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Bowen's Kale was a reference material produced by British chemist Humphry Bowen and used for the calibration of early scientific instruments intended to measure trace elements during the 1960s. With Peter Cawse, Bowen grew, dried, and crushed a large amount of marrow-stem kale (Brassica oleracea var. medullosa) into 100 kilograms (220 lb) of a homogeneous and stable powder in 1960 that was subsequently freely distributed to researchers around the world for over two decades. This was probably the first successful example of such a de facto standard. Bowen's Kale stimulated the preparation of further materials by other organizations for similar use. == See also == Reference standard == References == == Bibliography == Bowen, H. J. M., A standard biological material for elementary analysis. In P. W. Sallis (ed.), Proc. of the SAC Conference, Nottingham, UK, pp. 25–31. Cambridge: W. Heffer and Sons, 1965. Bowen, H. J. M., Kale as a reference material. In W. R. Wolf (ed.), Biological Reference Materials: Availability, uses and need for validation of nutrient measurement, pp. 3–17. John Wiley & Sons, 1984. Stoeppler, M., Wolf, W. R. and Jenks, P. J. (eds.), Reference Materials for Chemical Analysis: Certification, Availability and Proper Usage. Weinheim: Wiley-VCH, 2001. ISBN 3-527-30162-3. (See pages 4, 26, 59 & 216.)
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A trilaminar embryonic disc, trilaminary blastoderm, or trilaminar germ disk is an early stage in the development of triploblastic organisms, which include humans and many other animals. It is the next stage from the earlier bilaminar embryonic disc. It is an embryo which exists as three different germ layers – the ectoderm, the mesoderm and the endoderm. These layers are arranged on top of each other, giving rise to the name trilaminar, or "three-layered". The mesoderm is segmented further into the paraxial, intermediate and the lateral plate mesoderm. These three layers arise early in the third week (during gastrulation) from the epiblast (a portion of the mammalian inner cell mass). == References == == External links == Overview at edu.mt
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"page_id": 4850489,
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"title": "Trilaminar embryonic disc"
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An associative classifier (AC) is a kind of supervised learning model that uses association rules to assign a target value. The term associative classification was coined by Bing Liu et al., in which the authors defined a model made of rules "whose right-hand side are restricted to the classification class attribute". == Model == The model generated by an AC and used to label new records consists of association rules, where the consequent corresponds to the class label. As such, they can also be seen as a list of "if-then" clauses: if the record matches some criteria (expressed in the left side of the rule, also called antecedent), it is then labeled accordingly to the class on the right side of the rule (or consequent). Most ACs read the list of rules in order, and apply the first matching rule to label the new record. == Metrics == The rules of an AC inherit some of the metrics of association rules, like the support or the confidence. Metrics can be used to order or filter the rules in the model and to evaluate their quality. == Implementations == The first proposal of a classification model made of association rules was FBM. The approach was popularized by CBA, although other authors had also previously proposed the mining of association rules for classification. Other authors have since then proposed multiple changes to the initial model, like the addition of a redundant rule pruning phase or the exploitation of Emerging Patterns. Notable implementations include: CMAR CPAR L³ CAEP GARC ADT. == References ==
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"page_id": 58655546,
"source": null,
"title": "Associative classifier"
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Monoembryony is the emergence of one and only one seedling from a seed. A seed giving two or more seedlings is polyembryonic. Some of the nuclear cells surrounding the embryo sac start dividing and protrude into the embryo sac and develop into embryos. == References ==
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"page_id": 12976954,
"source": null,
"title": "Monoembryony"
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Haruo Hosoya (Japanese: 細矢 治夫, Hepburn: Hosoya Haruo, born 1936) is a Japanese chemist and emeritus professor of Ochanomizu University, Tokyo, Japan. He is the namesake of the Hosoya index used in discrete mathematics and computational chemistry. Hosoya was born in Kamakura, Japan to a family of an office worker. During 1955-1959 he studied at the University of Tokyo. In 1964 he wrote his Ph.D. thesis, "Study on the Structure of Reactive Intermediates and Reaction Mechanism". After postdoc work abroad (Ann Arbor, Michigan, with prof. John Platt), in 1969 he became associate professor at the Ochanomizu University, where he worked for 33 years until his retirement in 2002. After retirement he keeps working in computational chemistry. In 1971, Hosoya defined the topological index (a graph invariant) now known as the Hosoya index as the total number of matchings of a graph plus 1. The Hosoya index is often used in computer (mathematical) chemistry investigations for organic compounds. In 2002-2003 the Internet Electronic Journal of Molecular Design dedicated a series of issues to commemorate the 65th birthday of professor Hosoya. Hosoya's article "The Topological Index Z Before and After 1971" describes the history of the notion and the associated inside stories and details other Hosoya's achievements. Hosoya also introduced the triangle of numbers known as Hosoya's triangle (originally "Fibonacci triangle", but that name can be ambiguous). == Notes ==
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Algorithmic party platforms are a recent development in political campaigning where artificial intelligence (AI) and machine learning are used to shape and adjust party messaging dynamically. Unlike traditional platforms that are drafted well before an election, these platforms adapt based on real-time data such as polling results, voter sentiment, and trends on social media. This allows campaigns to remain responsive to emerging issues throughout the election cycle. These platforms rely on predictive analytics to segment voters into smaller, highly specific groups. AI analyzes demographic data, behavioral patterns, and online activities to identify which issues resonate most with each group. Campaigns then tailor their messages accordingly, ensuring that different voter segments receive targeted communication. This approach optimizes resources and enhances voter engagement by focusing on relevant issues. During the 2024 U.S. election, campaigns utilized these tools to adjust messaging on-the-fly. For example, the AI firm Resonate identified a voter segment labeled "Cyber Crusaders," consisting of socially conservative yet fiscally liberal individuals. Campaigns used this insight to quickly focus outreach and policy discussions around the concerns of this group, demonstrating how AI-driven platforms can influence strategy as events unfold. == Background and relevance in modern campaigns == The integration of artificial intelligence (AI) into political campaigns has introduced a significant shift in how party platforms are shaped and communicated. Traditionally, platforms were drafted months before elections and remained static throughout the campaign. However, algorithmic platforms now rely on continuous data streams to adjust messaging and policy priorities in real time. This allows campaigns to adapt to emerging voter concerns, ensuring their strategies remain relevant throughout the election cycle. AI systems analyze large volumes of data, including polling results, social media interactions, and voter behavior patterns. Predictive analytics tools segment voters into specific micro-groups based on demographic and behavioral data. Campaigns can then
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customize their messaging to align with the priorities of these smaller segments, adjusting their stances as trends develop during the campaign. This level of segmentation and customization ensures that outreach resonates with voters and maximizes engagement. Beyond messaging, AI also optimizes resource allocation by helping campaigns target specific efforts more effectively. With predictive analytics, campaigns can identify which areas or demographics are most likely to benefit from increased outreach, such as canvassing or targeted advertisements. AI tools monitor shifts in voter sentiment in real time, allowing campaigns to quickly pivot their strategies in response to developing events and voter priorities. This capability ensures that campaign resources are used efficiently, minimizing waste while maximizing impact throughout the election cycle. AI's use extends beyond national campaigns, with local and grassroots campaigns also leveraging these technologies to compete more effectively. By automating communication processes and generating customized voter outreach, smaller campaigns can now utilize AI to a degree previously available only to well-funded candidates. However, this growing reliance on AI raises concerns around transparency and the ethical implications of automated content creation, such as AI-generated ads and responses. AI technology, which was previously accessible only to large, well-funded campaigns, has become increasingly available to smaller, local campaigns. With declining costs and easier access, grassroots campaigns now have the ability to implement predictive analytics, automate communications, and generate targeted ads. This democratization of technology allows smaller campaigns to compete more effectively by dynamically adjusting to the concerns of their constituents. However, the growing use of AI in political campaigns raises concerns about transparency and the potential manipulation of voters. The ability to adjust messaging in real time introduces ethical questions about the authenticity of platforms and voter trust. Additionally, the use of synthetic media, including AI-generated ads and deepfakes, presents challenges in maintaining accountability
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and preventing disinformation in political discourse. == Impact on political platforms == Artificial intelligence (AI) has become instrumental in enabling political campaigns to adapt their platforms in real time, responding swiftly to evolving voter sentiments and emerging issues. By analyzing extensive datasets—including polling results, social media activity, and demographic information—AI systems provide campaigns with actionable insights that inform dynamic strategy adjustments. A study by Sanders, Ulinich, and Schneier (2023) demonstrated the potential of AI-based political issue polling, where AI chatbots simulated public opinion on various policy issues. The findings indicated that AI could effectively anticipate both the mean level and distribution of public opinion, particularly in ideological breakdowns, with correlations typically exceeding 85%. This suggests that AI can serve as a valuable tool for campaigns to gauge voter sentiment accurately and promptly. Moreover, AI facilitates the segmentation of voters into micro-groups based on demographic and behavioral data, allowing for tailored messaging that resonates with specific audiences. This targeted approach enhances voter engagement and optimizes resource allocation, as campaigns can focus their efforts on demographics most receptive to their messages. The dynamic nature of AI-driven platforms ensures that campaign strategies remain relevant and responsive throughout the election cycle. However, the integration of AI in political platforms also raises ethical and transparency concerns, particularly regarding the authenticity of dynamically adjusted messaging and the potential for voter manipulation. Addressing these challenges is crucial to maintaining voter trust and the integrity of the democratic process. In summary, AI significantly shapes political platforms in real time by providing campaigns with the tools to analyze voter sentiment, segment audiences, and adjust strategies dynamically. While offering substantial benefits in responsiveness and engagement, it is imperative to navigate the accompanying ethical considerations to ensure the responsible use of AI in political campaigning. == Ethical and transparency challenges ==
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While AI-driven platforms offer significant advantages, they also introduce ethical and transparency challenges. One primary concern is the potential for AI to manipulate voter perception. The ability to adjust messaging dynamically raises questions about the authenticity of political platforms, as voters may feel deceived if they perceive platforms as opportunistic or insincere. The use of synthetic media, including AI-generated advertisements and deepfakes, exacerbates these challenges. These tools have the potential to blur the line between reality and fiction, making it difficult for voters to discern genuine content from fabricated material. This has led to concerns about misinformation, voter manipulation, and the erosion of trust in democratic processes. Additionally, the lack of transparency in how AI systems operate poses significant risks. Many algorithms function as "black boxes," with their decision-making processes opaque even to their developers. This opacity makes it challenging to ensure accountability, particularly when AI-generated strategies lead to controversial or unintended outcomes. Efforts to address these challenges include calls for greater transparency in AI usage within campaigns. Policymakers and advocacy groups have proposed regulations requiring campaigns to disclose when AI is used in content creation or voter outreach. These measures aim to balance the benefits of AI with the need for ethical integrity and accountability. == Benefits of AI-driven platforms == Despite the challenges, AI-driven platforms offer numerous benefits that can enhance the democratic process. By tailoring messaging to specific voter concerns, AI helps campaigns address diverse needs more effectively. This targeted approach ensures that underrepresented groups receive attention, fostering a more inclusive political discourse. AI also democratizes access to advanced campaign tools. Smaller campaigns, which previously lacked the resources to compete with well-funded opponents, can now utilize AI to level the playing field. Predictive analytics, automated communications, and targeted advertisements empower grassroots movements to amplify their voices and
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"page_id": 78316349,
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engage constituents more effectively. Moreover, AI's ability to process vast amounts of data provides valuable insights into voter sentiment. By identifying trends and patterns, campaigns can address pressing issues proactively, fostering a more informed and responsive political environment. These capabilities also extend to crisis management, as AI enables campaigns to adjust swiftly in response to unforeseen events, ensuring stability and resilience. == References ==
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Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc. The "classical" pollination syndromes were first studied in the 19th century by the Italian botanist Federico Delpino. Although they are useful in understanding of plant-pollinator interactions, sometimes the pollinator of a plant species cannot be accurately predicted from the pollination syndrome alone, and caution must be exerted in making assumptions. The naturalist Charles Darwin surmised that the flower of the orchid Angraecum sesquipedale was pollinated by a then undiscovered moth with a proboscis whose length was unprecedented at the time. His prediction had gone unverified until 21 years after his death, when the moth was discovered and his conjecture vindicated. The story of its postulated pollinator has come to be seen as one of the celebrated predictions of the theory of evolution. == Abiotic == Abiotically pollinated flowers do not attract animal pollinators. Nevertheless, they often have suites of shared traits. === Wind === Wind-pollinated flowers may be small and inconspicuous, as well as green and not showy. They produce enormous numbers of relatively small pollen grains (hence wind-pollinated plants may be allergens, but seldom are animal-pollinated plants allergenic). Their stigmas may be large and feathery to catch the pollen grains. Insects may visit them to collect pollen; in some cases, these are ineffective pollinators and exert little natural selection on the flowers, but there are also examples of
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ambophilous flowers which are both wind and insect pollinated. Anemophilous, or wind pollinated flowers, are usually small and inconspicuous, and do not possess a scent or produce nectar. The anthers may produce a large number of pollen grains, while the stamens are generally long and protrude out of flower. === Water === Water-pollinated plants are aquatic and pollen is released into the water. Water currents therefore act as a pollen vector in a similar way to wind currents. Their flowers tend to be small and inconspicuous with many pollen grains and large, feathery stigmas to catch the pollen. However, this is relatively uncommon (only 2% of pollination is hydrophily) and most aquatic plants are insect-pollinated, with flowers that emerge into the air. Vallisneria is an example. == Biotic == === Insects === ==== Bees ==== Bee-pollinated flowers can be very variable in their size, shape and colouration. They can be open and bowl-shaped ('actinomorphic', radially symmetrical) or more complex and non-radially symmetric ('zygomorphic'), as is the case with many peas and foxgloves. Some bee flowers tend to be yellow or blue, often with ultraviolet nectar guides and scent. Nectar, pollen, or both are offered as rewards in varying amounts. The sugar in the nectar tends to be sucrose-dominated. A few bees collect oil from special glands on the flower. ==== Butterflies ==== Butterfly-pollinated flowers tend to be large and showy, pink or lavender in colour, frequently have a landing area, and are usually scented. Since butterflies do not digest pollen (with one exception), more nectar is offered than pollen. The flowers have simple nectar guides with the nectaries usually hidden in narrow tubes or spurs, reached by the long tongue of the butterflies. ==== Moths ==== Among the more important moth pollinators are the hawk moths (Sphingidae). Their behaviour is
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similar to hummingbirds: they hover in front of flowers with rapid wingbeats. Most are nocturnal or crepuscular. So moth-pollinated flowers tend to be white, night-opening, large and showy with tubular corollas and a strong, sweet scent produced in the evening, night or early morning. Much nectar is produced to fuel the high metabolic rates needed to power their flight. Other moths (Noctuids, Geometrids, Pyralids, for example) fly slowly and settle on the flower. They do not require as much nectar as the fast-flying hawk moths, and the flowers tend to be small (though they may be aggregated in heads). ==== Flies ==== Myophilous plants, those pollinated by flies, tend not to emit a strong scent, are typically purple, violet, blue, and white, and have open dishes or tubes. Sapromyophilous plants attract flies which normally visit dead animals or dung. Flowers mimic the odor of such objects. The plant provides them with no reward and they leave quickly unless it has traps to slow them down. Such plants are far less common than myophilous ones. === Beetles === Beetle-pollinated flowers are usually large, greenish or off-white in color and heavily scented. Scents may be spicy, fruity, or similar to decaying organic material. Most beetle-pollinated flowers are flattened or dish shaped, with pollen easily accessible, although they may include traps to keep the beetle longer. The plant's ovaries are usually well protected from the biting mouthparts of their pollinators. A number of cantharophilous plants are thermogenic, with flowers that can increase their temperature. This heat is thought to help further spread the scent, but the infrared light produced by this heat may also be visible to insects during the dark night, and act as a shining beacon to attract them. === Birds === Flowers pollinated by specialist nectarivores tend to be large,
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red or orange tubes with a lot of dilute nectar, secreted during the day. Since birds do not have a strong response to scent, they tend to be odorless. Flowers pollinated by generalist birds are often shorter and wider. Hummingbirds are often associated with pendulous flowers, whereas passerines (perching birds) need a landing platform so flowers and surrounding structures are often more robust. Also, many plants have anthers placed in the flower so that pollen rubs against the birds head/back as the bird reaches in for nectar. === Bats === There are major differences between bat pollination in the New World as opposed to the Old World. In the Old World pollinating bats are large fruit bats of the family Pteropodidae which do not have the ability to hover and must perch in the plant to lap the nectar; these bats furthermore do not have the ability to echolocate. Bat-pollinated flowers in this part of the world tend to be large and showy, white or light coloured, open at night and have strong musty odours. They are often large balls of stamens. In the Americas pollinating bats are tiny creatures called glossophagines which have both the ability to hover as well as echolocate, and have extremely long tongues. Plants in this part of the world are often pollinated by both bats and hummingbirds, and have long tubular flowers. Flowers in this part of the world are typically borne away from the trunk or other obstructions, and offer nectar for extended periods of time. In one essay, von Helversen et al. speculate that maybe some bell-shaped flowers have evolved to attract bats in the Americas, as the bell-shape might reflect the sonar pulses emitted by the bats in a recognisable pattern. A number of species of Marcgravia from Caribbean islands have
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evolved a special leaf just above the inflorescence to attract bats. The leaf petiole is twisted so the leaf sticks upwards, and the leaf is shaped like a concave disc or dish reflector. The leaf reflects echolocation signals from many directions, guiding the pollinating bats towards the flowers. The epiphytic bean Mucuna holtonii employs a similar tactic, but in this species it is a specialised petal that acts as a sonar reflector. In the New World bat pollinated flowers often have sulphur-scented compounds. Bat-pollinated plants have bigger pollen than their relatives. === Non-flying mammals === The characteristics of the pollination syndrome associated with pollination by mammals which are not bats are: a yeasty odour; cryptic, drab, axillary, geoflorous flowers or inflorescences often obscured from sight; large and sturdy flowers, or grouped together as multi-flowered inflorescences; either sessile flowers or inflorescences or subtended by a short and stout peduncle or pedicel; bowl-shaped flowers or inflorescences; copious, sucrose-rich nectar usually produced during the night; tough and wiry styles; an adequate distance between the stigma and nectar to fit the rostrum of the pollinating animal; and potentially a winter–spring flowering period. Many non-flying mammals are nocturnal and have an acute sense of smell, so the plants tend not to have bright showy colours, but instead excrete a strong odour. These plants also tend to produce large amounts of pollen because mammals are larger than some other pollinators, and lack the precision smaller pollinators can achieve. The Western-Australian endemic Honey possum (Tarsipes rostratus) is an unusual non-flying mammal pollinator in that it has adapted to feeding exclusively on pollen and nectar. It is known to forage on a wide variety of plants (particularly in the families Proteaceae and Myrtaceae) including many with typical bird-pollinated flowers such as Calothamnus quadrifidus and many species of Banksia.
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== Biology == Pollination syndromes reflect convergent evolution towards forms (phenotypes) that limit the number of species of pollinators visiting the plant. They increase the functional specialization of the plant with regard to pollination, though this may not affect the ecological specialization (i.e. the number of species of pollinators within that functional group). They are responses to common selection pressures exerted by shared pollinators or abiotic pollen vectors, which generate correlations among traits. That is, if two distantly related plant species are both pollinated by nocturnal moths, for example, their flowers will converge on a form which is recognised by the moths (e.g. pale colour, sweet scent, nectar released at the base of a long tube, night-flowering). === Advantages of specialization === Efficiency of pollination: the rewards given to pollinators (commonly nectar or pollen or both, but sometimes oil, scents, resins, or wax) may be costly to produce. Nectar can be cheap, but pollen is generally expensive as it is relatively high in nitrogen compounds. Plants have evolved to obtain the maximum pollen transfer for the minimum reward delivered. Different pollinators, because of their size, shape, or behaviour, have different efficiencies of transfer of pollen. And the floral traits affect efficiency of transfer: columbine flowers were experimentally altered and presented to hawkmoths, and flower orientation, shape, and colour were found to affect visitation rates or pollen removal. Pollinator constancy: to efficiently transfer pollen, it is best for the plant if the pollinator focuses on one species of plant, ignoring other species. Otherwise, pollen may be dropped uselessly on the stigmas of other species. Animals, of course, do not aim to pollinate, they aim to collect food as fast as they can. However, many pollinator species exhibit constancy, passing up available flowers to focus on one plant species. Why should animals
|
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specialize on a plant species, rather than move to the next flower of any species? Although pollinator constancy was recognized by Aristotle, the benefits to animals are not yet fully understood. The most common hypothesis is that pollinators must learn to handle particular types of flowers, and they have limited capacity to learn different types. They can only efficiently gather rewards from one type of flower. These honeybees selectively visit flowers from only one species for a period of time, as can be seen by the colour of the pollen in their baskets. === Advantages of generalization === Pollinators fluctuate in abundance and activity independently of their plants, and any one species may fail to pollinate a plant in a particular year. Thus a plant may be at an advantage if it attracts several species or types of pollinators, ensuring pollen transfer every year. Many species of plants have the back-up option of self-pollination, if they are not self-incompatible. === A continuum rather than discrete syndromes === Whilst it is clear that pollination syndromes can be observed in nature, there has been much debate amongst scientists as to how frequent they are and to what extent we can use the classical syndromes to classify plant-pollinator interactions. Although some species of plants are visited only by one type of animal (i.e. they are functionally specialized), many plant species are visited by very different pollinators. For example, a flower may be pollinated by bees, butterflies, and birds. Strict specialization of plants relying on one species of pollinator is relatively rare, probably because it can result in variable reproductive success across years as pollinator populations vary significantly. In such cases, plants should generalize on a wide range of pollinators, and such ecological generalization is frequently found in nature. A study in Tasmania found
|
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"page_id": 6161213,
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the syndromes did not usefully predict the pollinators. A critical re-evaluation of the syndromes suggests that on average about one third of the flowering plants can be classified into the classical syndromes. This reflects the fact that nature is much less predictable and straightforward than 19th-century biologists originally thought. Pollination syndromes can be thought of as extremes of a continuum of greater or lesser specialization or generalization onto particular functional groups of pollinators that exert similar selective pressures" and the frequency with which flowers conform to the expectations of the pollination syndromes is relatively rare. In addition, new types of plant-pollinator interaction, involving "unusual" pollinating animals are regularly being discovered, such as specialized pollination by spider hunting wasps (Pompilidae) and fruit chafers (Cetoniidae) in the eastern grasslands of South Africa. These plants do not fit into the classical syndromes, though they may show evidence of convergent evolution in their own right. An analysis of flower traits and visitation in 49 species in the plant genus Penstemon found that it was possible to separate bird- and bee- pollinated species quite well, but only by using floral traits which were not considered in the classical accounts of syndromes, such as the details of anther opening. Although a recent review concluded that there is "overwhelming evidence that functional groups exert different selection pressures on floral traits", the sheer complexity and subtlety of plant-pollinator interactions (and the growing recognition that non-pollinating organisms such as seed predators can affect the evolution of flower traits) means that this debate is likely to continue for some time. == See also == Pollinator-mediated selection Mutualism (biology) Floral biology Pollination trap Monocotyledon reproduction == References == == Bibliography ==
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In biology, overabundant species refers to an excessive number of individuals and occurs when the normal population density has been exceeded. Increase in animal populations is influenced by a variety of factors, some of which include habitat destruction or augmentation by human activity, the introduction of invasive species and the reintroduction of threatened species to protected reserves. Population overabundance can have a negative impact on the environment, and in some cases on the public as well. There are various methods through which populations can be controlled such as hunting, contraception, chemical controls, disease and genetic modification. Overabundant species is an important area of research as it can potentially impact the biodiversity of ecosystems. Most research studies have examined negative impacts of overabundant species, whereas very few have documented or performed an in-depth examination on positive impacts. As a result, this article focuses on the negative impact of overabundant species. == Definitions == When referring to animals as “overabundant”, various definitions apply. The following classes explore the different associations with overabundance: The inconvenience of animals in a certain region or area that threatens human livelihood, for example the tropics are considered to contain an overabundant population of the Anopheles mosquito which carries the malaria parasite. The population density of a preferred species has been reduced by another species population which is then considered as overabundant, for example predator populations of lions and hyenas reducing zebra and wildebeest numbers. A species population within a specific habitat exceeds the carrying capacity, for example national parks reducing herbivore populations to maintain and manage habitat equilibrium. The entire equilibrium consisting of animal and plant organisations is already out of balance, for example existing populations colonising new habitat. Out of all these classifications, class 4 is considered the most significant due to consequent ecological impacts. ==
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"page_id": 60621630,
"source": null,
"title": "Overabundant species"
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Causes == Overabundance may occur naturally, for example after weather events such as a period of high rainfall in which habitat conditions become optimal. However, other contributing factors include: === Anthropogenic disturbances === Natural habitats are altered by human activity resulting in habitat fragmentation, decrease in forest densities and wild fires. Other human disturbances include restrictions on hunting, agricultural land modification and predator removal or control within a region or area. The consequent change in land use and the presence or withdrawal of human influence can trigger a rapid increase in both native and non-native species populations. === Invasive species can be better adapted to specific environments === Invasive species are often overabundant as they outcompete native species for resources such as food and shelter which allows their population to thrive. Other factors influencing population growth include the lack of native predators or the less common presence of the introduced species within native predator habitat. === Overabundance due to translocation of threatened species to protected areas === Some methods in managing threatened species involve reintroducing species to enclosed reserves or island areas. Once these species are introduced, their populations can become overabundant as these areas serve to protect the targeted species against predators and competitors. This occurred for the Bettongia lesueur, the burrowing bettong, which was reintroduced to the Arid Recovery reserve in Australia: their population has increased from 30 to approximately 1532 individuals. Due to the damage within this reserve their population is considered overabundant. == Potential impacts == Overabundant species can have an adverse impact on ecosystems. Within ecosystems food resources and availability, competitors, and species composition can be negatively impacted on. === Impacts of overabundant herbivores === A common impact from overabundant herbivores is vegetative damage by overgrazing, where overgrazing refers to the effect of grazing having
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{
"page_id": 60621630,
"source": null,
"title": "Overabundant species"
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reached a level where other biodiversity within the ecosystem becomes threatened. Overgrazing can occur in both terrestrial and marine environments and can alter vegetation as well as the composition of vegetation. Population densities and the composition of fauna can also be negatively impacted on. Additionally, permanent ecological damage can be caused by overgrazing before maximum carrying capacity has been reached. Trophic relationships (i.e. feeding relationships in the ecosystem) can be altered by overabundant species, potentially causing a trophic cascade. Trophic cascades impact vegetation as well as invertebrates (including microorganisms) and birds. Furthermore, predator behaviour and populations may be indirectly affected. === Impacts of overabundant predators === Overabundant predators are considered harmful to local biodiversity as they prey on native species, compete for resources and can introduce disease. They can decrease native mammal populations and, in some cases, can cause species to become extinct which results in a cascading ecological impact. Examples of invasive species include: “cats (Felis catus), rats (Rattus rattus), mongoose (Urva auropunctata), stoats (Mustela erminea)” and red foxes (Vulpes vulpes). Such species have contributed to the extinction of approximately 58% of modern-day mammals, birds and reptiles. In Australia, red foxes and feral cats have contributed to many native mammals becoming threatened or extinct which has led to diminished vegetation as foraging mammals have an important ecological role in maintaining a healthy landscape. A particular example is where grassland vegetation diminished to shrub land as a result of seabirds being preyed on by Arctic foxes. Seabirds have an essential ecological role which consists of helping to maintain nutrient levels and soil fertility. “Invasive predators also threaten 596 species classed as "vulnerable" (217 species), "endangered" (223), or "critically endangered" (156), of which 23 are classed as “possibly extinct.” === Impact on society === It can be very costly to control
|
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"page_id": 60621630,
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"title": "Overabundant species"
}
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or eradicate overabundant species. For example, fencing regions as a protective measure against red foxes can cost approximately $10, 000 per kilometre while baiting an area of 35,0002 kilometres can cost about $1.3 million. == Invasive species == According to biology, invasive species are non-native animals that are introduced to a region or area outside of their usual habitat. Invasive species can either be introduced intentionally (if they have a beneficial purpose) or non-intentionally. In general, invasive species that become overabundant most commonly have a negative impact on local biodiversity with little research having found positive effects. Furthermore, an invasive species may have an initial positive benefit that fades as the species become overabundant and the cost of damage control increases. Invasive species can negatively impact food web structures. In terms of trophic levels, the initial introduction of a non-native species results in a higher species richness whereby the trophic relationships are altered by the additional resource (if an animal is not a predator at the top of the food chain) and consumer. However, the consequent degree of the impact on the local ecosystem once a species becomes overabundant is case dependent as some invasive species, like the brown tree snake in Guam, have caused numerous extinctions of native fauna, while others have had fewer damaging impacts on the environment. Costs of invasive species are estimated at millions and billions each year. === A focus on Australian Wildlife === ==== Red fox ==== The red fox, Vulpes Vulpes, was introduced to Australia during the 1870s. The established population has thrived in previous years due to the following factors: adaptability to climate conditions, the ability to live in a wide range of habitats including deserts and forests, and lastly human modification of Australian landscapes which are suitable environments for red foxes
|
{
"page_id": 60621630,
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"title": "Overabundant species"
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|
to thrive in. Red foxes have mainly had a negative impact on Australian fauna, with the exception of regulated rabbit populations. The diet of red foxes include a number of threatened native fauna which has contributed to their population declines and extinctions. Furthermore, populations of native fauna, mammals in particular, have increased through fox population control techniques. ==== Rabbit ==== Rabbits were initially introduced to Australia as pets during colonisation. Rabbits pose a threat to native herbivores as they compete for shared resources. Additionally, overgrazing and modification of habitat vegetation by rabbits allow introduced predators to thrive when hunting. Rabbits have thrived in Australia as they reproduce rapidly, have few predators to regulate their population and the climatic conditions is preferable, especially as the environmental conditions limit diseases that regulate rabbit populations on other continents. == Methods for controlling overabundant species == There are various methods for controlling overabundant populations. Some methods have been used over many years, for example culling, while others such as immunocontraception are still being researched. === Culling === Culling refers to selective elimination of animals to decrease a population. Two ways of culling involve killing animals by hunting and translocation of animals. Culling of animals may also be an option in reserves established for specific animal conservation as a way of managing their population density, examples include: elephants and hippos. Target animals can be hunted on the ground or culled by aerial pursuit, with the aim to eliminate the animal in one accurate hit to reduce or limit suffering before death. This method allows a large number of animals to be eliminated within a relatively short amount of time, however shots are not always accurate which can lead to the escape and suffering of individuals. === Baiting === Baiting is a common method of controlling
|
{
"page_id": 60621630,
"source": null,
"title": "Overabundant species"
}
|
overabundant populations, it involves the placement of lethal chemicals in food (the bait) that eliminates the animal. It is cost-effective and helps remove a large number of animals from a population, however if ingested by non-target animals it could potentially cause death depending on the type of bait the chemical is administered in, as well as the areas of bait placement. 1080 is a common chemical used in bait. 1080 once ingested causes death by inhibiting the animal's neurological functioning. It consists of an enzyme that native Australian fauna is tolerant to, however it can still be lethal if ingested. === Fumigation === Fumigation, which involves the spreading of poisonous gas, helps to selectively kill a large number of animals. It is a method used to control rabbit and fox populations in Australia by spraying a lethal chemical into warrens and dens. Chemicals used include phosphine for rabbits and carbon monoxide for foxes, both of which induce suffering prior to death. Difficulties with fumigation include pinpointing individual dens and warrens, which can be both time-consuming and hard work, as well as the restricted time period during which animals regularly inhabit their dens, for example during spring when offspring are born. === Disease === This method is used on select animals and is species specific, such as to control the rabbit population in Australia. It involves spreading a disease, for example "rabbit calicivirus disease", through bait or through capture and release programs. The aim is to have the disease spread through the targeted species population to reduce their numbers. Death may take up to 1 or 2 weeks in which the animal suffers from symptoms such as fever, loss of appetite and lethargy. === Contraception === Two methods for managing fertility in overabundant wildlife include the employment of biotechnology such as
|
{
"page_id": 60621630,
"source": null,
"title": "Overabundant species"
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|
immunocontraception, and surgery to neuter males or spay females. There are various factors that impact the effectiveness of contraceptive methods, some of which include: expense, longevity of the treatment effect, level of difficulty in administering the treatment, and whether or not the method has a negative impact on the individual or other species in the environment. An example of an immune-contraceptive is gonadotropin releasing hormone (GnRH). Studies have been conducted on various animals, for example white-tailed deer and cats, of which have shown that GnRH can be effective in reducing short term fertility. ==== Immunocontraception ==== Immunocontraception causes animals to become infertile which helps to control and reduce overabundant populations. Two methods of administration include vaccines and chemical implants. In some studies immunocontraception has shown to effectively reduce pregnancy rates, however this method is both time-consuming and expensive due to further research required to overcome challenges such as longevity of the contraceptive effect. ==== Surgery ==== This method can be effective in small populations as it is fairly accessible, however the procedure is costly, invasive as well as the individual being at risk of infection after surgery. Surgical sterilisation is permanent, as a result it may not be appropriate for use in native populations due to the risk of potentially losing genetic variation. == References ==
|
{
"page_id": 60621630,
"source": null,
"title": "Overabundant species"
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|
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speciation event (orthologs), or a duplication event (paralogs), or else a horizontal (or lateral) gene transfer event (xenologs). Homology among DNA, RNA, or proteins is typically inferred from their nucleotide or amino acid sequence similarity. Significant similarity is strong evidence that two sequences are related by evolutionary changes from a common ancestral sequence. Alignments of multiple sequences are used to indicate which regions of each sequence are homologous. == Identity, similarity, and conservation == The term "percent homology" is often used to mean "sequence similarity”, that is the percentage of identical residues (percent identity), or the percentage of residues conserved with similar physicochemical properties (percent similarity), e.g. leucine and isoleucine, is usually used to "quantify the homology." Based on the definition of homology specified above this terminology is incorrect since sequence similarity is the observation, homology is the conclusion. Sequences are either homologous or not. This involves that the term "percent homology" is a misnomer. As with morphological and anatomical structures, sequence similarity might occur because of convergent evolution, or, as with shorter sequences, by chance, meaning that they are not homologous. Homologous sequence regions are also called conserved. This is not to be confused with conservation in amino acid sequences, where the amino acid at a specific position has been substituted with a different one that has functionally equivalent physicochemical properties. Partial homology can occur where a segment of the compared sequences has a shared origin, while the rest does not. Such partial homology may result from a gene fusion event. == Orthology == Homologous sequences are orthologous if they are
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
}
|
inferred to be descended from the same ancestral sequence separated by a speciation event: when a species diverges into two separate species, the copies of a single gene in the two resulting species are said to be orthologous. Orthologs, or orthologous genes, are genes in different species that originated by vertical descent from a single gene of the last common ancestor. The term "ortholog" was coined in 1970 by the molecular evolutionist Walter Fitch. For instance, the plant Flu regulatory protein is present both in Arabidopsis (multicellular higher plant) and Chlamydomonas (single cell green algae). The Chlamydomonas version is more complex: it crosses the membrane twice rather than once, contains additional domains and undergoes alternative splicing. However, it can fully substitute the much simpler Arabidopsis protein, if transferred from algae to plant genome by means of genetic engineering. Significant sequence similarity and shared functional domains indicate that these two genes are orthologous genes, inherited from the shared ancestor. Orthology is strictly defined in terms of ancestry. Given that the exact ancestry of genes in different organisms is difficult to ascertain due to gene duplication and genome rearrangement events, the strongest evidence that two similar genes are orthologous is usually found by carrying out phylogenetic analysis of the gene lineage. Orthologs often, but not always, have the same function. Orthologous sequences provide useful information in taxonomic classification and phylogenetic studies of organisms. The pattern of genetic divergence can be used to trace the relatedness of organisms. Two organisms that are very closely related are likely to display very similar DNA sequences between two orthologs. Conversely, an organism that is further removed evolutionarily from another organism is likely to display a greater divergence in the sequence of the orthologs being studied. === Databases of orthologous genes and de novo orthology inference tools
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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|
=== Given their tremendous importance for biology and bioinformatics, orthologous genes have been organized in several specialized databases that provide tools to identify and analyze orthologous gene sequences. These resources employ approaches that can be generally classified into those that use heuristic analysis of all pairwise sequence comparisons, and those that use phylogenetic methods. Sequence comparison methods were first pioneered in the COGs database in 1997. These methods have been extended and automated in twelve different databases the most advanced being AYbRAH Analyzing Yeasts by Reconstructing Ancestry of Homologs as well as these following databases right now. Some tools predict orthologous de novo from the input protein sequences, might not provide any Database. Among these tools are SonicParanoid and OrthoFinder. eggNOG GreenPhylDB for plants InParanoid focuses on pairwise ortholog relationships OHNOLOGS is a repository of the genes retained from whole genome duplications in the vertebrate genomes including human and mouse. OMA OrthoDB appreciates that the orthology concept is relative to different speciation points by providing a hierarchy of orthologs along the species tree. OrthoInspector is a repository of orthologous genes for 4753 organisms covering the three domains of life OrthologID OrthoMaM for mammals OrthoMCL Roundup SonicParanoid is a graph based method that uses machine learning to reduce execution times and infer orthologs at the domain level. Tree-based phylogenetic approaches aim to distinguish speciation from gene duplication events by comparing gene trees with species trees, as implemented in databases and software tools such as: LOFT TreeFam OrthoFinder A third category of hybrid approaches uses both heuristic and phylogenetic methods to construct clusters and determine trees, for example: EnsemblCompara GeneTrees HomoloGene Ortholuge == Paralogy == Paralogous genes are genes that are related via duplication events in the last common ancestor (LCA) of the species being compared. They result from the mutation of
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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duplicated genes during separate speciation events. When descendants from the LCA share mutated homologs of the original duplicated genes then those genes are considered paralogs. As an example, in the LCA, one gene (gene A) may get duplicated to make a separate similar gene (gene B), those two genes will continue to get passed to subsequent generations. During speciation, one environment will favor a mutation in gene A (gene A1), producing a new species with genes A1 and B. Then in a separate speciation event, one environment will favor a mutation in gene B (gene B1) giving rise to a new species with genes A and B1. The descendants' genes A1 and B1 are paralogous to each other because they are homologs that are related via a duplication event in the last common ancestor of the two species. Additional classifications of paralogs include alloparalogs (out-paralogs) and symparalogs (in-paralogs). Alloparalogs are paralogs that evolved from gene duplications that preceded the given speciation event. In other words, alloparalogs are paralogs that evolved from duplication events that happened in the LCA of the organisms being compared. The example above is an example alloparalogy. Symparalogs are paralogs that evolved from gene duplication of paralogous genes in subsequent speciation events. From the example above, if the descendant with genes A1 and B underwent another speciation event where gene A1 duplicated, the new species would have genes B, A1a, and A1b. In this example, genes A1a and A1b are symparalogs. Paralogous genes can shape the structure of whole genomes and thus explain genome evolution to a large extent. Examples include the Homeobox (Hox) genes in animals. These genes not only underwent gene duplications within chromosomes but also whole genome duplications. As a result, Hox genes in most vertebrates are clustered across multiple chromosomes with the HoxA-D
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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clusters being the best studied. Another example are the globin genes which encode myoglobin and hemoglobin and are considered to be ancient paralogs. Similarly, the four known classes of hemoglobins (hemoglobin A, hemoglobin A2, hemoglobin B, and hemoglobin F) are paralogs of each other. While each of these proteins serves the same basic function of oxygen transport, they have already diverged slightly in function: fetal hemoglobin (hemoglobin F) has a higher affinity for oxygen than adult hemoglobin. Function is not always conserved, however. Human angiogenin diverged from ribonuclease, for example, and while the two paralogs remain similar in tertiary structure, their functions within the cell are now quite different. It is often asserted that orthologs are more functionally similar than paralogs of similar divergence, but several papers have challenged this notion. === Regulation === Paralogs are often regulated differently, e.g. by having different tissue-specific expression patterns (see Hox genes). However, they can also be regulated differently on the protein level. For instance, Bacillus subtilis encodes two paralogues of glutamate dehydrogenase: GudB is constitutively transcribed whereas RocG is tightly regulated. In their active, oligomeric states, both enzymes show similar enzymatic rates. However, swaps of enzymes and promoters cause severe fitness losses, thus indicating promoter–enzyme coevolution. Characterization of the proteins shows that, compared to RocG, GudB's enzymatic activity is highly dependent on glutamate and pH. === Paralogous chromosomal regions === Sometimes, large regions of chromosomes share gene content similar to other chromosomal regions within the same genome. They are well characterised in the human genome, where they have been used as evidence to support the 2R hypothesis. Sets of duplicated, triplicated and quadruplicated genes, with the related genes on different chromosomes, are deduced to be remnants from genome or chromosomal duplications. A set of paralogy regions is together called a paralogon. Well-studied
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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|
sets of paralogy regions include regions of human chromosome 2, 7, 12 and 17 containing Hox gene clusters, collagen genes, keratin genes and other duplicated genes, regions of human chromosomes 4, 5, 8 and 10 containing neuropeptide receptor genes, NK class homeobox genes and many more gene families, and parts of human chromosomes 13, 4, 5 and X containing the ParaHox genes and their neighbors. The Major histocompatibility complex (MHC) on human chromosome 6 has paralogy regions on chromosomes 1, 9 and 19. Much of the human genome seems to be assignable to paralogy regions. == Ohnology == Ohnologous genes are paralogous genes that have originated by a process of whole-genome duplication. The name was first given in honour of Susumu Ohno by Ken Wolfe. Ohnologues are useful for evolutionary analysis because all ohnologues in a genome have been diverging for the same length of time (since their common origin in the whole genome duplication). Ohnologues are also known to show greater association with cancers, dominant genetic disorders, and pathogenic copy number variations. == Xenology == Homologs resulting from horizontal gene transfer between two organisms are termed xenologs. Xenologs can have different functions if the new environment is vastly different for the horizontally moving gene. In general, though, xenologs typically have similar function in both organisms. The term was coined by Walter Fitch. == Homoeology == Homoeologous (also spelled homeologous) chromosomes or parts of chromosomes are those brought together following inter-species hybridization and allopolyploidization to form a hybrid genome, and whose relationship was completely homologous in an ancestral species. In allopolyploids, the homologous chromosomes within each parental sub-genome should pair faithfully during meiosis, leading to disomic inheritance; however in some allopolyploids, the homoeologous chromosomes of the parental genomes may be nearly as similar to one another as the homologous chromosomes,
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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|
leading to tetrasomic inheritance (four chromosomes pairing at meiosis), intergenomic recombination, and reduced fertility. == Gametology == Gametology denotes the relationship between homologous genes on non-recombining, opposite sex chromosomes. The term was coined by García-Moreno and Mindell. 2000. Gametologs result from the origination of genetic sex determination and barriers to recombination between sex chromosomes. Examples of gametologs include CHDW and CHDZ in birds. == See also == Deep homology EggNOG (database) Neofunctionalization OrthoDB Orthologous MAtrix (OMA) PhEVER Protein family Protein superfamily TreeFam Syntelog == References ==
|
{
"page_id": 1442624,
"source": null,
"title": "Sequence homology"
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|
The molecular formula C13H16N2O2 (molar mass : 232.27 g/mol, exact mass : 232.121178) may refer to: Aminoglutethimide Horsfiline 4,5-MDO-DMT 5,6-MDO-DMT Melatonin, a hormone Methylphenylpiracetam Mofebutazone
|
{
"page_id": 10093369,
"source": null,
"title": "C13H16N2O2"
}
|
This is a list of gases at standard conditions, which means substances that boil or sublime at or below 25 °C (77 °F) and 1 atm pressure and are reasonably stable. == List == This list is sorted by boiling point of gases in ascending order, but can be sorted on different values. "sub" and "triple" refer to the sublimation point and the triple point, which are given in the case of a substance that sublimes at 1 atm; "dec" refers to decomposition. "~" means approximately. Blue type items have an article available by clicking on the name. == Known as gas == The following list has substances known to be gases, but with an unknown boiling point. Fluoroamine Trifluoromethyl trifluoroethyl trioxide CF3OOOCF2CF3 boils between 10 and 20° Bis-trifluoromethyl carbonate boils between −10 and +10° possibly +12, freezing −60° Difluoroaminosulfinyl fluoride F2NS(O)F is a gas but decomposes over several hours Trifluoromethylsulfinyl chloride CF3S(O)Cl Nitrosyl cyanide ?−20° blue-green gas 4343-68-4 Thiazyl chloride NSCl greenish yellow gas; trimerises. == Possible == This list includes substances that may be gases. However reliable references are not available. cis-1-Fluoro-1-propene trans-1-Chloropropene ? cis-1-Chloropropene ? Perfluoro-1,2-butadiene Perfluoro-1,2,3-butatriene −5 polymerizes Perfluoropent-2-ene Perfluoropent-1-ene 29-30° Trifluoromethanesulfenylfluoride CF3SF Difluorocarbamyl fluoride F2NCOF −52° N-Sulfinyltrifluoromethaneamine CF3NSO 18° (Chlorofluoromethyl)silane 373-67-1 274.37 K (1.22 °C) Difluoromethylsilane 420-34-8 237.56 K (−35.59 °C) Trifluoromethyl sulfenic trifloromethyl ester Pentafluoro(penta-fluorethoxy)sulfur 900001-56-6 15° Ethenol 557-75-5 10.5° = vinyl alcohol (tautomerizes) 1,1,1,2,2,3,4,4,4-nonafluorobutane 2-10° melt −129° trans-2H-Heptafluoro-2-butene Pentafluoroethylhypochlorite around −10° Trifluoromethyl pentafluoroethyl sulfide 6° 33547-10-3 1,1,1-Trifluoro-N-(trifluoromethoxy)methanamine 671-63-6 0.6° 1-Chloro-1,1,2,2,3,3-hexafluoropropane 422-55-9 16.7 1-Chloro-1,1,2,3,3,3-hexafluoropropane 359-58-0 17.15 2-Chloro-1,1,1,2,3,3-hexafluoropropane 51346-64-6 16.7° 3-Chloro-1,1,1,2,2,3-hexafluoropropane 422-57-1 16.7° Trifluormethyl 1,2,2,2-tetrafluoroethyl ether 2356-62-9 11° 2-Chloro-1,1,1,3,3-pentafluoropropane HFC-235da 134251-06-2 8° 1,1,2,3,3-Pentafluoropropane 24270-66-4 −3.77 2,2,3,3,4,5,5-Heptafluoro oxolane (Heptafluoropropyl)carbonimidic difluoride 378-00-7 Pentafluoroethyl carbonimidic difluoride 428-71-7 (Trifluoromethyl)carbonimidic difluoride 371-71-1 CF3N=CF2 Perfluoro[N-methyl-(propylenamine)] 680-23-9 Perfluoro-N,N-dimethylvinylamine 13821-49-3 3,3,4-Trifluoro-2,4-bis-trifluoromethyl-[1,2]oxazetidine 714-52-3 Bis(trifluoromethyl) 2,2-difluoro-vinylamine 13747-23-4 Bis(trifluoromethyl) 1,2-difluoro-vinylamine 13747-24-5 1,1,2-Trifluoro-3-(trifluoromethyl)cyclopropane 2967-53-5 Bis(trifluoromethyl) 2-fluoro-vinylamine 25211-47-6
|
{
"page_id": 57017151,
"source": null,
"title": "List of gases"
}
|
2-Fluoro-1,3-butadiene 381-61-3 Trifluormethylcyclopropane 381-74-8 cis-1-Fluoro-1-butene 66675-34-1 trans-1-Fluoro-1-butene 66675-35-2 2-Fluoro-1-butene 3-Fluoro-1-butene trans-1-Fluoro-2-butene cis-2-fluoro-2-butene trans-2-fluoro-2-butene 1-Fluoro-2-methyl-1-propene 3-Fluoro-2-methyl-1-propene Perfluoro-2-methyl-1,3-butadiene 384-04-3 1,1,3,4,4,5,5,5-Pctafluoro-1,2-pentadiene 21972-01-0 == Near misses == This list includes substances that boil just above standard condition temperatures. Numbers are boiling temperatures in °C. 1,1,2,2,3-Pentafluoropropane 25–26 °C Dimethoxyborane 25.9 °C 1,4-Pentadiene 25.9 °C 2-Bromo-1,1,1-trifluoroethane 26 °C 1,2-Difluoroethane 26 °C Hydrogen cyanide 26 °C Trimethylgermane 26.2 °C 1,H-Pentafluorocyclobut-1-ene 1,H:2,H-hexafluorocyclobutane Tetramethylsilane 26.7 °C Chlorosyl trifluoride 27 °C 2,2-Dichloro-1,1,1-trifluoroethane 27.8 °C Perfluoroethyl 2,2,2-trifluoroethyl ether 27.89 °C Perfluoroethyl ethyl ether 28 °C Perfluorocyclopentadiene C5F6 28 °C 2-Butyne 29 °C Digermane 29 °C Perfluoroisopropyl methyl ether 29 °C Trifluoromethanesulfonyl chloride 29–32 °C Perfluoropentane 29.2 °C Rhenium(VI) fluoride 33.8 °C Chlorodimethylsilane 34.7 °C 1,2-Difluoropropane 43 °C 1,3-Difluoropropane 40-42 °C Dimethylarsine 36 °C Spiro[2.2]pentane 39 °C Ruthenium(VIII) oxide 40 °C Nickel carbonyl 42.1 °C Trimethylphosphine 43 °C == Unstable substances == Gallane liquid decomposes at 0 °C. Nitroxyl and diazene are simple nitrogen compounds known to be gases but they are too unstable and short lived to be condensed. Methanetellurol CH3TeH 25284-83-7 unstable at room temperature. Sulfur pentafluoride isocyanide isomerises to sulfur pentafluoride cyanide. == References == Haynes, W. M., ed. (2016). CRC Handbook of Chemistry and Physics (96th ed.). Boca Raton, Florida: CRC Press/Taylor & Francis. pp. 3–4–4–101. ISBN 978-1482260960.
|
{
"page_id": 57017151,
"source": null,
"title": "List of gases"
}
|
L-serine dehydratase may refer to: Serine dehydratase, an enzyme Threonine ammonia-lyase, an enzyme == See also == D-serine dehydratase, also called D-serine ammonia-lyase
|
{
"page_id": 11338563,
"source": null,
"title": "L-serine dehydratase"
}
|
The aza-Baylis–Hillman reaction or aza-BH reaction in organic chemistry is a variation of the Baylis–Hillman reaction and describes the reaction of an electron deficient alkene, usually an α,β-unsaturated carbonyl compound, with an imine in the presence of a nucleophile. The reaction product is an allylic amine. The reaction can be carried out in enantiomeric excess of up to 90% with the aid of bifunctional chiral BINOL and phosphinyl BINOL compounds, for example in the reaction of n-(4-chloro-benzylidene)-benzenesulfonamide with methyl vinyl ketone (MVK) in cyclopentyl methyl ether and toluene at -15°C. In one study a reaction mechanism for a specific aza-BH reaction is proposed. Given a set of reaction conditions the reaction is found to be first-order in the triphenylphosphine nucleophile, MVK and the tosylimine concentration in the rate determining step in the presence of a Brønsted acid such as phenol or benzoic acid. The presence of an acid facilitates the elimination reaction in the zwitterion by proton transfer which becomes much faster and no longer rate determining. A 6 membered cyclic transition state is proposed for this reaction step. Because this step is also reversible the presence of acid causes a racemisation process simply by mixing chiral aza-BH adduct, phosphine and acid. == Asymmetric aza-BH == Aza-BH reactions are known in asymmetric synthesis by making use of chiral ligands. In one study, for the first time, successful use was made of a chiral solvent based on an ionic liquid (IL). This solvent is a condensation product of L-(−)-malic acid (available from the chiral pool), boric acid catalyzed by sodium hydroxide. When the sodium counter ion is replaced by a bulky ammonium salt the resulting ionic liquid has a melting point of −32°C. This IL serves as the chiral solvent for the aza-BH reaction between N-(4-bromobenzylidene)-4-toluenesulfonamide and methyl vinyl ketone catalyzed
|
{
"page_id": 3343173,
"source": null,
"title": "Aza-Baylis–Hillman reaction"
}
|
by triphenylphosphine with chemical yield 34–39% and enantiomeric excess 71–84%. == References == == External links == https://www.organic-chemistry.org/Highlights/2006/30JanuaryA.shtm
|
{
"page_id": 3343173,
"source": null,
"title": "Aza-Baylis–Hillman reaction"
}
|
Things named after physicist Julian Schwinger include the following: Schwinger effect (Schwinger pair production) Schwinger function Schwinger limit Schwinger model Schwinger parametrization Schwinger representation Schwinger reversed-phase coupler Schwinger variational principle Schwinger's quantum action principle Schwinger–Dyson equation Schwinger–Tomonaga equation Fock–Schwinger gauge Jordan–Schwinger map Rarita–Schwinger equation Lippmann–Schwinger equation Kubo–Martin–Schwinger state Schwinger boson (Schwinger boson mean-field theory)
|
{
"page_id": 56427334,
"source": null,
"title": "List of things named after Julian Schwinger"
}
|
The Plasma Physics Laboratory at the University of Saskatchewan was established in 1959 by H. M. Skarsgard. Early work centered on research with a Betatron. == Facilities == === STOR-1M === STOR-1M is Canada's first tokamak built in 1983. In 1987 STOR-1M was the world’s first demonstration of alternating current in a tokamak. === STOR-M === STOR-M stands for Saskatchewan Torus-Modified. STOR-M is a tokamak located at the University of Saskatchewan. STOR-M is a small tokamak (major radius = 46 cm, minor radius = 12.5 cm) designed for studying plasma heating, anomalous transport and developing novel tokamak operation modes and advanced diagnostics. STOR-M is capable of a 30–40 millisecond plasma discharge with a toroidal magnetic field of between 0.5 and 1 tesla and a plasma current of between 20 and 50 kiloamperes. STOR-M has also demonstrated improved confinement induced by a turbulent heating pulse, electrode biasing and compact torus injection. == References == == External links == Official website
|
{
"page_id": 5047113,
"source": null,
"title": "Plasma Physics Laboratory (Saskatchewan)"
}
|
Mioara Mugur-Schächter is a French-Romanian physicist specialized in fundamental quantum mechanics, probability theory, and theory of communication of information. She is also an epistemologist. As a professor at the University of Reims, she founded there the Laboratoire de Mécanique Quantique et Structures de l'Information, which she directed until 1997. During an interview in 2015, Mugur-Schäcter explained how she worked on the invalidation of John von Neumann's no hidden variables proof during her PhD. Her academic advisor was Louis de Broglie. == References ==
|
{
"page_id": 9634634,
"source": null,
"title": "Mioara Mugur-Schächter"
}
|
Viral shedding is the expulsion and release of virus progeny following successful reproduction during a host cell infection. Once replication has been completed and the host cell is exhausted of all resources in making viral progeny, the viruses may begin to leave the cell by several methods. The term is variously used to refer to viral particles shedding from a single cell, from one part of the body into another, and from a body into the environment, where the virus may infect another host. Vaccine shedding is a form of viral shedding which can occur in instances of infection caused by some attenuated (or "live virus") vaccines. == Means == === Shedding from a cell into extracellular space === ==== Budding (through cell envelope) ==== "Budding" through the cell envelope into extracellular space is most effective for viruses that require their own envelope. In effect, the viral envelope is built from a part of the host cell membrane. Examples for viruses that shed through budding include HIV, HSV, SARS, and smallpox. When beginning the budding process, the viral nucleocapsid interacts with a certain region of the host cell membrane. During this interaction, the glycosylated viral envelope protein inserts itself into the cell membrane. In order to successfully bud from the host cell, the nucleocapsid of the virus must form a connection with the cytoplasmic tails of envelope proteins. Though budding does not immediately destroy the host cell, this process will slowly use up the cell membrane and eventually lead to the cell's demise. This is also how antiviral responses are able to detect virus-infected cells. Budding has been most extensively studied for viruses of eukaryotes. However, it has been demonstrated that viruses infecting prokaryotes of the domain Archaea also employ this mechanism of virion release. ==== Apoptosis (cell destruction) ====
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{
"page_id": 14353229,
"source": null,
"title": "Viral shedding"
}
|
Animal cells are programmed to self-destruct when they are under viral attack or damaged in some other way. By forcing the cell to undergo apoptosis or cell suicide, release of progeny into the extracellular space is possible. However, apoptosis does not necessarily result in the cell simply popping open and spilling its contents into the extracellular space. Rather, apoptosis is usually controlled and results in the cell's genome being chopped up, before apoptotic bodies of dead cell material clump off the cell to be absorbed by macrophages. This is a good way for a virus to get into macrophages either to infect them or simply travel to other tissues in the body. Although this process is primarily used by non-enveloped viruses, enveloped viruses may also use this. HIV is an example of an enveloped virus that exploits this process for the infection of macrophages. ==== Exocytosis (cell release) ==== Viruses that have envelopes that come from nuclear or endosomal membranes can leave the cell via exocytosis, in which the host cell is not destroyed. Viral progeny are synthesized within the cell, and the host cell's transport system is used to enclose them in vesicles; the vesicles of virus progeny are carried to the cell membrane and then released into the extracellular space. This is used primarily by non-enveloped viruses, although enveloped viruses display this too. An example is the use of recycling viral particle receptors in the enveloped varicella-zoster virus. == Contagiousness == A human with a viral disease can be contagious if they are shedding virus particles, even if they are unaware of doing so. Some viruses such as HSV-2 (which produces genital herpes) can cause asymptomatic shedding and therefore spread undetected from person to person, as no fever or other hints reveal the contagious nature of the host.
|
{
"page_id": 14353229,
"source": null,
"title": "Viral shedding"
}
|
== See also == Vaccine shedding - a form of viral shedding following administration of an attenuated (or "live virus") vaccine == References ==
|
{
"page_id": 14353229,
"source": null,
"title": "Viral shedding"
}
|
Alfred Senier (24 January 1853 – 29 June 1918) was a chemist and a Professor of Chemistry, Queen's College, Galway from 1891 until his death. He was one of the founding members of the Aristotelian Society. == Life == Alfred Senier was born 24 January 1853 in Burnley, England to Alfred Senier (1823–1893) and Jane (née Sutherland). His father, who was born in England, first emigrated to the Territory of Wisconsin in 1844 before returning to England in 1847 to become a pharmacist. He married Jane Sutherland and, in 1853, emigrated once more to Wisconsin, opening a pharmacy in Dover. In 1857, they moved to the nearby village of Mazomanie. He attended the University of Wisconsin and graduated from the University of Michigan in 1873 as a Doctor of Medicine. He died 29 June 1918 at the age of 65 in Galway, Ireland. == References == == Further reading == "Senier, Alfred". Who Was Who. Oxford University Press. 1 December 2007. doi:10.1093/ww/9780199540884.013.U202792. Retrieved 19 February 2012.
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{
"page_id": 34800461,
"source": null,
"title": "Alfred Senier"
}
|
In passing through matter, charged particles ionize and thus lose energy in many steps, until their energy is (almost) zero. The distance to this point is called the range of the particle. The range depends on the type of particle, on its initial energy and on the material through which it passes. For example, if the ionising particle passing through the material is a positive ion like an alpha particle or proton, it will collide with atomic electrons in the material via Coulombic interaction. Since the mass of the proton or alpha particle is much greater than that of the electron, there will be no significant deviation from the radiation's incident path and very little kinetic energy will be lost in each collision. As such, it will take many successive collisions for such heavy ionising radiation to come to a halt within the stopping medium or material. Maximum energy loss will take place in a head-on collision with an electron. Since large angle scattering is rare for positive ions, a range may be well defined for that radiation, depending on its energy and charge, as well as the ionisation energy of the stopping medium. Since the nature of such interactions is statistical, the number of collisions required to bring a radiation particle to rest within the medium will vary slightly with each particle (i.e., some may travel further and undergo fewer collisions than others). Hence, there will be a small variation in the range, known as straggling. The energy loss per unit distance (and hence, the density of ionization), or stopping power also depends on the type and energy of the particle and on the material. Usually, the energy loss per unit distance increases while the particle slows down. The curve describing this fact is called the Bragg curve. Shortly
|
{
"page_id": 5047118,
"source": null,
"title": "Range (particle radiation)"
}
|
before the end, the energy loss passes through a maximum, the Bragg Peak, and then drops to zero (see the figures in Bragg Peak and in stopping power). This fact is of great practical importance for radiation therapy. The range of alpha particles in ambient air amounts to only several centimeters; this type of radiation can therefore be stopped by a sheet of paper. Although beta particles scatter much more than alpha particles, a range can still be defined; it frequently amounts to several hundred centimeters of air. The mean range can be calculated by integrating the inverse stopping power over energy. == Scaling == The range of a heavy charged particle is approximately proportional to the mass of the particle and the inverse of the density of the medium, and is a function of the initial velocity of the particle. == See also == Stopping power (particle radiation) Attenuation length Radiation length == Further reading == Nakamura, K (1 July 2010). "Review of Particle Physics". Journal of Physics G: Nuclear and Particle Physics. 37 (7A): 1–708. Bibcode:2010JPhG...37g5021N. doi:10.1088/0954-3899/37/7A/075021. hdl:10481/34593. PMID 10020536. Williams, William S. C. (1992). Nuclear and particle physics (Reprinted (with corr.) ed.). Oxford: Clarendon Press. ISBN 978-0-19-852046-7. Leo, William R. (1994). Techniques for nuclear and particle physics experiments : a how-to approach (2nd rev. ed.). Berlin: Springer. ISBN 978-3-540-57280-0.
|
{
"page_id": 5047118,
"source": null,
"title": "Range (particle radiation)"
}
|
Mudundi Ramakrishna Raju is an Indian physicist, known for his research on the application of nuclear physics to cancer therapy. He hails from the Indian state of Andhra Pradesh and is the Managing Trustee of the International Cancer Center, Mahatma Gandhi Memorial Medical Trust located at Bhimavaram. He is reported to have 35 years of research experience in radiation therapy at various institutions in the US such as Massachusetts General Hospital, Harvard University, Massachusetts Institute of Technology, Lawrence Radiation Laboratory, University of California in Berkeley and Los Alamos National Laboratory and is credited with several articles on the topic. Raju was honored by the Government of India, in 2013, with the fourth highest Indian civilian award of Padma Shri. == See also == == References ==
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{
"page_id": 44761936,
"source": null,
"title": "Mudundi Ramakrishna Raju"
}
|
In molecular biology mir-193 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-193 microRNA precursor family at Rfam
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{
"page_id": 36373329,
"source": null,
"title": "Mir-193 microRNA precursor family"
}
|
Chlorocresol may refer to a number of different chemical compounds, of which two are of primary importance: 2-Chloro-m-cresol p-Chlorocresol
|
{
"page_id": 20579154,
"source": null,
"title": "Chlorocresol"
}
|
Bothrioneodermata is a clade of flatworms containing the Bothrioplanida and the Neodermata. == References ==
|
{
"page_id": 54592339,
"source": null,
"title": "Bothrioneodermata"
}
|
Guido Beck (29 August 1903 – 21 October 1988) was an Argentine physicist of German Bohemian origin, who was born in Liberec and died in Rio de Janeiro. He discovered all cylindrically symmetric nonrotating vacuum solutions in general relativity, which is the first instance of exactly solved gravitational waves. == Biography == Beck studied physics in Vienna and received his doctorate in 1925, under Hans Thirring. He worked in Leipzig in 1928 as an assistant to Werner Heisenberg. A combination of the troubled political climate of Europe in the 1930s, his own restlessness, and the Nazi persecutions in Germany, made the Jewish-born Beck a traveler in those years. Until 1935 he worked in Cambridge with Ernest Rutherford, Copenhagen, Prague, United States and Japan. In 1935, Beck was invited to work in the Soviet Union by Head of the Institute of Physics, Odessa University Yelpidifor Anempodistovich Kirillov. At the Odessa University Beck was head of the Department of Theoretical Physics and gave a course of theoretical physics in German; his lectures were simultaneously translated into Ukrainian by his assistant Yu.G. Vekshtein. In 1936–1937 Beck was head of the department of theoretical mechanics at the Institute of Water Transport Engineers in Odessa. Four of his Odessa students – VV Malyarov, MM Alperin, GV Skrotskii and PE Nemirovsky – became professors in Odessa and Moscow. In 1937, Guido Beck moved to France, where he was imprisoned when World War II broke out. In 1941, he fled to Portugal. From 1942 to 1943 he was a guest professor at the University of Coimbra and the University of Oporto. In 1943 he emigrated to Argentina. In Argentina, he was instrumental in training several Argentine physicists, including José Antonio Balseiro, and had a profound impact in developing physics in Argentina. He moved once more, this time
|
{
"page_id": 4457299,
"source": null,
"title": "Guido Beck"
}
|
to Brazil, in 1951, where his influence in developing physics was also great. He was called back to Argentina in 1962, after the death of Balseiro, and continued his work at the Instituto Balseiro. In 1975, he returned to Brazil, and worked in the Centro Brasileiro de Pesquisas Físicas (CBPF). Apart from his influence as a teacher in South America he contributed to a theory of beta-decay, which was later superseded by a more complete theory by Fermi. He was a friend of the famous writer Ernesto Sabato. He died in a car accident in Rio de Janeiro in 1988. == Honours == In 1977, he was given the doctoral degree of honour by the Darmstadt University of Technology, Germany for his exemplary activity as an academic teacher and his relentless efforts in establishing research institutions in physics. == References == == External links == Oral History interview transcript with Guido Beck on 22 April 1967, American Institute of Physics, Niels Bohr Library and Archives - interview by John L. Heilbron Media related to Guido Beck (physicist) at Wikimedia Commons
|
{
"page_id": 4457299,
"source": null,
"title": "Guido Beck"
}
|
The Hector Medal, formerly known as the Hector Memorial Medal, is a science award given by the Royal Society Te Apārangi in memory of Sir James Hector to researchers working in New Zealand. It is awarded annually in rotation for different sciences – currently there are three: chemical sciences; physical sciences; mathematical and information sciences. It is given to a researcher who "has undertaken work of great scientific or technological merit and has made an outstanding contribution to the advancement of the particular branch of science." It was previously rotated through more fields of science – in 1918 they were: botany, chemistry, ethnology, geology, physics (including mathematics and astronomy), zoology (including animal physiology). For a few years it was awarded biennially – it was not awarded in 2000, 2002 or 2004. In 1991 it was overtaken by the Rutherford Medal as the highest award given by the Royal Society of New Zealand. The obverse of the medal bears the head of James Hector and the reverse a Māori snaring a huia. The last confirmed sighting of a living huia predates the award of the medal by three years. == Recipients == == See also == Category:New Zealand scientists The Shorland Medal given by the New Zealand Association of Scientists List of chemistry awards List of mathematics awards List of physics awards == References == == External links == Hector Medal, Royal Society of New Zealand Te Apārangi
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{
"page_id": 22545239,
"source": null,
"title": "Hector Medal"
}
|
Dicalcium phosphate is the calcium phosphate with the formula CaHPO4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO42– anion involves the removal of two protons from phosphoric acid, H3PO4. It is also known as dibasic calcium phosphate or calcium monohydrogen phosphate. Dicalcium phosphate is used as a food additive, and it is found in some toothpastes as a polishing agent and biomaterial. == Preparation == Dibasic calcium phosphate is produced by neutralizing calcium hydroxide with phosphoric acid, precipitating the dihydrate as a solid. At 60 °C the anhydrous form is precipitated: To prevent degradation that would form hydroxyapatite, sodium pyrophosphate or trimagnesium phosphate octahydrate are added when, for example, dibasic calcium phosphate dihydrate is to be used as a polishing agent in toothpaste. In a continuous process CaCl2 can be treated with (NH4)2HPO4 to form the dihydrate: A slurry of the dihydrate is then heated to around 65–70 °C to form anhydrous CaHPO4 as a crystalline precipitate, typically as flat diamondoid crystals, which are suitable for further processing. Dibasic calcium phosphate dihydrate is formed in "brushite" calcium phosphate cements (CPC's), which have medical applications. An example of the overall setting reaction in the formation of "β-TCP/MCPM" (β-tricalcium phosphate/monocalcium phosphate) calcium phosphate cements is: == Structure == Three forms of dicalcium phosphate are known: dihydrate, CaHPO4•2H2O ('DCPD'), the mineral brushite monohydrate, CaHPO4•H2O ('DCPM') anhydrous CaHPO4 ('DCPA'), the mineral monetite. Below pH 4.8, the dihydrate and anhydrous forms of dicalcium phosphate are the most stable (insoluble) calcium phosphates. The structure of the anhydrous and dihydrated forms has been determined by X-ray crystallography, and the structure of the monohydrate was determined by electron crystallography. The dihydrate (shown in table above) as well as the monohydrate, adopt layered structures. == Uses and occurrence == Dibasic
|
{
"page_id": 3277656,
"source": null,
"title": "Dicalcium phosphate"
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|
calcium phosphate is mainly used as a dietary supplement in prepared breakfast cereals, dog treats, enriched flour, and noodle products. It is also used as a tableting agent in some pharmaceutical preparations, including some products meant to eliminate body odor. Dibasic calcium phosphate is also found in some dietary calcium supplements (e.g., Bonexcin). It is used in poultry feed. It is also used in some toothpastes as a tartar control agent. Heating dicalcium phosphate gives dicalcium diphosphate, a useful polishing agent: In the dihydrate (brushite) form, it is found in some kidney stones and dental calculi. == See also == Brushite Monocalcium phosphate Tricalcium phosphate == References ==
|
{
"page_id": 3277656,
"source": null,
"title": "Dicalcium phosphate"
}
|
Imi Tami is a private company and the largest industrial chemistry R&D centre in Israel. IMI TAMI is a member of the Israel Chemicals manufacturing concern. IMI TAMI has created a campus with research, analytical and testing laboratories, GMP compliant facilities, a mini-pilot and pilot plants for process development and small-scale production. == References == == External links == Imi Tami Institute for Research and Development Ltd
|
{
"page_id": 1901399,
"source": null,
"title": "Imi Tami Institute for Research and Development"
}
|
In nuclear physics, the island of stability is a predicted set of isotopes of superheavy elements that may have considerably longer half-lives than known isotopes of these elements. It is predicted to appear as an "island" in the chart of nuclides, separated from known stable and long-lived primordial radionuclides. Its theoretical existence is attributed to stabilizing effects of predicted "magic numbers" of protons and neutrons in the superheavy mass region. Several predictions have been made regarding the exact location of the island of stability, though it is generally thought to center near copernicium and flerovium isotopes in the vicinity of the predicted closed neutron shell at N = 184. These models strongly suggest that the closed shell will confer further stability towards fission and alpha decay. While these effects are expected to be greatest near atomic number Z = 114 (flerovium) and N = 184, the region of increased stability is expected to encompass several neighboring elements, and there may also be additional islands of stability around heavier nuclei that are doubly magic (having magic numbers of both protons and neutrons). Estimates of the stability of the nuclides within the island are usually around a half-life of minutes or days; some optimists propose half-lives on the order of millions of years. Although the nuclear shell model predicting magic numbers has existed since the 1940s, the existence of long-lived superheavy nuclides has not been definitively demonstrated. Like the rest of the superheavy elements, the nuclides within the island of stability have never been found in nature; thus, they must be created artificially in a nuclear reaction to be studied. Scientists have not found a way to carry out such a reaction, for it is likely that new types of reactions will be needed to populate nuclei near the center of the
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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island. Nevertheless, the successful synthesis of superheavy elements up to Z = 118 (oganesson) with up to 177 neutrons demonstrates a slight stabilizing effect around elements 110 to 114 that may continue in heavier isotopes, consistent with the existence of the island of stability. == Introduction == === Nuclide stability === The composition of a nuclide (atomic nucleus) is defined by the number of protons Z and the number of neutrons N, which sum to mass number A. Proton number Z, also named the atomic number, determines the position of an element in the periodic table. The approximately 3300 known nuclides are commonly represented in a chart with Z and N for its axes and the half-life for radioactive decay indicated for each unstable nuclide (see figure). As of 2019, 251 nuclides are observed to be stable (having never been observed to decay); generally, as the number of protons increases, stable nuclei have a higher neutron–proton ratio (more neutrons per proton). The last element in the periodic table that has a stable isotope is lead (Z = 82), with stability (i.e., half-lives of the longest-lived isotopes) generally decreasing in heavier elements, especially beyond curium (Z = 96). The half-lives of nuclei also decrease when there is a lopsided neutron–proton ratio, such that the resulting nuclei have too few or too many neutrons to be stable. The stability of a nucleus is determined by its binding energy, higher binding energy conferring greater stability. The binding energy per nucleon increases with atomic number to a broad plateau around A = 60, then declines. If a nucleus can be split into two parts that have a lower total energy (a consequence of the mass defect resulting from greater binding energy), it is unstable. The nucleus can hold together for a finite time because
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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there is a potential barrier opposing the split, but this barrier can be crossed by quantum tunneling. The lower the barrier and the masses of the fragments, the greater the probability per unit time of a split. Protons in a nucleus are bound together by the strong force, which counterbalances the Coulomb repulsion between positively charged protons. In heavier nuclei, larger numbers of uncharged neutrons are needed to reduce repulsion and confer additional stability. Even so, as physicists started to synthesize elements that are not found in nature, they found the stability decreased as the nuclei became heavier. Thus, they speculated that the periodic table might come to an end. The discoverers of plutonium (element 94) considered naming it "ultimium", thinking it was the last. Following the discoveries of heavier elements, of which some decayed in microseconds, it then seemed that instability with respect to spontaneous fission would limit the existence of heavier elements. In 1939, an upper limit of potential element synthesis was estimated around element 104, and following the first discoveries of transactinide elements in the early 1960s, this upper limit prediction was extended to element 108. === Magic numbers === As early as 1914, the possible existence of superheavy elements with atomic numbers well beyond that of uranium—then the heaviest known element—was suggested, when German physicist Richard Swinne proposed that superheavy elements around Z = 108 were a source of radiation in cosmic rays. Although he did not make any definitive observations, he hypothesized in 1931 that transuranium elements around Z = 100 or Z = 108 may be relatively long-lived and possibly exist in nature. In 1955, American physicist John Archibald Wheeler also proposed the existence of these elements; he is credited with the first usage of the term "superheavy element" in a 1958 paper published
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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with Frederick Werner. This idea did not attract wide interest until a decade later, after improvements in the nuclear shell model. In this model, the atomic nucleus is built up in "shells", analogous to electron shells in atoms. Independently of each other, neutrons and protons have energy levels that are normally close together, but after a given shell is filled, it takes substantially more energy to start filling the next. Thus, the binding energy per nucleon reaches a local maximum and nuclei with filled shells are more stable than those without. This theory of a nuclear shell model originates in the 1930s, but it was not until 1949 that German physicists Maria Goeppert Mayer and Johannes Hans Daniel Jensen et al. independently devised the correct formulation. The numbers of nucleons for which shells are filled are called magic numbers. Magic numbers of 2, 8, 20, 28, 50, 82 and 126 have been observed for neutrons, and the next number is predicted to be 184. Protons share the first six of these magic numbers, and 126 has been predicted as a magic proton number since the 1940s. Nuclides with a magic number of each—such as 16O (Z = 8, N = 8), 132Sn (Z = 50, N = 82), and 208Pb (Z = 82, N = 126)—are referred to as "doubly magic" and are more stable than nearby nuclides as a result of greater binding energies. In the late 1960s, more sophisticated shell models were formulated by American physicist William Myers and Polish physicist Władysław Świątecki, and independently by German physicist Heiner Meldner (1939–2019). With these models, taking into account Coulomb repulsion, Meldner predicted that the next proton magic number may be 114 instead of 126. Myers and Świątecki appear to have coined the term "island of stability", and American chemist
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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|
Glenn Seaborg, later a discoverer of many of the superheavy elements, quickly adopted the term and promoted it. Myers and Świątecki also proposed that some superheavy nuclei would be longer-lived as a consequence of higher fission barriers. Further improvements in the nuclear shell model by Soviet physicist Vilen Strutinsky led to the emergence of the macroscopic–microscopic method, a nuclear mass model that takes into consideration both smooth trends characteristic of the liquid drop model and local fluctuations such as shell effects. This approach enabled Swedish physicist Sven Nilsson et al., as well as other groups, to make the first detailed calculations of the stability of nuclei within the island. With the emergence of this model, Strutinsky, Nilsson, and other groups argued for the existence of the doubly magic nuclide 298Fl (Z = 114, N = 184), rather than 310Ubh (Z = 126, N = 184) which was predicted to be doubly magic as early as 1957. Subsequently, estimates of the proton magic number have ranged from 114 to 126, and there is still no consensus. == Discoveries == Interest in a possible island of stability grew throughout the 1960s, as some calculations suggested that it might contain nuclides with half-lives of billions of years. They were also predicted to be especially stable against spontaneous fission in spite of their high atomic mass. It was thought that if such elements exist and are sufficiently long-lived, there may be several novel applications as a consequence of their nuclear and chemical properties. These include use in particle accelerators as neutron sources, in nuclear weapons as a consequence of their predicted low critical masses and high number of neutrons emitted per fission, and as nuclear fuel to power space missions. These speculations led many researchers to conduct searches for superheavy elements in the 1960s
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
}
|
and 1970s, both in nature and through nucleosynthesis in particle accelerators. During the 1970s, many searches for long-lived superheavy nuclei were conducted. Experiments aimed at synthesizing elements ranging in atomic number from 110 to 127 were conducted at laboratories around the world. These elements were sought in fusion-evaporation reactions, in which a heavy target made of one nuclide is irradiated by accelerated ions of another in a cyclotron, and new nuclides are produced after these nuclei fuse and the resulting excited system releases energy by evaporating several particles (usually protons, neutrons, or alpha particles). These reactions are divided into "cold" and "hot" fusion, which respectively create systems with lower and higher excitation energies; this affects the yield of the reaction. For example, the reaction between 248Cm and 40Ar was expected to yield isotopes of element 114, and that between 232Th and 84Kr was expected to yield isotopes of element 126. None of these attempts were successful, indicating that such experiments may have been insufficiently sensitive if reaction cross sections were low—resulting in lower yields—or that any nuclei reachable via such fusion-evaporation reactions might be too short-lived for detection. Subsequent successful experiments reveal that half-lives and cross sections indeed decrease with increasing atomic number, resulting in the synthesis of only a few short-lived atoms of the heaviest elements in each experiment; as of 2022, the highest reported cross section for a superheavy nuclide near the island of stability is for 288Mc in the reaction between 243Am and 48Ca. Similar searches in nature were also unsuccessful, suggesting that if superheavy elements do exist in nature, their abundance is less than 10−14 moles of superheavy elements per mole of ore. Despite these unsuccessful attempts to observe long-lived superheavy nuclei, new superheavy elements were synthesized every few years in laboratories through light-ion bombardment and
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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cold fusion reactions; rutherfordium, the first transactinide, was discovered in 1969, and copernicium, eight protons closer to the island of stability predicted at Z = 114, was reached by 1996. Even though the half-lives of these nuclei are very short (on the order of seconds), the very existence of elements heavier than rutherfordium is indicative of stabilizing effects thought to be caused by closed shells; a model not considering such effects would forbid the existence of these elements due to rapid spontaneous fission. Flerovium, with the expected magic 114 protons, was first synthesized in 1998 at the Joint Institute for Nuclear Research in Dubna, Russia, by a group of physicists led by Yuri Oganessian. A single atom of element 114 was detected, with a lifetime of 30.4 seconds, and its decay products had half-lives measurable in minutes. Because the produced nuclei underwent alpha decay rather than fission, and the half-lives were several orders of magnitude longer than those previously predicted or observed for superheavy elements, this event was seen as a "textbook example" of a decay chain characteristic of the island of stability, providing strong evidence for the existence of the island of stability in this region. Even though the original 1998 chain was not observed again, and its assignment remains uncertain, further successful experiments in the next two decades led to the discovery of all elements up to oganesson, whose half-lives were found to exceed initially predicted values; these decay properties further support the presence of the island of stability. However, a 2021 study on the decay chains of flerovium isotopes suggests that there is no strong stabilizing effect from Z = 114 in the region of known nuclei (N = 174), and that extra stability would be predominantly a consequence of the neutron shell closure. Although known nuclei
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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|
still fall several neutrons short of N = 184 where maximum stability is expected (the most neutron-rich confirmed nuclei, 293Lv and 294Ts, only reach N = 177), and the exact location of the center of the island remains unknown, the trend of increasing stability closer to N = 184 has been demonstrated. For example, the isotope 285Cn, with eight more neutrons than 277Cn, has a half-life almost five orders of magnitude longer. This trend is expected to continue into unknown heavier isotopes in the vicinity of the shell closure. === Deformed nuclei === Though nuclei within the island of stability around N = 184 are predicted to be spherical, studies from the early 1990s—beginning with Polish physicists Zygmunt Patyk and Adam Sobiczewski in 1991—suggest that some superheavy elements do not have perfectly spherical nuclei. A change in the shape of the nucleus changes the position of neutrons and protons in the shell. Research indicates that large nuclei farther from spherical magic numbers are deformed, causing magic numbers to shift or new magic numbers to appear. Current theoretical investigation indicates that in the region Z = 106–108 and N ≈ 160–164, nuclei may be more resistant to fission as a consequence of shell effects for deformed nuclei; thus, such superheavy nuclei would only undergo alpha decay. Hassium-270 is now believed to be a doubly magic deformed nucleus, with deformed magic numbers Z = 108 and N = 162. It has a half-life of 9 seconds. This is consistent with models that take into account the deformed nature of nuclei intermediate between the actinides and island of stability near N = 184, in which a stability "peninsula" emerges at deformed magic numbers Z = 108 and N = 162. Determination of the decay properties of neighboring hassium and seaborgium isotopes near N
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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|
= 162 provides further strong evidence for this region of relative stability in deformed nuclei. This also strongly suggests that the island of stability (for spherical nuclei) is not completely isolated from the region of stable nuclei, but rather that both regions are instead linked through an isthmus of relatively stable deformed nuclei. == Predicted decay properties == The half-lives of nuclei in the island of stability itself are unknown since none of the nuclides that would be "on the island" have been observed. Many physicists believe that the half-lives of these nuclei are relatively short, on the order of minutes or days. Some theoretical calculations indicate that their half-lives may be long, on the order of 100 years, or possibly as long as 109 years. The shell closure at N = 184 is predicted to result in longer partial half-lives for alpha decay and spontaneous fission. It is believed that the shell closure will result in higher fission barriers for nuclei around 298Fl, strongly hindering fission and perhaps resulting in fission half-lives 30 orders of magnitude greater than those of nuclei unaffected by the shell closure. For example, the neutron-deficient isotope 284Fl (with N = 170) undergoes fission with a half-life of 2.5 milliseconds, and is thought to be one of the most neutron-deficient nuclides with increased stability in the vicinity of the N = 184 shell closure. Beyond this point, some undiscovered isotopes are predicted to undergo fission with still shorter half-lives, limiting the existence and possible observation of superheavy nuclei far from the island of stability (namely for N < 170 as well as for Z > 120 and N > 184). These nuclei may undergo alpha decay or spontaneous fission in microseconds or less, with some fission half-lives estimated on the order of 10−20 seconds in
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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the absence of fission barriers. In contrast, 298Fl (predicted to lie within the region of maximum shell effects) may have a much longer spontaneous fission half-life, possibly on the order of 1019 years. In the center of the island, there may be competition between alpha decay and spontaneous fission, though the exact ratio is model-dependent. The alpha decay half-lives of 1700 nuclei with 100 ≤ Z ≤ 130 have been calculated in a quantum tunneling model with both experimental and theoretical alpha decay Q-values, and are in agreement with observed half-lives for some of the heaviest isotopes. The longest-lived nuclides are also predicted to lie on the beta-stability line, for beta decay is predicted to compete with the other decay modes near the predicted center of the island, especially for isotopes of elements 111–115. Unlike other decay modes predicted for these nuclides, beta decay does not change the mass number. Instead, a neutron is converted into a proton or vice versa, producing an adjacent isobar closer to the center of stability (the isobar with the lowest mass excess). For example, significant beta decay branches may exist in nuclides such as 291Fl and 291Nh; these nuclides have only a few more neutrons than known nuclides, and might decay via a "narrow pathway" towards the center of the island of stability. The possible role of beta decay is highly uncertain, as some isotopes of these elements (such as 290Fl and 293Mc) are predicted to have shorter partial half-lives for alpha decay. Beta decay would reduce competition and would result in alpha decay remaining the dominant decay channel, unless additional stability towards alpha decay exists in superdeformed isomers of these nuclides. Considering all decay modes, various models indicate a shift of the center of the island (i.e., the longest-living nuclide) from 298Fl to
|
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"page_id": 66394,
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"title": "Island of stability"
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a lower atomic number, and competition between alpha decay and spontaneous fission in these nuclides; these include 100-year half-lives for 291Cn and 293Cn, a 1000-year half-life for 296Cn, a 300-year half-life for 294Ds, and a 3500-year half-life for 293Ds, with 294Ds and 296Cn exactly at the N = 184 shell closure. It has also been posited that this region of enhanced stability for elements with 112 ≤ Z ≤ 118 may instead be a consequence of nuclear deformation, and that the true center of the island of stability for spherical superheavy nuclei lies around 306Ubb (Z = 122, N = 184). This model defines the island of stability as the region with the greatest resistance to fission rather than the longest total half-lives; the nuclide 306Ubb is still predicted to have a short half-life with respect to alpha decay. The island of stability for spherical nuclei may also be a "coral reef" (i.e., a broad region of increased stability without a clear "peak") around N = 184 and 114 ≤ Z ≤ 120, with half-lives rapidly decreasing at higher atomic number, due to combined effects from proton and neutron shell closures. Another potentially significant decay mode for the heaviest superheavy elements was proposed to be cluster decay by Romanian physicists Dorin N. Poenaru and Radu A. Gherghescu and German physicist Walter Greiner. Its branching ratio relative to alpha decay is expected to increase with atomic number such that it may compete with alpha decay around Z = 120, and perhaps become the dominant decay mode for heavier nuclides around Z = 124. As such, it is expected to play a larger role beyond the center of the island of stability (though still influenced by shell effects), unless the center of the island lies at a higher atomic number than predicted.
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{
"page_id": 66394,
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"title": "Island of stability"
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== Possible natural occurrence == Even though half-lives of hundreds or thousands of years would be relatively long for superheavy elements, they are far too short for any such nuclides to exist primordially on Earth. Additionally, instability of nuclei intermediate between primordial actinides (232Th, 235U, and 238U) and the island of stability may inhibit production of nuclei within the island in r-process nucleosynthesis. Various models suggest that spontaneous fission will be the dominant decay mode of nuclei with A > 280, and that neutron-induced or beta-delayed fission—respectively neutron capture and beta decay immediately followed by fission—will become the primary reaction channels. As a result, beta decay towards the island of stability may only occur within a very narrow path or may be entirely blocked by fission, thus precluding the synthesis of nuclides within the island. The non-observation of superheavy nuclides such as 292Hs and 298Fl in nature is thought to be a consequence of a low yield in the r-process resulting from this mechanism, as well as half-lives too short to allow measurable quantities to persist in nature. Various studies utilizing accelerator mass spectroscopy and crystal scintillators have reported upper limits of the natural abundance of such long-lived superheavy nuclei on the order of 10−14 relative to their stable homologs. Despite these obstacles to their synthesis, a 2013 study published by a group of Russian physicists led by Valeriy Zagrebaev proposes that the longest-lived copernicium isotopes may occur at an abundance of 10−12 relative to lead, whereby they may be detectable in cosmic rays. Similarly, in a 2013 experiment, a group of Russian physicists led by Aleksandr Bagulya reported the possible observation of three cosmogenic superheavy nuclei in olivine crystals in meteorites. The atomic number of these nuclei was estimated to be between 105 and 130, with one nucleus likely
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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constrained between 113 and 129, and their lifetimes were estimated to be at least 3,000 years. Although this observation has yet to be confirmed in independent studies, it strongly suggests the existence of the island of stability, and is consistent with theoretical calculations of half-lives of these nuclides. The decay of heavy, long-lived elements in the island of stability is a proposed explanation for the unusual presence of the short-lived radioactive isotopes observed in Przybylski's Star. == Synthesis and difficulties == The manufacture of nuclei on the island of stability proves to be very difficult because the nuclei available as starting materials do not deliver the necessary sum of neutrons. Radioactive ion beams (such as 44S) in combination with actinide targets (such as 248Cm) may allow the production of more neutron rich nuclei nearer to the center of the island of stability, though such beams are not currently available in the required intensities to conduct such experiments. Several heavier isotopes such as 250Cm and 254Es may still be usable as targets, allowing the production of isotopes with one or two more neutrons than known isotopes, though the production of several milligrams of these rare isotopes to create a target is difficult. It may also be possible to probe alternative reaction channels in the same 48Ca-induced fusion-evaporation reactions that populate the most neutron-rich known isotopes, namely those at a lower excitation energy (resulting in fewer neutrons being emitted during de-excitation), or those involving evaporation of charged particles (pxn, evaporating a proton and several neutrons, or αxn, evaporating an alpha particle and several neutrons). This may allow the synthesis of neutron-enriched isotopes of elements 111–117. Although the predicted cross sections are on the order of 1–900 fb, smaller than when only neutrons are evaporated (xn channels), it may still be possible to
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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generate otherwise unreachable isotopes of superheavy elements in these reactions. Some of these heavier isotopes (such as 291Mc, 291Fl, and 291Nh) may also undergo electron capture (converting a proton into a neutron) in addition to alpha decay with relatively long half-lives, decaying to nuclei such as 291Cn that are predicted to lie near the center of the island of stability. However, this remains largely hypothetical as no superheavy nuclei near the beta-stability line have yet been synthesized and predictions of their properties vary considerably across different models. In 2024, a team of researchers at the JINR observed one decay chain of the known isotope 289Mc as a product in the p2n channel of the reaction between 242Pu and 50Ti, an experiment targeting neutron-deficient livermorium isotopes. This was the first successful report of a charged-particle exit channel in a hot fusion reaction between an actinide target and a projectile with Z ≥ 20. The process of slow neutron capture used to produce nuclides as heavy as 257Fm is blocked by short-lived isotopes of fermium that undergo spontaneous fission (for example, 258Fm has a half-life of 370 μs); this is known as the "fermium gap" and prevents the synthesis of heavier elements in such a reaction. It might be possible to bypass this gap, as well as another predicted region of instability around A = 275 and Z = 104–108, in a series of controlled nuclear explosions with a higher neutron flux (about a thousand times greater than fluxes in existing reactors) that mimics the astrophysical r-process. First proposed in 1972 by Meldner, such a reaction might enable the production of macroscopic quantities of superheavy elements within the island of stability; the role of fission in intermediate superheavy nuclides is highly uncertain, and may strongly influence the yield of such a reaction.
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{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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It may also be possible to generate isotopes in the island of stability such as 298Fl in multi-nucleon transfer reactions in low-energy collisions of actinide nuclei (such as 238U and 248Cm). This inverse quasifission (partial fusion followed by fission, with a shift away from mass equilibrium that results in more asymmetric products) mechanism may provide a path to the island of stability if shell effects around Z = 114 are sufficiently strong, though lighter elements such as nobelium and seaborgium (Z = 102–106) are predicted to have higher yields. Preliminary studies of the 238U + 238U and 238U + 248Cm transfer reactions have failed to produce elements heavier than mendelevium (Z = 101), though the increased yield in the latter reaction suggests that the use of even heavier targets such as 254Es (if available) may enable production of superheavy elements. This result is supported by a later calculation suggesting that the yield of superheavy nuclides (with Z ≤ 109) will likely be higher in transfer reactions using heavier targets. A 2018 study of the 238U + 232Th reaction at the Texas A&M Cyclotron Institute by Sara Wuenschel et al. found several unknown alpha decays that may possibly be attributed to new, neutron-rich isotopes of superheavy elements with 104 < Z < 116, though further research is required to unambiguously determine the atomic number of the products. This result strongly suggests that shell effects have a significant influence on cross sections, and that the island of stability could possibly be reached in future experiments with transfer reactions. == Other islands of stability == Further shell closures beyond the main island of stability in the vicinity of Z = 112–114 may give rise to additional islands of stability. Although predictions for the location of the next magic numbers vary considerably, two significant
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{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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islands are thought to exist around heavier doubly magic nuclei; the first near 354126 (with 228 neutrons) and the second near 472164 or 482164 (with 308 or 318 neutrons). Nuclides within these two islands of stability might be especially resistant to spontaneous fission and have alpha decay half-lives measurable in years, thus having comparable stability to elements in the vicinity of flerovium. Other regions of relative stability may also appear with weaker proton shell closures in beta-stable nuclides; such possibilities include regions near 342126 and 462154. Substantially greater electromagnetic repulsion between protons in such heavy nuclei may greatly reduce their stability, and possibly restrict their existence to localized islands in the vicinity of shell effects. This may have the consequence of isolating these islands from the main chart of nuclides, as intermediate nuclides and perhaps elements in a "sea of instability" would rapidly undergo fission and essentially be nonexistent. It is also possible that beyond a region of relative stability around element 126, heavier nuclei would lie beyond a fission threshold given by the liquid drop model and thus undergo fission with very short lifetimes, rendering them essentially nonexistent even in the vicinity of greater magic numbers. It has also been posited that in the region beyond A > 300, an entire "continent of stability" consisting of a hypothetical phase of stable quark matter, comprising freely flowing up and down quarks rather than quarks bound into protons and neutrons, may exist. Such a form of matter is theorized to be a ground state of baryonic matter with a greater binding energy per baryon than nuclear matter, favoring the decay of nuclear matter beyond this mass threshold into quark matter. If this state of matter exists, it could possibly be synthesized in the same fusion reactions leading to normal superheavy nuclei,
|
{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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|
and would be stabilized against fission as a consequence of its stronger binding that is enough to overcome Coulomb repulsion. == See also == Island of inversion Table of nuclides == Notes == == References == === Bibliography === == External links == Island ahoy! (Nature, 2006, with JINR diagram of heavy nuclides and predicted island of stability) Can superheavy elements (such as Z = 116 or 118) be formed in a supernova? Can we observe them? (Cornell, 2004 – "maybe") Second postcard from the island of stability (CERN, 2001; nuclides with 116 protons and mass 292) First postcard from the island of nuclear stability (CERN, 1999; first few Z = 114 atoms)
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{
"page_id": 66394,
"source": null,
"title": "Island of stability"
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Ammonia fungi are characterized by the rapid development and high germination rates of fruiting bodies in the presence of ammonia or other nitrogen-containing materials with alkaline soil conditions. These fungi naturally occur after decomposition events like animal excretion or death. Reproduction can be classified into two categories including early and late phase ammonia fungi. The addition of high amounts of ammonia, urea, or other nitrogen-containing materials can cause ideal soil conditions that the ammonia fungi thrive in and then revert back to pre-application conditions. Ammonia fungi that develop sporophores after applications of nitrogen-containing materials are currently being studied in the field and laboratory for their mechanisms of colonization, establishment, and occurrence of fruiting bodies. == Evolution == Fungi naturally need essential bioelements including nitrogen, phosphorus, iron, and other trace elements that would otherwise limit their growth. However, it is believed that the evolution of each species of ammonium transporters/ammonia permeases may have developed in a unique manner. One theory suggests the convergent evolution of nitrate assimilation cluster in green algae could have had a general selective advantage toward nitrate assimilation genes. Fungi may also have a mutualistic relationship towards the surrounding plants in which nitrogen is taken up by the plant in the form of ammonium through a protein transporter of fungal origin, leading to a relationship between plant and fungi. A symbiotic relationship between the arbuscular mycorrhizal fungi networks and plant roots may exist through the provision of nitrogen and phosphate. Evolution for species of ammonia fungi should be treated individually and generalizations may be hard to make for the whole category. == Environment == Ammonia fungi are typically found in temperate forested areas but have been documented in field environments. This is largely dependent on the species of ammonia fungi being referred to but environments with well-rotted wood
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{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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and plant debris are preferred by many species. Many species prefer to occupy dung including Peziza moravecii, Amblyosporium botrytiis, and Chaetomium globosum. Coprinopsis stercorea specifically grows solely on the dung of sheep, goats, and donkeys. Chaetomium globosum also reside on plants, soils, and straw in forested and mountain soils across a variety of biomes. Coprinopsis echinospora have been found on cotton clothing during decomposition research. Collybia cookei can be found on the decomposing remains of other mushrooms. Hebelome vinosophyllum can be found growing on the remains of animals in Vietnamese forests in Southeast Asia. Most species prefer woodland with nutrient-enriched nitrogen-treated soils. Species not only have preferences for sites but also more general locations in which to be found. Ascobolus denudatus can be found in Europe. Coprinopsis neophlyctidospora is new to science and has only been found in the boreal forests of Alberta, Canada. Coprinopsis phlycitdospora can be found in the Netherlands, Japan, New Zealand, and Australia. Crucispora rhombisperma has recently been discovered in Taiwan. Laccaria amethystina is mainly found in Northern temperate zones, in deciduous and coniferous forests, though it has been found in Central and South America as well. Anamika lactariolens can be found in China. Hebeloma radicosum can be found in Japan, Europe, and North America. Laccaria bicolor is found in temperate forests in North America and Northern Europe. === Symbiotic Relationships === Ammonia fungi contribute to the nitrogen cycle and play a significant role in maintaining it. This in turn helps soil bacteria, microbes, and the overall soil structure. The relationship between plant roots and mycorrhizal networks can fix nitrogen in the soil and provide symbiosis to other species such as leaf-cutter ants and termites. Ammonia fungi can also be symbiotes on larger scales with people, animals, and plants. Laccaria amethystina and Laccaria bicolor are edible,
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{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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but may not be considered a choice mushroom to consume. Coprinopsis cinera is edible when eaten directly after collecting. Ammonia fungi may also contribute to the ecosystem in other ways being more predatory than mutualistic. Laccaria bicolor is a species of carnivorous fungi, that will catch and kill springtails. Ammonia fungi also contribute to the denitrification of soils and reduce greenhouse gas emissions as well, making a symbiotic relationship with many more species and the soil itself. === Soil Conditions === The addition of ammonia or urea causes numerous chemical and biological changes, for example, the pH of soil litter is increased to 8–10 and the high alkaline conditions interrupts the process of nutrient recycling. Water content in soil increases after the application of urea or ammonia and then decreases after the development of early phase fungi. This usually takes about 6 months after a substantial addition of ammonia. Ammonia concentrations in the soil take up to 2 years to return to pre-application levels of ammonia with the assistance of the second round of late phase fungi. Ammonia fungi are most active in the O horizon of soil followed by the A and B horizons. == Reproduction == After ammonia application in forest soils, fungi can be classified into early phase ammonia fungi and late phase ammonia fungi depending on when they develop their fruiting bodies. Ammonia fungi develop in a specific order starting with anamorphic fungi, cup fungi (Ascomycota), and agaric fungi with small basidiomata. These fungi are considered early phase (EP) ammonia fungi. After the development of these fungi, argaric fungi with larger basidiomata develop and are classified as late phase (LP) ammonia fungi. These fungi reproduction cycles can be difficult to replicate in laboratory settings. In the field, successful reproduction cycles come with the colonization of the
|
{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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fungus and ability to produce its reproductive structures. === Early Phase Ammonia Fungi === Early phase (EP) ammonia fungi include anamorphic fungi, ascomycota, and smaller basidiomycota. These species occupy alkaline to nuetral soils that have higher ammonium-nitrogen concentrations. This is due to either a preference or tolerance to the high concentrations of ammonium. They are also saprotrophic. EP ammonia fungi typically only occur in one cycle. Anamorphic fungi develop first, being able to handle pH conditions above 8. Once they are able to reduce the pH to 7, ascomycota fungi develop. After the ascomycota fungi reduce the pH to 6, the smaller basidiomycota develop. This is considered the late part of early phase ammonia fungi. EP fungi can develop anywhere from 20–200 days after the application of urea. === Late Phase Ammonia Fungi === Once the pH is in the range of 3.5–6.0 the late phase ammonia fungi, larger basidiomata, will develop, occupying weaker acidic conditions. Anything that develops after this group of fungi will also be considered a LP ammonia fungus. These species are typically present 2–3 years after urea and ammonium applications. LP fungi use ammonium within the soil to develop and begin to turn it into nitrate-nitrogen gradually over time. Quantity and size of LP fungi are typically larger than EP fungi. LP ammonia fungi can occur over multiple cycles and typically last longer than EP fungi. This is based on the species composition and dominanace, along with treatment of urea and time of the year. LP fungi are biotrophic with few being saprobic. == Conservation Efforts == Propagation techniques are being developed in order to better understand Ammonia fungi and how they function within ammonium heavy sites. This however is difficult due to numerous abiotic and biotic factors including interactions between ammonia fungi species, interactions with
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{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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|
the agar media, and spore longevity. Germination can also be difficult in laboratory settings. Addressing the increasing threat to habitat for ammonia fungi is necessary through these methods to be able to better protect it. This includes not only conservation of the forests in which these fungi can be found but also soil conservation efforts too. Overall, protection of habitat for rare ammonia fungi will be necessary to protecting species in the long run. More research must also be done on fungi in general to discover more species of ammonia fungi and create better conservation management strategies for the fungi that are currently being threatened by human activity or under additional environmental stressors and threats. === Threats === Ammonia fungi are threatened by the same threats that most fungi experience including mining operations, deforestation, invasive agricultural practices, and land and air pollution. Air pollution in particular can damage mycorrhizal structures. Decomposition of excessive ammonia in the atmosphere may actually cause harm to fine mycorrhizal structures. == Further Research == Little is known about many species of ammonia fungi, with new fungi being discovered often. It is necessary to research ammonia fungi given their role in the nitrogen cycle and the role they play in soil conservation. There is also little information about the interactions between ammonia fungi and non-ammonia fungi, leading to gaps in literature which could help us to understand fungi in general. It will be necessary to continue researching ammonia fungi to begin to bridge some of the gaps that currently exist in this field. == Species == Anamorphic fungi Amblyosporium botrytis Cladorrhinum foescundissimum Doratomyces purpureofuscus Ascomycota Ascobolus denudatus Chaetomium globosum Psuedombrophila petrakii Peziza moravecii Humaria velonovskyi Basidiomycota Coprinopsis cinera Coprinopsis echinospora Coprinopsis neolagopus Coprinopsis neophlyctidospora Coprinopsis phlycitdospora Coprinopsis stercorea Crucispora rhombisperma Laccaria amethystina Lyophyllum tylicolor Sagaranella tylicolor
|
{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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|
Late Successional Phase Collybia cookei Anamika lactariolens Calocybe leucocephela Hebeloma luchuense Hebeloma radicosum Hebeloma spoliatum Hebelome vinosophyllum Laccaria bicolor == References ==
|
{
"page_id": 22479712,
"source": null,
"title": "Ammonia fungi"
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|
The names for the chemical elements 104 to 106 were the subject of a major controversy starting in the 1960s, described by some nuclear chemists as the Transfermium Wars because it concerned the elements following fermium (element 100) on the periodic table. This controversy arose from disputes between American scientists and Soviet scientists as to which had first isolated these elements. The final resolution of this controversy in 1997 also decided the names of elements 107 to 109. == Controversy == By convention, naming rights for newly discovered chemical elements go to their discoverers. For elements 104, 105, and 106, there was a controversy between Soviet researchers at the Joint Institute for Nuclear Research and American researchers at Lawrence Berkeley National Laboratory regarding which group had discovered them first. Both parties suggested their own names for elements 104 and 105, not recognizing the other's name. The American name of seaborgium for element 106 was also objectionable to some, because it referred to American chemist Glenn T. Seaborg who was still alive at the time this name was proposed. (Einsteinium and fermium had also been proposed as names of new elements while Albert Einstein and Enrico Fermi were still living, but only made public after their deaths, due to Cold War secrecy.) == Opponents == The two principal groups which were involved in the conflict over element naming were: An American group at Lawrence Berkeley Laboratory. A Russian group at Joint Institute for Nuclear Research in Dubna. and, as a kind of arbiter, The IUPAC Commission on Nomenclature of Inorganic Chemistry, which introduced its own proposal to the IUPAC General Assembly. The German group at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, who had (undisputedly) discovered elements 107 to 109, were dragged into the controversy when the Commission suggested that the
|
{
"page_id": 66400,
"source": null,
"title": "Transfermium Wars"
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|
name "hahnium", proposed for element 105 by the Americans, be used for GSI's element 108 instead. === Proposals === ==== Darmstadt ==== The names suggested for the elements 107 to 109 by the German group were: ==== IUPAC ==== In 1994, the IUPAC Commission on Nomenclature of Inorganic Chemistry proposed the following names: This attempted to resolve the dispute by sharing the namings of the disputed elements between Russians and Americans, replacing the name for 104 with one honoring the Dubna research center, and not naming 106 after Seaborg. == Objections to the IUPAC 94 proposal == This solution drew objections from the American Chemical Society (ACS) on the grounds that the right of the American group to propose the name for element 106 was not in question, and that group should have the right to name the element. Indeed, IUPAC decided that the credit for the discovery of element 106 should be awarded to Berkeley. Along the same lines, the German group protested against naming element 108 by the American suggestion "hahnium", mentioning the long-standing convention that an element is named by its discoverers. In addition, given that many American books had already used rutherfordium and hahnium for 104 and 105, the ACS objected to those names being used for other elements. In 1995, IUPAC abandoned the controversial rule and established a committee of national representatives aimed at finding a compromise. They suggested seaborgium for element 106 in exchange for the removal of all the other American proposals, except for the established name lawrencium for element 103. The equally entrenched name nobelium for element 102 was replaced by flerovium after Georgy Flyorov, following the recognition by the 1993 report that that element had been first synthesized in Dubna. This was rejected by American scientists and the decision was retracted.
|
{
"page_id": 66400,
"source": null,
"title": "Transfermium Wars"
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|
The name flerovium was later used for element 114. == Resolution (IUPAC 97) == In 1996, IUPAC held another meeting, reconsidered all names in hand, and accepted another set of recommendations; finally, it was approved and published in 1997 on the 39th IUPAC General Assembly in Geneva, Switzerland. Element 105 was named dubnium (Db), after Dubna in Russia, the location of the JINR; the American suggestions were used for elements 102, 103, 104, and 106. The name dubnium had been used for element 104 in the previous IUPAC recommendation. The American scientists "reluctantly" approved this decision. IUPAC pointed out that the Berkeley laboratory had already been recognized several times, in the naming of berkelium, californium, and americium, and that the acceptance of the names rutherfordium and seaborgium for elements 104 and 106 should be offset by recognizing JINR's contributions to the discovery of elements 104, 105, and 106. The following names were agreed in 1997 on the 39th IUPAC General Assembly in Geneva, Switzerland: Thus, the convention of the discoverer's right to name their elements was respected for elements 106 to 109, and the two disputed claims were "shared" between the two opponents. == Summary == In some countries uninvolved in the dispute, such as Poland, Denmark, India, and Indonesia, both kurchatovium for element 104 and hahnium for element 105 were used until 1997. == See also == List of chemical element name etymologies List of chemical element naming controversies (includes Z = 23, 41, 70, 71, 74) Systematic element name Chemical nomenclature == References == == External links == Elementymology & Elements Multidict Picture of a Seaborgium card autographed by Seaborg
|
{
"page_id": 66400,
"source": null,
"title": "Transfermium Wars"
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|
In Electrochemistry, the electrochemical equivalent (Eq or Z) of a chemical element is the mass of that element (in grams) transported by a specific quantity of electricity, usually expressed in grams per coulomb of electric charge. The electrochemical equivalent of an element is measured with a voltameter. == Definition == The electrochemical equivalent of a substance is the mass of the substance deposited to one of the electrodes when a current of 1 ampere is passed for 1 second, i.e. a quantity of electricity of one coulomb is passed. This is an useful experimental quantity as it helps in many calculations in electrochemistry. The formula for finding electrochemical equivalent is as follows: Z = M / q {\displaystyle Z=M/q} where M {\displaystyle M} is the mass of substance and q {\displaystyle q} is the charge passed. Since q = I t {\displaystyle q=It} , where I {\displaystyle I} is the current applied and t {\displaystyle t} is time, we also have Z = M / I t {\displaystyle Z=M/It} Alternative formula for finding electrochemical equivalent is as follows: Z = E / F {\displaystyle Z=E/F} where E {\displaystyle E} is the Equivalent weight of the substance and F {\displaystyle F} is Faraday constant. == Experimental analysis of eletrochemical equivalent == For example to determine the ECE of copper, a copper voltameter is often used. In this device, a vessel which consist of copper sulfate solution and in which two electrodes of copper are dipped. The middle plate is cathode and other outer plates are used as anode, this allows a deposit of copper to accumulate into the faces of copper cathode plates. The voltameter is connected in series with the battery, an ammeter, rheostat and switch. The cathode is first dried and weighed precisely. The current is switched on and
|
{
"page_id": 11797347,
"source": null,
"title": "Electrochemical equivalent"
}
|
measured as soon as possible and with a limited value of charge density (usually 1 A for every 50 m2). This is because if charge density is too much, the deposit may not stick with cathode and will wash off. == Eq values of some elements in kg/C == == References ==
|
{
"page_id": 11797347,
"source": null,
"title": "Electrochemical equivalent"
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Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characterized by multiple reproductive cycles over the course of its lifetime. Iteroparity can be further divided into continuous iteroparity (primates, including humans and chimpanzees) and seasonal iteroparity (birds, dogs, etc.) Some botanists use the parallel terms monocarpy and polycarpy. (See also plietesials.) In truly semelparous species, death after reproduction is part of an overall strategy that includes putting all available resources into maximizing reproduction, at the expense of future life (see § Trade-offs). In any iteroparous population there will be some individuals who happen to die after their first and before any second reproductive episode, but unless this is part of a syndrome of programmed death after reproduction, this would not be called "semelparity". This distinction is also related to the difference between annual and perennial plants: An annual is a plant that completes its life cycle in a single season, and is usually semelparous. Perennials live for more than one season and are usually (but not always) iteroparous. Semelparity and iteroparity are not, strictly speaking, alternative strategies, but extremes along a continuum of possible modes of reproduction. Many organisms considered to be semelparous can, under certain conditions, separate their single bout of reproduction into two or more episodes. == Overview == === Semelparity === The word "semelparity" was coined by evolutionary biologist Lamont Cole, and comes from the Latin semel ('once, a single time') and pario ('to beget'). This differs from iteroparity in that iteroparous species are able to have multiple reproductive cycles and therefore can mate more than once in their lifetime. Semelparity is also known as "big bang" reproduction, since the single reproductive event
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{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
}
|
of semelparous organisms is usually large as well as fatal. A classic example of a semelparous organism is (most) Pacific salmon (Oncorhynchus spp.), which live for many years in the ocean before swimming to the freshwater stream of its birth, spawning, and dying. Other semelparous animals include many insects, including some species of butterflies, cicadas, and mayflies, many arachnids, and some molluscs such as some species of squid and octopus. Semelparity also occurs in smelt and capelin, but other than bony fish it is a very rare strategy in vertebrates. In amphibians, it is known only among some Hyla frogs including the gladiator frog; in reptiles only a few lizards such as Labord's chameleon of southwestern Madagascar, Sceloporus bicanthalis of the high mountains of Mexico, and some species of Ichnotropis from dry savanna areas of Africa. Among mammals, it exists only in a few didelphid and dasyurid marsupials. Annual plants, including all grain crops and most domestic vegetables, are semelparous. Long-lived semelparous plants include century plant (agave), Lobelia telekii, and some species of bamboo. This form of lifestyle is consistent with r-selected strategies as many offspring are produced and there is low parental input, as one or both parents die after mating. All of the male's energy is diverting into mating and the immune system is repressed. High levels of corticosteroids are sustained over long periods of time. This triggers immune and inflammatory system failure and gastrointestinal hemorrhage, which eventually leads to death. === Iteroparity === The term iteroparity comes from the Latin itero, to repeat, and pario, to beget. An example of an iteroparous organism is a human—humans are biologically capable of having offspring many times over the course of their lives. Iteroparous vertebrates include all birds, most reptiles, virtually all mammals, and most fish. Among invertebrates, most mollusca
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
}
|
and many insects (for example, mosquitoes and cockroaches) are iteroparous. Most perennial plants are iteroparous. == Models == === Trade-offs === It is a biological precept that within its lifetime an organism has a limited amount of energy/resources available to it, and must always partition it among various functions such as collecting food and finding a mate. Of relevance here is the trade-off between fecundity, growth, and survivorship in its life history strategy. These trade-offs come into play in the evolution of iteroparity and semelparity. It has been repeatedly demonstrated that semelparous species produce more offspring in their single fatal reproductive episode than do closely related iteroparous species in any one of theirs. However, the opportunity to reproduce more than once in a lifetime, and possibly with greater care for the development of offspring produced, can offset this strictly numerical benefit. === Models based on non-linear trade-offs === One class of models that tries to explain the differential evolution of semelparity and iteroparity examines the shape of the trade-off between offspring produced and offspring forgone. In economic terms, offspring produced is equivalent to a benefit function, while offspring forgone is comparable to a cost function. The reproductive effort of an organism—the proportion of energy that it puts into reproducing, as opposed to growth or survivorship—occurs at the point where the distance between offspring produced and offspring forgone is the greatest. In some situations, the marginal cost of offspring produced decreases over time (each additional offspring is less "expensive" than the average of all previous offspring) and the marginal cost of offspring forgone increases. In these cases, the organism only devotes a portion of its resources to reproduction and uses the rest for growth and survivorship so that it can reproduce again in the future. In other situations, the marginal cost
|
{
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of offspring produced increases while the marginal cost of offspring forgone decreases. When this is the case, it is favorable for the organism to reproduce a single time. The individual devotes all of its resources to that one episode of reproduction, then dies as it has not reserved enough resources to meet its own ongoing survival needs. Empirical, quantitative support for this mathematical model is limited. === Bet-hedging models === A second set of models examines the possibility that iteroparity is a hedge against unpredictable juvenile survivorship (avoiding putting all one's eggs in one basket). Again, mathematical models have not found empirical support from real-world systems. In fact, many semelparous species live in habitats characterized by high (not low) environmental unpredictability, such as deserts and early successional habitats. === Cole's paradox and demographic models === The models that have the strongest support from living systems are demographic. In Lamont Cole's classic 1954 paper, he came to the conclusion that: For an annual species, the absolute gain in intrinsic population growth which could be achieved by changing to the perennial reproductive habit would be exactly equivalent to adding one individual to the average litter size. For example, imagine two species—an iteroparous species that has annual litters averaging three offspring each, and a semelparous species that has one litter of four, and then dies. These two species have the same rate of population growth, which suggests that even a tiny fecundity advantage of one additional offspring would favor the evolution of semelparity. This is known as Cole's paradox. In his analysis, Cole assumed that there was no mortality of individuals of the iteroparous species, even seedlings. Twenty years later, Charnov and Schaffer showed that reasonable differences in adult and juvenile mortality yield much more reasonable costs of semelparity, essentially solving Cole's paradox.
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{
"page_id": 22610793,
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An even more general demographic model was produced by Young. These demographic models have been more successful than the other models when tested with real-world systems. It has been shown that semelparous species have higher expected adult mortality, making it more economical to put all reproductive effort into the first (and therefore final) reproductive episode. == Semelparity == === Semelparity in mammals === ==== In Dasyuridae ==== ===== Small Dasyuridae ===== Semelparous species of Dasyuridae are typically small and carnivorous, with the exception of the northern quoll (Dasyurus hallucatus), which is large. Species with this reproductive strategy include members of the genus Antechinus, Phascogale tapoatafa and Phascogale culura. The males of all three groups exhibit similar characteristics that classify them as semelparous: First, all of the males of each species disappear immediately after the mating season. Also, males that are captured and isolated from others live for 2 to 3 years. If these captured males are allowed to mate, they die immediately after the mating season, like those in the wild. Their behaviour also changes drastically before and after the mating season. Before mating, males are extremely aggressive and will fight with other males if placed close together. Males that are captured before they are allowed to mate remain aggressive through the winter months. After the mating season, if allowed to mate, males become extremely lethargic and never regain their aggressiveness even if they survive to the next mating season. Other changes that occur post-mating include fur degradation and testicular degeneration. During adolescence, male fur is thick and becomes dull and thin after mating, but regains its original condition if the individual manages to survive past the mating season. The fur on the scrotum completely falls off and does not grow back, even if the male survives months after the
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{
"page_id": 22610793,
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first mating season. As the marsupial ages, its testicles grow until they reach a peak size and weight at the beginning of the mating season. After the individual mates, the weight and size of the testes and scrotum decrease. They remain small and do not produce spermatozoa later in life, if maintained in a laboratory. The 1966 Woolley study on Antechinus spp. noticed that males were only able to be maintained past mating in the laboratory, and no senile males were found in the wild, suggesting that all males die shortly after mating. ===== Corticosteroid concentration and increased male mortality ===== Studies on Antechinus stuartii reveal that male mortality is highly correlated to stress and andrenocortical activity. The study measured the corticosteroid concentration in males in the wild, males injected with cortisol, males injected with saline, and females in the wild. While both males and females exhibit high levels of corticosteroid concentration in the wild, this proves fatal only to males due to females having a higher maximum high affinity corticosteroid binding capacity (MCBC). Thus, free corticosteroid in the plasma of male A. stuartii rises sharply, while it remains constant in females. High levels of free corticosteroid, resulting from mating in wild males and injected cortisol in laboratory males, resulted in stomach ulcers, gastrointestinal bleeding, and liver abscesses, all of which increased mortality. These side-effects were not found in the males that were injected with saline, strengthening the hypothesis that high, free corticosteroids result in higher mortality in male dasyurids. A similar study on Phascogale calura showed that similar endocrine system changes happen in P. calura as A. stuartii. This supports stress-induced mortality as a characteristic of small dasyurid semelparity. ===== Large Dasyuridae ===== Dasyurus hallucatus, the northern quoll, is a large dasyurid and exhibits increased male mortality after the
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{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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mating season. Unlike smaller dasyurids, male die-off in D. hallucatus is not due to endocrine system changes, and there was no observed spermatogenic failure after the mating season ended. If male D. hallucatus survive past their first mating season, they may be able to engage in a second mating season. While the individuals in a 2001 study mostly died from vehicles or predation, researchers found evidence of physiological degradation in males, similar to the physiological degradation in small dasyurids. This includes fur loss, parasite infestations, and weight loss. As the mating period went on, males became increasingly anemic, but the anemia was not due to ulceration or gastrointestinal bleeding. Lack of elevated cortisol levels during mating periods in D. hallucatus means that there is no current universal explanation for the mechanism behind increased male mortality in Dasyuridae. Post-reproductive senescence has also been proposed as an explanation. ==== In opossums ==== ===== Grey slender mouse opossum (Marmosops incanus) ===== The grey slender mouse opossum exhibits a semelparous reproductive strategy in both males and females. Males disappear from their endemic area after the reproductive season (February–May). Males found months later (June–August) are of lighter body weight and the molar teeth are less worn down, suggesting these males belong to a different generation. There is a drop off in the female population, but during the months of July and August, evidence of a gap between generations like the male gap. There is also lower body weight and less molar wear observed in females found after August. This is further supported by the evidence that females that reproduce are not observed the following year. This species has been compared to a related species, Marmosa robinsoni, in order to answer what would happen if a female that has reproduced were to survive to the next
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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|
mating season. M. robinsoni has a monoestrus reproductive cycle, like M. incanus, and females are no longer fertile after 17 months so it is unlikely that females that survive past the drop off in female populations would be able to reproduce a second time. ===== Other mouse opossums ===== Gracilinanus microtarsus, or the Brazilian gracile opossum, is considered to be partially semelparous because male mortality increases significantly after the mating season, but some males survive to mate again in the next reproductive cycle. The males also exhibit similar physiological degradation, demonstrated in Antechinus and other semelparous marsupials, such as fur loss and increase of infection from parasites. === Semelparity in fish === ==== Pacific salmon ==== Highly elevated cortisol levels mediate the post-spawning death of semelparous Oncorhynchus Pacific salmon by causing tissue degeneration, suppressing the immune system, and impairing various homeostatic mechanisms. After swimming for such a long distance, salmon expend all of their energy on reproduction. One of the key factors in salmon rapid senescence is that these fish do not feed during reproduction so body weight is extremely reduced. In addition to physiological degradation, Pacific salmon become more lethargic as mating goes on, which makes some individuals more susceptible to predation because they have less energy to avoid predators. This also increases mortality rates of adults post-mating. === Semelparity in insects === Traditionally, semelparity was usually defined within the time-frame of a year. Critics of this criterion note that this scale is inappropriate in discussing patterns of insect reproduction because many insects breed more than once within one annual period, but generation times of less than one year. Under the traditional definition, insects are considered semelparous as a consequence of time scale rather than the distribution of reproductive effort over their adult life span. In order to resolve
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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|
this inconsistency, Fritz, Stamp & Halverson (1982) define semelparous insects as "insects that lay a single clutch of eggs in their lifetime and deposit them at one place are clearly semelparous or 'big bang' reproducers. Their entire reproductive effort is committed at one time and they die shortly after oviposition". Semelparous insects are found in Lepidoptera, Ephemeroptera, Dermaptera, Plecoptera, Strepsiptera, Trichoptera, and Hemiptera. ==== Examples in Lepidoptera ==== Females of certain families of Lepidoptera, like the spongy moth of family Erebidae, have reduced mobility or are wingless (apterous), so they disperse in the larval stage as opposed to in the adult stage. In iteroparous insects, dispersal mainly occurs in the adult stage. All semelparous Lepidopterans share similar characteristics: larvae only feed in restricted periods of the year because of the nutritional state of their host plants (as a result, they are univoltine), initial food supply is predictably abundant, and larval host plants are abundant and adjacent. Death most commonly occurs by starvation. In the case of the spongy moth, adults do not possess an active digestive system and cannot feed, but can drink moisture. Mating occurs fairly rapidly after adults emerge from their pupal form and, without a way to digest food, the adult moths die after about a week. == Evolutionary advantages to semelparity == === Current evolutionary advantages hypothesis === The evolution for semelparity in both sexes has occurred many times in plants, invertebrates, and fish. It is rare in mammals because mammals have obligate maternal care due to internal fertilization and incubation of offspring and nursing young after birth, which requires high maternal survival rate after fertilization and offspring weaning. Also, female mammals have relatively low reproductive rates compared to invertebrates or fish because they invest a lot of energy in maternal care. However, male reproductive rate
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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|
is much less constrained in mammals because only females bear young. A male that dies after one mating season can still produce a large number of offspring if he invests all of his energy in mating with many females. ==== Evolution in mammals ==== Scientists have hypothesized that natural selection has allowed semelparity to evolve in Dasyuridae and Didelphidae because of certain ecological constraints. Female mammals ancestral to these groups may have shortened their mating period to coincide with peak prey abundance. Because this window is so small, the females of these species exhibit a reproduction pattern where the estrous of all females occurs simultaneously. Selection would then favor aggressive males due to increased competition between males for access to females. Since the mating period is so short, it is more beneficial for males to expend all their energy on mating, even more so if they are unlikely to survive to the next mating season. ==== Evolution in fish ==== Reproduction is costly for anadromous salmonids, because their life history requires transition from saltwater to freshwater streams, and long migrations, which can be physiologically taxing. The transition between cold oceanic water to warm freshwater and steep elevation changes in Northern Pacific rivers could explain the evolution of semelparity because it would be extremely difficult to return to the ocean. A noticeable difference between semelparous fish and iteroparous salmonids is that egg size varies between the two types of reproductive strategies. Studies show that egg size is also affected by migration and body size. Egg number, however, shows little variation between semelparous and iteroparous populations or between resident and anadromous populations for females of the same body size. The current hypothesis behind this reason is that iteroparous species reduce the size of their eggs in order to improve the mother's chances
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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of survival, since she invests less energy in gamete formation. Semelparous species do not expect to live past one mating season, so females invest a lot more energy in gamete formation resulting in large eggs. Anadromous salmonids may also have evolved semelparity to boost the nutrition density of the spawning grounds. The most productive Pacific salmon spawning grounds contain the most carcasses of spawned adults. The dead bodies of the adult salmon decompose and provide nitrogen and phosphorus for algae to grow in the nutrient-poor water. Zooplankton then feed on the algae, and newly hatched salmon feed on the zooplankton. ==== Evolution in insects ==== An interesting trait has evolved in semelparous insects, especially in those that have evolved from parasitic ancestors, like in all subsocial and eusocial aculeate Hymenoptera. This is because larvae are morphologically specialized for development within a host's innards and thus are entirely helpless outside of that environment. Females would need to invest a lot of energy in protecting their eggs and hatched offspring. They do this through such behaviours as egg guarding. Mothers that actively defend offspring, for example, risk injury or death by doing so. This is not beneficial in an iteroparous species because the female risks dying and not reaching her full reproductive potential by not being able to reproduce in all reproductive periods in her lifetime. Since semelparous insects only live for one reproductive cycle, they can afford to expend energy on maternal care because those offspring are her only offspring. An iteroparous insect does not need to expend energy on the eggs of one mating period because it is likely that she will mate again. There is ongoing research in maternal care in semelparous insects from lineages not descended from parasites to further understand this relationship between semelparity and maternal care.
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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== See also == Annual plant – Plant which completes its life cycle within one growing season and then dies Behavioral ecology – Study of the evolutionary basis for animal behavior due to ecological pressures Ecology – Study of organisms and their environment Life history theory – Analytical framework to study life history strategies used by organisms Perennial plant – Plant that lives for more than two years r/K selection theory – Ecological theory concerning the selection of life history traits == References == == Further reading == "Semelparity". Nature Education Knowledge (peer-reviewed) – via Nature (journal) nature.com. de Wreede, R.E.; Klinger, T. "Reproductive strategies in algae". In Lovett-Doust, J.L.; Lovett-Doust, L.L. (eds.). Plant Reproductive Ecology: Patterns and strategies. Oxford University Press. pp. 267–276. Ranta, E.; Tesar, D.; Kaitala, V. (2002). "Environmental variability and semelparity vs. iteroparity as life histories". Journal of Theoretical Biology. 217 (3): 391–398. Bibcode:2002JThBi.217..391R. doi:10.1006/jtbi.2002.3029. PMID 12270282.
|
{
"page_id": 22610793,
"source": null,
"title": "Semelparity and iteroparity"
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|
Backpropagation through structure (BPTS) is a gradient-based technique for training recursive neural networks, proposed in a 1996 paper written by Christoph Goller and Andreas Küchler. == References ==
|
{
"page_id": 46465898,
"source": null,
"title": "Backpropagation through structure"
}
|
In molecular biology mir-198 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-198 microRNA precursor family at Rfam
|
{
"page_id": 36373353,
"source": null,
"title": "Mir-198 microRNA precursor family"
}
|
Superparasitism is a form of parasitism in which the host (typically an insect larva such as a caterpillar) is attacked more than once by a single species of parasitoid. Multiparasitism or coinfection, on the other hand, occurs when the host has been parasitized by more than one species. Host discrimination, whereby parasitoids can identify a host with parasites from an unparasitized host, is present in certain species of parasitoids and is used to avoid superparasitism and thus competition from other parasites. Superparasitism can result in transmission of viruses, and viruses may influence a parasitoid's behavior in favor of infecting already infected hosts, as is the case with Leptopilina boulardi. == Examples == One example of superparasitism is seen in Rhagoletis juglandis, also known as the walnut husk fly. During oviposition, female flies lacerate the tissue of the inner husk of the walnut and create a cavity for her eggs. The female flies oviposit and reinfest the same walnuts and even the same oviposition sites created by conspecifics. == References ==
|
{
"page_id": 2687852,
"source": null,
"title": "Superparasitism"
}
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