systems
Holistic planned grazing, using fencing and/or herders, seeks to restore grasslands by carefully planning movements of large herds of livestock to mimic the vast herds found in nature. The natural system being mimicked and used as a template is grazing animals concentrated by pack predators that must move on after eating, trampling, and manuring an area, and returning only after it has fully recovered. Its founder Allan Savory and some others have claimed potential in building soil, increasing biodiversity, and reversing desertification. However, many researchers have disputed Savory's claim. Studies have often found that the method increases desertification instead of reducing it.
Other uses
Some air conditioning systems use biomimicry in their fans to increase airflow while reducing power consumption. | Biomimetics | Wikipedia | 492 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Technologists like Jas Johl have speculated that the functionality of vacuole cells could be used to design highly adaptable security systems. "The functionality of a vacuole, a biological structure that guards and promotes growth, illuminates the value of adaptability as a guiding principle for security." The functions and significance of vacuoles are fractal in nature, the organelle has no basic shape or size; its structure varies according to the requirements of the cell. Vacuoles not only isolate threats, contain what's necessary, export waste, maintain pressure—they also help the cell scale and grow. Johl argues these functions are necessary for any security system design. The 500 Series Shinkansen used biomimicry to reduce energy consumption and noise levels while increasing passenger comfort. With reference to space travel, NASA and other firms have sought to develop swarm-type space drones inspired by bee behavioural patterns, and oxtapod terrestrial drones designed with reference to desert spiders.
Other technologies
Protein folding has been used to control material formation for self-assembled functional nanostructures. Polar bear fur has inspired the design of thermal collectors and clothing. The light refractive properties of the moth's eye has been studied to reduce the reflectivity of solar panels.
The Bombardier beetle's powerful repellent spray inspired a Swedish company to develop a "micro mist" spray technology, which is claimed to have a low carbon impact (compared to aerosol sprays). The beetle mixes chemicals and releases its spray via a steerable nozzle at the end of its abdomen, stinging and confusing the victim. | Biomimetics | Wikipedia | 330 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
Most viruses have an outer capsule 20 to 300 nm in diameter. Virus capsules are remarkably robust and capable of withstanding temperatures as high as 60 °C; they are stable across the pH range 2–10. Viral capsules can be used to create nano device components such as nanowires, nanotubes, and quantum dots. Tubular virus particles such as the tobacco mosaic virus (TMV) can be used as templates to create nanofibers and nanotubes, since both the inner and outer layers of the virus are charged surfaces which can induce nucleation of crystal growth. This was demonstrated through the production of platinum and gold nanotubes using TMV as a template. Mineralized virus particles have been shown to withstand various pH values by mineralizing the viruses with different materials such as silicon, PbS, and CdS and could therefore serve as a useful carriers of material. A spherical plant virus called cowpea chlorotic mottle virus (CCMV) has interesting expanding properties when exposed to environments of pH higher than 6.5. Above this pH, 60 independent pores with diameters about 2 nm begin to exchange substance with the environment. The structural transition of the viral capsid can be utilized in Biomorphic mineralization for selective uptake and deposition of minerals by controlling the solution pH. Possible applications include using the viral cage to produce uniformly shaped and sized quantum dot semiconductor nanoparticles through a series of pH washes. This is an alternative to the apoferritin cage technique currently used to synthesize uniform CdSe nanoparticles. Such materials could also be used for targeted drug delivery since particles release contents upon exposure to specific pH levels. | Biomimetics | Wikipedia | 343 | 45784 | https://en.wikipedia.org/wiki/Biomimetics | Technology | Biotechnology | null |
The clouded leopard (Neofelis nebulosa), also called mainland clouded leopard, is a wild cat inhabiting dense forests from the foothills of the Himalayas through Northeast India and Bhutan to mainland Southeast Asia into South China. It was first described in 1821 on the basis of a skin of an individual from China. The clouded leopard has large dusky-grey blotches and irregular spots and stripes reminiscent of clouds. Its head-and-body length ranges from with a long tail. It uses its tail for balancing when moving in trees and is able to climb down vertical tree trunks head first. It rests in trees during the day and hunts by night on the forest floor.
The clouded leopard is the sister taxon to other pantherine cats, having genetically diverged 9.32 to 4.47 million years ago. Today, the clouded leopard is locally extinct in Singapore, Taiwan, and possibly also in Hainan Island and Vietnam. The wild population is believed to be in decline with fewer than 10,000 adults and no more than 1,000 in each subpopulation. It has therefore been listed as Vulnerable on the IUCN Red List since 2008. The population is threatened by large–scale deforestation and commercial poaching for the wildlife trade. Its body parts are offered for decoration and clothing, though it is legally protected in most range countries.
The clouded leopard has been kept in zoological gardens since the early 20th century. Captive breeding programs were initiated in the 1980s. In captivity, the clouded leopard has an average lifespan of 11 years.
Taxonomy and phylogeny
Felis nebulosa was proposed by Edward Griffith in 1821 who first described a skin of a clouded leopard that was brought alive from Guangdong in China to the menagerie at Exeter Exchange in London.
Felis macrosceloides proposed by Brian Houghton Hodgson in 1841 was a clouded leopard specimen from Nepal.
Felis brachyura proposed by Robert Swinhoe in 1862 was a clouded leopard skin from Taiwan.
The generic name Neofelis was proposed by John Edward Gray in 1867 who subordinated all three to this genus.
At present, N. nebulosa is considered a monotypic species due to lack of evidence for subspeciation. | Clouded leopard | Wikipedia | 447 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
Felis diardi proposed by Georges Cuvier in 1823 was based on a clouded leopard skin from Java.
It was considered a clouded leopard subspecies by Reginald Innes Pocock in 1917. In 2006, it was identified as a distinct Neofelis species, the Sunda clouded leopard. Populations in Taiwan and Hainan Island are considered to belong to the mainland clouded leopard.
Phylogeny
Skulls of clouded leopard and Panthera species were analysed morphologically in the 1960s. Results indicate that the clouded leopard forms an evolutionary link between the Pantherinae and the Felinae.
Phylogenetic analysis of the nuclear DNA in tissue samples from all Felidae species revealed that the evolutionary radiation of the Felidae began in the Miocene around in Asia. Analysis of mitochondrial DNA of all Felidae species indicates a radiation at .
The clouded leopard is the sister taxon to all other members of the Pantherinae, diverging , based on analysis of their nuclear DNA.
The clouded leopard from mainland Asia reached Borneo and Sumatra via a now submerged land bridge probably during the Pleistocene, when populations became isolated during periods of global cooling and warming. Genetic analysis of hair samples of the clouded leopard and its sister species the Sunda clouded leopard (N. diardi) indicates that they diverged 2.0–0.93 million years ago.
Characteristics
The clouded leopard's fur is of a dark grey or ochreous ground-color, often largely obliterated by black and dark dusky-grey blotched pattern. There are black spots on the head, and the ears are black. Partly fused or broken-up stripes run from the corner of the eyes over the cheek, from the corner of the mouth to the neck, and along the nape to the shoulders. Elongated blotches continue down the spine and form a single median stripe on the loins. Two large blotches of dark dusky-grey hair on the side of the shoulders are each emphasized posteriorly by a dark stripe, which passes on to the foreleg and breaks up into irregular spots. The flanks are marked by dark dusky-grey irregular blotches bordered behind by long, oblique, irregularly curved or looped stripes. These blotches yielding the clouded pattern suggest the English name of the cat. The underparts and legs are spotted, and the tail is marked by large, irregular, paired spots. Its legs are short and stout, and paws broad. Females are slightly smaller than males. | Clouded leopard | Wikipedia | 492 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
Its hyoid bone is ossified, making it possible to purr. Its pupils contract into vertical slits. Irises are brownish yellow to grayish green. Melanistic clouded leopards are uncommon. It has rather short limbs compared to the other big cats. Its hind limbs are longer than its front limbs to allow for increased jumping and leaping capabilities. Its ulnae and radii are not fused, which also contributes to a greater range of motion when climbing trees and stalking prey. Clouded leopards weigh between . Females vary in head-to-body length from , with a tail long. Males are larger at with a tail long.
Its shoulder height varies from .
Its skull is long and low with strong occipital and sagittal crests. The canine teeth are exceptionally long, the upper being about three times as long as the basal width of the socket. The first premolar is usually absent. The upper pair of canines measure or longer.
It has a bite force at the canine tip of 544.3 Newton and a bite force quotient at the canine tip of 122.4.
The clouded leopard is often referred to as a "modern-day sabre-tooth" because it has the largest canines in proportion to its body size.
Distribution and habitat
The clouded leopard occurs from the Himalayan foothills in Nepal, Bhutan and India to Myanmar, southeastern Bangladesh, Thailand, Peninsular Malaysia and to south of the Yangtze River in China. It is locally extinct in Singapore and Taiwan.
Clouded leopards were found in Nepal in 1987 and 1988, having previously been presumed to be extinct in the country. Since then, the clouded leopard has been recorded in Shivapuri Nagarjun National Park and in Annapurna Conservation Area. Between 2014 and 2015, it was also recorded in Langtang National Park at an elevation range of . | Clouded leopard | Wikipedia | 373 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
In India, it occurs in the states of Sikkim, northern West Bengal, Tripura, Mizoram, Manipur, Assam, Nagaland and Arunachal Pradesh, as well as in the Meghalaya subtropical forests. In Pakke Tiger Reserve, a clouded leopard was photographed in semi-evergreen forest at an elevation of . In Sikkim, clouded leopards were photographed by camera traps at elevations of between April 2008 and May 2010 in the Khangchendzonga Biosphere Reserve. In Manas National Park, 16 individuals were recorded during a survey in November 2010 to February 2011. Between January 2013 and March 2018, clouded leopards were also recorded in Dampa Tiger Reserve, Eaglenest Wildlife Sanctuary and Singchung-Bugun Village Community Reserve, in Meghalaya's Nongkhyllem National Park and Balpakram-Baghmara landscape.
In Bhutan, it was recorded in Royal Manas National Park, Jigme Singye Wangchuck National Park, Phibsoo Wildlife Sanctuary, Jigme Dorji National Park, Phrumsengla National Park, Bumdeling Wildlife Sanctuary and several non-protected areas. In Bangladesh, it was recorded in Sangu Matamuhari in the Chittagong Hill Tracts in 2016. In Myanmar, it was recorded by camera traps for the first time in the hill forests of Karen State in 2015.
In Thailand, it inhabits relatively open, dry tropical forest in Huai Kha Khaeng Wildlife Sanctuary and closed-forest habitats in Khao Yai National Park. In Laos, it was recorded in Nam Et-Phou Louey National Protected Area in dry evergreen and semi-evergreen forests. In Cambodia, it was recorded in deciduous dipterocarp forest in Phnom Prich Wildlife Sanctuary between 2008 and 2009, and in Central Cardamom Mountains National Park, Southern Cardamom National Park, Botum Sakor National Park and Phnom Samkos Wildlife Sanctuary between 2012 and 2016. In Peninsular Malaysia, it was recorded in Taman Negara National Park, Ulu Muda Forest, Pasoh Forest Reserve, Belum-Temengor, Temengor Forest Reserve and in a few linkages between 2009 and 2015. | Clouded leopard | Wikipedia | 457 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
The last confirmed record of a Formosan clouded leopard dates to 1989, when the skin of a young individual was found in the Taroko National Park. It was not recorded during an extensive camera trapping survey conducted from 1997 to 2012 in more than 1,450 sites inside and outside Taiwanese protected areas.
Behaviour and ecology
The clouded leopard is a solitary cat. Early accounts depict it as a rare, secretive, arboreal, and nocturnal inhabitant of dense primary forest.
It is one of the most talented climbers among the cats. Captive clouded leopards have been observed to climb down vertical tree trunks head first, and hang on to branches with their hind paws bent around branchings of tree limbs. They are capable of supination and can hang down from branches only by bending their hind paws and their tail around them. They can jump up to high.
They use trees as daytime rest sites, but also spend time on the ground when hunting at night. Captive clouded leopards have been observed to scent mark by spraying urine and rubbing their heads on prominent objects.
Their vocalisations include a short high-pitched meow call, a loud crying call, both emitted when a cat is trying to locate another one over a long or short distance; they prusten and raise their muzzle when meeting each other in a friendly manner; when aggressive, they growl with a low-pitched sound and hiss with exposed teeth and wrinkled nose.
Radio-collared clouded leopards were foremost active by night but also showed crepuscular activity peaks.
Clouded leopards recorded in northeast India were most active in the late evening after sunset.
Home ranges have only been estimated in Thailand:
Four individuals were radio-collared in Phu Khieo Wildlife Sanctuary from April 2000 to February 2003. Home ranges of two females were and , and of two males and .
Two individuals were radio-collared during a study from 1997 to 1999 in the Khao Yai National Park. The home range of one female was , of the one male . Both individuals had a core area of .
In 2016, clouded leopards were detected in the forest complex of Khlong Saeng Wildlife Sanctuary and Khao Sok National Park during camera trapping surveys; 15 individuals were identified in a core zone of with population density estimated at 5.06 individuals per ; but only 12 individuals were identified in an edge zone of , which is more disturbed by humans, with density estimated at 3.13 individuals per . | Clouded leopard | Wikipedia | 497 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
Hunting and diet
When hunting, the clouded leopard stalks its prey or waits for the prey to approach. After making and feeding on a kill, it usually retreats into trees to digest and rest. Its prey includes both arboreal and terrestrial vertebrates.
Pocock presumed that it is adapted for preying upon herbivorous mammals of considerable bulk because of its powerful build, long canines and the deep penetration of its bites. In Thailand, clouded leopards have been observed preying on southern pig-tailed macaque (Macaca nemestrina), Indian hog deer (Axis porcinus), Bengal slow loris (Nycticebus bengalensis), Asiatic brush-tailed porcupine (Atherurus macrourus), Malayan pangolin (Manis javanica) and Berdmore's ground squirrel (Menetes berdmorei). Known prey species in China include barking deer (Muntiacus sp.) and pheasants.
In northern Peninsular Malaysia, a male clouded leopard was photographed while carrying a binturong (Arctictis binturong) in its jaws.
Reproduction and life cycle
Both males and females average 26 months at first reproduction. The female is in estrus for about six days, with her estrous cycle lasting about 30 days. In the wild, mating usually occurs between December and March. The pair mates multiple times over the course of several days. The male grasps the female by the neck who responds with vocalization. Occasionally, he also bites her during courtship and is very aggressive during sexual encounters. Females can bear one litter each year. The male is not involved in raising the cubs.
The female gives birth to a litter of one to five, mostly three cubs, after a gestation period of 93 ± 6 days. Cubs are born with closed eyes and weigh from . Their spots are solid dark, rather than dark rings. Their eyes open after about 10 days. They are active within five weeks and fully weaned at around three months of age. They attain the adult coat pattern at around six months and become independent after around 10 months.
Captive clouded leopards have an average lifespan of 11 years.
One individual has lived to be almost 17 years old.
The generation length of the clouded leopard is about seven years.
Threats | Clouded leopard | Wikipedia | 467 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
Clouded leopard require larger areas of intact forest than are present in many parts of their range. They are threatened by habitat loss following large–scale deforestation and commercial poaching for the wildlife trade. In Myanmar, 301 body parts of at least 279 clouded leopards, mostly skins and skeletons, were observed in four markets surveyed between 1991 and 2006, despite the protected status of clouded leopards in Myanmar. Some markets are located near Myanmar's borders with China and Thailand and are used to facilitate cross-border smuggling.
In Nepal, 27 cases of clouded leopard body parts were discovered between November 1988 and March 2020 in nine districts of the country, comprising at least 51 individual clouded leopards. In 17 of these cases, the poachers and traders were arrested.
Conservation
The clouded leopard is listed in CITES Appendix I. Hunting is banned in Bangladesh, China, India, Malaysia, Myanmar, Nepal, Taiwan, Thailand and Vietnam. These bans, however, are poorly enforced in India, Malaysia and Thailand.
In the United States, the clouded leopard is listed as endangered under the Endangered Species Act, prohibiting trade in live animals or body parts.
International Clouded Leopard Day is celebrated each year on 4 August since 2018 in zoos and conservation organizations all over the world.
In captivity
Clouded leopards have been kept in zoos since the early 20th century. The international studbook was initiated in the 1970s. Coordinated breeding programs were started in the 1980s and encompass the European Endangered Species Programme, the Species Survival Plan, and the Indian Conservation Breeding Programme. As of 2014, 64 institutions keep clouded leopards.
Early captive-breeding programs involving clouded leopards were not successful, largely due to ignorance of their courtship behaviour. Males have the reputation of being aggressive towards females. For breeding success, it has been deemed extremely important that male and female clouded leopards are compatible. Introducing pairs at a young age gives them opportunities to bond and breed successfully. Facilities breeding clouded leopards need to provide the female with a secluded, off-exhibit area. There has been some recent captive breeding success using artificial insemination with cubs successfully born in 1992, 2015 and 2017.
A study on morbidity and mortality rate of 271 captive clouded leopards across 44 zoos in Europe, Asia and Australia showed that 17% of them died because of respiratory disease, 12% due to maternal neglect and starvation, 10% from generalized infectious disease, 10% from digestive diseases, and 10% from trauma. | Clouded leopard | Wikipedia | 495 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
In March 2011, two breeding females at the Nashville Zoo at Grassmere gave birth to three cubs, which were raised by zookeepers. Each cub weighed . In June 2011, two cubs were born at the Point Defiance Zoo & Aquarium. The breeding pair was brought from the Khao Kheow Open Zoo in Thailand in an ongoing education and research exchange program. Four cubs were born at Nashville Zoo in 2012. In May 2015, four cubs were born in Point Defiance Zoo & Aquarium.
In culture
The clouded leopard is the state animal of the Indian state of Meghalaya. In the 1970s, the print of Rama Samaraweera's painting Clouded leopard was a best-seller in the US. | Clouded leopard | Wikipedia | 142 | 45798 | https://en.wikipedia.org/wiki/Clouded%20leopard | Biology and health sciences | Felines | Animals |
Dijkstra's algorithm ( ) is an algorithm for finding the shortest paths between nodes in a weighted graph, which may represent, for example, a road network. It was conceived by computer scientist Edsger W. Dijkstra in 1956 and published three years later.
Dijkstra's algorithm finds the shortest path from a given source node to every other node. It can be used to find the shortest path to a specific destination node, by terminating the algorithm after determining the shortest path to the destination node. For example, if the nodes of the graph represent cities, and the costs of edges represent the average distances between pairs of cities connected by a direct road, then Dijkstra's algorithm can be used to find the shortest route between one city and all other cities. A common application of shortest path algorithms is network routing protocols, most notably IS-IS (Intermediate System to Intermediate System) and OSPF (Open Shortest Path First). It is also employed as a subroutine in algorithms such as Johnson's algorithm.
The algorithm uses a min-priority queue data structure for selecting the shortest paths known so far. Before more advanced priority queue structures were discovered, Dijkstra's original algorithm ran in time, where is the number of nodes. proposed a Fibonacci heap priority queue to optimize the running time complexity to . This is asymptotically the fastest known single-source shortest-path algorithm for arbitrary directed graphs with unbounded non-negative weights. However, specialized cases (such as bounded/integer weights, directed acyclic graphs etc.) can be improved further. If preprocessing is allowed, algorithms such as contraction hierarchies can be up to seven orders of magnitude faster.
Dijkstra's algorithm is commonly used on graphs where the edge weights are positive integers or real numbers. It can be generalized to any graph where the edge weights are partially ordered, provided the subsequent labels (a subsequent label is produced when traversing an edge) are monotonically non-decreasing.
In many fields, particularly artificial intelligence, Dijkstra's algorithm or a variant offers a uniform cost search and is formulated as an instance of the more general idea of best-first search.
History | Dijkstra's algorithm | Wikipedia | 458 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Dijkstra thought about the shortest path problem while working as a programmer at the Mathematical Center in Amsterdam in 1956. He wanted to demonstrate the capabilities of the new ARMAC computer. His objective was to choose a problem and a computer solution that non-computing people could understand. He designed the shortest path algorithm and later implemented it for ARMAC for a slightly simplified transportation map of 64 cities in the Netherlands (he limited it to 64, so that 6 bits would be sufficient to encode the city number). A year later, he came across another problem advanced by hardware engineers working on the institute's next computer: minimize the amount of wire needed to connect the pins on the machine's back panel. As a solution, he re-discovered Prim's minimal spanning tree algorithm (known earlier to Jarník, and also rediscovered by Prim). Dijkstra published the algorithm in 1959, two years after Prim and 29 years after Jarník.
Algorithm
The algorithm requires a starting node, and node N, with a distance between the starting node and N. Dijkstra's algorithm starts with infinite distances and tries to improve them step by step: | Dijkstra's algorithm | Wikipedia | 235 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Create a set of all unvisited nodes: the unvisited set.
Assign to every node a distance from start value: for the starting node, it is zero, and for all other nodes, it is infinity, since initially no path is known to these nodes. During execution, the distance of a node N is the length of the shortest path discovered so far between the starting node and N.
From the unvisited set, select the current node to be the one with the smallest (finite) distance; initially, this is the starting node (distance zero). If the unvisited set is empty, or contains only nodes with infinite distance (which are unreachable), then the algorithm terminates by skipping to step 6. If the only concern is the path to a target node, the algorithm terminates once the current node is the target node. Otherwise, the algorithm continues.
For the current node, consider all of its unvisited neighbors and update their distances through the current node; compare the newly calculated distance to the one currently assigned to the neighbor and assign the smaller one to it. For example, if the current node A is marked with a distance of 6, and the edge connecting it with its neighbor B has length 2, then the distance to B through A is 6 + 2 = 8. If B was previously marked with a distance greater than 8, then update it to 8 (the path to B through A is shorter). Otherwise, keep its current distance (the path to B through A is not the shortest).
After considering all of the current node's unvisited neighbors, the current node is removed from the unvisited set. Thus a visited node is never rechecked, which is correct because the distance recorded on the current node is minimal (as ensured in step 3), and thus final. Repeat from step 3.
Once the loop exits (steps 3–5), every visited node contains its shortest distance from the starting node.
Description
The shortest path between two intersections on a city map can be found by this algorithm using pencil and paper. Every intersection is listed on a separate line: one is the starting point and is labeled (given a distance of) 0. Every other intersection is initially labeled with a distance of infinity. This is done to note that no path to these intersections has yet been established. At each iteration one intersection becomes the current intersection. For the first iteration, this is the starting point. | Dijkstra's algorithm | Wikipedia | 499 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
From the current intersection, the distance to every neighbor (directly-connected) intersection is assessed by summing the label (value) of the current intersection and the distance to the neighbor and then relabeling the neighbor with the lesser of that sum and the neighbor's existing label. I.e., the neighbor is relabeled if the path to it through the current intersection is shorter than previously assessed paths. If so, mark the road to the neighbor with an arrow pointing to it, and erase any other arrow that points to it. After the distances to each of the current intersection's neighbors have been assessed, the current intersection is marked as visited. The unvisited intersection with the smallest label becomes the current intersection and the process repeats until all nodes with labels less than the destination's label have been visited.
Once no unvisited nodes remain with a label smaller than the destination's label, the remaining arrows show the shortest path.
Pseudocode
In the following pseudocode, is an array that contains the current distances from the to other vertices, i.e. is the current distance from the source to the vertex . The array contains pointers to previous-hop nodes on the shortest path from source to the given vertex (equivalently, it is the next-hop on the path from the given vertex to the source). The code , searches for the vertex in the vertex set that has the least value. returns the length of the edge joining (i.e. the distance between) the two neighbor-nodes and . The variable on line 14 is the length of the path from the node to the neighbor node if it were to go through . If this path is shorter than the current shortest path recorded for , then the distance of is updated to .
1 function Dijkstra(Graph, source):
2
3 for each vertex v in Graph.Vertices:
4 dist[v] ← INFINITY
5 prev[v] ← UNDEFINED
6 add v to Q
7 dist[source] ← 0
8
9 while Q is not empty:
10 u ← vertex in Q with minimum dist[u]
11 remove u from Q
12
13 for each neighbor v of u still in Q:
14 alt ← dist[u] + Graph.Edges(u, v)
15 if alt < dist[v]:
16 dist[v] ← alt
17 prev[v] ← u
18
19 return dist[], prev[] | Dijkstra's algorithm | Wikipedia | 505 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
To find the shortest path between vertices and , the search terminates after line 10 if . The shortest path from to can be obtained by reverse iteration:
1 S ← empty sequence
2 u ← target
3 if prev[u] is defined or u = source: // Proceed if the vertex is reachable
4 while u is defined: // Construct the shortest path with a stack S
5 insert u at the beginning of S // Push the vertex onto the stack
6 u ← prev[u] // Traverse from target to source
Now sequence is the list of vertices constituting one of the shortest paths from to , or the empty sequence if no path exists.
A more general problem is to find all the shortest paths between and (there might be several of the same length). Then instead of storing only a single node in each entry of all nodes satisfying the relaxation condition can be stored. For example, if both and connect to and they lie on different shortest paths through (because the edge cost is the same in both cases), then both and are added to . When the algorithm completes, data structure describes a graph that is a subset of the original graph with some edges removed. Its key property is that if the algorithm was run with some starting node, then every path from that node to any other node in the new graph is the shortest path between those nodes graph, and all paths of that length from the original graph are present in the new graph. Then to actually find all these shortest paths between two given nodes, a path finding algorithm on the new graph, such as depth-first search would work.
Using a priority queue
A min-priority queue is an abstract data type that provides 3 basic operations: , and . As mentioned earlier, using such a data structure can lead to faster computing times than using a basic queue. Notably, Fibonacci heap or Brodal queue offer optimal implementations for those 3 operations. As the algorithm is slightly different in appearance, it is mentioned here, in pseudocode as well: | Dijkstra's algorithm | Wikipedia | 408 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
1 function Dijkstra(Graph, source):
2 create vertex priority queue Q
3
4 dist[source] ← 0 // Initialization
5 Q.add_with_priority(source, 0) // associated priority equals dist[·]
6
7 for each vertex v in Graph.Vertices:
8 if v ≠ source
9 prev[v] ← UNDEFINED // Predecessor of v
10 dist[v] ← INFINITY // Unknown distance from source to v
11 Q.add_with_priority(v, INFINITY)
12
13
14 while Q is not empty: // The main loop
15 u ← Q.extract_min() // Remove and return best vertex
16 for each neighbor v of u: // Go through all v neighbors of u
17 alt ← dist[u] + Graph.Edges(u, v)
18 if alt < dist[v]:
19 prev[v] ← u
20 dist[v] ← alt
21 Q.decrease_priority(v, alt)
22
23 return dist, prev
Instead of filling the priority queue with all nodes in the initialization phase, it is possible to initialize it to contain only source; then, inside the if alt < dist[v] block, the becomes an operation.
Yet another alternative is to add nodes unconditionally to the priority queue and to instead check after extraction (u ← Q.extract_min()) that it isn't revisiting, or that no shorter connection was found yet in the if alt < dist[v] block. This can be done by additionally extracting the associated priority p from the queue and only processing further if p == dist[u] inside the while Q is not empty loop.
These alternatives can use entirely array-based priority queues without decrease-key functionality, which have been found to achieve even faster computing times in practice. However, the difference in performance was found to be narrower for denser graphs.
Proof
To prove the correctness of Dijkstra's algorithm, mathematical induction can be used on the number of visited nodes.
Invariant hypothesis: For each visited node , is the shortest distance from to , and for each unvisited node , is the shortest distance from to when traveling via visited nodes only, or infinity if no such path exists. (Note: we do not assume is the actual shortest distance for unvisited nodes, while is the actual shortest distance) | Dijkstra's algorithm | Wikipedia | 507 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Base case
The base case is when there is just one visited node, . Its distance is defined to be zero, which is the shortest distance, since negative weights are not allowed. Hence, the hypothesis holds.
Induction
Assuming that the hypothesis holds for visited nodes, to show it holds for nodes, let be the next visited node, i.e. the node with minimum . The claim is that is the shortest distance from to .
The proof is by contradiction. If a shorter path were available, then this shorter path either contains another unvisited node or not.
In the former case, let be the first unvisited node on this shorter path. By induction, the shortest paths from to and through visited nodes only have costs and respectively. This means the cost of going from to via has the cost of at least + the minimal cost of going from to . As the edge costs are positive, the minimal cost of going from to is a positive number. However, is at most because otherwise w would have been picked by the priority queue instead of u. This is a contradiction, since it has already been established that + a positive number < .
In the latter case, let be the last but one node on the shortest path. That means . That is a contradiction because by the time is visited, it should have set to at most .
For all other visited nodes , the is already known to be the shortest distance from already, because of the inductive hypothesis, and these values are unchanged.
After processing , it is still true that for each unvisited node , is the shortest distance from to using visited nodes only. Any shorter path that did not use , would already have been found, and if a shorter path used it would have been updated when processing .
After all nodes are visited, the shortest path from to any node consists only of visited nodes. Therefore, is the shortest distance.
Running time
Bounds of the running time of Dijkstra's algorithm on a graph with edges and vertices can be expressed as a function of the number of edges, denoted , and the number of vertices, denoted , using big-O notation. The complexity bound depends mainly on the data structure used to represent the set . In the following, upper bounds can be simplified because is for any simple graph, but that simplification disregards the fact that in some problems, other upper bounds on may hold.
For any data structure for the vertex set , the running time i s: | Dijkstra's algorithm | Wikipedia | 497 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
where and are the complexities of the decrease-key and extract-minimum operations in , respectively.
The simplest version of Dijkstra's algorithm stores the vertex set as a linked list or array, and edges as an adjacency list or matrix. In this case, extract-minimum is simply a linear search through all vertices in , so the running time is .
For sparse graphs, that is, graphs with far fewer than edges, Dijkstra's algorithm can be implemented more efficiently by storing the graph in the form of adjacency lists and using a self-balancing binary search tree, binary heap, pairing heap, Fibonacci heap or a priority heap as a priority queue to implement extracting minimum efficiently. To perform decrease-key steps in a binary heap efficiently, it is necessary to use an auxiliary data structure that maps each vertex to its position in the heap, and to update this structure as the priority queue changes. With a self-balancing binary search tree or binary heap, the algorithm requires
time in the worst case; for connected graphs this time bound can be simplified to . The Fibonacci heap improves this to
When using binary heaps, the average case time complexity is lower than the worst-case: assuming edge costs are drawn independently from a common probability distribution, the expected number of decrease-key operations is bounded by , giving a total running time of
Practical optimizations and infinite graphs
In common presentations of Dijkstra's algorithm, initially all nodes are entered into the priority queue. This is, however, not necessary: the algorithm can start with a priority queue that contains only one item, and insert new items as they are discovered (instead of doing a decrease-key, check whether the key is in the queue; if it is, decrease its key, otherwise insert it). This variant has the same worst-case bounds as the common variant, but maintains a smaller priority queue in practice, speeding up queue operations. | Dijkstra's algorithm | Wikipedia | 399 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Moreover, not inserting all nodes in a graph makes it possible to extend the algorithm to find the shortest path from a single source to the closest of a set of target nodes on infinite graphs or those too large to represent in memory. The resulting algorithm is called uniform-cost search (UCS) in the artificial intelligence literature and can be expressed in pseudocode as
procedure uniform_cost_search(start) is
node ← start
frontier ← priority queue containing node only
expanded ← empty set
do
if frontier is empty then
return failure
node ← frontier.pop()
if node is a goal state then
return solution(node)
expanded.add(node)
for each of node's neighbors n do
if n is not in expanded and not in frontier then
frontier.add(n)
else if n is in frontier with higher cost
replace existing node with n
Its complexity can be expressed in an alternative way for very large graphs: when is the length of the shortest path from the start node to any node satisfying the "goal" predicate, each edge has cost at least , and the number of neighbors per node is bounded by , then the algorithm's worst-case time and space complexity are both in .
Further optimizations for the single-target case include bidirectional variants, goal-directed variants such as the A* algorithm (see ), graph pruning to determine which nodes are likely to form the middle segment of shortest paths (reach-based routing), and hierarchical decompositions of the input graph that reduce routing to connecting and to their respective "transit nodes" followed by shortest-path computation between these transit nodes using a "highway". Combinations of such techniques may be needed for optimal practical performance on specific problems. | Dijkstra's algorithm | Wikipedia | 348 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Optimality for comparison-sorting by distance
As well as simply computing distances and paths, Dijkstra's algorithm can be used to sort vertices by their distances from a given starting vertex.
In 2023, Haeupler, Rozhoň, Tětek, Hladík, and Tarjan (one of the inventors of the 1984 heap), proved that, for this sorting problem on a positively-weighted directed graph, a version of Dijkstra's algorithm with a special heap data structure has a runtime and number of comparisons that is within a constant factor of optimal among comparison-based algorithms for the same sorting problem on the same graph and starting vertex but with variable edge weights. To achieve this, they use a comparison-based heap whose cost of returning/removing the minimum element from the heap is logarithmic in the number of elements inserted after it rather than in the number of elements in the heap.
Specialized variants
When arc weights are small integers (bounded by a parameter ), specialized queues can be used for increased speed. The first algorithm of this type was Dial's algorithm for graphs with positive integer edge weights, which uses a bucket queue to obtain a running time . The use of a Van Emde Boas tree as the priority queue brings the complexity to . Another interesting variant based on a combination of a new radix heap and the well-known Fibonacci heap runs in time . Finally, the best algorithms in this special case run in time and time.
Related problems and algorithms
Dijkstra's original algorithm can be extended with modifications. For example, sometimes it is desirable to present solutions which are less than mathematically optimal. To obtain a ranked list of less-than-optimal solutions, the optimal solution is first calculated. A single edge appearing in the optimal solution is removed from the graph, and the optimum solution to this new graph is calculated. Each edge of the original solution is suppressed in turn and a new shortest-path calculated. The secondary solutions are then ranked and presented after the first optimal solution.
Dijkstra's algorithm is usually the working principle behind link-state routing protocols. OSPF and IS-IS are the most common. | Dijkstra's algorithm | Wikipedia | 448 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Unlike Dijkstra's algorithm, the Bellman–Ford algorithm can be used on graphs with negative edge weights, as long as the graph contains no negative cycle reachable from the source vertex s. The presence of such cycles means that no shortest path can be found, since the label becomes lower each time the cycle is traversed. (This statement assumes that a "path" is allowed to repeat vertices. In graph theory that is normally not allowed. In theoretical computer science it often is allowed.) It is possible to adapt Dijkstra's algorithm to handle negative weights by combining it with the Bellman-Ford algorithm (to remove negative edges and detect negative cycles): Johnson's algorithm.
The A* algorithm is a generalization of Dijkstra's algorithm that reduces the size of the subgraph that must be explored, if additional information is available that provides a lower bound on the distance to the target.
The process that underlies Dijkstra's algorithm is similar to the greedy process used in Prim's algorithm. Prim's purpose is to find a minimum spanning tree that connects all nodes in the graph; Dijkstra is concerned with only two nodes. Prim's does not evaluate the total weight of the path from the starting node, only the individual edges.
Breadth-first search can be viewed as a special-case of Dijkstra's algorithm on unweighted graphs, where the priority queue degenerates into a FIFO queue.
The fast marching method can be viewed as a continuous version of Dijkstra's algorithm which computes the geodesic distance on a triangle mesh.
Dynamic programming perspective
From a dynamic programming point of view, Dijkstra's algorithm is a successive approximation scheme that solves the dynamic programming functional equation for the shortest path problem by the Reaching method.
In fact, Dijkstra's explanation of the logic behind the algorithm:
is a paraphrasing of Bellman's Principle of Optimality in the context of the shortest path problem. | Dijkstra's algorithm | Wikipedia | 415 | 45809 | https://en.wikipedia.org/wiki/Dijkstra%27s%20algorithm | Mathematics | Graph theory | null |
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and joints' that create the form and shape of human-made structures. Structural engineers also must understand and calculate the stability, strength, rigidity and earthquake-susceptibility of built structures for buildings and nonbuilding structures. The structural designs are integrated with those of other designers such as architects and building services engineer and often supervise the construction of projects by contractors on site. They can also be involved in the design of machinery, medical equipment, and vehicles where structural integrity affects functioning and safety. See glossary of structural engineering.
Structural engineering theory is based upon applied physical laws and empirical knowledge of the structural performance of different materials and geometries. Structural engineering design uses a number of relatively simple structural concepts to build complex structural systems. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals.
History
Structural engineering dates back to 2700 B.C. when the step pyramid for Pharaoh Djoser was built by Imhotep, the first engineer in history known by name. Pyramids were the most common major structures built by ancient civilizations because the structural form of a pyramid is inherently stable and can be almost infinitely scaled (as opposed to most other structural forms, which cannot be linearly increased in size in proportion to increased loads).
The structural stability of the pyramid, whilst primarily gained from its shape, relies also on the strength of the stone from which it is constructed, and its ability to support the weight of the stone above it. The limestone blocks were often taken from a quarry near the building site and have a compressive strength from 30 to 250 MPa (MPa = Pa × 106). Therefore, the structural strength of the pyramid stems from the material properties of the stones from which it was built rather than the pyramid's geometry.
Throughout ancient and medieval history most architectural design and construction were carried out by artisans, such as stonemasons and carpenters, rising to the role of master builder. No theory of structures existed, and understanding of how structures stood up was extremely limited, and based almost entirely on empirical evidence of 'what had worked before' and intuition. Knowledge was retained by guilds and seldom supplanted by advances. Structures were repetitive, and increases in scale were incremental. | Structural engineering | Wikipedia | 478 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
No record exists of the first calculations of the strength of structural members or the behavior of structural material, but the profession of a structural engineer only really took shape with the Industrial Revolution and the re-invention of concrete (see History of Concrete). The physical sciences underlying structural engineering began to be understood in the Renaissance and have since developed into computer-based applications pioneered in the 1970s.
Timeline
1452–1519 Leonardo da Vinci made many contributions.
1638: Galileo Galilei published the book Two New Sciences in which he examined the failure of simple structures.
1660: Hooke's law by Robert Hooke.
1687: Isaac Newton published Philosophiæ Naturalis Principia Mathematica, which contains his laws of motion.
1750: Euler–Bernoulli beam equation.
1700–1782: Daniel Bernoulli introduced the principle of virtual work.
1707–1783: Leonhard Euler developed the theory of buckling of columns.
1826: Claude-Louis Navier published a treatise on the elastic behaviors of structures.
1873: Carlo Alberto Castigliano presented his dissertation "Intorno ai sistemi elastici", which contains his theorem for computing displacement as the partial derivative of the strain energy. This theorem includes the method of "least work" as a special case.
1874: Otto Mohr formalized the idea of a statically indeterminate structure.
1922: Timoshenko corrects the Euler–Bernoulli beam equation.
1936: Hardy Cross' publication of the moment distribution method, an important innovation in the design of continuous frames.
1941: Alexander Hrennikoff solved the discretization of plane elasticity problems using a lattice framework.
1942: Richard Courant divided a domain into finite subregions.
1956: J. Turner, R. W. Clough, H. C. Martin, and L. J. Topp's paper on the "Stiffness and Deflection of Complex Structures" introduces the name "finite-element method" and is widely recognized as the first comprehensive treatment of the method as it is known today.
Structural failure | Structural engineering | Wikipedia | 428 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
The history of structural engineering contains many collapses and failures. Sometimes this is due to obvious negligence, as in the case of the Pétion-Ville school collapse, in which Rev. Fortin Augustin " constructed the building all by himself, saying he didn't need an engineer as he had good knowledge of construction" following a partial collapse of the three-story schoolhouse that sent neighbors fleeing. The final collapse killed 94 people, mostly children.
In other cases structural failures require careful study, and the results of these inquiries have resulted in improved practices and a greater understanding of the science of structural engineering. Some such studies are the result of forensic engineering investigations where the original engineer seems to have done everything in accordance with the state of the profession and acceptable practice yet a failure still eventuated. A famous case of structural knowledge and practice being advanced in this manner can be found in a series of failures involving box girders which collapsed in Australia during the 1970s.
Theory
Structural engineering depends upon a detailed knowledge of applied mechanics, materials science, and applied mathematics to understand and predict how structures support and resist self-weight and imposed loads. To apply the knowledge successfully a structural engineer generally requires detailed knowledge of relevant empirical and theoretical design codes, the techniques of structural analysis, as well as some knowledge of the corrosion resistance of the materials and structures, especially when those structures are exposed to the external environment. Since the 1990s, specialist software has become available to aid in the design of structures, with the functionality to assist in the drawing, analyzing and designing of structures with maximum precision; examples include AutoCAD, StaadPro, ETABS, Prokon, Revit Structure, Inducta RCB, etc. Such software may also take into consideration environmental loads, such as earthquakes and winds.
Profession
Structural engineers are responsible for engineering design and structural analysis. Entry-level structural engineers may design the individual structural elements of a structure, such as the beams and columns of a building. More experienced engineers may be responsible for the structural design and integrity of an entire system, such as a building.
Structural engineers often specialize in particular types of structures, such as buildings, bridges, pipelines, industrial, tunnels, vehicles, ships, aircraft, and spacecraft. Structural engineers who specialize in buildings may specialize in particular construction materials such as concrete, steel, wood, masonry, alloys and composites. | Structural engineering | Wikipedia | 478 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
Structural engineering has existed since humans first started to construct their structures. It became a more defined and formalized profession with the emergence of architecture as a distinct profession from engineering during the industrial revolution in the late 19th century. Until then, the architect and the structural engineer were usually one and the same thing – the master builder. Only with the development of specialized knowledge of structural theories that emerged during the 19th and early 20th centuries, did the professional structural engineers come into existence.
The role of a structural engineer today involves a significant understanding of both static and dynamic loading and the structures that are available to resist them. The complexity of modern structures often requires a great deal of creativity from the engineer in order to ensure the structures support and resist the loads they are subjected to. A structural engineer will typically have a four or five-year undergraduate degree, followed by a minimum of three years of professional practice before being considered fully qualified.
Structural engineers are licensed or accredited by different learned societies and regulatory bodies around the world (for example, the Institution of Structural Engineers in the UK). Depending on the degree course they have studied and/or the jurisdiction they are seeking licensure in, they may be accredited (or licensed) as just structural engineers, or as civil engineers, or as both civil and structural engineers.
Another international organisation is IABSE(International Association for Bridge and Structural Engineering). The aim of that association is to exchange knowledge and to advance the practice of structural engineering worldwide in the service of the profession and society.
Specializations
Building structures
Structural building engineering is primarily driven by the creative manipulation of materials and forms and the underlying mathematical and scientific ideas to achieve an end that fulfills its functional requirements and is structurally safe when subjected to all the loads it could reasonably be expected to experience. This is subtly different from architectural design, which is driven by the creative manipulation of materials and forms, mass, space, volume, texture, and light to achieve an end which is aesthetic, functional, and often artistic. | Structural engineering | Wikipedia | 400 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
The structural design for a building must ensure that the building can stand up safely, able to function without excessive deflections or movements which may cause fatigue of structural elements, cracking or failure of fixtures, fittings or partitions, or discomfort for occupants. It must account for movements and forces due to temperature, creep, cracking, and imposed loads. It must also ensure that the design is practically buildable within acceptable manufacturing tolerances of the materials. It must allow the architecture to work, and the building services to fit within the building and function (air conditioning, ventilation, smoke extract, electrics, lighting, etc.). The structural design of a modern building can be extremely complex and often requires a large team to complete.
Structural engineering specialties for buildings include:
Earthquake engineering
Façade engineering
Fire engineering
Roof engineering
Tower engineering
Wind engineering
Earthquake engineering structures
Earthquake engineering structures are those engineered to withstand earthquakes.
The main objectives of earthquake engineering are to understand the interaction of structures with the shaking ground, foresee the consequences of possible earthquakes, and design and construct the structures to perform during an earthquake.
Earthquake-proof structures are not necessarily extremely strong like the El Castillo pyramid at Chichen Itza shown above.
One important tool of earthquake engineering is base isolation, which allows the base of a structure to move freely with the ground.
Civil engineering structures
Civil structural engineering includes all structural engineering related to the built environment. It includes:
The structural engineer is the lead designer on these structures, and often the sole designer. In the design of structures such as these, structural safety is of paramount importance (in the UK, designs for dams, nuclear power stations and bridges must be signed off by a chartered engineer).
Civil engineering structures are often subjected to very extreme forces, such as large variations in temperature, dynamic loads such as waves or traffic, or high pressures from water or compressed gases. They are also often constructed in corrosive environments, such as at sea, in industrial facilities, or below ground.
resisted and significant deflections of structures.
The forces which parts of a machine are subjected to can vary significantly and can do so at a great rate. The forces which a boat or aircraft are subjected to vary enormously and will do so thousands of times over the structure's lifetime. The structural design must ensure that such structures can endure such loading for their entire design life without failing.
These works can require mechanical structural engineering:
Boilers and pressure vessels
Coachworks and carriages
Cranes
Elevators
Escalators
Marine vessels and hulls
Aerospace structures | Structural engineering | Wikipedia | 504 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
Aerospace structure types include launch vehicles, (Atlas, Delta, Titan), missiles (ALCM, Harpoon), Hypersonic vehicles (Space Shuttle), military aircraft (F-16, F-18) and commercial aircraft (Boeing 777, MD-11). Aerospace structures typically consist of thin plates with stiffeners for the external surfaces, bulkheads, and frames to support the shape and fasteners such as welds, rivets, screws, and bolts to hold the components together.
Nanoscale structures
A nanostructure is an object of intermediate size between molecular and microscopic (micrometer-sized) structures. In describing nanostructures it is necessary to differentiate between the number of dimensions on the nanoscale. Nanotextured surfaces have one dimension on the nanoscale, i.e., only the thickness of the surface of an object is between 0.1 and 100 nm. Nanotubes have two dimensions on the nanoscale, i.e., the diameter of the tube is between 0.1 and 100 nm; its length could be much greater. Finally, spherical nanoparticles have three dimensions on the nanoscale, i.e., the particle is between 0.1 and 100 nm in each spatial dimension. The terms nanoparticles and ultrafine particles (UFP) often are used synonymously although UFP can reach into the micrometer range. The term 'nanostructure' is often used when referring to magnetic technology.
Structural engineering for medical science
Medical equipment (also known as armamentarium) is designed to aid in the diagnosis, monitoring or treatment of medical conditions. There are several basic types: diagnostic equipment includes medical imaging machines, used to aid in diagnosis; equipment includes infusion pumps, medical lasers, and LASIK surgical machines; medical monitors allow medical staff to measure a patient's medical state. Monitors may measure patient vital signs and other parameters including ECG, EEG, blood pressure, and dissolved gases in the blood; diagnostic medical equipment may also be used in the home for certain purposes, e.g. for the control of diabetes mellitus. A biomedical equipment technician (BMET) is a vital component of the healthcare delivery system. Employed primarily by hospitals, BMETs are the people responsible for maintaining a facility's medical equipment.
Structural elements
Any structure is essentially made up of only a small number of different types of elements:
Columns
Beams
Plates
Arches
Shells
Catenaries | Structural engineering | Wikipedia | 509 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
Many of these elements can be classified according to form (straight, plane / curve) and dimensionality (one-dimensional / two-dimensional):
Columns
Columns are elements that carry only axial force (compression) or both axial force and bending (which is technically called a beam-column but practically, just a column). The design of a column must check the axial capacity of the element and the buckling capacity.
The buckling capacity is the capacity of the element to withstand the propensity to buckle. Its capacity depends upon its geometry, material, and the effective length of the column, which depends upon the restraint conditions at the top and bottom of the column. The effective length is where is the real length of the column and K is the factor dependent on the restraint conditions.
The capacity of a column to carry axial load depends on the degree of bending it is subjected to, and vice versa. This is represented on an interaction chart and is a complex non-linear relationship.
Beams
A beam may be defined as an element in which one dimension is much greater than the other two and the applied loads are usually normal to the main axis of the element. Beams and columns are called line elements and are often represented by simple lines in structural modeling.
cantilevered (supported at one end only with a fixed connection)
simply supported (fixed against vertical translation at each end and horizontal translation at one end only, and able to rotate at the supports)
fixed (supported in all directions for translation and rotation at each end)
continuous (supported by three or more supports)
a combination of the above (ex. supported at one end and in the middle)
Beams are elements that carry pure bending only. Bending causes one part of the section of a beam (divided along its length) to go into compression and the other part into tension. The compression part must be designed to resist buckling and crushing, while the tension part must be able to adequately resist the tension.
Trusses | Structural engineering | Wikipedia | 395 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
A truss is a structure comprising members and connection points or nodes. When members are connected at nodes and forces are applied at nodes members can act in tension or compression. Members acting in compression are referred to as compression members or struts while members acting in tension are referred to as tension members or ties. Most trusses use gusset plates to connect intersecting elements. Gusset plates are relatively flexible and unable to transfer bending moments. The connection is usually arranged so that the lines of force in the members are coincident at the joint thus allowing the truss members to act in pure tension or compression.
Trusses are usually used in large-span structures, where it would be uneconomical to use solid beams.
Plates
Plates carry bending in two directions. A concrete flat slab is an example of a plate. Plates are understood by using continuum mechanics, but due to the complexity involved they are most often designed using a codified empirical approach, or computer analysis.
They can also be designed with yield line theory, where an assumed collapse mechanism is analyzed to give an upper bound on the collapse load. This technique is used in practice but because the method provides an upper-bound (i.e. an unsafe prediction of the collapse load) for poorly conceived collapse mechanisms, great care is needed to ensure that the assumed collapse mechanism is realistic.
Shells
Shells derive their strength from their form and carry forces in compression in two directions. A dome is an example of a shell. They can be designed by making a hanging-chain model, which will act as a catenary in pure tension and inverting the form to achieve pure compression.
Arches
Arches carry forces in compression in one direction only, which is why it is appropriate to build arches out of masonry. They are designed by ensuring that the line of thrust of the force remains within the depth of the arch. It is mainly used to increase the bountifulness of any structure.
Catenaries
Catenaries derive their strength from their form and carry transverse forces in pure tension by deflecting (just as a tightrope will sag when someone walks on it). They are almost always cable or fabric structures. A fabric structure acts as a catenary in two directions.
Materials
Structural engineering depends on the knowledge of materials and their properties, in order to understand how different materials support and resist loads. It also involves a knowledge of Corrosion engineering to avoid for example galvanic coupling of dissimilar materials. | Structural engineering | Wikipedia | 495 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
Common structural materials are:
Iron: wrought iron, cast iron
Concrete: reinforced concrete, prestressed concrete
Alloy: steel, stainless steel
Masonry
Timber: hardwood, softwood
Aluminium
Composite materials: plywood
Other structural materials: adobe, bamboo, carbon fibre, fiber reinforced plastic, mudbrick, roofing materials | Structural engineering | Wikipedia | 61 | 45829 | https://en.wikipedia.org/wiki/Structural%20engineering | Technology | Disciplines | null |
Tetanus (), also known as lockjaw, is a bacterial infection caused by Clostridium tetani and characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually lasts for a few minutes. Spasms occur frequently for three to four weeks. Some spasms may be severe enough to fracture bones. Other symptoms of tetanus may include fever, sweating, headache, trouble swallowing, high blood pressure, and a fast heart rate. The onset of symptoms is typically 3 to 21 days following infection. Recovery may take months; about 10% of cases prove to be fatal.
C. tetani is commonly found in soil, saliva, dust, and manure. The bacteria generally enter through a break in the skin, such as a cut or puncture wound caused by a contaminated object. They produce toxins that interfere with normal muscle contractions. Diagnosis is based on the presenting signs and symptoms. The disease does not spread between people.
Tetanus can be prevented by immunization with the tetanus vaccine. In those who have a significant wound and have had fewer than three doses of the vaccine, both vaccination and tetanus immune globulin are recommended. The wound should be cleaned, and any dead tissue should be removed. In those who are infected, tetanus immune globulin, or, if unavailable, intravenous immunoglobulin (IVIG) is used. Muscle relaxants may be used to control spasms. Mechanical ventilation may be required if a person's breathing is affected.
Tetanus occurs in all parts of the world but is most frequent in hot and wet climates where the soil has a high organic content. In 2015, there were about 209,000 infections and about 59,000 deaths globally. This is down from 356,000 deaths in 1990. In the US, there are about 30 cases per year, almost all of which were in people who had not been vaccinated. An early description of the disease was made by Hippocrates in the 5th century BC. The cause of the disease was determined in 1884 by Antonio Carle and Giorgio Rattone at the University of Turin, and a vaccine was developed in 1924.
Signs and symptoms | Tetanus | Wikipedia | 477 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Tetanus often begins with mild spasms in the jaw muscles—also known as lockjaw. Similar spasms can also be a feature of trismus. The spasms can also affect the facial muscles, resulting in an appearance called risus sardonicus. Chest, neck, back, abdominal muscles, and buttocks may be affected. Back muscle spasms often cause arching, called opisthotonus. Sometimes, the spasms affect muscles utilized during inhalation and exhalation, which can lead to breathing problems.
Prolonged muscular action causes sudden, powerful, and painful contractions of muscle groups, called tetany. These episodes can cause fractures and muscle tears. Other symptoms include fever, headache, restlessness, irritability, feeding difficulties, breathing problems, burning sensation during urination, urinary retention, and loss of stool control.
Even with treatment, about 10% of people who contract tetanus die. The mortality rate is higher in unvaccinated individuals, and in people over 60 years of age.
Incubation period
The incubation period of tetanus may be up to several months but is usually about ten days. In general, the farther the injury site is from the central nervous system, the longer the incubation period. However, shorter incubation periods will have more severe symptoms. In trismus nascentium (i.e. neonatal tetanus), symptoms usually appear from 4 to 14 days after birth, averaging about 7 days. On the basis of clinical findings, four different forms of tetanus have been described.
Generalized tetanus
Generalized tetanus is the most common type of tetanus, representing about 80% of cases. The generalized form usually presents with a descending pattern. The first sign is trismus or lockjaw, then facial spasms (called risus sardonicus), followed by stiffness of the neck, difficulty in swallowing, and rigidity of pectoral and calf muscles. Other symptoms include elevated temperature, sweating, elevated blood pressure, and episodic rapid heart rate. Spasms may occur frequently and last for several minutes, with the body shaped into a characteristic form called opisthotonos. Spasms continue for up to four weeks, and complete recovery may take months.
Neonatal tetanus | Tetanus | Wikipedia | 478 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Neonatal tetanus (trismus nascentium) is a form of generalized tetanus that occurs in newborns, usually those born to mothers who themselves have not been vaccinated. If the mother has been vaccinated against tetanus, the infants acquire passive immunity, and are thus protected. It usually occurs through infection of the unhealed umbilical stump, particularly when the stump is cut with a non-sterile instrument. As of 1998, neonatal tetanus was common in many developing countries, and was responsible for about 14% (215,000) of all neonatal deaths. In 2010, the worldwide death toll was approximately 58,000 newborns. As the result of a public health campaign, the death toll from neonatal tetanus was reduced by 90% between 1990 and 2010, and by 2013, the disease had been largely eliminated from all but 25 countries. Neonatal tetanus is rare in developed countries.
Local tetanus
Local tetanus is an uncommon form of the disease, in which people have persistent contraction of muscles in the same anatomic area as the injury. The contractions may persist for many weeks before gradually subsiding. Local tetanus is generally milder; only about 1% of cases are fatal, but it may precede the onset of generalized tetanus.
Cephalic tetanus
Cephalic tetanus is the rarest form of the disease (0.9–3% of cases), and is limited to muscles and nerves in the head. It usually occurs after trauma to the head area, including: skull fracture, laceration, eye injury, dental extraction, and otitis media, but it has been observed from injuries to other parts of the body. Paralysis of the facial nerve is most frequently implicated, which may cause lockjaw, facial palsy, or ptosis, but other cranial nerves can also be affected. Cephalic tetanus may progress to a more generalized form of the disease. Due to its rarity, clinicians may be unfamiliar with the clinical presentation, and may not suspect tetanus as the illness. Treatment can be complicated, as symptoms may be concurrent with the initial injury that caused the infection. Cephalic tetanus is more likely than other forms of tetanus to be fatal, with the progression to generalized tetanus carrying a 15–30% case fatality rate.
Cause | Tetanus | Wikipedia | 500 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Tetanus is caused by the tetanus bacterium, Clostridium tetani. The disease is an international health problem, as C. tetani endospores are ubiquitous. Endospores can be introduced into the body through a puncture wound (penetrating trauma). Due to C. tetani being an anaerobic bacterium, it and its endospores thrive in environments that lack oxygen, such as a puncture wound. With the changes in oxygen levels, the turkey drumstick-shaped endospore can quickly spread.
The disease occurs almost exclusively in people who are inadequately immunized. It is more common in hot, damp climates with soil rich in organic matter. Manure-treated soils may contain spores, as they are widely distributed in the intestines and feces of many animals, such as horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. In agricultural areas, a significant number of human adults may harbor the organism.
The spores can also be found on skin surfaces and in contaminated heroin. Rarely, tetanus can be contracted through surgical procedures, intramuscular injections, compound fractures, and dental infections. Animal bites can transmit tetanus.
Tetanus is often associated with rust, especially rusty nails. Although rust itself does not cause tetanus, objects that accumulate rust are often found outdoors or in places that harbor soil bacteria. Additionally, the rough surface of rusty metal provides crevices for dirt containing C. tetani, while a nail affords a means to puncture the skin and deliver endospores deep within the body at the site of the wound. An endospore is a non-metabolizing survival structure that begins to metabolize and cause infection once in an adequate environment. Hence, stepping on a nail (rusty or not) may result in a tetanus infection, as the low-oxygen (anaerobic) environment may exist under the skin, and the puncturing object can deliver endospores to a suitable environment for growth. It is a common misconception that rust itself is the cause; a related misconception is that a puncture from a rust-free nail is not a risk.
Pathophysiology | Tetanus | Wikipedia | 463 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Tetanus neurotoxin (TeNT) binds to the presynaptic membrane of the neuromuscular junction, is internalized, and is transported back through the axon until it reaches the central nervous system. Here, it selectively binds to and is transported into inhibitory neurons via endocytosis. It then leaves the vesicle for the neuron cytosol, where it cleaves vesicle associated membrane protein (VAMP) synaptobrevin, which is necessary for membrane fusion of small synaptic vesicles (SSV's). SSV's carry neurotransmitter to the membrane for release, so inhibition of this process blocks neurotransmitter release.
Tetanus toxin specifically blocks the release of the neurotransmitters GABA and glycine from inhibitory neurons. These neurotransmitters keep overactive motor neurons from firing and also play a role in the relaxation of muscles after contraction. When inhibitory neurons are unable to release their neurotransmitters, motor neurons fire out of control, and muscles have difficulty relaxing. This causes the muscle spasms and spastic paralysis seen in tetanus infection.
The tetanus toxin, tetanospasmin, is made up of a heavy chain and a light chain. There are three domains, each of which contributes to the pathophysiology of the toxin. The heavy chain has two of the domains. The N-terminal side of the heavy chain helps with membrane translocation, and the C-terminal side helps the toxin locate the specific receptor site on the correct neuron. The light chain domain cleaves the VAMP protein once it arrives in the inhibitory neuron cytosol.
There are four main steps in tetanus's mechanism of action: binding to the neuron, internalization of the toxin, membrane translocation, and cleavage of the target VAMP.
Neurospecific binding | Tetanus | Wikipedia | 410 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
The toxin travels from the wound site to the neuromuscular junction through the bloodstream, where it binds to the presynaptic membrane of a motor neuron. The heavy chain C-terminal domain aids in binding to the correct site, recognizing and binding to the correct glycoproteins and glycolipids in the presynaptic membrane. The toxin binds to a site that will be taken into the neuron as an endocytic vesicle that will travel down the axon, past the cell body, and down the dendrites to the dendritic terminal at the spine and central nervous system. Here, it will be released into the synaptic cleft, and allowed to bind with the presynaptic membrane of inhibitory neurons in a similar manner seen with the binding to the motor neuron.
Internalization
Tetanus toxin is then internalized again via endocytosis, this time, in an acidic vesicle. In a mechanism not well understood, depolarization caused by the firing of the inhibitory neuron causes the toxin to be pulled into the neuron inside vesicles.
Membrane translocation
The toxin then needs a way to get out of the vesicle and into the neuron cytosol for it to act on its target. The low pH of the vesicle lumen causes a conformational change in the toxin, shifting it from a water-soluble form to a hydrophobic form. With the hydrophobic patches exposed, the toxin can slide into the vesicle membrane. The toxin forms an ion channel in the membrane that is nonspecific for Na+, K+, Ca2+, and Cl− ions. There is a consensus among experts that this new channel is involved in the translocation of the toxin's light chain from the inside of the vesicle to the neuron cytosol, but the mechanism is not well understood or agreed upon. It has been proposed that the channel could allow the light chain (unfolded from the low pH environment) to leave through the toxin pore, or that the pore could alter the electrochemical gradient enough, by letting in or out ions, to cause osmotic lysis of the vesicle, spilling the vesicle's contents.
Enzymatic target cleavage | Tetanus | Wikipedia | 480 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
The light chain of the tetanus toxin is zinc-dependent protease. It shares a common zinc protease motif (His-Glu-Xaa-Xaa-His) that researchers hypothesized was essential for target cleavage until this was more recently confirmed by experiment: when all zinc was removed from the neuron with heavy metal chelators, the toxin was inhibited, only to be reactivated when the zinc was added back in. The light chain binds to VAMP, and cleaves it between Gln76 and Phe77. Without VAMP, vesicles holding the neurotransmitters needed for motor neuron regulation (GABA and glycine) cannot be released, causing the above-mentioned deregulation of motor neurons and muscle tension.
Diagnosis
There are currently no blood tests for diagnosing tetanus. The diagnosis is based on the presentation of tetanus symptoms and does not depend upon isolation of the bacterium, which is recovered from the wound in only 30% of cases and can be isolated from people without tetanus. Laboratory identification of C. tetani can be demonstrated only by the production of tetanospasmin in mice. Having recently experienced head trauma may indicate cephalic tetanus if no other diagnosis has been made.
The "spatula test" is a clinical test for tetanus that involves touching the posterior pharyngeal wall with a soft-tipped instrument and observing the effect. A positive test result is the involuntary contraction of the jaw (biting down on the "spatula"), and a negative test result would normally be a gag reflex attempting to expel the foreign object. A short report in The American Journal of Tropical Medicine and Hygiene states that, in an affected subject research study, the spatula test had a high specificity (zero false-positive test results) and a high sensitivity (94% of infected people produced a positive test).
Prevention
Unlike many infectious diseases, recovery from naturally acquired tetanus does not usually result in immunity. This is due to the extreme potency of the tetanospasmin toxin. Tetanospasmin will likely be lethal before it will provoke an immune response. | Tetanus | Wikipedia | 454 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Tetanus can be prevented by vaccination with tetanus toxoid. The CDC recommends that adults receive a booster vaccine every ten years, and standard care practice in many places is to give the booster to any person with a puncture wound who is uncertain of when they were last vaccinated, or if they have had fewer than three lifetime doses of the vaccine. The booster may not prevent a potentially fatal case of tetanus from the current wound, however, as it can take up to two weeks for tetanus antibodies to form.
In children under the age of seven, the tetanus vaccine is often administered as a combined vaccine, DPT/DTaP vaccine, which also includes vaccines against diphtheria and pertussis. For adults and children over seven, the Td vaccine (tetanus and diphtheria) or Tdap (tetanus, diphtheria, and acellular pertussis) is commonly used.
The World Health Organization certifies countries as having eliminated maternal or neonatal tetanus. Certification requires at least two years of rates of less than 1 case per 1,000 live births. In 1998 in Uganda, 3,433 tetanus cases were recorded in newborn babies; of these, 2,403 died. After a major public health effort, Uganda was certified as having eliminated maternal and neonatal tetanus in 2011.
Post-exposure prophylaxis
Tetanus toxoid can be given in case of suspected exposure to tetanus. In such cases, it can be given with or without tetanus immunoglobulin (also called tetanus antibodies or tetanus antitoxin). It can be given as intravenous therapy or by intramuscular injection.
The guidelines for such events in the United States for people at least 11 years old (and not pregnant) are as follows:
Treatment
Mild tetanus
Mild cases of tetanus can be treated with:
Tetanus immunoglobulin (TIG), also called tetanus antibodies or tetanus antitoxin. It can be given as intravenous therapy or by intramuscular injection.
Antibiotic therapy to reduce toxin production. Metronidazole intravenous (IV) is a preferred treatment.
Benzodiazepines can be used to control muscle spasms. Options include diazepam and lorazepam, oral or IV. | Tetanus | Wikipedia | 506 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Severe tetanus
Severe cases will require admission to intensive care. In addition to the measures listed above for mild tetanus:
Human tetanus immunoglobulin injected intrathecally (which increases clinical improvement from 4% to 35%).
Tracheotomy and mechanical ventilation for 3 to 4 weeks. Tracheotomy is recommended for securing the airway, because the presence of an endotracheal tube is a stimulus for spasm.
Magnesium sulfate, as an intravenous infusion, to control spasm and autonomic dysfunction.
Diazepam as a continuous IV infusion.
The autonomic effects of tetanus can be difficult to manage (alternating hyper- and hypotension hyperpyrexia/hypothermia), and may require IV labetalol, magnesium, clonidine, or nifedipine.
Drugs, such as diazepam or other muscle relaxants, can be given to control the muscle spasms. In extreme cases, it may be necessary to paralyze the person with curare-like drugs, and use a mechanical ventilator.
To survive a tetanus infection, the maintenance of an airway and proper nutrition are required. An intake of and at least 150 g of protein per day is often given in liquid form through a tube directly into the stomach (percutaneous endoscopic gastrostomy), or through a drip into a vein (parenteral nutrition). This high-caloric diet maintenance is required because of the increased metabolic strain brought on by the increased muscle activity. Full recovery takes 4 to 6 weeks because the body must regenerate destroyed nerve axon terminals.
The antibiotic of choice is metronidazole. It can be given intravenously, by mouth, or by rectum. Of likewise efficiency is penicillin, but some raise the concern of provoking spasms because it inhibits GABA receptor, which is already affected by tetanospasmin.
Epidemiology | Tetanus | Wikipedia | 421 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
In 2013, it caused about 59,000 deaths—down from 356,000 in 1990. Tetanus, notably the neonatal form, remains a significant public health problem in non-industrialized countries, with 59,000 newborns dying worldwide in 2008 as a result of neonatal tetanus. In the United States, from 2000 through 2007, an average of 31 cases were reported per year. Nearly all of the cases in the United States occur in unimmunized individuals, or individuals who have allowed their inoculations to lapse.
In animals
Tetanus is found primarily in goats and sheep. The following are clinical symptoms found in affected goats and sheep. Extended head and neck, tail rigors
(tail becomes rigid and straight), abnormal gait (walking becomes stiff and abnormal), arched back, stiffness of the jaw muscles, lockjaw,
twitching of eyes, drooping eyelids, difficulty swallowing, difficulty or inability to eat and drink, abdominal bloat, spasms (uncontrolled muscular contractions) before death.
Death sometimes is due to asphyxiation, secondary to respiratory paralysis.
History
Tetanus was well known to ancient civilizations, who recognized the relationship between wounds and fatal muscle spasms. In 1884, Arthur Nicolaier isolated the strychnine-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1884 by Antonio Carle and Giorgio Rattone, two pathologists of the University of Turin, who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting pus from a person with fatal tetanus into their sciatic nerves, and testing their reactions while tetanus was spreading.
In 1891, C. tetani was isolated from a human victim by Kitasato Shibasaburō, who later showed that the organism could produce disease when injected into animals and that the toxin could be neutralized by specific antibodies. In 1897, Edmond Nocard showed that tetanus antitoxin induced passive immunity in humans, and could be used for prophylaxis and treatment. Tetanus toxoid vaccine was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.
Etymology
The word tetanus comes from the , which is further from the . | Tetanus | Wikipedia | 501 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
Research
There is insufficient evidence that tetanus can be treated or prevented by vitamin C. This is at least partially due to the fact that the historical trials that were conducted in attempts to look for a possible connection between vitamin C and alleviating tetanus patients were of poor quality. | Tetanus | Wikipedia | 58 | 45831 | https://en.wikipedia.org/wiki/Tetanus | Biology and health sciences | Infectious disease | null |
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound.
The driver is a linear motor connected to a diaphragm, which transmits the motor's movement to produce sound by moving air. An audio signal, typically originating from a microphone, recording, or radio broadcast, is electronically amplified to a power level sufficient to drive the motor, reproducing the sound corresponding to the original unamplified signal. This process functions as the inverse of a microphone. In fact, the dynamic speaker driver—the most common type—shares the same basic configuration as a dynamic microphone, which operates in reverse as a generator.
The dynamic speaker was invented in 1925 by Edward W. Kellogg and Chester W. Rice. When the electrical current from an audio signal passes through its voice coil—a coil of wire capable of moving axially in a cylindrical gap containing a concentrated magnetic field produced by a permanent magnet—the coil is forced to move rapidly back and forth due to Faraday's law of induction; this attaches to a diaphragm or speaker cone (as it is usually conically shaped for sturdiness) in contact with air, thus creating sound waves. In addition to dynamic speakers, several other technologies are possible for creating sound from an electrical signal, a few of which are in commercial use. | Loudspeaker | Wikipedia | 322 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
For a speaker to efficiently produce sound, especially at lower frequencies, the speaker driver must be baffled so that the sound emanating from its rear does not cancel out the (intended) sound from the front; this generally takes the form of a speaker enclosure or speaker cabinet, an often rectangular box made of wood, but sometimes metal or plastic. The enclosure's design plays an important acoustic role thus determining the resulting sound quality. Most high fidelity speaker systems (picture at right) include two or more sorts of speaker drivers, each specialized in one part of the audible frequency range. The smaller drivers capable of reproducing the highest audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers and those for low frequencies are called woofers. Sometimes the reproduction of the very lowest frequencies (20–~50 Hz) is augmented by a so-called subwoofer often in its own (large) enclosure. In a two-way or three-way speaker system (one with drivers covering two or three different frequency ranges) there is a small amount of passive electronics called a crossover network which helps direct components of the electronic signal to the speaker drivers best capable of reproducing those frequencies. In a so-called powered speaker system, the power amplifier actually feeding the speaker drivers is built into the enclosure itself; these have become more and more common especially as computer speakers.
Smaller speakers are found in devices such as radios, televisions, portable audio players, personal computers (computer speakers), headphones, and earphones. Larger, louder speaker systems are used for home hi-fi systems (stereos), electronic musical instruments, sound reinforcement in theaters and concert halls, and in public address systems.
Terminology
The term loudspeaker may refer to individual transducers (also known as drivers) or to complete speaker systems consisting of an enclosure and one or more drivers. | Loudspeaker | Wikipedia | 386 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
To adequately and accurately reproduce a wide range of frequencies with even coverage, most loudspeaker systems employ more than one driver, particularly for higher sound pressure level (SPL) or maximum accuracy. Individual drivers are used to reproduce different frequency ranges. The drivers are named subwoofers (for very low frequencies); woofers (low frequencies); mid-range speakers (middle frequencies); tweeters (high frequencies); and sometimes supertweeters, for the highest audible frequencies and beyond. The terms for different speaker drivers differ, depending on the application. In two-way systems there is no mid-range driver, so the task of reproducing the mid-range sounds is divided between the woofer and tweeter. When multiple drivers are used in a system, a filter network, called an audio crossover, separates the incoming signal into different frequency ranges and routes them to the appropriate driver. A loudspeaker system with n separate frequency bands is described as n-way speakers: a two-way system will have a woofer and a tweeter; a three-way system employs a woofer, a mid-range, and a tweeter. Loudspeaker drivers of the type pictured are termed dynamic (short for electrodynamic) to distinguish them from other sorts including moving iron speakers, and speakers using piezoelectric or electrostatic systems. | Loudspeaker | Wikipedia | 287 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
History
Johann Philipp Reis installed an electric loudspeaker in his telephone in 1861; it was capable of reproducing clear tones, but later revisions could also reproduce muffled speech. Alexander Graham Bell patented his first electric loudspeaker (a moving iron type capable of reproducing intelligible speech) as part of his telephone in 1876, which was followed in 1877 by an improved version from Ernst Siemens. During this time, Thomas Edison was issued a British patent for a system using compressed air as an amplifying mechanism for his early cylinder phonographs, but he ultimately settled for the familiar metal horn driven by a membrane attached to the stylus. In 1898, Horace Short patented a design for a loudspeaker driven by compressed air; he then sold the rights to Charles Parsons, who was issued several additional British patents before 1910. A few companies, including the Victor Talking Machine Company and Pathé, produced record players using compressed-air loudspeakers. Compressed-air designs are significantly limited by their poor sound quality and their inability to reproduce sound at low volume. Variants of the design were used for public address applications, and more recently, other variations have been used to test space-equipment resistance to the very loud sound and vibration levels that the launching of rockets produces.
Moving-coil
The first experimental moving-coil (also called dynamic) loudspeaker was invented by Oliver Lodge in 1898. The first practical moving-coil loudspeakers were manufactured by Danish engineer Peter L. Jensen and Edwin Pridham in 1915, in Napa, California. Like previous loudspeakers these used horns to amplify the sound produced by a small diaphragm. Jensen was denied patents. Being unsuccessful in selling their product to telephone companies, in 1915 they changed their target market to radios and public address systems, and named their product Magnavox. Jensen was, for years after the invention of the loudspeaker, a part owner of The Magnavox Company.
The moving-coil principle commonly used today in speakers was patented in 1925 by Edward W. Kellogg and Chester W. Rice. The key difference between previous attempts and the patent by Rice and Kellogg is the adjustment of mechanical parameters to provide a reasonably flat frequency response. | Loudspeaker | Wikipedia | 459 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
These first loudspeakers used electromagnets, because large, powerful permanent magnets were generally not available at a reasonable price. The coil of an electromagnet, called a field coil, was energized by a current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil, filtering the power supply of the amplifier that the loudspeaker was connected to. AC ripple in the current was attenuated by the action of passing through the choke coil. However, AC line frequencies tended to modulate the audio signal going to the voice coil and added to the audible hum. In 1930 Jensen introduced the first commercial fixed-magnet loudspeaker; however, the large, heavy iron magnets of the day were impractical and field-coil speakers remained predominant until the widespread availability of lightweight alnico magnets after World War II.
First loudspeaker systems
In the 1930s, loudspeaker manufacturers began to combine two and three drivers or sets of drivers each optimized for a different frequency range in order to improve frequency response and increase sound pressure level. In 1937, the first film industry-standard loudspeaker system, "The Shearer Horn System for Theatres", a two-way system, was introduced by Metro-Goldwyn-Mayer. It used four 15" low-frequency drivers, a crossover network set for 375 Hz, and a single multi-cellular horn with two compression drivers providing the high frequencies. John Kenneth Hilliard, James Bullough Lansing, and Douglas Shearer all played roles in creating the system. At the 1939 New York World's Fair, a very large two-way public address system was mounted on a tower at Flushing Meadows. The eight 27" low-frequency drivers were designed by Rudy Bozak in his role as chief engineer for Cinaudagraph. High-frequency drivers were likely made by Western Electric. | Loudspeaker | Wikipedia | 398 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Altec Lansing introduced the 604, which became their most famous coaxial Duplex driver, in 1943. It incorporated a high-frequency horn that sent sound through a hole in the pole piece of a 15-inch woofer for near-point-source performance. Altec's "Voice of the Theatre" loudspeaker system was first sold in 1945, offering better coherence and clarity at the high output levels necessary in movie theaters. The Academy of Motion Picture Arts and Sciences immediately began testing its sonic characteristics; they made it the film house industry standard in 1955.
In 1954, Edgar Villchur developed the acoustic suspension principle of loudspeaker design. This allowed for better bass response than previously obtainable from drivers mounted in larger cabinets. He and his partner Henry Kloss formed the Acoustic Research company to manufacture and market speaker systems using this principle. Subsequently, continuous developments in enclosure design and materials led to significant audible improvements.
The most notable improvements to date in modern dynamic drivers, and the loudspeakers that employ them, are improvements in cone materials, the introduction of higher-temperature adhesives, improved permanent magnet materials, improved measurement techniques, computer-aided design, and finite element analysis. At low frequencies, Thiele/Small parameters electrical network theory has been used to optimize bass driver and enclosure synergy since the early 1970s.
Driver design: dynamic loudspeakers
Speaker systems
Speaker system design involves subjective perceptions of timbre and sound quality, measurements and experiments. Adjusting a design to improve performance is done using a combination of magnetic, acoustic, mechanical, electrical, and materials science theory, and tracked with high-precision measurements and the observations of experienced listeners. A few of the issues speaker and driver designers must confront are distortion, acoustic lobing, phase effects, off-axis response, and crossover artifacts. Designers can use an anechoic chamber to ensure the speaker can be measured independently of room effects, or any of several electronic techniques that, to some extent, substitute for such chambers. Some developers eschew anechoic chambers in favor of specific standardized room setups intended to simulate real-life listening conditions. | Loudspeaker | Wikipedia | 440 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Individual electrodynamic drivers provide their best performance within a limited frequency range. Multiple drivers (e.g. subwoofers, woofers, mid-range drivers, and tweeters) are generally combined into a complete loudspeaker system to provide performance beyond that constraint. The three most commonly used sound radiation systems are the cone, dome and horn-type drivers.
Full-range drivers
A full- or wide-range driver is a speaker driver designed to be used alone to reproduce an audio channel without the help of other drivers and therefore must cover the audio frequency range required by the application. These drivers are small, typically in diameter to permit reasonable high-frequency response, and carefully designed to give low-distortion output at low frequencies, though with reduced maximum output level. Full-range drivers are found, for instance, in public address systems, in televisions, small radios, intercoms, and some computer speakers.
In hi-fi speaker systems, the use of wide-range drivers can avoid undesirable interactions between multiple drivers caused by non-coincident driver location or crossover network issues but also may limit frequency response and output abilities (most especially at low frequencies). Hi-fi speaker systems built with wide-range drivers may require large, elaborate or, expensive enclosures to approach optimum performance.
Full-range drivers often employ an additional cone called a whizzer: a small, light cone attached to the joint between the voice coil and the primary cone. The whizzer cone extends the high-frequency response of the driver and broadens its high-frequency directivity, which would otherwise be greatly narrowed due to the outer diameter cone material failing to keep up with the central voice coil at higher frequencies. The main cone in a whizzer design is manufactured so as to flex more in the outer diameter than in the center. The result is that the main cone delivers low frequencies and the whizzer cone contributes most of the higher frequencies. Since the whizzer cone is smaller than the main diaphragm, output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm.
Limited-range drivers, also used alone, are typically found in computers, toys, and clock radios. These drivers are less elaborate and less expensive than wide-range drivers, and they may be severely compromised to fit into very small mounting locations. In these applications, sound quality is a low priority.
Subwoofer | Loudspeaker | Wikipedia | 506 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
A subwoofer is a woofer driver used only for the lowest-pitched part of the audio spectrum: typically below 200 Hz for consumer systems, below 100 Hz for professional live sound, and below 80 Hz in THX-approved systems. Because the intended range of frequencies is limited, subwoofer system design is usually simpler in many respects than for conventional loudspeakers, often consisting of a single driver enclosed in a suitable enclosure. Since sound in this frequency range can easily bend around corners by diffraction, the speaker aperture does not have to face the audience, and subwoofers can be mounted in the bottom of the enclosure, facing the floor. This is eased by the limitations of human hearing at low frequencies; Such sounds cannot be located in space, due to their large wavelengths compared to higher frequencies which produce differential effects in the ears due to shadowing by the head, and diffraction around it, both of which we rely upon for localization clues.
To accurately reproduce very low bass notes, subwoofer systems must be solidly constructed and properly braced to avoid unwanted sounds from cabinet vibrations. As a result, good subwoofers are typically quite heavy. Many subwoofer systems include integrated power amplifiers and electronic subsonic-filters, with additional controls relevant to low-frequency reproduction (e.g. a crossover knob and a phase switch). These variants are known as active or powered subwoofers. In contrast, passive subwoofers require external amplification.
In typical installations, subwoofers are physically separated from the rest of the speaker cabinets. Because of propagation delay and positioning, their output may be out of phase with the rest of the sound. Consequently, a subwoofer's power amp often has a phase-delay adjustment which may be used improve performance of the system as a whole. Subwoofers are widely used in large concert and mid-sized venue sound reinforcement systems. Subwoofer cabinets are often built with a bass reflex port, a design feature which if properly engineered improves bass performance and increases efficiency.
Woofer
A woofer is a driver that reproduces low frequencies. The driver works with the characteristics of the speaker enclosure to produce suitable low frequencies. Some loudspeaker systems use a woofer for the lowest frequencies, sometimes well enough that a subwoofer is not needed. Additionally, some loudspeakers use the woofer to handle middle frequencies, eliminating the mid-range driver. | Loudspeaker | Wikipedia | 509 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Mid-range driver
A mid-range speaker is a loudspeaker driver that reproduces a band of frequencies generally between 1–6 kHz, otherwise known as the mid frequencies (between the woofer and tweeter). Mid-range driver diaphragms can be made of paper or composite materials and can be direct radiation drivers (rather like smaller woofers) or they can be compression drivers (rather like some tweeter designs). If the mid-range driver is a direct radiator, it can be mounted on the front baffle of a loudspeaker enclosure, or, if a compression driver, mounted at the throat of a horn for added output level and control of radiation pattern.
Tweeter
A tweeter is a high-frequency driver that reproduces the highest frequencies in a speaker system. A major problem in tweeter design is achieving wide angular sound coverage (off-axis response), since high-frequency sound tends to leave the speaker in narrow beams. Soft-dome tweeters are widely found in home stereo systems, and horn-loaded compression drivers are common in professional sound reinforcement. Ribbon tweeters have gained popularity as the output power of some designs has been increased to levels useful for professional sound reinforcement, and their output pattern is wide in the horizontal plane, a pattern that has convenient applications in concert sound.
Coaxial drivers
A coaxial driver is a loudspeaker driver with two or more combined concentric drivers. Coaxial drivers have been produced by Altec, Tannoy, Pioneer, KEF, SEAS, B&C Speakers, BMS, Cabasse and Genelec.
System design
Crossover
Used in multi-driver speaker systems, the crossover is an assembly of filters that separate the input signal into different frequency bands according to the requirements of each driver. Hence the drivers receive power only in the sound frequency range they were designed for, thereby reducing distortion in the drivers and interference between them. Crossovers can be passive or active. | Loudspeaker | Wikipedia | 410 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
A passive crossover is an electronic circuit that uses a combination of one or more resistors, inductors and capacitors. These components are combined to form a filter network and are most often placed between the full frequency-range power amplifier and the loudspeaker drivers to divide the amplifier's signal into the necessary frequency bands before being delivered to the individual drivers. Passive crossover circuits need no external power beyond the audio signal itself, but have some disadvantages: they may require larger inductors and capacitors due to power handling requirements. Unlike active crossovers which include a built-in amplifier, passive crossovers have an inherent attenuation within the passband, typically leading to a reduction in damping factor before the voice coil.
An active crossover is an electronic filter circuit that divides the signal into individual frequency bands before power amplification, thus requiring at least one power amplifier for each band. Passive filtering may also be used in this way before power amplification, but it is an uncommon solution, being less flexible than active filtering. Any technique that uses crossover filtering followed by amplification is commonly known as bi-amping, tri-amping, quad-amping, and so on, depending on the minimum number of amplifier channels.
Some loudspeaker designs use a combination of passive and active crossover filtering, such as a passive crossover between the mid- and high-frequency drivers and an active crossover for the low-frequency driver. | Loudspeaker | Wikipedia | 297 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Passive crossovers are commonly installed inside speaker boxes and are by far the most common type of crossover for home and low-power use. In car audio systems, passive crossovers may be in a separate box, necessary to accommodate the size of the components used. Passive crossovers may be simple for low-order filtering, or complex to allow steep slopes such as 18 or 24 dB per octave. Passive crossovers can also be designed to compensate for undesired characteristics of driver, horn, or enclosure resonances, and can be tricky to implement, due to component interaction. Passive crossovers, like the driver units that they feed, have power handling limits, have insertion losses, and change the load seen by the amplifier. The changes are matters of concern for many in the hi-fi world. When high output levels are required, active crossovers may be preferable. Active crossovers may be simple circuits that emulate the response of a passive network or may be more complex, allowing extensive audio adjustments. Some active crossovers, usually digital loudspeaker management systems, may include electronics and controls for precise alignment of phase and time between frequency bands, equalization, dynamic range compression and limiting.
Enclosures
Most loudspeaker systems consist of drivers mounted in an enclosure, or cabinet. The role of the enclosure is to prevent sound waves emanating from the back of a driver from interfering destructively with those from the front. The sound waves emitted from the back are 180° out of phase with those emitted forward, so without an enclosure they typically cause cancellations which significantly degrade the level and quality of sound at low frequencies.
The simplest driver mount is a flat panel (baffle) with the drivers mounted in holes in it. However, in this approach, sound frequencies with a wavelength longer than the baffle dimensions are canceled out because the antiphase radiation from the rear of the cone interferes with the radiation from the front. With an infinitely large panel, this interference could be entirely prevented. A sufficiently large sealed box can approach this behavior.
Since panels of infinite dimensions are impossible, most enclosures function by containing the rear radiation from the moving diaphragm. A sealed enclosure prevents transmission of the sound emitted from the rear of the loudspeaker by confining the sound in a rigid and airtight box. Techniques used to reduce the transmission of sound through the walls of the cabinet include thicker cabinet walls, internal bracing and lossy wall material. | Loudspeaker | Wikipedia | 499 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
However, a rigid enclosure reflects sound internally, which can then be transmitted back through the loudspeaker diaphragm—again resulting in degradation of sound quality. This can be reduced by internal absorption using absorptive materials such as glass wool, wool, or synthetic fiber batting, within the enclosure. The internal shape of the enclosure can also be designed to reduce this by reflecting sounds away from the loudspeaker diaphragm, where they may then be absorbed.
Other enclosure types alter the rear sound radiation so it can add constructively to the output from the front of the cone. Designs that do this (including bass reflex, passive radiator, transmission line, etc.) are often used to extend the effective low-frequency response and increase the low-frequency output of the driver.
To make the transition between drivers as seamless as possible, system designers have attempted to time align the drivers by moving one or more driver mounting locations forward or back so that the acoustic center of each driver is in the same vertical plane. This may also involve tilting the driver back, providing a separate enclosure mounting for each driver, or using electronic techniques to achieve the same effect. These attempts have resulted in some unusual cabinet designs.
The speaker mounting scheme (including cabinets) can also cause diffraction, resulting in peaks and dips in the frequency response. The problem is usually greatest at higher frequencies, where wavelengths are similar to, or smaller than, cabinet dimensions.
Horn loudspeakers
Horn loudspeakers are the oldest form of loudspeaker system. The use of horns as voice-amplifying megaphones dates at least to the 17th century, and horns were used in mechanical gramophones as early as 1877. Horn loudspeakers use a shaped waveguide in front of or behind the driver to increase the directivity of the loudspeaker and to transform a small diameter, high-pressure condition at the driver cone surface to a large diameter, low-pressure condition at the mouth of the horn. This improves the acoustic—electro/mechanical impedance match between the driver and ambient air, increasing efficiency, and focusing the sound over a narrower area. | Loudspeaker | Wikipedia | 441 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
The size of the throat, mouth, the length of the horn, as well as the area expansion rate along it must be carefully chosen to match the driver to properly provide this transforming function over a range of frequencies. The length and cross-sectional mouth area required to create a bass or sub-bass horn dictates a horn many feet long. Folded horns can reduce the total size, but compel designers to make compromises and accept increased cost and construction complications. Some horn designs not only fold the low-frequency horn but use the walls in a room corner as an extension of the horn mouth. In the late 1940s, horns whose mouths took up much of a room wall were not unknown among hi-fi fans. Room-sized installations became much less acceptable when two or more were required.
A horn-loaded speaker can have a sensitivity as high as 110 dB at 2.83 volts (1 watt at 8 ohms) at 1 meter. This is a hundredfold increase in output compared to a speaker rated at 90 dB sensitivity and is invaluable in applications where high sound levels are required or amplifier power is limited.
Transmission line loudspeaker
A transmission line loudspeaker is a loudspeaker enclosure design that uses an acoustic transmission line within the cabinet, compared to the simpler enclosure-based designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long (generally folded) damped pathway within the speaker enclosure, which allows greater control and efficient use of speaker energy.
Wiring connections | Loudspeaker | Wikipedia | 321 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Most home hi-fi loudspeakers use two wiring points to connect to the source of the signal (for example, to the audio amplifier or receiver). To accept the wire connection, the loudspeaker enclosure may have binding posts, spring clips, or a panel-mount jack. If the wires for a pair of speakers are not connected with respect to the proper electrical polarity, the loudspeakers are said to be out of phase or more properly out of polarity. Given identical signals, motion in the cone of an out of polarity loudspeaker is in the opposite direction of the others. This typically causes monophonic material in a stereo recording to be canceled out, reduced in level, and made more difficult to localize, all due to destructive interference of the sound waves. The cancellation effect is most noticeable at frequencies where the loudspeakers are separated by a quarter wavelength or less; low frequencies are affected the most. This type of miswiring error does not damage speakers, but is not optimal for listening.
With sound reinforcement system, PA system and instrument amplifier speaker enclosures, cables and some type of jack or connector are typically used. Lower- and mid-priced sound system and instrument speaker cabinets often use 1/4" jacks. Higher-priced and higher-powered sound system cabinets and instrument speaker cabinets often use Speakon connectors. Speakon connectors are considered to be safer for high-wattage amplifiers, because the connector is designed so that human users cannot touch the connectors.
Wireless speakers
Wireless speakers are similar to wired powered speakers, but they receive audio signals using radio frequency (RF) waves rather than over audio cables. There is an amplifier integrated in the speaker's cabinet because the RF waves alone are not enough to drive the speaker. Wireless speakers still need power, so require a nearby AC power outlet, or onboard batteries. Only the wire for the audio is eliminated.
Specifications | Loudspeaker | Wikipedia | 393 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Speaker specifications generally include:
Speaker or driver type (individual units only) – full-range, woofer, tweeter, or mid-range.
Size of individual drivers. For cone drivers, the quoted size is generally the outside diameter of the basket. However, it may less commonly also be the diameter of the cone surround, measured apex to apex, or the distance from the center of one mounting hole to its opposite. Voice-coil diameter may also be specified. If the loudspeaker has a compression horn driver, the diameter of the horn throat may be given.
Rated power – power, and peak power a loudspeaker can handle. A driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies. In some jurisdictions, power handling has a legal meaning allowing comparisons between loudspeakers under consideration. Elsewhere, the variety of meanings for power handling capacity can be quite confusing.
Impedance – typically 4 Ω (ohms), 8 Ω, etc.
Baffle or enclosure type (enclosed systems only) – Sealed, bass reflex, etc.
Number of drivers (complete speaker systems only) – two-way, three-way, etc.
Class of loudspeaker:
Class 1: maximum SPL 110-119 dB, the type of loudspeaker used for reproducing a person speaking in a small space or for background music; mainly used as fill speakers for Class 2 or Class 3 speakers; typically small 4" or 5" woofers and dome tweeters
Class 2: maximum SPL 120-129 dB, the type of medium power-capable loudspeaker used for reinforcement in small to medium spaces or as fill speakers for Class 3 or Class 4 speakers; typically 5" to 8" woofers and dome tweeters
Class 3: maximum SPL 130-139 dB, high power-capable loudspeakers used in main systems in small to medium spaces; also used as fill speakers for class 4 speakers; typically 6.5" to 12" woofers and 2" or 3" compression drivers for high frequencies
Class 4: maximum SPL 140 dB and higher, very high power-capable loudspeakers used as mains in medium to large spaces (or for fill speakers for these medium to large spaces); 10" to 15" woofers and 3" compression drivers | Loudspeaker | Wikipedia | 483 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
and optionally:
Crossover frequency(ies) (multi-driver systems only) – The nominal frequency boundaries of the division between drivers.
Frequency response – The measured, or specified, output over a specified range of frequencies for a constant input level varied across those frequencies. It sometimes includes a variance limit, such as within "± 2.5 dB."
Thiele/Small parameters (individual drivers only) – these include the driver's Fs (resonance frequency), Qts (a driver's Q; more or less, its damping factor at resonant frequency), Vas (the equivalent air compliance volume of the driver), etc.
Sensitivity – The sound pressure level produced by a loudspeaker in a non-reverberant environment, often specified in dB and measured at 1 meter with an input of 1 watt (2.83 rms volts into 8 Ω), typically at one or more specified frequencies. Manufacturers often use this rating in marketing material.
Maximum sound pressure level – The highest output the loudspeaker can manage, short of damage or not exceeding a particular distortion level. Manufacturers often use this rating in marketing material—commonly without reference to frequency range or distortion level.
Electrical characteristics of dynamic loudspeakers
To make sound, a loudspeaker is driven by modulated electric current (produced by an amplifier) that passes through a speaker coil which then (through inductance) creates a magnetic field around the coil. The electric current variations that pass through the speaker are thus converted to a varying magnetic field, whose interaction with the driver's magnetic field moves the speaker diaphragm, which thus forces the driver to produce air motion that is similar to the original signal from the amplifier. | Loudspeaker | Wikipedia | 356 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
The load that a driver presents to an amplifier consists of a complex electrical impedance—a combination of resistance and both capacitive and inductive reactance, which combines properties of the driver, its mechanical motion, the effects of crossover components (if any are in the signal path between amplifier and driver), and the effects of air loading on the driver as modified by the enclosure and its environment. Most amplifiers' output specifications are given at a specific power into an ideal resistive load; however, a loudspeaker does not have a constant impedance across its frequency range. Instead, the voice coil is inductive, the driver has mechanical resonances, the enclosure changes the driver's electrical and mechanical characteristics, and a passive crossover between the drivers and the amplifier contributes its own variations. The result is a load impedance that varies widely with frequency, and usually a varying phase relationship between voltage and current as well, also changing with frequency. Some amplifiers can cope with the variation better than others can.
Electromechanical measurements
Examples of typical loudspeaker measurement are: amplitude and phase characteristics vs. frequency; impulse response under one or more conditions (e.g. square waves, sine wave bursts, etc.); directivity vs. frequency (e.g. horizontally, vertically, spherically, etc.); harmonic and intermodulation distortion vs. sound pressure level (SPL) output, using any of several test signals; stored energy (i.e. ringing) at various frequencies; impedance vs. frequency; and small-signal vs. large-signal performance. Most of these measurements require sophisticated and often expensive equipment to perform. The sound pressure level (SPL) a loudspeaker produces is measured in decibels (dBspl). | Loudspeaker | Wikipedia | 367 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
Efficiency vs. sensitivity
Loudspeaker efficiency is defined as the sound power output divided by the electrical power input. Most loudspeakers are inefficient transducers; only about 1% of the electrical energy sent by an amplifier to a typical home loudspeaker is converted to acoustic energy. The remainder is converted to heat, mostly in the voice coil and magnet assembly. The main reason for this is the difficulty of achieving proper impedance matching between the acoustic impedance of the drive unit and the air it radiates into. The efficiency of loudspeaker drivers varies with frequency as well. For instance, the output of a woofer driver decreases as the input frequency decreases because of the increasingly poor impedance match between air and the driver.
Driver ratings based on the SPL for a given input are called sensitivity ratings and are notionally similar to efficiency. Sensitivity is usually defined as the SPL in decibels at 1 W electrical input, measured at 1 meter, often at a single frequency. The voltage used is often 2.83 VRMS, which results in 1 watt into a nominal 8 Ω speaker impedance. Measurements taken with this reference are quoted as dB with 2.83 V @ 1 m.
The sound pressure output is measured at (or mathematically scaled to be equivalent to a measurement taken at) one meter from the loudspeaker and on-axis (directly in front of it), under the condition that the loudspeaker is radiating into an infinitely large space and mounted on an infinite baffle. Clearly then, sensitivity does not correlate precisely with efficiency, as it also depends on the directivity of the driver being tested and the acoustic environment in front of the actual loudspeaker. For example, a cheerleader's horn produces more sound output in the direction it is pointed by concentrating sound waves from the cheerleader in one direction, thus focusing them. The horn also improves impedance matching between the voice and the air, which produces more acoustic power for a given speaker power. In some cases, improved impedance matching (via careful enclosure design) lets the speaker produce more acoustic power. | Loudspeaker | Wikipedia | 439 | 45871 | https://en.wikipedia.org/wiki/Loudspeaker | Technology | Media and communication | null |
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