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[ A ] + K d {\displaystyle [AR]={\frac {[R]_{t}\,[A]}{[A]+K_{d}}}} This is the Hill-Langmuir equation, which is practically the Hill equation described for the agonist binding. In chemistry, this relationship is called the Langmuir equation, which describes the adsorption of molecules onto sites of a surface (see adsorption). [ R ] t {\displaystyle [R]_{t}} is the total number of binding sites, and when the equation is plotted it is the horizontal asymptote to which the plot tends; more binding sites will be occupied as the ligand concentration increases, but there will never be 100% occupancy. The binding affinity is the concentration needed to occupy 50% of the sites; the lower this value is the easier it is for the ligand to occupy the binding site. The binding of the ligand to the receptor at equilibrium follows the same kinetics as an enzyme at steady-state (Michaelis–Menten equation) without the conversion of the bound substrate to product. Agonists and antagonists can have various effects on ligand binding. They can change the maximum number of binding sites, the affinity of the ligand to the receptor, both effects together or even more bizarre effects when the system being studied is more intact, such as in tissue samples. (Tissue absorption, desensitization, and other non equilibrium steady-state can be a problem.) A surmountable drug changes the binding affinity: competitive ligand: K d ′ = K d 1 + [ B ] K b {\displaystyle K_{d}'=K_{d}{\frac {1+[B]}{K_{b}}}} cooperative allosteric ligand: K d ′ = K d K B + [ B ] K B + [ B ] α {\displaystyle K_{d}'=K_{d}{\frac {K_{B}+[B]}{K_{B}+{\frac {[B]}{\alpha }}}}} A nonsurmountable drug changes the maximum binding: noncompetitive binding: [ R ] t ′ = [ R ] t 1 + [ B ] K b {\displaystyle [R]'_{t}={\frac {[R]_{t}}{1+{\frac {[B]}{K_{b}}}}}} irreversible binding The Schild
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regression also can reveal if there are more than one type of receptor and it can show if the experiment was done wrong as the system has not reached equilibrium. == Radioligand binding assays == The first radio-receptor assay (RRA) was done in 1970 by Lefkowitz et al., using a radiolabeled hormone to determine the binding affinity for its receptor. A radio-receptor assay requires the separation of the bound from the free ligand. This is done by filtration, centrifugation or dialysis. A method that does not require separation is the scintillation proximity assay that relies on the fact that β-rays from 3H travel extremely short distances. The receptors are bound to beads coated with a polyhydroxy scintillator. Only the bound ligands to be detected. Today, the fluorescence method is preferred to radioactive materials due to a much lower cost, lower hazard, and the possibility of multiplexing the reactions in a high-throughput manner. One problem is that fluorescent-labeled ligands have to bear a bulky fluorophore that may cause it to hinder the ligand binding. Therefore, the fluorophore used, the length of the linker, and its position must be carefully selected. An example is by using FRET, where the ligand's fluorophore transfers its energy to the fluorophore of an antibody raised against the receptor. Other detection methods such as surface plasmon resonance do not even require fluorophores. == See also == Dose-response relationship == References == == Further reading == Kenakin T (1993). Pharmacological analysis of drug-receptor interaction. New York: Raven Press. == External links == curvefit.com - Dose-response curves in the presence of antagonists, for a clear explanation.
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"page_id": 9374505,
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"title": "Schild equation"
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SNPlex is a platform for SNP genotyping sold by Applied Biosystems (ABI). It is based on capillary electrophoresis to separate varying fragments of DNA, which allows the assay to be performed on ABI's 3730xl DNA analyzers. Currently, up to 48 SNPs can be genotyped in a single reaction. == References == == External links == SNPlex Genotyping System
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"page_id": 15141674,
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"title": "SNPlex"
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Sharps waste is a form of biomedical waste composed of used "sharps", which includes any device or object used to puncture or lacerate the skin. Sharps waste is classified as biohazardous waste and must be carefully handled. Common medical materials treated as sharps waste are hypodermic needles, disposable scalpels and blades, contaminated glass and certain plastics, and guidewires used in surgery. == Qualifying materials == In addition to needles and blades, anything attached to them, such as syringes and injection devices, is also considered sharps waste. Blades can include razors, scalpels, X-Acto knives, scissors, or any other items used for cutting in a medical or biological research setting, regardless of whether they have been contaminated with biohazardous material. While glass and sharp plastic are considered sharps waste, their handling methods can vary. Glass items which have been contaminated with a biohazardous material are treated with the same concern as needles and blades, even if unbroken. If glass is contaminated, it is still often treated as a sharp, because it can break during the disposal process. Contaminated plastic items which are not sharp can be disposed of in a biohazardous waste receptacle instead of a sharps container. == Dangers involved == Injuries from sharps waste can pose a large public health concern, as used sharps may contain biohazardous material. It is possible for this waste to spread blood-borne pathogens if contaminated sharps penetrate the skin. The spread of these pathogens is directly responsible for the transmission of blood-borne diseases, such as hepatitis B (HBV), hepatitis C (HCV), and HIV. Health care professionals expose themselves to the risk of transmission of these diseases when handling sharps waste. The large volume handled by health care professionals on a daily basis increases the chance that an injury may occur. The general public can occasionally
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"page_id": 3410731,
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"title": "Sharps waste"
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be at risk of sustaining injuries from sharps waste as well when hypodermic needles are improperly disposed of by injection drug users. == Sharps containers == Hard plastic containers known as sharps containers are used to safely dispose of hypodermic needles and other sharp medical instruments, such as IV catheters and disposable scalpels. They are often sealable and self-locking, as well as rigid, which prevents waste from penetrating or damaging the sides of the container. In the United States, sharps containers are usually red and marked with the universal biohazard symbol for ease of recognition. Elsewhere, they are often yellow. Waste is loaded into the container until it reaches a certain height, which is usually around three-quarters of the way full. At that point, the container is emptied or disposed of. Sharps containers may be single use, in which case they are disposed of along with the waste they contain, or reusable, in which case they are robotically emptied and sterilized before being returned for re-use. Airports and large institutions commonly have sharps containers available in restrooms for safe disposal for users of injection drugs, such as insulin-dependent diabetics. Medical facilities and laboratories are also equipped with sharps containers, as well as the equipment required to safely sterilize or dispose of them. This minimizes the distance the containers have to travel and the number of people to come in contact with the sharps waste. Smaller clinics or offices in the US without such facilities are required by federal regulations to hire the services of a company that specializes in transporting and properly disposing of the hazardous wastes. == Disposal == Extreme care must be taken in the management and disposal of sharps waste. The goal in sharps waste management is to safely handle all materials until they can be properly
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"page_id": 3410731,
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disposed of. The final step in the disposal of sharps waste is to dispose of them in an autoclave. A less common approach is to incinerate them; typically only chemotherapy sharps waste is incinerated. Steps must be taken along the way to minimize the risk of injury from this material, while maximizing the amount of sharps material disposed. Strict hospital protocols and government regulations that instruct health care providers on how to manage sharps waste help ensure that the waste is handled as effectively and safely as possible. Disposal methods vary by country and locale, but common methods of disposal are either by truck service or, in the United States, by disposal of sharps through the mail. Truck service involves trained personnel collecting sharps waste, and often medical waste, at the point of generation, and hauling it away by truck to a destruction facility. Similarly, the mail-back sharps disposal method allows generators to ship sharps waste to the disposal facility directly through the U.S. mail in specially designed and approved shipping containers. Mail-back sharps disposal allows waste generators to dispose of smaller amounts of sharps more economically than if they were to hire out a truck service. Recent legislation in France has stated that pharmaceutical companies supplying self injection medications are responsible for the disposal of spent needles. Previously popular needle clippers and caps are no longer acceptable as safety devices, and either sharps box or needle destruction devices are required. A report by the Canadian Mental Health Association found that supervised injection sites help reduce the amount of discarded needles on streets. == Injection technology == With more than sixteen billion injections administered annually worldwide, needles are the largest contributor to sharps waste. For this reason, many new technologies surrounding injections have been developed, mostly related to safety mechanisms.
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"page_id": 3410731,
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"title": "Sharps waste"
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As these technologies have been developed, governments have attempted to make them commonplace to ensure sharps waste safety. In 2000, the Needlestick Safety and Prevention Act was passed, along with the 2001 Bloodborne Pathogens Standard. Safety syringes help reduce occurrences of accidental needlesticks. One of the most recent developments has been the auto-disable injection device. These injection devices automatically disable after a single use. This can be done by retracting the needle back into the syringe or rendering the syringe plunger inoperable. With the injection device now inoperable, it cannot be reused. Shielding the needle after the injection is another approach for safe management of sharps. These are hands free methods usually involving a hinging cap that can be pressed on a table to seal the needle. Another technology in sharps waste management relating to injections is the needle remover. Varying approaches can be taken with the main goal to separate the needle from the syringe. This allows the sharp needle to be quarantined and disposed of separately from the syringe. There is debate around the use of these devices, as they involve an additional step in the handling of sharps waste. == In the developing world == Sharps waste is of great concern in developing and transitional regions of the world. Factors such as high disease prevalence and lack of health care professionals amplify the dangers involved with sharps waste, and the cost of newer disposal technology makes them unlikely to be used. As with the rest of the world, injection waste make up the largest portion of sharps waste. However, injection use is much more prevalent in the developing world. One of the contributors to this increase is a larger emphasis placed on injections for therapeutic purposes. It has been estimated that 95% of all injections in developing
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regions are for therapeutic purposes. The average person has been estimated to receive 1.5 injections per year. Newly developed injection technologies are rarely used to provide these injections due to added costs. Therefore, the majority of injections are given with standard disposable syringes in developing regions. The infrastructure of developing regions is not equipped to deal with this large volume of contaminated sharps waste. Contrary to the industrialized world, disposal incinerators and transportation networks are not always available. Cost restraints make the purchase of single use disposable containers unrealistic. Facilities are often overwhelmed with patients and understaffed with educated workers. Demand on these facilities can limit the emphasis or enforcement of waste disposal protocols. These factors leave a dangerous quantity of sharps waste in the environment. Contrasts between the industrialized and developing world segment can be seen in accidental needle stick injuries. These occur at a rate of .18 to .74 per person per year in industrialized nations and .93 to 4.68 per person per year in developing and transitional nations (Hutin, Hauri, Armstrong, 2003). Improper sharps management is a major factor involved in what is categorized as unsafe injections. Annually these account for 21 million, 2 million, and 260,000 of new HBV, HCV, and HIV infections annually. 40-65% of new HBV and HCV infections are due to percutaneous occupational exposure. == Further reading == Kotwal, Atul (March 2005). "Innovation, diffusion and safety of a medical technology: a review of the literature on injection practices". Social Science & Medicine. 60 (5): 1133–1147. doi:10.1016/j.socscimed.2004.06.044. PMID 15589680. == References == == External links == EPA Recommended Needle Disposal Options for Self Injectors WHO Health Care Waste Management
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{
"page_id": 3410731,
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"title": "Sharps waste"
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Digallate may refer to: a salt of digallic acid a molecule containing two gallic acid moieties, like Theaflavin digallate
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{
"page_id": 29100842,
"source": null,
"title": "Digallate"
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Ramalina leptocarpha, also known as the western strap lichen, is a species of cartilage lichen found in Oregon, California, and Baja California. The range of this species extends from the coast as far inland as the Sierra Nevada mountain range. R. leptocarpha often grows in epiphytic association with Ramalina menziesii. Trebouxia decolorans is its primary algal photobiont. This species was first described in 1858 by Edward Tuckerman from a collection made in Monterey, California. == References ==
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{
"page_id": 76745517,
"source": null,
"title": "Ramalina leptocarpha"
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Biorheology is a scientific journal in the field of biorheology, the study of the deformation and flow properties (rheology) of biological fluids, published by IOS Press. It is published quarterly since 2018. It was established in 1962 by founding editors A.L. Copley and G.W. Scott Blair. It is currently edited by Herbert H. Lipowsky (Penn State University) and Brian M. Cooke (Australian Institute of Tropical Health and Medicine). == References ==
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{
"page_id": 61475631,
"source": null,
"title": "Biorheology (journal)"
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Preference regression is a statistical technique used by marketers to determine consumers’ preferred core benefits. It usually supplements product positioning techniques like multi dimensional scaling or factor analysis and is used to create ideal vectors on perceptual maps. == Application == Starting with raw data from surveys, researchers apply positioning techniques to determine important dimensions and plot the position of competing products on these dimensions. Next they regress the survey data against the dimensions. The independent variables are the data collected in the survey. The dependent variable is the preference datum. Like all regression methods, the computer fits weights to best predict data. The resultant regression line is referred to as an ideal vector because the slope of the vector is the ratio of the preferences for the two dimensions. If all the data is used in the regression, the program will derive a single equation and hence a single ideal vector. This tends to be a blunt instrument so researchers refine the process with cluster analysis. This creates clusters that reflect market segments. Separate preference regressions are then done on the data within each segment. This provides an ideal vector for each segment. == Alternative methods == Self-stated importance method is an alternative method in which direct survey data is used to determine the weightings rather than statistical imputations. A third method is conjoint analysis in which an additive method is used. == See also == Marketing Product management Positioning (marketing) Marketing research Perceptual mapping Multidimensional scaling Factor analysis Linear discriminant analysis#Marketing Preference-rank translation == References == Park, S. T.; Chu, W. (2009). "Pairwise preference regression for cold-start recommendation". Proceedings of the third ACM conference on Recommender systems - RecSys '09. p. 21. doi:10.1145/1639714.1639720. ISBN 9781605584355. Jarboe, G.R.; McDaniel, C.D.; Gates, R.H. (1992). "Preference regression modeling of multiple option
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{
"page_id": 265008,
"source": null,
"title": "Preference regression"
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healthcare delivery systems". Journal of Ambulatory Care Marketing, 5(1), p.71-82.
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{
"page_id": 265008,
"source": null,
"title": "Preference regression"
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Capsulimonas is a Gram-negative, non-spore-forming, aerobic and non-motile genus of bacteria from the family of Capsulimonadaceae with one known species (Capsulimonas corticalis). Capsulimonas corticalis has been isolated from the surface of a beech (Fagus crenata) == See also == List of bacterial orders List of bacteria genera == References ==
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{
"page_id": 70847281,
"source": null,
"title": "Capsulimonas"
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In agriculture and in animal fancy, a breeder is an animal used for selective breeding. A breeder is usually a purebred animal, bred with the intent of producing purebred, or even show-quality animals. However, in some cases, a breeding animal is crossbred with another breed or a mixed breed with the intent of combining aspects of two or more different breeds. == Purebred and registered animals == If the breeding is for a purebred animal that will be used for exhibition or future breeding (pets or livestock), the animal must be registered and conform to the criteria laid out for that breed in a breed standard kept by a central authority, such as a kennel club for dogs. In addition, the breed club, kennel club, or other governing authority may have other restrictions on the type of animal that can be used for breeding to produce offspring that can be registered. For example, some horse registries allow backbred and crossbred individuals to be breeders. However, most dog registries do not accept crossbred animals for registration, except in exceptional circumstances and only by permission. Most kennel clubs allow any registered individual to be a breeder, however the individual breed club may have additional criteria such as having to pass certain eligibility requirements. == Terminology == In animal fancy, there are specialized words for breeding animals in some species. (Not to be confused with the words for an animal's parents, sire and dam.) == See also == Animal breeding Animal fancy Animal husbandry == References == == External links == breeders-international.com - The worldwide Community for Breeders
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{
"page_id": 1379121,
"source": null,
"title": "Breeder (animal)"
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Cytochrome P450, family 74, also known as CYP74, is a cytochrome P450 family in land plant supposed to derived from horizontal gene transfer of marine animal CYPs. == References ==
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{
"page_id": 65538868,
"source": null,
"title": "CYP74 family"
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Mangrove restoration is the regeneration of mangrove forest ecosystems in areas where they have previously existed. Restoration can be defined as "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed." Mangroves can be found throughout coastal wetlands of tropical and subtropical environments. Mangroves provide essential ecosystem services such as water filtration, aquatic nurseries, medicinal materials, food, and lumber. Additionally, mangroves play a vital role in climate change mitigation through carbon sequestration and protection from coastal erosion, sea level rise, and storm surges. Mangrove habitat is declining due to human activities such as clearing land for industry and climate change. Mangrove restoration is critical as mangrove habitat continues to rapidly decline. Different methods have been used to restore mangrove habitat, such as looking at historical topography, or mass seed dispersal. Fostering the long-term success of mangrove restoration is attainable by involving local communities through stakeholder engagement. == Mangroves Across the World == Mangroves are typically found in tropical regions of the world on the coasts of America, Australia, Asia, and Africa. Mangrove ecosystems are found in about 120 countries in the world and make up 0.7% of the world's tropical forests. In most of these regions mangroves provide many services including; shelter, climate regulation through carbon sequestration, decrease coastal erosion, create a link between terrestrial and marine ecosystems, and maintain water quality along the coast. Mangroves have recently become susceptible to deforestation due to human activities and extreme weather. Aquaculture, agriculture, and urbanization are some of the reasons why mangroves are being damaged or destroyed. == Environmental context == Historically, mangroves have been identified two different ways: the species of trees and shrubs that can tolerate brackish water conditions, or the species that fall under the mangrove family, Rhizophoraceae as well as trees of
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the genus Rhizophora. The majority of mangrove genera and families are not closely related, but they do however, share some adaptive commonalities. These unique qualities that allow mangroves to thrive in aversive conditions are pneumatophoric roots, stilt roots, salt-excreting leaves, and viviparous water-dispersed propagules. Mangrove communities occur between the latitudes of 30° N to 37° S and grow in waters where tidal height is between 1 and 4 meters. They can be found in various geographic areas from oceanic islands to riverine systems and in warm temperate climates to arid and wet tropics. Despite having a relatively large range of habitat, mangroves thrive in optimal areas. In warmer, humid climates, mangrove canopies may reach a height of 30–40 m. In colder, arid environments, mangroves form isolated patches with stunted growth, reaching about 1–2 m. == Functions and values of mangroves == Mangrove forests, along with the animal species they shelter, represent globally significant sources of biodiversity and provide humanity with valuable ecosystem services. They are used by mammals, reptiles and migratory birds as feeding and breeding grounds, and provide crucial habitats for fish and crustacean species of commercial importance. The Atlantic goliath grouper for instance, which is currently listed as critically endangered due to overfishing, utilizes mangroves as a nursery for the first 5–6 years of life. The roots of the mangrove physically buffer shorelines from the erosive impacts of ocean waves and storms. Additionally, they protect riparian zones by absorbing floodwaters and slowing down the flow of sediment-loaded river water. This allows sediments to drop to the bottom where they are held in place, thus containing potentially toxic waste products and improving the quality of water and sanitation in coastal communities. To the human communities who rely on them, mangrove forests represent local sources of sustainable income from the
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harvest of fish and timber, as well as non-timber forest products such as medicinal plants, palm leaves and honey. On a global scale, they have been shown to sequester carbon in quantities comparable to higher-canopy terrestrial rainforests, which means that they may play a role in climate change mitigation. It has been shown that even though mangrove forests only account for 0.5% of the worlds coastal habitats it has a much higher sequestration rate of carbon compared to other coastal habitats (except for salt marshes). In addition to physically protecting coastlines from the projected sea-level rise associated with climate change. === Mangroves as climate change mitigation === Mangrove forests have a potential to mitigate climate change, such as through the sequestration of carbon from the atmosphere directly, and by providing protection from storms, which are expected to become more intense and frequent into the 21st century. A summary of coastal wetland carbon, including mangroves, is seen in the accompanying image. Wetland plants, like mangroves, take in carbon dioxide when they perform photosynthesis. They then convert this into biomass made of complex carbon compounds. Being the most carbon-rich tropical forest, mangroves are highly productive and are found to store three to four times more carbon than other tropical forests. This is known as blue carbon. Mangroves make up only 0.7% of tropical forest area worldwide, yet studies calculate the effect of mangrove deforestation to contribute 10% of global CO2 emissions from deforestation. The image to the right shows the global distribution of above ground carbon from mangroves. As can be seen, most of this carbon is located in Indonesia, followed by Brazil, Malaysia and Nigeria. Indonesia has one of the highest rates of mangrove loss, yet the most carbon stored from mangroves. Therefore, it is suggested that if the correct policy
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is implemented, countries like Indonesia can make considerable contributions to global carbon fluxes. The UN estimate deforestation and forest degradation to make up 17% of global carbon emissions, which makes it the second most polluting sector, following the energy industry. The cost of this globally is estimated to total $42 billion. Therefore, in recent years, there has been more focus on the importance of mangroves, with initiatives being developed to use reforestation as a mitigation tool for climate change. == Mangrove loss and degradation == The issue of restoration is critical today since mangrove forests are being lost very quickly – at an even faster rate than tropical rainforests inland. During the 1970s, mangroves occupied as much as 200,000 km2, encompassing approximately 75% of the world's coastlines. Now, global mangrove area has experienced significant decline where at least 35% has been lost. Mangroves are continuing to diminish at a rate of 1-2% per year. Much of this lost mangrove area was destroyed to make room for industry, housing and tourism development; for aquaculture, primarily shrimp farms; and for agriculture, such as rice paddies, livestock pasture and salt production. Other drivers of mangrove forest destruction include activities that divert their sources of freshwater, such as groundwater withdrawals, the building of dams, and the building of roads and drainage canals across tidal flats. Another indirect human activity, climate change, also threatens mangrove habitat. Sea levels are on the rise as polar ice caps melt from increasing temperatures and thermal expansion. Depending on sediment accumulation, mangrove habitats will generally respond to sea level change in three different ways: (1) If the sediment in the mangrove forest rises faster than the sea level, plants from further inland may move into the area as the mangroves retreat; (2) if the rate of sediment accumulation is
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equal to the rate of sea level rise, the forest survives and is stable during this period and (3) if the rate of soil accumulation is slower than the rate of sea level rise, the mangrove forest will be submerged by the sea. However, mangroves may then adapt and spread more inland as new territory is made for mangrove habitat. It is important to note that changes may deviate from these three general scenarios depending on local morphological/topographical features. However, there are limits to the capacity of mangroves to adapt to climate change. It is projected that a 1-meter rise in sea level could inundate and destroy mangrove forests in many regions around the globe. Mangroves play a vital role in delivering essential ecosystem services for the benefit of both humans and wildlife. The loss of these invaluable services will have a significant negative impact on the world. Mangrove habitat loss leaves coastal communities vulnerable to the risks of flooding, shoreline erosion, saline intrusion, and increased storm activity. Ecosystem services such as water purification and collection of raw materials are not possible if mangroves are utilized unsustainably. Furthermore, the decline of mangrove communities heavily impacts the plants and animals that rely on the habitat for survival. Loss of mangroves leads to reduced water quality, reduced biodiversity, increased sedimentation threatening coral reefs, and collapse of intertidal food webs and aquatic nurseries. Since mangroves are carbon sinks, their destruction can release large amounts of stored carbon and contribute to the effects of global warming. == Restoration process == Mangroves are sensitive ecosystems, changing dynamically in response to storms, sediment blockage, and fluctuations in sea level and present a "moving target" for restoration efforts. Mangroves are considered to be one of the easiest coastal systems to restore because of their seedlings ability to
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survive where adult trees are not present. The most common method simply consists in planting single-species stands of mangroves in areas thought to be suitable, without consideration of whether or not they supported mangroves in the past. This approach usually fails over the long term because the underlying soil and hydrological requirements of the mangroves are not being met. Mangrove survival is dependent on many factors including soil salinity, sedimentation, groundwater availability, and tidal changes which can vary greatly in small areas. This means, each tree in a mangrove forest will grow slightly different resulting from its unique surrounding conditions. More informed methods aim to bring a damaged mangrove area back into its preexisting condition, taking into account not only ecosystem factors but also social, cultural and political perspectives. These approaches begin with the understanding that a damaged mangrove area may be able to repair itself through the natural processes of secondary succession, without being physically planted, provided that its tidal and freshwater hydrology is functioning normally and there is an adequate supply of seedlings. If natural renewal does occur, Twilley et al. 1996 predicts species composition will be largely determined by the very earliest saplings to colonize the recovering stand. This prediction is supported by the actual studies of Clarke et al. 2000, Clarke et al. 2001, Ross et al. 2006 and Sousa et al. 2007. A second approach to mangrove restoration is the ecological mangrove restoration (EMR) approach. This approach mainly focuses on correcting the hydrology of a mangrove ecosystem for long lasting health of the area while the plantation approach does not truly take into account the dynamics of the ecosystem. While some planting may be required in the EMR approach, the expectation is that mangrove seedlings will be able to naturally recolonize. Steps to the EMR
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approach are as follows: Assess the ecology, especially reproduction and distribution patterns, of the mangrove species at the disturbed site; Map the topographical elevations and hydrological patterns that determine how seedlings should establish themselves at the site; Assess the changes made to the site that currently prevent the site from recovering by itself; Design a restoration plan that begins by restoring the normal range of elevations and tidal hydrology at the site; and Monitor the site to determine if the restoration has been successful in light of the original objectives. This may include introducing structures such as detached breakwaters, to protect the site from wave action and allow for adequate sediment build-up. The actual planting of seedlings is a last resort, since it fails in many cases; it should be considered only if natural recruitment of seedlings fails to reach the restoration objective. Restoring mangroves by traditional methods, manually, is slow and difficult work. An alternative has been proposed to use quadcopters to carry and deposit seed pods. According to Irina Fedorenko and Susan Graham of BioCarbon Engineering, a drone can do an amount of work in days that is equivalent to weeks of planting by humans using traditional methods, at a fraction of the cost. Drones can also carry and plant seeds in difficult-to-reach or dangerous areas where humans cannot work easily. Drones can be used to develop planting patterns for areas and to monitor growth of new forests. === Stakeholder engagement === An important but often overlooked aspect of mangrove restoration efforts is the role that the local communities play as stakeholders in the process and the outcome. If a restoration project is put in place without support of the local community, it may result in backlash, wasted funding, and wasted efforts. An important aspect to consider is
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whether society deems if restoration of mangroves is worth the investment effort. This is ultimately determined by human self interest, and whether the decision will maximize their personal utility. Another obstacle that projects may face is how to quantify the economic value of mangrove restoration. Ecological services of mangroves are difficult to determine, "as most of them are of indirect nature and non-marketed." Support of local communities are a crucial aspect in the long-term success of mangrove restoration. Not only can locals provide knowledge about the environment, their participation through employment and funding strategies will encourage them to keep maintaining the mangroves after initial success of the project. A case study in the Philippines gathered data on local people's participation in a mangrove restoration project. Locals can play a major participatory role in mangrove restoration projects, so encouraging and strengthening their participation is particularly important. However, in order for participation to occur, there must be benefits and incentives provided to engage the community. If benefits are not received, local people are discouraged from participating. This study found that participation in mangrove restoration improves livelihoods and increases social capital, which directly benefits their access to information and services. Participation in mangrove restoration can provide more than just tangible benefits, it also leads to more sustainable and long-term rewards. === Reducing emissions from deforestation and forest degradation === It is estimated that approximately 15% of total anthropogenic carbon emissions a year can be attributed to carbon emissions from tropical deforestation. In 2008, the United Nations launched the "Reducing Emissions from Deforestation and forest Degradation (REDD)" program to combat climate change through the reduction of carbon emissions and enhancement of carbon sinks from forests. It is the opinion of literary scholars that the REDD program can increase carbon sequestration from mangroves and therefore
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}
|
reduce carbon in the atmosphere. The REDD+ mechanism, as part of the REDD program, provides financial support to stakeholders in developing countries to avoid deforestation and forest degradation. The estimated impacts of REDD+ globally, could reach up to 2.5 billion tons of CO2 each year. An examples of REDD+ implementation can be seen in Thailand, where carbon markets give farmers incentive to conserve mangrove forests, by compensating for the opportunity cost of shrimp farming. === Mangroves for the Future === Moreover, the Mangroves for the Future (MFF) initiative, led by IUCN and UNDP, encourages the rehabilitation of mangroves by engaging with local stakeholders and creating a platform for change. In Indonesia, one project planted 40,000 mangroves, which then encouraged local government to take up similar initiatives on a larger scale. Mangrove restoration and protection is also seen as a climate change mitigation strategy under COP21, the international agreement to target climate change, with countries being able to submit the act in their Nationally Appropriate Mitigation Approaches (NAMAs). Ten of the world's least developed countries are now prioritizing mangrove restoration in their NAMAs. == See also == UN Decade on Ecosystem Restoration Reforestation == References == === Sources === Food and Agriculture Organization of the United Nations, Rome. "The world's mangroves 1980-2005. A Thematic Study Prepared in the Framework of the Global Forest Resources Assessment 2005", FAO Forestry Paper 153, 2007. Forest Service Manual. "Ecological Restoration and Resilience", National Forest Resource Management, Chapter 2020, 2000. Intergovernmental Panel on Climate Change. "IPCC Fourth Assessment Report. Climate Change 2001. Working Group II: Impacts, Adaptation and Vulnerability". 19.3.3.5, Mangrove Ecosystems. Lewis, Roy R. "Mangrove Field of Dreams: If We Build It, Will They Come?", Society of Wetland Scientists Research Brief. Wetland Science and Practice. 27(1):15-18, 2009. Lewis, Roy R. "Methods and criteria for successful
|
{
"page_id": 36309813,
"source": null,
"title": "Mangrove restoration"
}
|
mangrove forest restoration", Chapter 28, pp. 787–800 in G.M.E. Perillo, E. Wolanski, D. R. Cahoon, and M.M. Brinson (eds.) "Coastal Wetlands: An Integrated Ecosystem Approach". Elsevier Press, 2009. Millennium Ecosystem Assessment. "Ecosystems and Human Well-Being: Wetlands and Water Synthesis", World Resources Institute, Washington, DC, 2005. Quarto, Alfredo, Mangrove Action Project. "Ecological Mangrove Restoration (EMR) and Training Project. Concept Note for EMR Workshops in Asia and Latin America", 2010. Wetlands International. "Ecological Mangrove Restoration in Thailand", 2012. Mangrove Restoration.com
|
{
"page_id": 36309813,
"source": null,
"title": "Mangrove restoration"
}
|
In crystallography, materials science and metallurgy, Vegard's law is an empirical finding (heuristic approach) resembling the rule of mixtures. In 1921, Lars Vegard discovered that the lattice parameter of a solid solution of two constituents is approximately a weighted mean of the two constituents' lattice parameters at the same temperature: a A ( 1 − x ) B x = ( 1 − x ) a A + x a B {\displaystyle a_{\mathrm {A} _{(1-x)}\mathrm {B} _{x}}=(1-x)\ a_{\mathrm {A} }+x\ a_{\mathrm {B} }} e.g., in the case of a mixed oxide of uranium and plutonium as used in the fabrication of MOX nuclear fuel: a U 0.93 P u 0.07 O 2 = 0.93 a U O 2 + 0.07 a P u O 2 {\displaystyle a_{\mathrm {U_{0.93}Pu_{0.07}O_{2}} }=0.93\ a_{\mathrm {UO_{2}} }+0.07\ a_{\mathrm {PuO_{2}} }} Vegard's law assumes that both components A and B in their pure form (i.e., before mixing) have the same crystal structure. Here, aA(1-x)Bx is the lattice parameter of the solid solution, aA and aB are the lattice parameters of the pure constituents, and x is the molar fraction of B in the solid solution. Vegard's law is seldom perfectly obeyed; often deviations from the linear behavior are observed. A detailed study of such deviations was conducted by King. However, it is often used in practice to obtain rough estimates when experimental data are not available for the lattice parameter for the system of interest. For systems known to approximately obey Vegard's law, the approximation may also be used to estimate the composition of a solution from knowledge of its lattice parameters, which are easily obtained from diffraction data. For example, consider the semiconductor compound InPxAs(1-x). A relation exists between the constituent elements and their associated lattice parameters, a, such that: a I n P x
|
{
"page_id": 8981301,
"source": null,
"title": "Vegard's law"
}
|
A s ( 1 − x ) = x a I n P + ( 1 − x ) a I n A s {\displaystyle a_{\mathrm {InP} _{x}\mathrm {As} _{(1-x)}}=x\ a_{\mathrm {InP} }+(1-x)\ a_{\mathrm {InAs} }} When variations in lattice parameters are very small across the entire composition range, Vegard's law becomes equivalent to Amagat's law. == Relationship to band gaps in semiconductors == In many binary semiconducting systems, the band gap in semiconductors is approximately a linear function of the lattice parameter. Therefore, if the lattice parameter of a semiconducting system follows Vegard's law, one can also write a linear relationship between the band gap and composition. Using InPxAs(1-x) as before, the band gap energy, E g {\displaystyle E_{g}} , can be written as: E g , I n P A s = x E g , I n P + ( 1 − x ) E g , I n A s {\displaystyle E_{g,\mathrm {InPAs} }=x\ E_{g,\mathrm {InP} }+(1-x)\ E_{g,\mathrm {InAs} }} Sometimes, the linear interpolation between the band gap energies is not accurate enough, and a second term to account for the curvature of the band gap energies as a function of composition is added. This curvature correction is characterized by the bowing parameter, b: E g , I n P A s = x E g , I n P + ( 1 − x ) E g , I n A s − b x ( 1 − x ) {\displaystyle E_{g,\mathrm {InPAs} }=x\ E_{g,\mathrm {InP} }+(1-x)\ E_{g,\mathrm {InAs} }-bx\ (1-x)} == Mineralogy == The following excerpt from Takashi Fujii (1960) summarises well the limits of Vegard’s law in the context of mineralogy and also makes the link with the Gladstone–Dale equation: In mineralogy, the tacit assumption for the linear correlation of the density and
|
{
"page_id": 8981301,
"source": null,
"title": "Vegard's law"
}
|
the chemical composition of a solid solution is twofold: one is an ideal solid solution and the other identical or nearly identical molar volumes of the components. … Coefficients of thermal expansion and compressibilities of the ideal solid solution can be discussed in the same manner. But when the solid solution is ideal, the linear correlation of molar heat capacities and chemical composition is possible. The linear correlation of refractive index and chemical composition of an isotropic solid solution can be derived from the Gladstone–Dale equation, but it is required that the system must be ideal and the molar volumes of the components are equal or nearly equal. If the concept of the volume fraction is introduced, density, coefficient of thermal expansion, compressibility and refractive index can be correlated linearly with the volume fraction in an ideal system.“ == See also == When considering the empirical correlation of some physical properties and the chemical composition of solid compounds, other relationships, rules, or laws, also closely resembles Vegard's law, and in fact the more general rule of mixtures: Amagat's law Gladstone–Dale equation Kopp's law Kopp–Neumann law Rule of mixtures == References ==
|
{
"page_id": 8981301,
"source": null,
"title": "Vegard's law"
}
|
TB10Cs3H1 is a member of the H/ACA-like class of non-coding RNA (ncRNA) molecule that guide the sites of modification of uridines to pseudouridines of substrate RNAs. It is known as a small nucleolar RNA (snoRNA) thus named because of its cellular localization in the nucleolus of the eukaryotic cell. TB10Cs3H1 is predicted to guide the pseudouridylation of SSU ribosomal RNA (rRNA) at residue Ψ263. == References ==
|
{
"page_id": 21105467,
"source": null,
"title": "TB10Cs3H1 snoRNA"
}
|
TRNA(m1G9/m1A9)-methyltransferase may refer to: TRNA (adenine9-N1)-methyltransferase TRNA (guanine9-N1)-methyltransferase
|
{
"page_id": 38603585,
"source": null,
"title": "TRNA(m1G9/m1A9)-methyltransferase"
}
|
Functional diversity, composition, and species richness affect the biogeochemical processes of ecosystems. However, the degree to which these factors influence ecosystems and whether that influence is significant is debated. In the article The Influence of Functional Diversity and Composition on Ecosystem Processes, scientists reported on an experiment in which they studied the effects of plant species diversity, functional diversity, and functional composition on ecosystem processes, as measured in six response variables (productivity, plant % N, plant tot. N, soil NH4, soil NO3, and light penetration). 289 plots were designed with varying amounts of the three controlled factors. Each plot contained up to 32 perennial savannah-grassland species representing up to five plant functional groups. These species were not equal in their functional impact to the ecosystem. The statistical results show that functional diversity and species composition significantly affected the six response variables to a greater extent than species diversity. By themselves, all three factors significantly affected ecosystem processes and also influenced each other. The mechanisms and degree by which they influenced each other are unclear. The Tilman article doesn't purport to have the definite answer. Uncertainty is implied in the major conclusions of the paper: "...the number of functionally different roles represented in an ecosystem may be a stronger determinant of ecosystem processes than the total number of species, per se. However, species diversity and functional diversity are correlated..." This study implies that to progress, scientists on both sides of the diversity–function debate must develop a holistic model that acknowledges the inextricable relationship between diversity and function. In the fourth installment of the Ecological Society of America's Issues in Ecology series, the David Tilman et al. study was used to support the argument for a positive correlation between diversity and productivity. Following its release, the Issues authors were accused of being
|
{
"page_id": 11406148,
"source": null,
"title": "Diversity–function debate"
}
|
deliberately misleading, presenting controversial findings as fact. Wardle charged that the diversity experiments reported in Tilman et al., despite being stated in “Issues” as solid fact, were confounded by an experimental design that assumed "that biological communities are randomly assembled with regard to the ecosystem property being investigated." This phenomenon is termed the "selection probability effect." The Issues article, however, does not present this opinion as fact. It discusses the sampling effect as a possible mechanism, not as an irrefutable mechanism. Furthermore, its conclusions are marked by uncertainty: although species diversity and functional diversity are correlated, functional diversity may play a larger role in ecosystem processes than the total number of species. Some of the services provided by ecosystems include the components used in fabricating food, clothing, medicine, and energy production. Recreation and passive ecosystem services are significant as well. These include fishing, hunting, hiking, birding, camping, water filtration/purification, climate moderation, flood mitigation, erosion prevention, and pest management. As reported in Expert Estimates About Effects of Biodiversity on Ecosystem Processes and Services, ecosystem process rates correlate strongly with biodiversity, and these processes are crucial for ecosystem services. == See also == Ecological effects of biodiversity == References == == External links == Ecological Society of America Society for Conservation Biology
|
{
"page_id": 11406148,
"source": null,
"title": "Diversity–function debate"
}
|
In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (R−O−O−R′). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily breaks, producing free radicals of the form RO• (the dot represents an unpaired electron). Thus, organic peroxides are useful as initiators for some types of polymerization, such as the acrylic, unsaturated polyester, and vinyl ester resins used in glass-reinforced plastics. MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can explosively combust. Organic peroxides, like their inorganic counterparts, are often powerful bleaching agents. == Types of organic peroxides == Organic peroxides are classified (i) by the presence or absence of a hydroxyl (−OH) terminus and (ii) by the presence of alkyl vs acyl substituents. Examples of organic peroxides One gap in the classes of organic peroxides is diphenyl peroxide. Quantum chemical calculations predict that it undergoes a nearly barrierless reaction akin to the benzidine rearrangement. == Properties == The O−O bond length in peroxides is about 1.45 Å, and the R−O−O angles (R = H, C) are about 110° (water-like). Characteristically, the C−O−O−R (R = H, C) dihedral angles are about 120°. The O−O bond is relatively weak, with a bond dissociation energy of 45–50 kcal/mol (190–210 kJ/mol), less than half the strengths of C−C, C−H, and C−O bonds. == Biology == Peroxides play important roles in biology. Hundreds of peroxides and hydroperoxides are known, being derived from fatty acids, steroids, and terpenes. The prostaglandins are biosynthesized by initial formation of a bicyclic peroxide ("endoperoxide") derived from arachidonic acid. Many aspects of biodegradation or aging are attributed to the formation and decay of peroxides formed from oxygen in air. Countering these effects, an array
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
of biological and artificial antioxidants destroy peroxides. In fireflies, oxidation of luciferins, which is catalyzed by luciferases, yields a peroxy compound 1,2-dioxetane. The dioxetane is unstable and decays spontaneously to carbon dioxide and excited ketones, which release excess energy by emitting light (bioluminescence). == Industrial uses == === In polymer chemistry === Many peroxides are used as a radical initiators, e.g., to enable polymerization of acrylates. Industrial resins based on acrylic and/or methacrylic acid esters are invariably produced by radical polymerization with organic peroxides at elevated temperatures. The polymerization rate is adjusted by suitable choice of temperature and type of peroxide. Methyl ethyl ketone peroxide, benzoyl peroxide and to a smaller degree acetone peroxide are used as initiators for radical polymerization of some thermosets, e.g. unsaturated polyester and vinyl ester resins, often encountered when making fiberglass or carbon fiber composites (CFRP), with examples including boats, RV units, bath tubs, pools, sporting equipment, wind turbine blades, and a variety of industrial applications. Benzoyl peroxide, peroxyesters/peroxyketals, and alkylperoxy monocarbonates are used in production of polystyrene, expanded polystyrene, and High Impact Polystyrene, and benzoyl peroxide is utilized for many acrylate based adhesive applications. Thermoplastic production techniques for many industrial polymerization applications include processes which are carried out in bulk, solution, or suspension type batches. Relevant polymers include: polyvinyl chloride (PVC), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), Polystyrene, and Polycarbonates. === Bleaching and disinfecting agents === Benzoyl peroxide and hydrogen peroxide are used as bleaching and "maturing" agents for treating flour to make its grain release gluten more easily; the alternative is letting the flour slowly oxidize by air, which is too slow for the industrialized era. Benzoyl peroxide is an effective topical medication for treating most forms of acne. == Preparation == === From hydrogen peroxide === Dialkyl peroxides, e.g.,
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
dicumyl peroxide, are synthesized by addition of hydrogen peroxide to alkenes or by O-alkylation of hydroperoxides. Diacyl peroxides are typically prepared by treating hydrogen peroxide with acid chlorides or acid anhydrides in the presence of base: H2O2 + 2 RCOCl → (RCO2)2 + 2 HCl H2O2 + (RCO)2O → (RCO2)2 + H2O The reaction competes with hydrolysis of the acylating agent but the hydroperoxide anion is a superior nucleophile relative to hydroxide. Unsymmetrical diacyl peroxides can be produced by treating acyl chlorides with the peroxy acid. Peresters, an example being tert-Butyl peroxybenzoate, are produced by treating acid anhydrides or acid chlorides with hydroperoxides. === From O2 === Cyclic peroxides can be obtained by cycloaddition of singlet oxygen (generated by UV radiation) to dienes. An important example is rubrene. Six-membered cyclic peroxides are called endo peroxides. The four-membered dioxetanes can be obtained by 2+2 cycloaddition of oxygen to alkenes. The hazards associated with storage of ethers in air is attributed to the formation of hydroperoxides via the direct albeit slow reaction of triplet oxygen with C-H bonds. == Reactions == === Homolysis === Organic peroxides are widely used to initiate polymerization of olefins, e.g. the formation of polyethylene. A key step is homolysis: ROOR ⇌ 2 RO. The tendency to homolyze is also exploited to modify polymers by grafting or visbreaking, or cross-link polymers to create a thermoset. When used for these purposes, the peroxide is highly diluted, so the heat generated by the exothermic decomposition is safely absorbed by the surrounding medium (e.g. polymer compound or emulsion). === Self-oxidation === Especially when in concentrated form, organic peroxides can decompose by self-oxidation, since organic peroxides contain both an oxidizer (the O-O bond) and fuel (C-H and C-C bonds). A "self-accelerating decomposition" occurs when the rate of peroxide decomposition generates heat at
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
a faster rate than it can be dissipated to the environment. Temperature is the main factor in the rate of decomposition. The lowest temperature at which a packaged organic peroxide will undergo a self-accelerating decomposition within a week is defined as the self-accelerating decomposition temperature (SADT). A large fire at the Arkema Chemical Plant in Crosby, Texas (USA) in 2017 was caused by the decomposition of various organic peroxides following power failure and subsequent loss of cooling systems. This occurred due to extreme flooding from Hurricane Harvey, which destroyed main and back-up power generators at the site. === Cumene process === Hydroperoxides are intermediates or reagents in major commercial processes. In the cumene process, acetone and phenol are produced by decomposition of cumene hydroperoxide (Me = methyl): C6H5CMe2(O2H) → C6H5OH + O=CMe2 === Anthraquinone process === Anthrahydroquinone reacts spontaneously with oxygen to form anthraquinone and hydrogen peroxide, possibly through some organic peroxide intermediate. After extracting the hydrogen peroxide the anthraquinone is catalytically reduced to anthrahydroquinone and reused in the process. There are other hydroquinones reacting in a similar fashion. === Reduction === Organoperoxides can be reduced to alcohols with lithium aluminium hydride, as described in this idealized equation: 4 ROOH + LiAlH4 → LiAlO2 + 2 H2O + 4 ROH The phosphite esters and tertiary phosphines also effect reduction: ROOH + PR3 → P(OR)3 + ROH Cleavage to ketones and alcohols occurs in the base-catalyzed Kornblum–DeLaMare rearrangement, which involves the breaking of bonds within peroxides to form these products. Some peroxides are drugs, whose action is based on the formation of radicals at desired locations in the organism. For example, artemisinin and its derivatives, such as artesunate, possess the most rapid action of all current drugs against falciparum malaria. Artesunate is also efficient in reducing egg production in Schistosoma haematobium
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
infection. === Organic synthesis === tert-Butyl hydroperoxide is used for epoxidation and hydroxylation reagents in conjunction with metal catalysts. == Analysis of peroxides == Several analytical methods are used for qualitative and quantitative determination of peroxides. A simple qualitative detection of peroxides is carried out with the iodine-starch reaction. Here peroxides, hydroperoxides or peracids oxidize the added potassium iodide into iodine, which reacts with starch producing a deep-blue color. Commercial paper indicators using this reaction are available. This method is also suitable for quantitative evaluation, but it can not distinguish between different types of peroxide compounds. Discoloration of various indigo dyes in presence of peroxides is used instead for this purpose. For example, the loss of blue color in leuco-methylene blue is selective for hydrogen peroxide. Quantitative analysis of hydroperoxides can be performed using potentiometric titration with lithium aluminium hydride. Another way to evaluate the content of peracids and peroxides is the volumetric titration with alkoxides such as sodium ethoxide. === Active oxygen in peroxides === Each peroxy group is considered to contain one active oxygen atom. The concept of active oxygen content is useful for comparing the relative concentration of peroxy groups in formulations, which is related to the energy content. In general, energy content increases with active oxygen content, and thus the higher the molecular weight of the organic groups, the lower the energy content and, usually, the lower the hazard. The term active oxygen is used to specify the amount of peroxide present in any organic peroxide formulation. One of the oxygen atoms in each peroxide group is considered "active". The theoretical amount of active oxygen can be described by the following equation: A [ O ] theoretical ( % ) = 16 p m × 100 , {\displaystyle A[\mathrm {O} ]_{\text{theoretical}}(\%)=16{\frac {p}{m}}\times 100,} where p is
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
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|
the number of peroxide groups in the molecule, and m is the molecular mass of the pure peroxide. Organic peroxides are often sold as formulations that include one or more phlegmatizing agents. That is, for safety sake or performance benefits the properties of an organic peroxide formulation are commonly modified by the use of additives to phlegmatize (desensitize), stabilize, or otherwise enhance the organic peroxide for commercial use. Commercial formulations occasionally consist of mixtures of organic peroxides, which may or may not be phlegmatized. == Safety == Peroxides are also strong oxidizers and easily react with skin, cotton and wood pulp. For safety reasons, peroxidic compounds are stored in a cool, opaque container, as heating and illumination accelerate their chemical reactions. Small amounts of peroxides, which emerge from storage or reaction vessels are neutralized using reducing agents such as iron(II) sulfate. Safety measures in industrial plants producing large amounts of peroxides include the following: 1) The equipment is located within reinforced concrete structures with foil windows, which would relieve pressure and not shatter in case of explosion. 2) The products are bottled in small containers and are moved to a cold place promptly after the synthesis. 3) The containers are made of non-reactive materials such as stainless steel, some aluminium alloys or dark glass. For safe handling of concentrated organic peroxides, an important parameter is temperature of the sample, which should be maintained below the self accelerating decomposition temperature of the compound. The shipping of organic peroxides is restricted. The US Department of Transportation lists organic peroxide shipping restrictions and forbidden materials in 49 CFR 172.101 Hazardous Materials Table based on the concentration and physical state of the material: == See also == Alkenyl peroxides Peroxyacyl nitrates Ozonide == External links == Organic Peroxide Producers Safety Division OSH Answers –
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
organic peroxides "The Perils of Peroxides". carolina.com. Burlington, NC: Carolina Biological Supply Company. Archived from the original on 2007-12-18. European Organic Peroxide Safety Group == References ==
|
{
"page_id": 2296644,
"source": null,
"title": "Organic peroxides"
}
|
Martian geysers (or CO2 jets) are putative sites of small gas and dust eruptions that occur in the south polar region of Mars during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms – are the two most visible types of features ascribed to these eruptions. Martian geysers are distinct from geysers on Earth, which are typically associated with hydrothermal activity. These are unlike any terrestrial geological phenomenon. The reflectance (albedo), shapes and unusual spider appearance of these features have stimulated a variety of hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of jet or geyser-like activity on Mars. Their characteristics, and the process of their formation, are still a matter of debate. These features are unique to the south polar region of Mars in an area informally called the 'cryptic region', at latitudes 60° to 80° south and longitudes 150°W to 310°W; this 1 meter deep carbon dioxide (CO2) ice transition area—between the scarps of the thick polar ice layer and the permafrost—is where clusters of the apparent geyser systems are located. The seasonal frosting and defrosting of carbon dioxide ice results in the appearance of a number of features, such dark dune spots with spider-like rilles or channels below the ice, where spider-like radial channels are carved between the ground and the carbon dioxide ice, giving it an appearance of spider webs, then, pressure accumulating in their interior ejects gas and dark basaltic sand or dust, which is deposited on the ice surface and thus, forming dark dune spots. This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars. However, it would seem that
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
multiple years would be required to carve the larger spider-like channels. There is no direct data on these features other than images taken in the visible and infrared spectra. == History == The geological features informally called dark dune spots and spiders were separately discovered on images acquired by the MOC camera on board the Mars Global Surveyor during 1998–1999. At first it was generally thought they were unrelated features because of their appearance, so from 1998 through 2000 they were reported separately on different research publications ( and -respectively). "Jet" or "geyser" models were proposed and refined from 2000 onwards. The name 'spiders' was coined by Malin Space Science Systems personnel, the developers of the camera. One of the first and most interesting spider photos was found by Greg Orme in October 2000. The unusual shape and appearance of these 'spider webs' and spots caused a lot of speculation about their origin. The first years' surveillance showed that during the following Martian years, 70% of the spots appear at exactly the same place, and a preliminary statistical study obtained between September 1999 and March 2005, indicated that dark dune spots and spiders are related phenomena as functions of the cycle of carbon dioxide (CO2) condensing as "dry ice" and sublimating. It was also initially suggested that the dark spots were simply warm patches of bare ground, but thermal imaging during 2006 revealed that these structures were as cold as the ice that covers the area, indicating they were a thin layer of dark material lying on top of the ice and kept chilled by it. However, soon after their first detection, they were discovered to be negative topographical features – i.e. radial troughs or channels of what today are thought to be geyser-like vent systems. == Morphology == The
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
geysers' two most prominent features (dark dune spots and spider channels) appear at the beginning of the Martian spring on dune fields covered with carbon dioxide (CO2 or 'dry ice'), mainly at the ridges and slopes of the dunes; by the beginning of winter, they disappear. Dark spots' shape is generally round, on the slopes it is usually elongated, sometimes with streams—possibly of water—that accumulate in pools at the bottom of the dunes. Dark dune spots are typically 15 to 46 metres (50 to 150 feet) wide and spaced several hundred feet apart. The size of spots varies, and some are as small as 20 m across,—however, the smaller size seen is limited by imaging resolution—and can grow and coalesce into formations several kilometres wide. Spider features, when viewed individually, form a round lobed structure reminiscent of a spider web radiating outward in lobes from a central point. Its radial patterns represent shallow channels or ducts in the ice formed by the flow of the sublimation gas toward the vents. The entire spider channel network is typically 160–300 m across, although there are large variations. Each geyser's characteristic form appears to depend on a combination of such factors as local fluid or gas composition and pressure, ice thickness, underlying gravel type, local climate and meteorological conditions. The geysers' boundary does not seem to correlate with any other properties of the surface such as elevation, geological structure, slope, chemical composition or thermal properties. The geyser-like system produce low-albedo spots, fans and blotches, with small radial spider-like channel networks most often associated with their location. At first, the spots seem to be grey, but later their centres darken because they gradually get covered with dark ejecta, thought to be mainly basaltic sand. Not all dark spots observed in early spring are associated
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
with spider landforms, however, a preponderance of dark spots and streaks on the cryptic terrain are associated with the appearance of spiders later in the season. Time-lapsed imagery performed by NASA confirms the apparent ejection of dark material following the radial growth of spider channels in the ice. Time-lapsed imaging of a single area of interest also shows that small dark spots generally indicate the position of spider features not yet visible; it also shows that spots expand significantly, including dark fans emanating from some of the spots, which increase in prominence and develop clear directionality indicative of wind action. Some branching ravines modify, some destroy and others create crust in a dynamic near-surface process that extensively reworks the terrain creating and destroying surface layers. Thus, Mars seems to have a dynamic process of recycling of its near surface crust of carbon dioxide. Growth process is rapid, happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars. A number of geophysical models have been investigated to explain the various colors and shapes' development of these geysers on the southern polar ice cap of Mars. == Geyser mechanism models == The strength of the eruptions is estimated to range from simple upsurges to high-pressure eruptions at speeds of 160 kilometres per hour (99 mph) or more, carrying dark basaltic sand and dust plumes high aloft. The current proposed models dealing with the possible forces powering the geyser-like system are discussed next. === Atmospheric pressure === The surface atmospheric pressure on Mars varies annually around: 6.7–8.8 mbar and 7.5–9.7 mbar; daily around 6.4–6.8 mbar. Because of the pressure changes subsurface gases expand and contract periodically, causing a downward gas flow during increase of and expulsion during decrease of atmospheric pressure.
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
This cycle was first quantified with measurements of the surface pressure, which varies annually with amplitude of 25%. Clathrate hydrate model This model proposes downward gas flow during increase of and upward flow during decrease of atmospheric pressure. In the defrosting process, ices (clathrate) may partly migrate into the soil and partly may evaporate. These locations can be in connection with the formation of dark dune spots and the arms of spiders as gas travel paths. === Dry venting === Some teams propose dry venting of carbon dioxide (CO2) gas and sand, occurring between the ice and the underlying bedrock. It is known that a CO2 ice slab is virtually transparent to solar radiation where 72% of solar energy incident at 60 degrees off vertical will reach the bottom of a 1 m thick layer. In addition, separate teams from Taiwan and France measured the ice thickness in several target areas, and discovered that the greatest thickness of the CO2 frost layer in the geysers' area is about 0.76–0.78 m, supporting the geophysical model of dry venting powered by sunlight. As the southern spring CO2 ice receives enough solar energy, it starts sublimation of the CO2 ice from the bottom. This vapor accumulates under the slab rapidly increasing pressure and erupting. High-pressure gas flows through at speeds of 160 kilometres per hour (99 mph) or more; under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves. The dark material falls back to the surface and may be taken up slope by wind, creating dark wind streak patterns on the ice cap. This model is consistent with past observations. The location, size and direction of these fans are useful to quantifying seasonal winds and sublimation
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
activity. It is clear that sublimation of the base of the seasonal ice cap is more than capable of generating a substantial overpressure, which is four orders of magnitude higher than the ice overburden pressure and five orders of magnitude higher than atmospheric pressure as discussed above. The observation that a few dark spots form before sunrise, with significant spot formation occurring immediately following sunrise, supports the notion that the system is powered by solar energy. Eventually the ice is completely removed and the dark granular material is back on the surface; the cycle repeats many times. Laboratory experiments performed in 2016 were able to trigger dust eruptions from a layer of dust inside a CO2 ice slab under Martian atmospheric conditions, lending support to the CO2 jet and fan production model. === Water-driven erosion === Data obtained by the Mars Express satellite, made it possible in 2004 to confirm that the southern polar cap has an average of 3 kilometres (1.9 mi) thick slab of CO2 ice with varying contents of frozen water, depending on its latitude: the bright polar cap itself, is a mixture of 85% CO2 ice and 15% water ice. The second part comprises steep slopes known as 'scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains. This transition area between the scarps and the permafrost is the 'cryptic region', where clusters of geysers are located. This model explores the possibility of active water-driven erosive structures, where soil and water derived from the shallow sub-surface layer is expelled up by CO2 gas through fissures eroding joints to create spider-like radiating tributaries capped with mud-like material and/or ice. === Geothermal === A European team proposes that the features could be a sign that non-solar energy source is responsible
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
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|
of the jets, subsurface heat wave for instance. This model is difficult to reconcile with the evidence collected in the form of thermal emission (infrared) imaging, which shows that the fans, spots and blotches are produced by expulsion of cold fluids or cold gases. === Carbon dioxide and water cycling === Michael C. Malin, a planetary scientist and designer of the cameras used by the Mars Global Surveyor that obtained the earliest images of the CO2 geyser phenomenon, is studying the images acquired of specific areas and he tracks their changes over a period of a few years. In 2000, he modelled the fans and spots' dynamics as a complex process of carbon dioxide (CO2) and water sublimation and re-precipitation. The typical pattern of defrosting proceeds from the initiation of small, dark spots typically located at the margins of dunes; these spots individually enlarge and eventually all coalesce. The pattern the enlargement follows is distinct and characteristic: a dark nuclear spot enlarges slowly, often with a bright outer zone or 'halo'. As these are progressive, centripetal phenomena, each location of the light zone is overtaken by an expanding dark zone. Although initially developed along dune margins, spot formation quickly spreads onto and between dunes. As spring progresses, fan-shaped tails ('spiders') develop from the central spot. Defrosting occurs as the low albedo polar sand heats beneath an optically thin layer of frost, causing the frost to evaporate. This is the dark nucleus of the spots seen on dunes. As the vapor moves laterally, it encounters cold air and precipitates, forming the bright halo. This precipitated frost is again vaporized as the uncovered zone of sand expands; the cycle repeats many times. == European Space Agency == While the European Space Agency (ESA) has not yet formulated a theory or model, they
|
{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
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|
have stated that the process of frost sublimation is not compatible with a few important features observed in the images, and that the location and shape of the spots is at odds with a physical explanation, specifically, because the channels appear to radiate downhill as much as they radiate uphill, defying gravity. == Hypothetical biological origin == A team of Hungarian scientists propose that the dark dune spots and channels may be colonies of photosynthetic Martian microorganisms, which over-winter beneath the ice cap, and as the sunlight returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When it has completely melted, they rapidly desiccate and turn black surrounded by a grey aureole. The Hungarian scientists think that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time. Since their discovery, fiction writer Arthur C. Clarke promoted these formations as deserving of study from an astrobiological perspective. A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, the structures might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from UV solar radiation. British and German teams also consider the possibility that organic matter, microbes, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a geothermal energy source. However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis. (See
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{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
also: Life on Mars.) == Lander mission == There is no direct data on these features other than images taken in the visible and infrared spectra, and development of the Mars Geyser Hopper lander is under consideration to study the geyser-like systems. It has not yet been formally proposed nor funded. == See also == == References == == External links == Martian "Spiders" photo repository. Arthur C. Clarke on "Martian Spider" features: 1 Archived 6 July 2017 at the Wayback Machine
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{
"page_id": 18418502,
"source": null,
"title": "Geysers on Mars"
}
|
Space ethics, astroethics or astrobioethics is a discipline of applied ethics that discusses the moral and ethical implications arising from astrobiological research, space exploration and space flight. It deals with practical contemporary issues like the protection of the space environment and hypothetical future issues pertaining to our interaction with extraterrestrial life forms. Specific issues of space ethics include space debris mitigation, the militarization of space and the ethics of SETI and METI, but also more theoretical topics like space colonization, terraforming, directed panspermia and space mining. The field also concerns itself with more fundamental moral questions, such as the value of abiotic environments in space, the intrinsic value of extraterrestrial life, and how humans should treat extraterrestrial non-intelligent life (like microbes) and extraterrestrial intelligent life (and whether this distinction should be made in the first place). Astroethical issues are often discussed as elements of broader issues such as general environmental protection and imperialism. Astroethics have been described as an emerging discipline gaining in attention, a "necessity for astrobiology" and a "true issue for the future of astrobiology". == Ethical guidelines for space exploration == === Planetary Protection === A guiding principle in astroethics is that of Planetary Protection (PP), which seeks to prevent the introduction of lifeforms from Earth to other celestial bodies (forward contamination) and vice versa (back contamination), and thereby possible adverse consequences on existing ecospheres resulting from such contamination. This principle is anchored in the UN Outer Space Treaty, which was established in 1967 and has since been signed and ratified by all space-faring nations. === Precautionary Principle === The precautionary principle was defined in the 1998 Wingspread Conference on the Precautionary Principle. This approach is supposed to guide decisions in the face of a lack of scientific knowledge or consensus on a matter. In a 2010
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"page_id": 70126407,
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"title": "Space ethics"
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COSPAR workshop at Princeton University, 26 experts embraced the precautionary principle and concluded that "further investigations before interference that is likely to be harmful to Earth and other extraterrestrial bodies, including extraterrestrial life and the contamination and disturbance of celestial environments", are to be conducted. === Other Astroethical Principles for SETI === SETI astrobiologist Margaret Race and Methodist theologian Richard Randolph have outlined 4 principles for the search for extra-terrestrial life within the Solar System: Cause no harm to Earth, its life, or its diverse ecosystems. Respect the ecosystem on the surveyed celestial body, do not irreparably alter it or its evolutionary trajectory. Follow proper scientific procedures with honesty and integrity during all phases of exploration. Ensure international participation by all interested parties. == Issues == A wide range of concrete issues is discussed in astroethics. Some of them are herein elaborated. === Sterility === Assumptions about outer space, particularly regarding space colonization, have characterized outer space as sterile and therefore a terra nullius. This assumption does not hold true, particularly considering that Earth is part of it. === Space debris === Millions of pieces of space debris, defunct artificial objects in space, are orbiting Earth. On average, one cataloged piece of space debris falls back onto the planet every day, potentially posing a risk to organisms and property. In total, an estimated 80 tons of space debris re-enter Earth's atmosphere every year. Due to the high friction with the atmospheric gases, the debris burns up, causing the release of its chemical components, which may contribute to atmospheric pollution and ozone depletion. Additionally, space debris orbits the Earth at extremely high velocity. In Low Earth Orbit, where all crewed space stations and many satellites are located, debris typically reaches speeds of around 8 km/s (approximately 18,000 mph or 29,000 km/h).
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{
"page_id": 70126407,
"source": null,
"title": "Space ethics"
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As a result, even tiny pieces of debris can severely damage or destroy satellites and spacecraft in the event of a collision. This could pose a threat to the lives of astronauts on crewed missions and lead to the phenomenon of Kessler syndrome, where a collision of objects in space produces new fragments of space debris that could set off a chain reaction of more collisions. This could render the space around Earth untraversable for space missions and unsuitable for the use of satellites. As of March 2022, there are no legally binding international laws about who is responsible for the extraction of space debris, or mandating a reduction of new space debris brought into Earth's orbit. However, space agencies of several countries have implemented their own standards and policies to reduce introduction of new space debris, and the Inter-Agency Space Debris Coordination Committee (IADC) has been founded to address issues regarding orbital debris. Additionally, JAXA is researching an electromagnetic tether that could be used to pull debris down into the atmosphere. The moral problem is that those in power (space agencies) can launch material into the Earth's orbit for their own gains without being held accountable for it, while the general public has to bear the consequences (such as atmospheric pollution or the risk of being hit by space debris). === Satellite surveillance === Reconnaissance satellites are used for a variety of military and intelligence purposes, such as optical imaging and signals intelligence. It has been noted that such data could infringe on people's privacy and thereby lead to ethical and legal issues. It could also turn into a source of national security threats if such information got into malevolent hands. In order to ensure ethically correct obtainment and use of satellite data, leading researchers in law, meteorology and
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{
"page_id": 70126407,
"source": null,
"title": "Space ethics"
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atmospheric science have called for new policy which would lead to more transparency and security. === Weaponizing space === In 1967, the Outer Space Treaty was signed, spurred by the development of intercontinental ballistic missiles, the Soviet Union's launch of Sputnik, the first artificial satellite, and the following arms race with the United States. The treaty outlaws all kinds of military action (including weapon tests) in space, limits the use of space to peaceful purposes only and ensures that all nations on Earth are free to explore space. This treaty has since been called into question multiple times, especially by President of the United States Donald Trump. On June 18, 2018, Trump announced plans to establish a space force, which would constitute a new, sixth branch of the United States military. He expressed that "When it comes to defending America, it is not enough to merely have an American presence in space. We must have American dominance in space". On December 20, 2019, the United States Space Force Act was signed into law with votes from both Democratic and Republican senators and House members. As a result, the United States Space Force was founded. This was seen by some as an American contestation of the Outer Space Treaty. Viktor Bondarev, chair of the Federation Council Committee on Defense and Security, responded by saying that if the US were to go further and withdraw from the 1967 treaty, there would be "a tough response aimed at ensuring world security." This is despite Russia itself having a space force branch in their military. === Private spaceflight and space tourism === The emergence of space tourism gives rise to a number of ethical concerns. Future frequent and large-scale landings on celestial bodies like the moon may damage or pollute landing sites and the
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{
"page_id": 70126407,
"source": null,
"title": "Space ethics"
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areas around them. While scientific activity in space is benign, this cannot be guaranteed for actions by private people. If, how, by what criteria and by whom laws should be made to ensure that space tourism doesn't negatively impact other celestial bodies is a question of astroethics. === Terraforming other celestial bodies === Terraforming is a controversial astroethical matter. Proponents of terraforming, like Robert Zubrin, argue that humans, being the only technologically advanced and intelligent species on Earth, have a moral obligation to make other celestial bodies habitable for Earth's lifeforms to ensure their survival after the inevitable destruction of our planet. The other, ecocentrist and biocentrist side of the debate criticizes this position as anthropocentrism and argues that other celestial bodies may already contain life which always has intrinsic value, no matter how advanced it may be. They oppose the interplanetary contamination and changes to the other world that would stem from terraforming, as they could endanger the indigenous life and alter its evolutionary trajectory. === Ethicality of SETI and METI === SETI and especially METI (Active SETI) are not uncontroversial and come with their own ethical implications. METI has been criticized as incompatible with the precautionary principle because it could reveal the location of our planet to potentially malevolent alien species. It therefore also potentially puts all of humanity at risk without the need for their individual prior consent, which violates the basic scientific rule of informed consent that all other science must abide by. Reflecting on human history, some authors even fear the enslavement of humanity, should we be discovered by a more advanced species. Similarly, Stephen Hawking, one of the most prominent METI critics, warned of the potential consequences of a meeting with such a species, citing the near-extinction of Aboriginal Tasmanians as an equivalent case
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{
"page_id": 70126407,
"source": null,
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from human history. Concerns regarding the ethicality of METI might be a solution to the Fermi paradox. It is proposed that extraterrestrial life forms may abstain from attempting interstellar communication due to the potential danger it may pose to them, in line with the precautionary principle. Other astroethical considerations regarding METI are the lack of legally enforceable protocols about the steps that should be taken once extraterrestrial life is discovered, the unpredictability of cultural consequences of that discovery (potential paradigm changes in policy, nations, religions, etc.), who will get to speak for humanity in case contact is made, how and by whom that person or group of people should be selected, and what the contents of the messages should be. === Value of extraterrestrial life === A further point of contention in the field is whether extraterrestrial life has intrinsic value and therefore if humans have a moral obligation to protect it. This becomes even more difficult when considering the wide span of possible extraterrestrial life forms and whether our treatment of them should differ based on criteria such as their advancement and intelligence. As former NASA chief historian Steven J. Dick put it, "Does Mars belong to the Martians, even if the Martians are only microbes?" Dick argues that the first step in deciding how we should interact with life forms is to assess their moral status, which is complicated by our ambiguous relations with animals on earth, sheltering some species as pets while eating and exterminating others. The principle of planetary protection provides that all life on other celestial bodies is worthy of protection from harm (also in the form of contamination) and therefore confers rights even on hypothetical extraterrestrial microbes, a situation that contrasts with our treatment of microbes and even most higher-developed organisms on Earth. This
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"page_id": 70126407,
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difference in treatment is hardly justifiable. Therefore, according to Dick, astroethical considerations will broaden our current ethical horizon: they will unveil such inconsistencies and double standards and move humanity from an anthropocentric ethic (ascribing intrinsic value only to rationing beings) to a cosmocentric or biocentric one that values all living things. In fact, Dick says that the finding of extraterrestrial life would "necessitate" a transition away from the anthropocentric approach because it would no longer be consistently applicable to a cosmos that harbors life beyond Earth. === Space burial === The decision to include several grams of human cremains onboard Peregrine Lunar Lander flight 01 was criticized by the Navajo Nation, whose president, Buu Nygren, argued that the Moon is sacred to the Navajo and other American Indian nations, saying "As stewards of our culture and traditions, it is our responsibility to voice our grievances when actions are taken that could desecrate sacred spaces and disregard deeply held cultural beliefs". Celestis CEO Charles Chafer responded that "[the company] reject[s] the whole premise that this is somehow desecration" and that "nobody owns the Moon". The launch was not successful in reaching the Moon. == References == == See also == Environmental ethics Ethics of technology
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"page_id": 70126407,
"source": null,
"title": "Space ethics"
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The Ecological Society of Germany, Austria and Switzerland is a learned society for the promotion of scientific ecology in German-speaking countries. The society is the world's third largest scientific society in the field of ecology after the Ecological Society of America and the British Ecological Society. == Goals == Promotion of basic and applied ecological research Supporting co-operation between all ecological disciplines Improving the scientific exchange of ecologists in German-speaking countries and beyond Supporting ecological education at universities and other institutions of higher education Promoting the application and implementation of ecological knowledge and methods in practice Representation of ecological interests in public To this end, the society organises an annual conference with workshops, awards prizes, publishes the international journal Basic and Applied Ecology and writes statements such as on new genetic engineering (2023), biodiversity loss (2022) and the United Nations Sustainable Development Goals (2015). == Conferences and network == The annual meeting is one of the most important ecological conferences in the German-speaking region. Since 1972, the society organizes these meetings over five days at different Universities in Germany, Austria or Switzerland. One day is used for ecological excursions into the surrounding area. The meetings are organised under a conference theme that reflects current discourses in scientific-ecological research. The focus is on terrestrial ecology including limnology. The largest conference was held in Leipzig with over 1000 participants in 2023. The society is member of the German National Committee of Biology (DNK), of the German Life Sciences Association (VBiO), of the umbrella organisation of agricultural research (DAF), of the European Ecological Federation (EEF) and the International Association for Ecology (INTECOL). == Publications == The society publishes the international journal Basic and Applied Ecology (Elsevier) since 2000. For members, information are distributed by the German-language magazine Nachrichten der GfÖ twice a year.
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{
"page_id": 79104837,
"source": null,
"title": "Ecological Society of Germany, Austria and Switzerland"
}
|
The publicationVerhandlungen der Gesellschaft für Ökologie (ISSN 0171-1113) published from 1972 to 2000 articles of summaries of oral presentations or posters at the annual conference. A long-standing publisher was Jörg Pfadenhauer (1987–2000). == Specialist groups == Many activities of the society are organized by the specialist groups. These working groups mirror the wide spectrum of ecological topics of the GfÖ. Specialist groups like Population Biology or Macroecology organize own small conferences. Agroecology (since 2021) Soil ecology (since 2002) Computational ecology Macroecology Conservation and restoration ecology (since 2015) Ecosystem science (since 1998) Plant population biology (since 1988) Urabn ecology Dryland research Environmental education Forest ecology (since 2012) Young Modellers in Ecology (seit 2005) == History == The society was founded by 18 ecologists in Giessen in 1970 as the Working Group Ecology. Amont these ecologists were Heinz Ellenberg, Wolfgang Haber, Lore Steubing, Heinrich Walter and Otti Wilmanns. In 1972, the first president Lore Steubing invited to the first conference in Giessen. In 1973 were the working group registered as Gesellschaft für Ökologie in the register of associations. At the beginning of the 2000s, the society became internationally orientated and the English-language journal Basic and Applied Ecology was launched and the conferences were held in English. Presidents of the society before Christian Ammer (since 2019) were Lore Steubing (1970–1972), Paul Müller (1972–1976), Karl-Friedrich Schreiber (1976–1979), Wolfgang Haber (1979–1990), Wilhelm Kuttler (1993–1996), Robert Guderian (1997–1999), Jörg Pfadenhauer (2000–2005) and Volkmar Wolters (2005–2019). == GfÖ Medal of Honour == This award goes to persons with a significant contribution to the scientific ecology. == References == [[Category:Biology societies]] [[Category:1970 establishments]] [[Category:Ecology organizations]] [[Category:Biology organisations based in Germany]]
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"page_id": 79104837,
"source": null,
"title": "Ecological Society of Germany, Austria and Switzerland"
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|
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymously with amorphous solid; however, these terms refer specifically to amorphous materials that undergo a glass transition. Examples of amorphous solids include glasses, metallic glasses, and certain types of plastics and polymers. == Etymology == The term "Amorphous" comes from the Greek a ("without"), and morphé ("shape, form"). == Structure == Amorphous materials have an internal structure of molecular-scale structural blocks that can be similar to the basic structural units in the crystalline phase of the same compound. Unlike in crystalline materials, however, no long-range regularity exists: amorphous materials cannot be described by the repetition of a finite unit cell. Statistical measures, such as the atomic density function and radial distribution function, are more useful in describing the structure of amorphous solids. Although amorphous materials lack long range order, they exhibit localized order on small length scales. By convention, short range order extends only to the nearest neighbor shell, typically only 1-2 atomic spacings. Medium range order may extend beyond the short range order by 1-2 nm. == Fundamental properties of amorphous solids == === Glass transition at high temperatures === The freezing from liquid state to amorphous solid - glass transition - is considered one of the very important and unsolved problems of physics. === Universal low-temperature properties of amorphous solids === At very low temperatures (below 1-10 K), a large family of amorphous solids have various similar low-temperature properties. Although there are various theoretical models, neither glass transition nor low-temperature properties of glassy solids are well understood on the fundamental physics level. Amorphous solids is an important area of condensed matter
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{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
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physics aiming to understand these substances at high temperatures of glass transition and at low temperatures towards absolute zero. From the 1970s, low-temperature properties of amorphous solids were studied experimentally in great detail. For all of these substances, specific heat has a (nearly) linear dependence as a function of temperature, and thermal conductivity has nearly quadratic temperature dependence. These properties are conventionally called anomalous being very different from properties of crystalline solids. On the phenomenological level, many of these properties were described by a collection of tunnelling two-level systems. Nevertheless, the microscopic theory of these properties is still missing after more than 50 years of the research. Remarkably, a dimensionless quantity of internal friction is nearly universal in these materials. This quantity is a dimensionless ratio (up to a numerical constant) of the phonon wavelength to the phonon mean free path. Since the theory of tunnelling two-level states (TLSs) does not address the origin of the density of TLSs, this theory cannot explain the universality of internal friction, which in turn is proportional to the density of scattering TLSs. The theoretical significance of this important and unsolved problem was highlighted by Anthony Leggett. == Nano-structured materials == Amorphous materials will have some degree of short-range order at the atomic-length scale due to the nature of intermolecular chemical bonding. Furthermore, in very small crystals, short-range order encompasses a large fraction of the atoms; nevertheless, relaxation at the surface, along with interfacial effects, distorts the atomic positions and decreases structural order. Even the most advanced structural characterization techniques, such as X-ray diffraction and transmission electron microscopy, can have difficulty distinguishing amorphous and crystalline structures at short-size scales. == Characterization of amorphous solids == Due to the lack of long-range order, standard crystallographic techniques are often inadequate in determining the structure of amorphous
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{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
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solids. A variety of electron, X-ray, and computation-based techniques have been used to characterize amorphous materials. Multi-modal analysis is very common for amorphous materials. === X-ray and neutron diffraction === Unlike crystalline materials, which exhibit strong Bragg diffraction, the diffraction patterns of amorphous materials are characterized by broad and diffuse peaks. As a result, detailed analysis and complementary techniques are required to extract real space structural information from the diffraction patterns of amorphous materials. It is useful to obtain diffraction data from both X-ray and neutron sources as they have different scattering properties and provide complementary data. Pair distribution function analysis can be performed on diffraction data to determine the probability of finding a pair of atoms separated by a certain distance. Another type of analysis that is done with diffraction data of amorphous materials is radial distribution function analysis, which measures the number of atoms found at varying radial distances away from an arbitrary reference atom. From these techniques, the local order of an amorphous material can be elucidated. === X-ray absorption fine-structure spectroscopy === X-ray absorption fine-structure spectroscopy is an atomic scale probe making it useful for studying materials lacking in long-range order. Spectra obtained using this method provide information on the oxidation state, coordination number, and species surrounding the atom in question as well as the distances at which they are found. === Atomic electron tomography === The atomic electron tomography technique is performed in transmission electron microscopes capable of reaching sub-Angstrom resolution. A collection of 2D images taken at numerous different tilt angles is acquired from the sample in question and then used to reconstruct a 3D image. After image acquisition, a significant amount of processing must be done to correct for issues such as drift, noise, and scan distortion. High-quality analysis and processing using atomic
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{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
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|
electron tomography results in a 3D reconstruction of an amorphous material detailing the atomic positions of the different species that are present. === Fluctuation electron microscopy === Fluctuation electron microscopy is another transmission electron microscopy-based technique that is sensitive to the medium-range order of amorphous materials. Structural fluctuations arising from different forms of medium-range order can be detected with this method. Fluctuation electron microscopy experiments can be done in conventional or scanning transmission electron microscope mode. === Computational techniques === Simulation and modeling techniques are often combined with experimental methods to characterize structures of amorphous materials. Commonly used computational techniques include density functional theory, molecular dynamics, and reverse Monte Carlo. == Uses and observations == === Amorphous thin films === Amorphous phases are important constituents of thin films. Thin films are solid layers of a few nanometres to tens of micrometres thickness that are deposited onto a substrate. So-called structure zone models were developed to describe the microstructure of thin films as a function of the homologous temperature (Th), which is the ratio of deposition temperature to melting temperature. According to these models, a necessary condition for the occurrence of amorphous phases is that (Th) has to be smaller than 0.3. The deposition temperature must be below 30% of the melting temperature. === Superconductivity === Regarding their applications, amorphous metallic layers played an important role in the discovery of superconductivity in amorphous metals made by Buckel and Hilsch. The superconductivity of amorphous metals, including amorphous metallic thin films, is now understood to be due to phonon-mediated Cooper pairing. The role of structural disorder can be rationalized based on the strong-coupling Eliashberg theory of superconductivity. === Thermal protection === Amorphous solids typically exhibit higher localization of heat carriers compared to crystalline, giving rise to low thermal conductivity. Products for thermal protection,
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{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
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such as thermal barrier coatings and insulation, rely on materials with ultralow thermal conductivity. === Technological uses === Today, optical coatings made from TiO2, SiO2, Ta2O5 etc. (and combinations of these) in most cases consist of amorphous phases of these compounds. Much research is carried out into thin amorphous films as a gas-separating membrane layer. The technologically most important thin amorphous film is probably represented by a few nm thin SiO2 layers serving as isolator above the conducting channel of a metal-oxide semiconductor field-effect transistor (MOSFET). Also, hydrogenated amorphous silicon (Si:H) is of technical significance for thin-film solar cells. === Pharmaceutical use === In the pharmaceutical industry, some amorphous drugs have been shown to offer higher bioavailability than their crystalline counterparts as a result of the higher solubility of the amorphous phase. However, certain compounds can undergo precipitation in their amorphous form in vivo and can then decrease mutual bioavailability if administered together. Studies of GDC-0810 ASDs show a strong interrelationship between microstructure, physical properties and dissolution performance. === In soils === Amorphous materials in soil strongly influence bulk density, aggregate stability, plasticity, and water holding capacity of soils. The low bulk density and high void ratios are mostly due to glass shards and other porous minerals not becoming compacted. Andisol soils contain the highest amounts of amorphous materials. == Phase == Amorphous phases were a phenomenon of particular interest for the study of thin-film growth. The growth of polycrystalline films is often used and preceded by an initial amorphous layer, the thickness of which may amount to only a few nm. The most investigated example is represented by the unoriented molecules of thin polycrystalline silicon films. Wedge-shaped polycrystals were identified by transmission electron microscopy to grow out of the amorphous phase only after the latter has exceeded a certain
|
{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
}
|
thickness, the precise value of which depends on deposition temperature, background pressure, and various other process parameters. The phenomenon has been interpreted in the framework of Ostwald's rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. == Notes == == References == == Further reading == R. Zallen (1969). The Physics of Amorphous Solids. Wiley Interscience. S.R. Elliot (1990). The Physics of Amorphous Materials (2nd ed.). Longman. A. Zaccone (2023). Theory of Disordered Solids. Springer. N. Cusack (1969). The Physics of Structurally Disordered Matter: An Introduction. IOP Publishing. N.H. March; R.A. Street; M.P. Tosi, eds. (1969). Amorphous Solids and the Liquid State. Springer. D.A. Adler; B.B. Schwartz; M.C. Steele, eds. (1969). Physical Properties of Amorphous Materials. Springer. A. Inoue; K. Hasimoto, eds. (1969). Amorphous and Nanocrystalline Materials. Springer.
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{
"page_id": 2889,
"source": null,
"title": "Amorphous solid"
}
|
Carnism is a concept used in discussions of humanity's relation to other animals, defined as a prevailing ideology in which people support the use and consumption of animal products, especially meat. Carnism is presented as a dominant belief system supported by a variety of defense mechanisms and mostly unchallenged assumptions. The term carnism was coined by social psychologist and author Melanie Joy in 2001 and popularized by her book Why We Love Dogs, Eat Pigs, and Wear Cows (2009). Central to the ideology is the acceptance of meat-eating as "natural", "normal", "necessary", and (sometimes) "nice", known as the "Four Ns". An important feature of carnism is the classification of only particular species of animal as food, and the acceptance of practices toward those animals that would be rejected as unacceptable cruelty if applied to other species. This classification is culturally relative, so that, for example, dogs are eaten by some people in Korea but may be pets in the West, while cows are eaten in the West but protected in much of India. == History == Analyzing the history of vegetarianism and opposition to it from ancient Greece to the present day, literary scholar Renan Larue found certain commonalities in what he described as carnist arguments. According to him, carnists typically held that vegetarianism is a ludicrous idea unworthy of attention, that mankind is invested with dominion over animals by divine authority, and that abstaining from violence against animals would pose a threat to humans. He found that the views that farmed animals do not suffer, and that slaughter is preferable to death by disease or predation, gained currency in the nineteenth century, but that the former had precedent in the writings of Porphyry, a vegetarian who advocated the humane production of animal products which do not require animals to
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
}
|
be slaughtered, such as wool. In the 1970s, traditional views on the moral standing of animals were challenged by animal rights advocates, including psychologist Richard Ryder, who in 1971 introduced the notion of speciesism. This is defined as the assignment of value and rights to individuals solely on the basis of their species membership. In 2001, psychologist and animal rights advocate Melanie Joy coined the term carnism for a form of speciesism that she argues underpins using animals for food, and particularly killing them for meat. Joy compares carnism to patriarchy, arguing that both are dominant normative ideologies that go unrecognized because of their ubiquity: We don't see meat eating as we do vegetarianism – as a choice, based on a set of assumptions about animals, our world, and ourselves. Rather, we see it as a given, the "natural" thing to do, the way things have always been and the way things will always be. We eat animals without thinking about what we are doing and why, because the belief system that underlies this behavior is invisible. This invisible belief system is what I call carnism. Sandra Mahlke argues that carnism is the "central crux of speciesism" because the eating of meat motivates ideological justification for other forms of animal exploitation. Abolitionist Gary Francione argues against this that carnism is not a hidden ideology, but a conscious choice; in his view some animals are viewed as food and others family because humans regard non-humans as property, and they may value that property as they please. == Features == === Edible or inedible === A central aspect of carnism is that animals are categorized as edible, inedible, pets, vermin, predators, or entertainment animals, according to people's schemata – mental classifications that determine, and are determined by, our beliefs and desires. There
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
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|
is cultural variability regarding which animals count as food. Dogs are eaten in China, and South Korea, but elsewhere are not viewed as food, either because they are loved or, as in the Middle East and parts of India, regarded as unclean. Cows are eaten in the West, but revered in much of India. Pigs are rejected by Muslims and Jews but widely regarded by other groups as edible. Joy and other psychologists argue that these taxonomies determine how the animals within them are treated, influence subjective perceptions of their sentience and intelligence, and reduce or increase empathy and moral concern for them. === Meat paradox === Jeff Mannes writes that carnism is rooted in a paradox between most people's values and actions: they oppose harming animals, and yet eat them. He argues that this conflict leads to cognitive dissonance, which people attempt to attenuate through psychic numbing. The apparent conflict between caring about animals and embracing diets which require them to be harmed has been termed the "meat paradox". There is experimental evidence supporting the idea that the meat paradox induces cognitive dissonance in Westerners. Westerners are more willing to eat animals which they regard as having lesser mental capacities and moral standing, and conversely, to attribute lesser mental faculties and moral standing to animals which are eaten. Furthermore, the relationship is causative: the categorization of animals as food or not affects people's perception of their mental characteristics, and the act of eating meat itself causes people to attribute diminished mental capacity to animals. For example, in one study people rated an unfamiliar exotic animal as less intelligent if they were told native people hunted it, and in another they regarded cows as less intelligent after eating beef jerky. Avoiding consideration of the provenance of animal products is another
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
}
|
strategy. Joy argues that this is why meat is rarely served with the animal's head or other intact body parts. === Justification === Joy introduced the idea of the "Three Ns of Justification", writing that meat-eaters regard meat consumption as "normal, natural, and necessary". She argues that the "Three Ns" have been invoked to justify other ideologies, including slavery and denying women the right to vote, and are widely recognized as problematic only after the ideology they support has been dismantled. The argument holds that people are conditioned to believe that humans evolved to eat meat, that it is expected of them, and that they need it to survive or be strong. These beliefs are said to be reinforced by various institutions, including religion, family and the media. Although scientists have shown that humans can get enough protein in their diets without eating meat, the belief that meat is required persists. Moreover, a 2022 study published in PNAS calls into question the impact of meat consumption on shaping the evolution of the human species. Building on Joy's work, psychologists conducted a series of studies in the United States and Australia, published in 2015, that found the great majority of meat-eaters' stated justifications for consuming meat were based on the "Four Ns" – "natural, normal, necessary, and nice". The arguments were that humans are omnivores (natural), that most people eat meat (normal), that vegetarian diets are lacking in nutrients (necessary), and that meat tastes good (nice). Meat-eaters who endorsed these arguments more strongly reported less guilt about their dietary habits. They tended to objectify animals, have less moral concern for them and attribute less consciousness to them. They were also more supportive of social inequality and hierarchical ideologies, and less proud of their consumer choices. Helena Pedersen, in her review of
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
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|
Joy's original book, suggested Joy's theory was too broad and did not account for variation in people's beliefs and attitudes; for example, Pedersen argues that Joy's argument that people dissociate animal products from their animal origins cannot account for some hunters who make explicit connection between the two as a justification for consumption or for former vegetarians who have changed their attitudes towards the consumption of animal products. Pedersen also says that Joy seems to present the consumption of animal-products as arising from ignorance of how they are produced, however Pedersen disagrees that people would simply change their consumption if they were more informed. === "Saved from slaughter" narratives === An illustration of dissonance reduction is the prominence given to "saved from slaughter" stories, in which the media focus on one animal that evaded slaughter, while ignoring the millions that did not. Joy wrote that this dichotomy is characteristic of carnism. Animals at the center of these narratives include Wilbur in Charlotte's Web (1952); the eponymous and fictional star of Babe (1995); Christopher Hogwood in Sy Montgomery's The Good, Good Pig (2006); the Tamworth Two; Emily the Cow and Cincinnati Freedom. The American National Thanksgiving Turkey Presentation is cited as another example. A 2012 study found that most media reporting on it celebrated the poultry industry while marginalizing the link between living animals and meat. == Non-academic reception == Opinion pieces in The Huffington Post, The Statesman, and The Drum praised the idea, saying the term made it easier to discuss, and challenge, the practices of animal exploitation. An article in the beef industry outlet Drovers Cattle Network criticized the use of the term, saying it implied that eating animal foods was a "psychological sickness". == See also == Food studies Moral psychology Non-vegetarianism Psychology of eating meat Speciesism Taboo
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
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|
food and drink Veganism List of vegan media == Notes == == References == == Further reading == Castricano, Jodey, and Rasmus R. Simonsen, eds. (2016). Critical Perspectives on Veganism. Basingstoke, United Kingdom: Palgrave Macmillan. Kanerva, Minna (2021). The New Meatways and Sustainability. Bielefeld, Germany: transcript Verlag. Herzog, Hal (2010). Some We Love, Some We Hate, Some We Eat. New York: Harper Collins. Joy, Melanie (2015). "Beyond carnism and toward rational, authentic food choices", TEDx talk. Monteiro, Christopher A., Tamara D. Pfeiler, Marcus D. Patterson and Michael A. Milburn (2017). "The Carnism Inventory: Measuring the ideology of eating animals". Appetite 113: 51–62. doi:10.1016/j.appet.2017.02.011. Potts, Annie, ed. (2016). Meat Culture. Leiden, Netherlands: Brill. Vialles, Noëlie (1994). Animal to Edible. Cambridge: Cambridge University Press.
|
{
"page_id": 39193418,
"source": null,
"title": "Carnism"
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Andrzej Sołtan (25 October 1897 – 10 December 1959) was a Polish nuclear physicist. He also worked on spectroscopy in the band between far ultraviolet and X-rays. During his visit to Caltech in 1932–33, together with H. Richard Crane and Charles Christian Lauritsen, he discovered a method for producing neutron beams, by bombarding lithium or beryllium nuclei with accelerated deuterons. He was appointed professor at Warsaw University in 1947, a member of the Polish Academy of Sciences in 1952, and in 1955 he became the first director of the Institute of Nuclear Studies in Świerk, Otwock County near Warsaw, now known as the National Centre for Nuclear Research. He served as president of the Polish Physical Society between 1952 and 1955. He is buried (with his wife Marta, also a physicist) in the "Avenue of the Meritorious" of Warsaw's Powązki Cemetery. The institute where he worked was renamed the Soltan Institute of Nuclear Studies in 1982. == References ==
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"page_id": 10685260,
"source": null,
"title": "Andrzej Sołtan"
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|
The Journal of Food Science is a peer-reviewed scientific journal that was established in 1936 and is published by John Wiley & Sons on behalf of the Institute of Food Technologists in Chicago, Illinois. From 1996 to 2005, it was ranked eighth among impact in scientific journals publishing food science and technology. == History == The journal was founded in 1936 as Food Research with Fred W. Tanner (University of Illinois at Urbana–Champaign) as editor in chief. Published bimonthly by Garrard Press, it was a publication that dealt with food science and technology research. The first issue had nine articles in it. By the end of 1936, 55 papers were published. In 1950, Food Research was purchased by the Institute of Food Technologists and Zoltan I. Kertesz was named Editor-In-Chief in 1951. Kertesz and most of his successors also served as editors of Food Technology, the institute's magazine founded in 1947. He was replaced by Martin S. Peterson in July 1952, who served until December 1960. George F. Stewart (University of California, Davis) took over in January 1961, renaming Food Research to it current name. He was succeeded by Walter M. Urbain in July 1966. Ernest J. Briskey edited from June 1970 until January 1971. In January 1971, all of the applied research articles were shifted from Food Technology to the Journal of Food Science and Bernard J. Liska became editor-in-chief until 1981. He was succeeded by Aaron E. Wasserman who stepped down in 1990. Robert E. Berry became editor-in-chief in 1990 and stayed until 1998. From 1996 the journal was sectioned by discipline (food chemistry, food engineering, food microbiology, nutrition, and sensory analysis). Subsequently, Owen R. Fennema was editor until September 2003, during which time the journal's publication frequency increased from six issues a year to its current nine
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{
"page_id": 8719182,
"source": null,
"title": "Journal of Food Science"
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|
issues. The current Editor-in-Chief of JFS is Edward Allen Foegeding, a distinguished professor of food chemistry at North Carolina State University though he will step down from that role at the end of 2020 after having served since 2012. Richard W. Hartel of the University of Wisconsin will take over starting in January 2021. Since 2007, the entire journal from its 1936 beginnings can be accessed online. == See also == Food portal == References == == External links == Official website Journal of Food Science information Non-profit journals information on Journal of Food Science
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{
"page_id": 8719182,
"source": null,
"title": "Journal of Food Science"
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The pulse vaccination strategy is a method used to eradicate an epidemic by repeatedly vaccinating a group at risk, over a defined age range, until the spread of the pathogen has been stopped. It is most commonly used during measles and polio epidemics to quickly stop the spread and contain the outbreak. == Mathematical model == Where T= time units is a constant fraction p of susceptible subjects vaccinated in a relatively short time. This yields the differential equations for the susceptible and vaccinated subjects as d S d t = μ N − μ S − β I N S , S ( n T + ) = ( 1 − p ) S ( n T − ) n = 0 , 1 , 2 , … {\displaystyle {\frac {dS}{dt}}=\mu N-\mu S-\beta {\frac {I}{N}}S,S(nT^{+})=(1-p)S(nT^{-})n=0,1,2,\dots } d V d t = − μ V , V ( n T + ) = V ( n T − ) + p S ( n T − ) n = 0 , 1 , 2 , … {\displaystyle {\frac {dV}{dt}}=-\mu V,V(nT^{+})=V(nT^{-})+pS(nT^{-})n=0,1,2,\dots } Further, by setting I = 0, one obtains that the dynamics of the susceptible subjects is given by: S ∗ ( t ) = 1 − p 1 − ( 1 − p ) E − μ T E − μ M O D ( t , T ) {\displaystyle S^{*}(t)=1-{\frac {p}{1-(1-p)E^{-\mu T}}}E^{-\mu MOD(t,T)}} and that the eradication condition is: R 0 ∫ 0 T S ∗ ( t ) d t < 1 {\displaystyle R_{0}\int _{0}^{T}{S^{*}(t)dt}<1} == See also == Critical community size Epidemic model Herd immunity Pulse Polio Ring vaccination Vaccine-naive == References == == External links == Immunisation Immunisation schedule for children in the UK. Published by the UK Department of Health. CDC.gov - 'National Immunization
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"page_id": 42863440,
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"title": "Pulse vaccination strategy"
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Program: leading the way to healthy lives', US Centers for Disease Control (CDC information on vaccinations) CDC.gov - Vaccines timeline History of Vaccines Medical education site from the College of Physicians of Philadelphia, the oldest medical professional society in the US Images of vaccine-preventable diseases
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{
"page_id": 42863440,
"source": null,
"title": "Pulse vaccination strategy"
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Yoel Rephaeli (Hebrew: יואל רפאלי) is an Israeli-American cosmologist. He is a Professor of Physics at Tel Aviv University, Israel. Rephaeli studies the Sunyaev-Zel'dovich effect [1] and the astrophysics of galaxy clusters. == References == == External links == Y. Rephaeli, "Comptonization Of The Cosmic Microwave Background: The Sunyaev-Zeldovich Effect", Annual Review of Astronomy and Astrophysics, Volume 33, 1995, pp. 541–580., Volume 33, 1995, pp. 541–580.
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{
"page_id": 5376849,
"source": null,
"title": "Yoel Rephaeli"
}
|
Paleotempestology is the study of past tropical cyclone activity by means of geological proxies as well as historical documentary records. The term was coined by American meteorologist Kerry Emanuel. == Examples == === Non-tropical examples === == See also == Tropical cyclone Tropical cyclone observation Tropical cyclones and climate change == Notes == == References == === Citations === === General sources === == Further reading == Elsner, James B.; Kara, A. Birol (1999). Hurricanes of the North Atlantic: Climate and Society. New York: Oxford University Press. pp. 49–51, 378. ISBN 978-0-19-512508-5. Huang, Yun (2009-01-01). "Sediment records of modern and prehistoric hurricane strikes in Weeks Bay, Alabama". LSU Master's Theses. doi:10.31390/gradschool_theses.1922. S2CID 135330841. Kar, Devyani (2010-01-01). "Integration of paleotempestology with coastal risk and vulnerability assessment: case studies from the Dominican Republic and Nicaragua". LSU Doctoral Dissertations. doi:10.31390/gradschool_dissertations.2009. S2CID 134409924. Knowles, Jason (2004-01-01). "Coastal lake-sediment records of prehistoric hurricane strikes in Honduras and Turks and Caicos Islands of the Caribbean basin". LSU Master's Theses. doi:10.31390/gradschool_theses.3433. S2CID 134921929. Liu, Kam-biu (2004). "Paleotempestology: Principles, Methods, and Examples from Gulf Coast Lake Sediments". In Murnane, R. J.; Liu, Kam-biu (eds.). Hurricanes and Typhoons: Past, Present, and Future. New York: Columbia University Press. pp. 13–57. ISBN 978-0-231-12388-4. Liu, Kam-biu (2007). "Paleotempestology". In Elias, Scott A. (ed.). Encyclopedia of Quaternary Science. Vol. 3. Amsterdam: Elsevier. pp. 1978–1986. ISBN 978-0-444-51922-1. Nott, Jonathan (2004). "Palaeotempestology: the study of prehistoric tropical cyclones—a review and implications for hazard assessment". Environment International. 30 (3): 433–447. Bibcode:2004EnInt..30..433N. doi:10.1016/j.envint.2003.09.010. PMID 14987874. Revkin, Andrew C. (July 24, 2001). "Experts Unearth a Stormy Past". The New York Times. Pouzet, Pierre; Maanan, Mohamed (2020). "Climatological influences on major storm events during the last millennium along the Atlantic coast of France". Scientific Reports. 10 (1): 12059. Bibcode:2020NatSR..1012059P. doi:10.1038/s41598-020-69069-w. PMC 7374694. == External links == Western North Atlantic
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{
"page_id": 72158034,
"source": null,
"title": "List of paleotempestology records"
}
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Basin 8,000 Year palaeotempestology Database 2018 palaeotempestology Resource Center Shipwrecks, tree rings and hurricanes
|
{
"page_id": 72158034,
"source": null,
"title": "List of paleotempestology records"
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The Juliá–Colonna epoxidation is an asymmetric poly-leucine catalyzed nucleophilic epoxidation of electron deficient olefins in a triphasic system. The reaction was reported by Sebastian Juliá at the Chemical Institute of Sarriá in 1980, with further elaboration by both Juliá and Stefano Colonna (Istituto di Chimica Industriale dell'Università, Milan, Italy). In the original triphasic protocol, the chalcone substrate is soluble in the organic phase, generally toluene or carbon tetrachloride. The alkaline hydrogen peroxide oxidant is soluble primarily in the aqueous phase, and the reaction occurs at the insoluble polymer layer at the interface of the two phases. Alternative biphasic and monophasic protocols have been developed with increased substrate accessibility and reaction rate. The efficient enantioselective catalytic epoxidation under mild conditions is of great synthetic utility. Not only are epoxides effective synthons for a range of transformations, they have a significant presence in natural products structures. Furthermore, the reaction has been effectively scaled up to industrially useful levels, with work conducted notably by Bayer and Evonik. Finally, the enzyme-like activity of the poly-amino acid segments is suggestive of a role of the reaction in the prebiotic origin of life. == Reaction mechanism == The Juliá–Colonna epoxidation is an asymmetric nucleophilic epoxidation of electron-deficient olefins such as α,β-unsaturated ketones. The general mechanism shown in Figure 2 applies to all nucleophilic epoxidations but is controlled in this reaction by the poly-leucine catalyst. The hydroperoxide anion and chalcone assemble in a complex with the poly-leucine catalyst before reacting to form a peroxide enolate intermediate. The intermediate subsequently closes, as controlled by the catalyst structure, to form the epoxide product stereoselectively. === Ternary complex formation === The poly-leucine strands demonstrate enzyme-like kinetics with a first-order dependence on and eventual saturation with both the hydroperoxide anion (KM= 30 mM) and the olefin substrate (KM=110 mM.) Kinetic study
|
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suggests that the reaction proceeds by random steady-state formation of a ternary (polyleucine+hydroperoxide anion+olefin) complex. Both substrates must bind prior to reaction, and while either may bind first, initial hydroperoxide binding is kinetically preferred. The rapid equilibrium enabling complex formation is followed by the rate-limiting formation of the peroxide enolate (Figure 3). === Mechanistic origin of stereoselectivity === All of the reactants associate with the polyleucine catalyst prior to reaction to form the hydroperoxide enolate intermediate. The catalyst orients the reactants and, even more significantly, the peroxide enolate intermediate by a series of hydrogen bonding interactions with the four N-terminal amino groups in the poly-leucine α-helix. While other models have been proposed, computations by Kelly et al. have suggested that the NH-2, NH-3, and NH-4 form an isosceles triangle available for hydrogen bonding as an intermediate-stabilizing oxyanion hole. While olefin binding to either the endo or exo face of the helix is sterically allowed, only endo binding orients the NH-4 group to bind with the hydroperoxide moiety allowing for hydroxide displacement in the final reaction step (Figure 4). == Catalyst == === Poly-amino acid selection === Enantioselectivity is maximized by poly-amino acid sequences containing the greatest α-helical content; these include poly-leucine and poly-alanine. Both poly-L- and poly-D-amino acids are available and cause the opposite stereoinduction. === Catalyst generation === The original poly-leucine catalysts were formed by reacting leucine-N-carboxyanhydrides with an initiator such as an amine, an alcohol or water (Figure 5). In triphasic systems, the polymer catalyst must be soaked in the organic solvent and peroxide solution to generate a gel prior to reaction. – Especially in biphasic systems, reaction time may be reduced and enantioselectivity increased by activating the catalyst with NaOH prior to reaction. Furthermore, in biphasic systems the polymer may be immobilized on polystyrene, polyethylene glycol (PEG),
|
{
"page_id": 29887314,
"source": null,
"title": "Juliá–Colonna epoxidation"
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or silica gel and formed into a paste. === Catalyst secondary structure === The active component of the catalyst assumes an α-helical structure where the four to five N-terminal residues are actively involved in catalysis. While active catalysts have been generated from scalemic leucine, consistent enantiomeric content must be maintained through the N-terminal region to give appropriate handedness to the structure. While the greatest enantioselectivity was originally observed when n=30 residues, a 10-mer leucine polypeptide is of sufficient length to provide significant enantioselectivity Following improvement of the original procedure, greater enantioselectivity has been observed for lower molecular weight polymers, presumably due to the greater number of N-termini available per mass used. == Scope == The Juliá–Colonna epoxidation of electron-deficient olefins was originally demonstrated with chalcones, but it was soon extended to other systems with electron withdrawing moieties such as α,β-unsaturated ketones, esters, and amides. The reaction has also demonstrated efficiency with sulfone substrates, and the scope of the reaction is being expanded with further methodological investigation. Several classes of substrates, however, are not suitable for the Juliá–Colonna Epoxidation. These include: compounds sensitive to hydroxide. compounds with acidic protons on the α or α’ positions. electron rich olefins. The nucleophilic epoxidation is naturally complementary in scope to electrophilic epoxidations such as the Sharpless epoxidation and Jacobsen epoxidation. == Stereoselectivity == === Catalyst structure === The stereoinduction of the Juliá–Colonna epoxidation is dependent on the α-helical secondary structure of the poly-leucine catalyst. While the consistent stereochemistry of the N-terminal amino acids is necessary for this induction, even a 10-mer leucine polypeptide is of sufficient length to provide significant enantioselectivity. === Chiral amplification by scalemic catalysts === This dependence solely on the N-terminal region of the helix is most pronounced in enantioselective stereoinduction by scalemic catalysts. Even a 40% enantiomeric excess of L
|
{
"page_id": 29887314,
"source": null,
"title": "Juliá–Colonna epoxidation"
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|
vs. D-leucine in catalyst formation can yield the same enantiomeric enriched epoxide as the enantiopure catalyst. The relationship between catalyst and product enantiopurity can be closely approximated with a Bernoullian statistical model: een=(Ln-Dn)/(Ln+Dn) where L and D are the proportions of L- and D-leucine used to generate the catalytic polymers and n is the length of the catalytic component. Chiral amino acids, including leucine, have been generated in electrical discharge experiments designed to mimic the prebiotic conditions on Earth, and they have been found in scalemic mixtures in meteorites. It has been suggested that poly-amino acid fragments analogous to the Juliá–Colonna catalyst may have been initiated by imidazole or cyanide derivatives, and the resulting fragments may have played a catalytic role in the origin of enantiomeric enrichment ubiquitous in life today. == Variations == === Silica-grafted catalysts === Silica-grafted polyleucine has been shown to effectively catalyze epoxidation of α,β-unsaturated aromatic ketones. The silica graft allows for the catalyst to be easily recovered with only mild loss of activity and is particularly useful for scale-up reactions. === Biphasic (non-aqueous) reaction conditions === For the alternative biphasic protocol, the olefin substrate is dissolved in tetrahydrofuran (THF) along with the urea hydrogen peroxide (UHP) oxidant and a tertiary amine base such as 8-diazabicyclo[5.4.0]undec-7-ene (DBU.) The immobilized polymer catalyst forms a paste which serves as the reaction site. The two phase reaction conditions extended the range of enones to which the reaction could be applied. === Monophasic reaction conditions with PEG-immobilized polyleucine === A soluble initiator O,O′-bis(2-aminoethyl)polyethylene glycol (diaminoPEG) for poly-leucine assembly was utilized to generate a THF-soluble triblock polymer. Utilization of this catalyst in homogeneous reaction conditions enabled marked extension of the methodology to α,β-unsaturated ketones, dienes, and bis-dienes. === Phase transfer co-catalysis === Addition of tetrabutylammonium bromide as a phase transfer catalyst
|
{
"page_id": 29887314,
"source": null,
"title": "Juliá–Colonna epoxidation"
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|
dramatically increases the rate of reaction. The co-catalyst is presumed to increase the concentration of the peroxide oxidant in the organic phase enabling more efficient access to the reactive ternary complex. These conditions were developed for application to two phase systems but also function for three phase systems and have been utilized up to the 100g scale === Scale-up === Immobilized catalysts have been used in membrane reactors and are being investigated for application to continuous flow fixed bed reactors. == Applications to synthesis == === Total synthesis of Diltiazem === Adger et al. utilized the biphasic Juliá–Colonna epoxidation with immobilized poly-L-leucine (I-PLL) and urea hydrogen peroxide (UHP), and 8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the key step in the efficient synthesis of Diltiazem (Figure 6.) Diltiazem is a commercially available pharmaceutical which acts as a calcium channel blocker. === Total synthesis of (+)-clausenamide === Cappi et al. utilized the Juliá–Colonna epoxidation with PEG-immobilized poly-L-leucine (PEG-PLL) and DABCO hydrogen peroxide (DABCO-H2O2) or urea hydrogen peroxide (UHP) in a miniature fixed-bed continuous flow reactor system (Figure 7.) This protocol was exploited to synthesize (+)-clausenamide as a proof of concept in the development of the novel reaction protocol; (+)-clausenamide exhibits anti-amnesiac and hepatoprotective activity. === Total synthesis of (+)-goniotriol 7, (+)-goniofufurone 8, (+)-8-acetylgoniotriol 9 and gonio-pypyrone === Chen et al. utilized the biphasic Juliá–Colonna Epoxidation protocol with urea hydrogen peroxide (UHP), poly-L-leucine (PLL), and 8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a key step in the synthesis of a family of styryl lactones isolated from Goniothalamus giganteus (Figure 8.) These compounds, including (+)-goniotriol 7, (+)-goniofufurone 8, (+)-8-acetylgoniotriol 9 and gonio-pypyrone, have demonstrated cytotoxic activity against human tumor cells. == See also == Prilezhaev reaction Jørgensen epoxidation Asymmetric nucleophilic epoxidation == References == == External links == https://www.organic-chemistry.org/Highlights/2004/22November.shtm
|
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"page_id": 29887314,
"source": null,
"title": "Juliá–Colonna epoxidation"
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Free carrier absorption occurs when a material absorbs a photon, and a carrier (electron or hole) is excited from an already-excited state to another, unoccupied state in the same band (but possibly a different subband). This intraband absorption is different from interband absorption because the excited carrier is already in an excited band, such as an electron in the conduction band or a hole in the valence band, where it is free to move. In interband absorption, the carrier starts in a fixed, nonconducting band and is excited to a conducting one. In the simplest approximation, the Drude model, free carrier absorption is proportional to the square of the wavelength. == Quantum mechanical approach == It is well known that the optical transition of electrons and holes in the solid state is a useful clue to understand the physical properties of the material. However, the dynamics of the carriers are affected by other carriers and not only by the periodic lattice potential. Moreover, the thermal fluctuation of each electron should be taken into account. Therefore, a statistical approach is needed. To predict the optical transition with appropriate precision, one chooses an approximation, called the assumption of quasi-thermal distributions, of the electrons in the conduction band and of the holes in the valence band. In this case, the diagonal components of the density matrix become negligible after introducing the thermal distribution function, ρ λ λ 0 = 1 e ( ε λ , k − μ ) β + 1 = f λ , k {\displaystyle \rho _{\lambda \lambda }^{0}={\frac {1}{e^{(\varepsilon _{\lambda ,k}-\mu )\beta }+1}}=f_{\lambda ,k}} This is the Fermi–Dirac distribution for the distribution of electron energies ε {\displaystyle \varepsilon } . Thus, summing over all possible states (l and k) yields the total number of carriers N. N λ =
|
{
"page_id": 22350680,
"source": null,
"title": "Free carrier absorption"
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|
∑ λ f λ , k {\displaystyle N_{\lambda }=\sum \limits _{\lambda }{f_{\lambda ,k}}} === The optical susceptibility === Using the above distribution function, the time evolution of the density matrix can be ignored, which greatly simplifies the analysis. ρ c v i n t ( k , t ) = ∫ d ω 2 π d c v ε ( ω ) e i ( ε c , k − ε v , k − ω ) t ℏ ( ε c , k − ε v , k − ω − i γ ) ( f v , k − f c , k ) {\displaystyle \rho _{cv}^{\mathop {\rm {int}} }(k,t)=\int {{\frac {d\omega }{2\pi }}{\frac {d_{cv}\varepsilon (\omega )e^{i(\varepsilon _{c,k}-\varepsilon _{v,k}-\omega )t}}{\hbar (\varepsilon _{c,k}-\varepsilon _{v,k}-\omega -i\gamma )}}(f_{v,k}-f_{c,k})}} The optical polarization is P ( t ) = tr [ ρ ( t ) d ] {\displaystyle P(t)={\text{tr}}[\rho (t)d]} With this relation and after adjusting the Fourier transformation, the optical susceptibility is χ ( ω ) = − ∑ k | d c v | 2 L 3 ( f v , k − f c , k ) ( 1 ℏ ( ε v , k − ε c , k + ω + i γ ) − 1 ℏ ( ε c , k − ε v , k + ω + i γ ) ) {\displaystyle \chi (\omega )=-\sum \limits _{k}{\frac {\left|{d_{cv}}\right|^{_{2}}}{L^{3}}}(f_{v,k}-f_{c,k})\left({{\frac {1}{\hbar (\varepsilon _{v,k}-\varepsilon _{c,k}+\omega +i\gamma )}}-{\frac {1}{\hbar (\varepsilon _{c,k}-\varepsilon _{v,k}+\omega +i\gamma )}}}\right)} === Absorption coefficient === The transition amplitude corresponds to the absorption of energy and the absorbed energy is proportional to the optical conductivity which is the imaginary part of the optical susceptibility after frequency is multiplied. Therefore, in order to obtain the absorption coefficient that is crucial quantity for investigation of electronic structure, we can
|
{
"page_id": 22350680,
"source": null,
"title": "Free carrier absorption"
}
|
use the optical susceptibility. α ( ω ) = 4 π ω n b c χ ″ ( ω ) = 4 π ω n b c ∑ k | d c v | 2 ( f v , k − f c , k ) δ ( ℏ ( ε v , k − ε c , k + ω ) ) {\displaystyle {\begin{aligned}\alpha (\omega )&={\frac {4\pi \omega }{n_{b}c}}\chi ''(\omega )\\&={\frac {4\pi \omega }{n_{b}c}}\sum \limits _{k}{\left|{d_{cv}}\right|^{2}(f_{v,k}-f_{c,k})\delta (\hbar (\varepsilon _{v,k}-\varepsilon _{c,k}+\omega ))}\end{aligned}}} The energy of free carriers is proportional to the square of momentum ( E ∼ k 2 {\displaystyle E\sim k^{2}} ). Using the band gap energy E g {\displaystyle E_{g}} and the electron-hole distribution function, we can obtain the absorption coefficient with some mathematical calculation. The final result is α ( ω ) = α 0 d ℏ ω E 0 ( ℏ ω − E g − E 0 ( d ) E 0 ) ( d − 2 ) / 2 ∑ k Θ ( ℏ ω − E g − E 0 ( d ) ) A ( ω ) {\displaystyle \alpha (\omega )=\alpha _{0}^{d}{\frac {\hbar \omega }{E_{0}}}\left({\frac {\hbar \omega -E_{g}-E_{0}^{(d)}}{E_{0}}}\right)^{(d-2)/2}\sum \limits _{k}{\Theta (\hbar \omega -E_{g}-E_{0}^{(d)})A(\omega )}} This result is important to understand the optical measurement data and the electronic properties of metals and semiconductors. The absorption coefficient is negative when the material supports stimulated emission, which is the basis for the operation of lasers, particularly semiconductor laser. == References == 1. H. Haug and S. W. Koch, "[1] ", World Scientific (1994). sec.5.4 a
|
{
"page_id": 22350680,
"source": null,
"title": "Free carrier absorption"
}
|
A solvated electron is a free electron in a solution, in which it behaves like an anion. An electron's being solvated in a solution means it is bound by the solution. The notation for a solvated electron in formulas of chemical reactions is "e−". Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and many other solvents – in fact, in any solvent that mediates outer-sphere electron transfer. The solvated electron is responsible for a great deal of radiation chemistry. == Ammonia solutions == Liquid ammonia will dissolve all of the alkali metals and other electropositive metals such as Ca, Sr, Ba, Eu, and Yb (also Mg using an electrolytic process), giving characteristic blue solutions. For alkali metals in liquid ammonia, the solution is blue when dilute and copper-colored when more concentrated (> 3 molar). These solutions conduct electricity. The blue colour of the solution is due to ammoniated electrons, which absorb energy in the visible region of light. The diffusivity of the solvated electron in liquid ammonia can be determined using potential-step chronoamperometry. Solvated electrons in ammonia are the anions of salts called electrides. Na + 6 NH3 → [Na(NH3)6]+ + e− The reaction is reversible: evaporation of the ammonia solution produces a film of metallic sodium. === Case study: Li in NH3 === A lithium–ammonia solution at −60 °C is saturated at about 15 mol% metal (MPM). When the concentration is increased in this range electrical conductivity increases from 10−2 to 104 Ω−1cm−1 (larger than liquid mercury). At around 8 MPM, a "transition to the metallic state" (TMS) takes place (also called a "metal-to-nonmetal transition" (MNMT)). At 4 MPM a liquid-liquid phase separation takes place: the less dense gold-colored phase becomes immiscible from a
|
{
"page_id": 4459356,
"source": null,
"title": "Solvated electron"
}
|
denser blue phase. Above 8 MPM the solution is bronze/gold-colored. In the same concentration range the overall density decreases by 30%. == Other solvents == Alkali metals also dissolve in some small primary amines, such as methylamine and ethylamine and hexamethylphosphoramide, forming blue solutions. Tetrahydrofuran (THF) dissolves alkali metal, but a Birch reduction (see § Applications) analogue does not proceed without a diamine ligand. Solvated electron solutions of the alkaline earth metals magnesium, calcium, strontium and barium in ethylenediamine have been used to intercalate graphite with these metals. == Water == Solvated electrons are involved in the reaction of alkali metals with water, even though the solvated electron has only a fleeting existence. Below pH = 9.6 the hydrated electron reacts with the hydronium ion giving atomic hydrogen, which in turn can react with the hydrated electron giving hydroxide ion and usual molecular hydrogen H2. Solvated electrons can be found even in the gas phase. This implies their possible existence in the upper atmosphere of Earth and involvement in nucleation and aerosol formation. Its standard electrode potential value is −2.88 V. The equivalent conductivity of 177 Mho cm2 is similar to that of hydroxide ion. This value of equivalent conductivity corresponds to a diffusivity of 4.75 × 10 − 5 {\displaystyle \times 10^{-5}} cm2s−1. == Reactivity == Although quite stable, the blue ammonia solutions containing solvated electrons degrade rapidly in the presence of catalysts to give colorless solutions of sodium amide: 2 [Na(NH3)6]+e− → H2 + 2 NaNH2 + 10 NH3 Electride salts can be isolated by the addition of macrocyclic ligands such as crown ether and cryptands to solutions containing solvated electrons. These ligands strongly bind the cations and prevent their re-reduction by the electron. [Na(NH3)6]+e− + cryptand → [Na(cryptand)]+e−+ 6 NH3 The solvated electron reacts with oxygen to
|
{
"page_id": 4459356,
"source": null,
"title": "Solvated electron"
}
|
form a superoxide radical (O2.−). With nitrous oxide, solvated electrons react to form nitroxyl radicals (NO.). == Uses == Solvated electrons are involved in electrode processes, a broad area with many technical applications (electrosynthesis, electroplating, electrowinning). A specialized use of sodium-ammonia solutions is the Birch reduction. Other reactions where sodium is used as a reducing agent also are assumed to involve solvated electrons, e.g. the use of sodium in ethanol as in the Bouveault–Blanc reduction. Work by Cullen et al. showed that metal-ammonia solutions can be used to intercalate a range of layered materials, which can then be exfoliated in polar, aprotic solvents, to produce ionic solutions of two-dimensional materials. An example of this is the intercalation of graphite with potassium and ammonia, which is then exfoliated by spontaneous dissolution in THF to produce a graphenide solution. == History == The observation of the color of metal-electride solutions is generally attributed to Humphry Davy. In 1807–1809, he examined the addition of grains of potassium to gaseous ammonia (liquefaction of ammonia was invented in 1823). James Ballantyne Hannay and J. Hogarth repeated the experiments with sodium in 1879–1880. W. Weyl in 1864 and C. A. Seely in 1871 used liquid ammonia, whereas Hamilton Cady in 1897 related the ionizing properties of ammonia to that of water. Charles A. Kraus measured the electrical conductance of metal ammonia solutions and in 1907 attributed it to the electrons liberated from the metal. In 1918, G. E. Gibson and W. L. Argo introduced the solvated electron concept. They noted based on absorption spectra that different metals and different solvents (methylamine, ethylamine) produce the same blue color, attributed to a common species, the solvated electron. In the 1970s, solid salts containing electrons as the anion were characterized. == References == == Further reading ==
|
{
"page_id": 4459356,
"source": null,
"title": "Solvated electron"
}
|
In statistics, econometrics, epidemiology, genetics and related disciplines, causal graphs (also known as path diagrams, causal Bayesian networks or DAGs) are probabilistic graphical models used to encode assumptions about the data-generating process. Causal graphs can be used for communication and for inference. They are complementary to other forms of causal reasoning, for instance using causal equality notation. As communication devices, the graphs provide formal and transparent representation of the causal assumptions that researchers may wish to convey and defend. As inference tools, the graphs enable researchers to estimate effect sizes from non-experimental data, derive testable implications of the assumptions encoded, test for external validity, and manage missing data and selection bias. Causal graphs were first used by the geneticist Sewall Wright under the rubric "path diagrams". They were later adopted by social scientists and, to a lesser extent, by economists. These models were initially confined to linear equations with fixed parameters. Modern developments have extended graphical models to non-parametric analysis, and thus achieved a generality and flexibility that has transformed causal analysis in computer science, epidemiology, and social science. Recent advances include the development of large-scale causality graphs, such as CauseNet, which compiles over 11 million causal relations extracted from web sources to support causal question answering and reasoning. == Construction and terminology == The causal graph can be drawn in the following way. Each variable in the model has a corresponding vertex or node and an arrow is drawn from a variable X to a variable Y whenever Y is judged to respond to changes in X when all other variables are being held constant. Variables connected to Y through direct arrows are called parents of Y, or "direct causes of Y," and are denoted by Pa(Y). Causal models often include "error terms" or "omitted factors" which represent all
|
{
"page_id": 44239711,
"source": null,
"title": "Causal graph"
}
|
unmeasured factors that influence a variable Y when Pa(Y) are held constant. In most cases, error terms are excluded from the graph. However, if the graph author suspects that the error terms of any two variables are dependent (e.g. the two variables have an unobserved or latent common cause) then a bidirected arc is drawn between them. Thus, the presence of latent variables is taken into account through the correlations they induce between the error terms, as represented by bidirected arcs. == Fundamental tools == A fundamental tool in graphical analysis is d-separation, which allows researchers to determine, by inspection, whether the causal structure implies that two sets of variables are independent given a third set. In recursive models without correlated error terms (sometimes called Markovian), these conditional independences represent all of the model's testable implications. == Example == Suppose we wish to estimate the effect of attending an elite college on future earnings. Simply regressing earnings on college rating will not give an unbiased estimate of the target effect because elite colleges are highly selective, and students attending them are likely to have qualifications for high-earning jobs prior to attending the school. Assuming that the causal relationships are linear, this background knowledge can be expressed in the following structural equation model (SEM) specification. Model 1 Q 1 = U 1 C = a ⋅ Q 1 + U 2 Q 2 = c ⋅ C + d ⋅ Q 1 + U 3 S = b ⋅ C + e ⋅ Q 2 + U 4 , {\displaystyle {\begin{aligned}Q_{1}&=U_{1}\\C&=a\cdot Q_{1}+U_{2}\\Q_{2}&=c\cdot C+d\cdot Q_{1}+U_{3}\\S&=b\cdot C+e\cdot Q_{2}+U_{4},\end{aligned}}} where Q 1 {\displaystyle Q_{1}} represents the individual's qualifications prior to college, Q 2 {\displaystyle Q_{2}} represents qualifications after college, C {\displaystyle C} contains attributes representing the quality of the college attended, and S {\displaystyle
|
{
"page_id": 44239711,
"source": null,
"title": "Causal graph"
}
|
S} the individual's salary. Figure 1 is a causal graph that represents this model specification. Each variable in the model has a corresponding node or vertex in the graph. Additionally, for each equation, arrows are drawn from the independent variables to the dependent variables. These arrows reflect the direction of causation. In some cases, we may label the arrow with its corresponding structural coefficient as in Figure 1. If Q 1 {\displaystyle Q_{1}} and Q 2 {\displaystyle Q_{2}} are unobserved or latent variables their influence on C {\displaystyle C} and S {\displaystyle S} can be attributed to their error terms. By removing them, we obtain the following model specification: Model 2 C = U C S = β C + U S {\displaystyle {\begin{aligned}C&=U_{C}\\S&=\beta C+U_{S}\end{aligned}}} The background information specified by Model 1 imply that the error term of S {\displaystyle S} , U S {\displaystyle U_{S}} , is correlated with C's error term, U C {\displaystyle U_{C}} . As a result, we add a bidirected arc between S and C, as in Figure 2. Since U S {\displaystyle U_{S}} is correlated with U C {\displaystyle U_{C}} and, therefore, C {\displaystyle C} , C {\displaystyle C} is endogenous and β {\displaystyle \beta } is not identified in Model 2. However, if we include the strength of an individual's college application, A {\displaystyle A} , as shown in Figure 3, we obtain the following model: Model 3 Q 1 = U 1 A = a ⋅ Q 1 + U 2 C = b ⋅ A + U 3 Q 2 = e ⋅ Q 1 + d ⋅ C + U 4 S = c ⋅ C + f ⋅ Q 2 + U 5 , {\displaystyle {\begin{aligned}Q_{1}&=U_{1}\\A&=a\cdot Q_{1}+U_{2}\\C&=b\cdot A+U_{3}\\Q_{2}&=e\cdot Q_{1}+d\cdot C+U_{4}\\S&=c\cdot C+f\cdot Q_{2}+U_{5},\end{aligned}}} By removing the latent variables from the
|
{
"page_id": 44239711,
"source": null,
"title": "Causal graph"
}
|
model specification we obtain: Model 4 A = a ⋅ Q 1 + U A C = b ⋅ A + U C S = β ⋅ C + U S , {\displaystyle {\begin{aligned}A&=a\cdot Q_{1}+U_{A}\\C&=b\cdot A+U_{C}\\S&=\beta \cdot C+U_{S},\end{aligned}}} with U A {\displaystyle U_{A}} correlated with U S {\displaystyle U_{S}} . Now, β {\displaystyle \beta } is identified and can be estimated using the regression of S {\displaystyle S} on C {\displaystyle C} and A {\displaystyle A} . This can be verified using the single-door criterion, a necessary and sufficient graphical condition for the identification of a structural coefficients, like β {\displaystyle \beta } , using regression. == References ==
|
{
"page_id": 44239711,
"source": null,
"title": "Causal graph"
}
|
Jessica Hua is an associate professor in the Department of Biological Sciences at Binghamton University, NY. In addition Hua is the Director for the Center for Integrated Watershed Studies at Binghamton University which focuses on understanding watersheds and the human influences on them through research. She is a herpetologist and oversees her own lab, The Hua Lab, where they focus on ecological interactions, evolutionary processes and ecological-evolutionary feedbacks. Hua's background has led to her appreciation of education with coming from a refugee family who "epitomizes the concept of the American Dream". Her research aims to help others gain opportunities while also establishing a lab that is inclusive and diverse. Hua also enjoys a variety of sports and plays disc golf professionally since 2016. == Education == Hua received her Bachelor of Arts Degree in Biology and Kinesiology from Southwestern University, TX, in 2008 where she had gone to the university for basketball and picked biology for her major with the intention of going to medical school. However, in her Junior year of college she had gotten a lab position with Ben Pierce who ultimately changed her career interests towards research and studying herpetology. Following her completion of her B.A., Hua went to the University of Pittsburgh, PA, and received her Ph.D. in 2014. Hua worked with Rick Relyea on researching the effects of contaminants on amphibians. This experience led Hua to become a Herpetologists' League member. The article "Differential Host Susceptibility to Batrachochytrium dendrobatidis, an Emerging Amphibian Pathogen" was published during her graduate education in which she was a co-author for. The research was focused on a fungal pathogen that afflicted amphibians, called Batrachochytrium dendrobatidis, and how amphibian species varied in their sensitivity to this pathogen. == Career and research == === Post-doctorate === Hua completed her postdoc at Purdue
|
{
"page_id": 70585185,
"source": null,
"title": "Jessica Hua"
}
|
University, IN, from 2014 to 2015. She had studied amphibian disease ecology along with her advisor Jason Hoverman. In her research article on "The contribution of phenotypic plasticity to the evolution of insecticide tolerance in amphibian populations" she discussed how wood frog populations were seen to have higher tolerance to the pesticide carbaryl when they lived closer to agriculture compared to wood frog populations that were further from farmlands, which follows the evolutionary responses known for pesticides. There was also constitutive tolerance (tolerance that is always expressed despite environmental conditions) seen for frog populations near agriculture but was not seen in populations that were away from agriculture, leading Hua to note that genetic assimilation, a process cause by phenotypic plasticity, may be influencing evolutionary responses with unique environments. === Teaching === At Binghamton University Hua has taught a variety of courses on ecology. These classes aim to educate students on the principles of ecology, how to apply ecology, the significance and diversity of wetlands, as well as how humans impact ecology. === Research === The Hua Lab investigates mechanisms involving ecology, evolution, and ecological-evolutionary feedbacks. Hua focuses her lab's research on understanding the impact of chemicals on aquatic systems through ecological and evolutionary mechanisms while working with a variety of organisms from amphibians to insects to isopods. ==== Ecotoxicology ==== Researches human interaction in ecology to understand how human-related activities, such as pollution, has impacted aquatic ecosystems at all levels of the ecosystem. Questions being explored involve species interactions, responses to pollutants and how human activities impact ecological interactions. To study ecotoxicology, field research is conducted as well as DNA extractions, mesocosm studies and a variety of assays including ones on toxicity, behaviors and waterborne corticosterone. ==== Evotoxicology ==== This is an evolutionary approach on toxicology interested in researching if
|
{
"page_id": 70585185,
"source": null,
"title": "Jessica Hua"
}
|
wildlife can become tolerant to pollutants through evolving tolerance to toxins such as pesticides. Model systems of wood frogs are used to study this topic since wood frogs have a high degree of variance with their pollutant tolerance. In lab they have seen that wood frog populations near agriculture have higher tolerance to the insecticides which shows evolved tolerance to pesticides. ==== Ecological-evolutionary feedbacks (disease ecology) ==== This area of research focuses on human activities impacting ecology through studying evolution. The questions asked here consist of how evolving pollutant tolerance can be associated with ecological costs or how plasticity to pollutants influence species relationships and interactions in the environment. Three types of parasites have been significant in this topic of research including trematodes, Ranavirus and Batrachochytrium dendrobatidis. Future directions with this research involve collaborations with varying people and labs such as Devin Jones, Relyea, Hoverman labs, Obed Hernandez Gomez and Ivan Gomez-Mestre. == Outreach == The Hua Lab does a variety of outreach in their community from the local elementary schools up to high school students and the general public to learn and interact with ecology hands-on. Hua had stated that "We're hoping to change perceptions and decouple the idea of 'these are humans — and this is wildlife.' Instead, we want people to realize that everything is connected". She views that communicating research effectively to the broader population is vital to making a difference in the world. === Hua Lab Wild Waders === This program incorporates field ecology with art to create a hands-on experience with studying nature in order to showcase the diversity of wetland organisms, discuss current issues putting these ecosystems at risk and to illustrate the significance of ecological and evolutionary perspectives for conservation of wetlands. The Hua Lab has hosted art shows for this program
|
{
"page_id": 70585185,
"source": null,
"title": "Jessica Hua"
}
|
including in 2017 called "Where the Wetlands End" and in 2016 "Tadpoles, Trematodes, and Toxins- Oh My!". One art show Hua had measured how effective this outreach was in the community by doing pre and post surveys which lead to there being a 20% increase in understanding the importance of wetlands. === Evolution: Teacher's K-12 Workshop === Aims to explain the theory of evolution through scientific content and instructional strategies in a 6-day workshop to high school teachers who in turn will teach their classrooms these concepts. === Creek Connections === Introduces high schoolers to the waterways in their local community with the partnership of Allegheny College and K-12 schools. === Humans, Chemicals, and the Environment: Teacher's K-12 Workshop === Instructs teachers on current research in ecotoxicology to improve knowledge on how chemicals influence nature with a focus on ecological and evolutionary principles in a 6-day workshop. === Fish Hatchery Open House === An educational exhibit for the public about wildlife habitats with the partnership of PA State Hatchery. == Grants == Hua had most recently received the National Science Foundation Career Award which the grant provides $947,030 for her research on evolutionary disease ecology. The project is titled "Evolutionary Disease Ecology - Can Evolutionary Responses to Environmental Change Modify the Biodiversity-Disease Relationship?" and will receive funding from March 2022 through February 2027. This award will allow Hua to dive further in her research to understand if variances in tolerance to pesticides affect biodiversity and its relationship with disease susceptibility since increased biodiversity is usually seen to have decreased susceptibility to diseases, however this concept is not fully understood. There is also an educational aspect to this project to showcase the interconnections of ecology and disease by featuring a citizen science program where third-grade students and their teachers from local
|
{
"page_id": 70585185,
"source": null,
"title": "Jessica Hua"
}
|
communities can learn about data collection in a hands-on manner which will be used by the lab and they will get to learn about biodiversity and its relationship with disease. Another grant Hua has received for $251,407 was the National Science Foundation Division of Environmental Biology Population and Community Ecology (2017-2022). == Honors and awards == == Select publications == Searle, C.L., Gervasi, S.S., Hua, J., Hammond, J.I., Relyea, R.A., Olson, D.H. and Blaustein, A.R. (2011), Differential Host Susceptibility to Batrachochytrium dendrobatidis, an Emerging Amphibian Pathogen. Conservation Biology, 25: 965-974. https://doi.org/10.1111/j.1523-1739.2011.01708.x Hua, J., Morehouse, N.I. and Relyea, R. (2013), Pesticide tolerance in amphibians: induced tolerance in susceptible populations, constitutive tolerance in tolerant populations. Evol Appl, 6: 1028-1040. https://doi.org/10.1111/eva.12083 Gervasi, S.S., Urbina, J., Hua, J., Chestnut, T., Relyea, R., and Blaustein, A.R. (2013), Experimental Evidence for American Bullfrog (Lithobates catesbeianus) Susceptibility to Chytrid Fungus (Batrachochytrium dendrobatidis). EcoHealth, 10:166–171. https://doi.org/10.1007/s10393-013-0832-8 Hua, J. and Relyea, R. (2014), Chemical cocktails in aquatic systems: Pesticide effects on the response and recovery of >20 animal taxa. Environmental Pollution, 189: 18-26. https://doi.org/10.1016/j.envpol.2014.02.007 Miles, J.C., Hua J., Sepulveda, M.S., Krupke, C.H. and Hoverman, J.T. (2018), Correction: Effects of clothianidin on aquatic communities: Evaluating the impacts of lethal and sublethal exposure to neonicotinoids. PLOS ONE 13(3): e0194634. https://doi.org/10.1371/journal.pone.0194634 Shidemantle, G., Buss, N. and Hua, J. (2022), Are glucocorticoids good indicators of disturbance across populations that exhibit cryptic variation in contaminant tolerance?. Animal Conservation, 25: 273-284. https://doi.org/10.1111/acv.12737 == References == == External links == Jessica Hua publications indexed by Google Scholar The Hua Lab Instagram @hua_lab_uw
|
{
"page_id": 70585185,
"source": null,
"title": "Jessica Hua"
}
|
A "red neuron" (acidophilic or "eosinophilic" neuron) is a pathological finding in neurons, generally of the central nervous system, indicative of acute neuronal injury and subsequent apoptosis or necrosis. Acidophilic neurons are often found in the first 12–24 hours after an ischemic injury such as a stroke. Since neurons are permanent cells, they are most susceptible to hypoxic injury. The red coloration is due to pyknosis or degradation of the nucleus and loss of Nissl bodies which are normally stained blue (basophilic) on hematoxylin & eosin staining (H&E stain). This leaves only the degraded proteins which stains red (eosinophilic). Acidophilic neurons also can be stained with acidic dyes other than eosin (e.g. acid fuchsin and light green yellowish). == References ==
|
{
"page_id": 42666851,
"source": null,
"title": "Red neuron"
}
|
A conservative replacement (also called a conservative mutation or a conservative substitution or a homologous replacement) is an amino acid replacement in a protein that changes a given amino acid to a different amino acid with similar biochemical properties (e.g. charge, hydrophobicity and size). Conversely, a radical replacement, or radical substitution, is an amino acid replacement that exchanges an initial amino acid by a final amino acid with different physicochemical properties. == Description == There are 20 naturally occurring amino acids, however some of these share similar characteristics. For example, leucine and isoleucine are both aliphatic, branched hydrophobes. Similarly, aspartic acid and glutamic acid are both small, negatively charged residues. Although there are many ways to classify amino acids, they are often sorted into six main classes on the basis of their structure and the general chemical characteristics of their side chains (R groups). Physicochemical distances aim at quantifying the intra-class and inter-class dissimilarity between amino acids based on their measurable properties, and many such measures have been proposed in the literature. Owing to their simplicity, two of the most commonly used measures are the ones of Grantham (1974) and Miyata et al (1979). A conservative replacement is therefore an exchange between two amino acids separated by a small physicochemical distance. Conversely, a radical replacement is an exchange between two amino acids separated by a large physicochemical distance. == Impact on function == Conservative replacements in proteins often have a better effect on function than non-conservative replacements. The reduced effect of conservative replacements on function can also be seen in the occurrence of different replacements in nature. Non-conservative replacements between proteins are far more likely to be removed by natural selection due to their deleterious effects. == See also == Segregating site Ultra-conserved element Sequence alignment Sequence alignment software ==
|
{
"page_id": 44632934,
"source": null,
"title": "Conservative replacement"
}
|
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