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49,732,031 | https://en.wikipedia.org/wiki/Transition%20metal%20NHC%20complex | In coordination chemistry, a transition metal NHC complex is a metal complex containing one or more N-heterocyclic carbene ligands. Such compounds are the subject of much research, in part because of prospective applications in homogeneous catalysis. One such success is the second generation Grubbs catalyst.
Historically, N-heterocyclic carbenes were thought to mimic properties of tertiary phosphines. Many steric and electronic differences exist between the two ligands. Compared to phosphine ligands, NHC ligands' cone angle is more complex. The imidazole ring of the NHC ligand is angled away from the metal center, yet the substituents at the 1,3 positions of the imidazole ring are angled towards it. The presence of the ligand inside of the metal coordination sphere affects the metal reactivity. In terms of electronic effects, NHC are often stronger sigma donation.
Synthesis
From free NHCs
The popularization of NHC ligands can be traced to Arduengo, who reported the deprotonation of dimesitylimidazolium cation to give IMes. IMes is a free NHC that can be used as a ligand. Other NHCs have been isolated as the free ligands. Aside from IMes, another important NHC ligand is IPr, which features diisopropylphenyl groups in place of the mesityl groups. NHCs with saturated backbones include SIMes and SIPr.
Transmetallation of silver-NHC reagents
Usually, transition metal NHC complexes are prepared less directly. A popular method entails transmetallation of silver-NHC complexes. Such reagents are generated by the reaction of silver(I) oxide with the imidazolium salt.
Other methods
A third method involves decarboxylation of NHC-carboxylates. In this approach, N-methylimidazoles react with methyl formate to give zwitterionic N,N'-dimethylimidazolium-2-carboxylate. This zwitterion decarboxylates in the presence of metal ions to give N,N'dimethylimidazolidene-based NHC complexes.
See also
Palladium–NHC complex
References
Organometallic chemistry
Transition metals
Coordination complexes
Coordination chemistry | Transition metal NHC complex | Chemistry | 492 |
66,984 | https://en.wikipedia.org/wiki/Reforestation | Reforestation is the practice of restoring previously existing forests and woodlands that have been destroyed or damaged. The prior forest destruction might have happened through deforestation, clearcutting or wildfires. Three important purposes of reforestation programs are for harvesting of wood, for climate change mitigation, and for ecosystem and habitat restoration purposes. One method of reforestation is to establish tree plantations, also called plantation forests. They cover about 131 million ha worldwide, which is 3% of the global forest area and 45% of the total area of planted forests.
Globally, planted forests increased from 4.1% to 7.0% of the total forest area between 1990 and 2015. Plantation forests made up 280 million ha (hectare) in 2015, an increase of about 40 million ha in the previous ten years. Of the planted forests worldwide, 18% of that area consists of exotic or introduced species while the rest consist of species native to the country where they are planted.
There are limitations and challenges with reforestation projects, especially if they are in the form of tree plantations. Firstly, there can be competition with other land uses and displacement risk. Secondly, tree plantations are often monocultures which comes with a set of disadvantages, for example biodiversity loss. Lastly, there is also the problem that stored carbon is released at some point.
The effects of reforestation will be farther in the future than those of proforestation (the conservation of intact forests). Instead of planting entirely new areas, it might be better to reconnect forested areas and restore the edges of forest. This protects their mature core and makes them more resilient and longer-lasting. It takes much longer − several decades − for the carbon sequestration benefits of reforestation to become similar to those from mature trees in tropical forests. Therefore, reducing deforestation is usually more beneficial for climate change mitigation than is reforestation.
Many countries carry out reforestation programs. For example, in China, the Three Northern Protected Forest Development Program – informally known as the "Great Green Wall" – was launched in 1978 and scheduled to last until 2050. It aims to eventually plant nearly 90 million acres of new forest in a 2,800-mile stretch of northern China. Such programs often blur the boundaries between reforestation and afforestation (the latter being the establishment of a forest in an area where there was no forest before).
Definition
Reforestation according to the IPCC means the "conversion to forest of land that has previously contained forests but that has been converted to some other use".
According to FAO terminology, reforestation is defined as the re-establishment of forest through planting and/or deliberate seeding on land classified as forest.
Afforestation on the other hand means establishing new forest on lands that were not forest before (for example, abandoned agriculture). It is the process of restoring and recreating areas of woodlands or forests that may have existed long ago but were deforested or otherwise removed at some point in the past or lacked it naturally (for example, natural grasslands).
Purposes
Harvesting of wood
Reforestation is not only used for recovery of accidentally destroyed forests. In some countries, such as Finland, many of the forests are managed by the wood products and pulp and paper industry. In such an arrangement, like other crops, trees are planted to replace those that have been cut. The Finnish Forest Act from 1996 obliges the forest to be replanted after felling. In such circumstances, the industry can cut the trees in a way to allow easier reforestation.
Reforestation, if several indigenous species are used, can provide other benefits in addition to financial returns, including restoration of the soil, rejuvenation of local flora and fauna, and the capturing and sequestering of 38 tons of carbon dioxide per hectare per year.
Climate change mitigation
There are four primary ways in which reforestation and reducing deforestation can increase carbon sequestration and thus help with climate change mitigation. First, by increasing the volume of existing forest. Second, by increasing the carbon density of existing forests at a stand and landscape scale. Third, by expanding the use of forest products that will sustainably replace fossil-fuel emissions. Fourth, by reducing carbon emissions that are caused from deforestation and degradation.
Ecosystem restoration
Plantation forests are intensively managed, composed of one or two species, even-aged, planted with regular spacing, and established mainly for productive purposes. Other planted forests, which comprise 55 percent of all planted forests, are not intensively managed, and they may resemble natural forests at stand maturity. The purposes of other planted forests may include ecosystem restoration and the protection of soil and water values.
Methods
Forest plantations
Plantation forests cover about 131 million ha, which is 3 percent of the global forest area and 45 percent of the total area of planted forests.
Over 90% of the world's forests regenerate organically, and more than half are covered by forest management plans or equivalents.
Globally, planted forests increased from 4.1% to 7.0% of the total forest area between 1990 and 2015. Plantation forests made up 280 million ha (hectare) in 2015, an increase of about 40 million ha in the previous ten years. Of the planted forests worldwide, 18% of that planted area consists of exotic or introduced species while the rest consist of species native to the country where they are planted.
Using existing trees and roots
Planting new trees often leads to up to 90% of seedlings failing. However, even in deforested areas, existing root systems often exist. Growth can be accelerated by pruning and coppicing where a few branches of new shoots are cut and often used for charcoal, itself a major driver of deforestation. Since new seeds are not planted, it is cheaper. Additionally, they are much more likely to survive as their root systems already exist and can tap into groundwater during harsher seasons with no rain. While this method has existed for centuries, it is now sometimes referred to as farmer-managed natural regeneration or assisted natural regeneration.
Financial incentives
Policies that promote reforestation for incentives in return have shown promising results of being an effective and motivative concept to re-plant globally on a mass scale.
Some incentives for reforestation can be as simple as a financial compensation. A compensated reduction of deforestation approach has been proposed which would reward developing countries that disrupt any further act of deforestation: Countries that participate and take the option to reduce their emissions from deforestation during a committed period of time would receive financial compensation for the carbon dioxide emissions that they avoided. To raise the payments, the host country would issue government bonds or negotiate some kind of loan with a financial institution that would want to take part in the compensation promised to the other country. The funds received by the country could be invested to help find alternatives to the extensive cutdown of forests. This whole process of cutting emissions would be voluntary, but once the country has agreed to lower their emissions they would be obligated to reduce their emissions. However, if a country was not able to meet their obligation, their target would get added to their next commitment period. The authors of these proposals see this as a solely government-to-government agreement; private entities would not participate in the compensation trades.
Another emerging revenue source to fund reforestation projects deals with the sale of carbon sequestration credits, which can be sold to companies and individuals looking to compensate their carbon footprint. This approach allows for private landowners and farmers to gain a revenue from the reforestation of their lands, while simultaneously benefiting from improved soil health and increased productivity.
Alongside past financial incentive strategies, reforestation tax benefits have been another way the government has encouraged companies to promote reforestation tactics through the promises of a tax break.
As many landholders seek to earn carbon credits through sequestration, their participation also encourages biodiversity and provides ecosystem services for crops and livestock.
Challenges
There is often insufficient integration between the different purposes of reforestation, namely economic utilization, enhancement of biodiversity and carbon sequestration. This can lead to a range of different challenges.
Competition with other land uses and displacement risk
Reforestation can compete with other land uses, such as food production, livestock grazing, and living space, for further economic growth. Reforestation can also divert large amounts of water from other activities. A map created by the World Resources Institute in collaboration with the IUCN identifies 2 billion hectares for potential forest restoration and is criticized for including 900 million hectares of grasslands. An assessment of the pledges of governments for reforestation found that the sum of global pledges translates to a required land area of 1.2bn hectares, until 2060, which is equal to a tenth of the global land area und thus deemed unrealistic without a significant encroachment on non-forest areas. Experts are calling for a better integration of social data, such as the dependence of livelihoods on specific land uses, into restoration efforts. Possible solutions include the integration of other land uses into forests through agroforestry, such as growing coffee plants under trees, reducing the delineation between forests and other land uses.
A study found that almost 300 million people live on tropical forest restoration opportunity land in the Global South, constituting a large share of low-income countries' populations, and argues for prioritized inclusion of "local communities" in forest restoration projects.
There are calls for a more selective approach to identifying reforestation areas, taking into account the possible displacement of customary land uses.
Biodiversity loss
Reforesting sometimes results in extensive canopy creation that prevents growth of diverse vegetation in the shadowed areas and generating soil conditions that hamper other types of vegetation. Trees used in some reforesting efforts (for example, Eucalyptus globulus) tend to extract large amounts of moisture from the soil, preventing the growth of other plants. The European Commission found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to irreversible effects in terms of biodiversity loss and soil degradation.
The effects reforestation has on biodiversity is not limited to just other forms of vegetation, it can affect all forms of living organisms all contained in the present ecosystem. Due to the major role trees have on ecosystems it is important to better understand components like the ecosystem, waterways, and species present in areas that are being re-planted. Prior research helps limit the depletion of biodiversity which can hinder medicinal discoveries, and alter gene flow in organisms.
A debated issue in managed reforestation is whether the succeeding forest will have the same biodiversity as the original forest. If the forest is replaced with only one species of tree and all other vegetation is prevented from growing back, a monoculture forest similar to agricultural crops would be the result. However, most reforestation involves the planting of different selections of seedlings taken from the area, often of multiple species.
Stored carbon being released
There is also the risk that, through a forest fire or insect outbreak, much of the stored carbon in a reforested area could make its way back to the atmosphere. Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forests. An example of this can be seen in the peatlands in Central Africa, which house an abundance of carbon in the mud called peat. Much like the forest fire or insect outbreak which can harm tropical rainforests, money can also be seen an incentive to harm forests and be paid off to protect it. The global greenhouse gas emissions caused by damage to tropical rainforests may be underestimated by a factor of six.
Also the possible harvesting and utilization of wood from reforested areas, limits the permanence of carbon sequestered through reforestation. For example, it was found that nearly half of the pledges under the Bonn Challenge were areas earmarked for commercial wood use.
Additionally the effects of afforestation and reforestation will be farther in the future than those of proforestation (the conservation of intact forests). It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation.
Some researchers note that instead of planting entirely new areas, reconnecting forested areas and restoring the edges of forest, to protect their mature core and make them more resilient and longer-lasting, should be prioritized.
Implementation challenges
There are some implementation challenges
Seed shortage: the Seed to Forest Alliance was founded in 2022 in response to a global seed shortage. It will promote the establishment of national seed banks, while focusing on the tropics and biodiversity hotspots.
Seedling survival rate: a common challenge for reforestation is the low survival rate of seedlings. Planted trees often do not mature, for example due to difficult climatic conditions or insufficient care after planting.
By country
Asia
China
According to China's government, the forest coverage of the country grew from 10% of the overall territory in 1949 to 25% in 2024.
China has introduced the Green Wall of China project, which aims to halt the expansion of the Gobi desert through the planting of trees. There has been a 47-million-hectare increase in forest area in China since the 1970s. The total number of trees amounted to be about 35 billion and 4.55% of China's land mass increased in forest coverage. The forest coverage was 12% in the early 1980s and had reached 16.55% by 2001.
China announced two large reforestation programs, the Natural Forest Protection Program and the Returning Farmland to Forest program, in late 1998. The programs were piloted in Sichuan, Shaanxi, and Gansu in 1999. They became widely implemented in 2000. The Natural Forest Protection Program called for major reductions in timber harvest, forest conservation, and instituted logging bans in most of Sichuan, Yunnan, Guizhou, and Tibet. The program provided for alternative employment opportunities for former logging industry workers, including hiring them for reforestation work. The Returning Farmland to Forest program paid farmers to plant trees on less productive farmland and provided them with a yearly subsidy for lost income. In 2015 China announced a plan to plant 26 billion trees by the year 2025; that is, two trees for every Chinese citizen per year.
Between 2013 and 2018, China planted 338,000 square kilometres of forests, at a cost of $82.88 billion. By 2018, 21.7% of China's territory was covered by forests, a figure the government wants to increase to 26% by 2035. The total area of China is 9,596,961 square kilometres (see China), so 412,669 square kilometres more needs to be planted. According to the government's plan, by 2050, 30% of China's territory should be covered by forests.
In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award in the Inspiration and Action category for their successful reforestation efforts, which began upon discovering the survival of a single tree.
From 2016 to 2021, 3976 square kilometers of forests were planted in the Tibet Autonomous Region, with plans for 20 million trees to be planted before 2023.
In the years 2012–2022 China restored more than of forests. China committed to plant and conserve 70 billion trees by the year 2030 as part of the Trillion Tree Campaign.
The Jane Goodall Institute launched the Million Tree Project in Kulun Qi, Inner Mongolia to plant one million trees. China used 24 million hectares of new forest to offset 21% of Chinese fossil fuel emissions in 2000.
The Chinese government requires mining companies to restore the environment around exhausted mines by refilling excavated pits and planting crops or trees. Many mining companies use these recovered mines for ecotourism business.
Launched in 1978 and scheduled to last until 2050, the Three Northern Protected Forest Development Program – informally known as the "Great Green Wall" – aims to eventually plant nearly 90 million acres of new forest in a 2,800-mile stretch of northern China.
Over 69.3 million hectares of forest were planted across China from 1999 to 2013. This large-scale reforestation contributed to China’s forests sequestering 1.11 ± 0.38 Gt carbon per yr over the period 2010 to 2016. This amounted to about 45 percent of the yearly greenhouse gas emissions during that period in China.
India
Jadav Payeng had received national awards for reforestation efforts, known as the "Molai forest". He planted 1400 hectares of forest on the bank of river Brahmaputra alone. There are active reforestation efforts throughout the country. In 2016, India had more than 50 million trees planted in Uttar Pradesh and in 2017, more than 66 million trees planted in Madhya Pradesh. In addition to this and individual efforts, there are startup companies, such as Afforest, that are being created over the country working on reforestation.
Lots of plantation are being carried out in the Indian continent but the survivability is very poor especially for massive plantations, with less than 20% survivability rate. To improve the forest cover and to achieve the national mission of forest cover of 33%, there is a need to improve the methods of plantation. Rather than mass planting, there is a need to work on performance measurement & tracking of trees growth. Taking this into consideration, a non-profit organization Ek Kadam Sansthan in Jaipur is leading the development of a module of mass tracking for plantations. The pilot has been done successfully and the organization is hoping to implement nationwide by the end of 2021.
Japan
The Ministry of Agriculture, Forestry and Fishery explain that about two-thirds of Japanese land is covered with forests, and it was almost unchanged from 1966 to 2012. Japan needs to reduce 26% of green house gas emission from 2013 by 2030 to accomplish Paris Agreement and is trying to reduce 2% of them by forestry.
Mass environmental and human-body pollution along with relating deforestation, water pollution, smoke damage, and loss of soils caused by mining operations in Ashio, Tochigi became the first environmental social issue in Japan, efforts by Shōzō Tanaka had grown to large campaigns against copper operation. This led to the creation of 'Watarase Yusuichi Pond', to settle the pollution which is a Ramsar site today. Reforestation was conducted as a part of afforestation due to inabilities of self-recovering by the natural land itself due to serious soil pollution and loss of woods consequence in loss of soils for plants to grow, thus needing artificial efforts involving introducing of healthy soils from outside. Starting from around 1897, about 50% of once bald mountains are now back to green.
Pakistan
The Billion Tree Tsunami was launched in 2014 by planting 10 billion trees, by the provincial government of Khyber Pakhtunkhwa (KPK) and Imran Khan, as a response to the challenge of global warming. Pakistan's Billion Tree Tsunami restored 350,000 hectares of forests and degraded land to surpass its Bonn Challenge commitment.
In 2018, Pakistan's prime minister Imran Khan declared that the country will plant 10 billion trees in the next five years.
In 2020, the Pakistani government launched an initiative to hire 63,600 laborers to plant trees in the northern Punjab region, with indigenous species such as acacia, mulberry and moringa. This initiative was meant to alleviate unemployment caused by lockdowns to mitigate the spread of COVID-19.
Philippines
In 2011, the Philippines established the National Greening Program as a priority program to help reduce poverty, promote food security, environmental stability, and biodiversity conservation, as well as enhance climate change mitigation and adaptation in the country. The program paved the way for the planting of almost 1.4 billion seedlings in about 1.66 million hectares nationwide during the 2011–2016 period. The Food and Agriculture Organization of the United Nations ranked the Philippines fifth among countries reporting the greatest annual forest area gain, which reached 240,000 hectares during the 2010–2015 period.
Thailand
Efforts are being made in Thailand to restore the land after 800,000 hectares of forest have been destroyed in exchange for cash crop land to grow maize. Agroforestry has become part of the solution to fix the damage caused by deforestation. Agroforestry would affect the agriculture and atmosphere in Thailand in numerous ways. By planting a combination of different tree species, these trees are able to change the microclimatic conditions. Nutrient cycling also occurs when trees are incorporated in the agricultural system. It is also probable that the soil erosion that occurred as a result of deforestation can be mediated when these trees are planted.
Europe
Armenia
The Armenia Tree Project was founded in 1994 to address environmental and economic concerns related to Armenia's dwindling forests. Since its founding, the organization has planted more than 6.5 million trees in communities throughout Armenia.
My Forest Armenia was founded in 2019 and has since planted 910,000 trees in Armenia.
Iceland
Prior to the deforestation of Iceland in the Middle Ages, some 40% of the land was forested. Today, the country is about 2% forested, with the Icelandic Forest Service aiming to increase that share to 10% through reforestation and natural regrowth.
Ireland
In 2019 the government of Ireland decided to plant 440 million trees by 2040. The decision is part of the government's plan to make Ireland carbon neutral by 2050 with renewable energy, land use change and carbon tax.
Ireland is also driven to increase sustainable timber consumption while also adding more eco friendly work positions. They also have taken efforts to limit the use of methane emissions by signing a pledge to draw back methane use by 30%.
Germany
By the 14th century, forests in heavily populated areas had been devastated by industry, many of which required wood for their activities. Peter Stromer (1310–1388), lord of the Stromer trading and commercial company, was spurred by this shortage to "conduct forest culture experiments". In 1368 he successfully sowed fir and pine seeds in the Nuremberg Reichswald, which over time ended the wood shortage and established the "triumph of the pine in the Nuremberg Reichswald" (at the expense of other deciduous trees). The "doctrine of coniferous sowing" spread widely through forestry regulations and other writing at the time.
Reforestation is required as part of the federal forest law. 31% of Germany is forested, according to the second forest inventory of 2001–2003. The size of the forest area in Germany increased between the first and the second forest inventory due to forestation of degenerated bogs and agricultural areas.
United Kingdom
Since the 1980s, 8.5 million trees have been planted in the United Kingdom in an area of the Midlands around the villages of Moira and Donisthorpe, close to Leicester. The area is called The National Forest. An even larger reforestation project, called The Northern Forest, is beginning in South Yorkshire. It aims to plant 50 million trees. Despite this, the UK government has been criticized for not achieving its tree planting goals. There have also been concerns of non-native tree planting disturbing the ecological integrity and processes of what would be a native habitat restoration.
Middle East
Israel
Since 1948, large reforestation and afforestation projects were accomplished in Israel. 240 million trees have been planted. The carbon sequestration rate in these forests is similar to the European temperate forests.
Israel and only one other country was documented to have a net increase of forestation in the 2000s. This type of progress could be attributed to the social practices that Israel incorporates into their society.
Lebanon
For thousands of years Lebanon was covered by forests; one particular species of interest, Cedrus libani was exceptionally valuable and was almost eliminated due to lumbering operations. Many ancient cultures along the Mediterranean Sea harvested these trees including the Phoenicians who used cedar, pine and juniper for boat building, the Romans, who cut them down for lime-burning kilns, and the Ottomans, who used much of the remaining cedar forests of Lebanon as fuel in steam trains in the early 20th century. Despite two millennia of deforestation, forests in Lebanon still cover 13.6% of the country, and other wooded lands represent 11%.
Law No. 558, which was ratified by the Lebanese Parliament on April 19, 1996, aims to protect and expand existing forests, classifying all forests of cedar, fir, high juniper, evergreen cypress and other trees, whether diverse or homogeneous, whether state-owned or not as conserved forests.
Since 2011 more than 600,000 trees, including cedars and other native species, have been planted throughout Lebanon as part of the Lebanon Reforestation Initiative, which aims to restore Lebanon's native forests. Projects financed locally and by international charity are performing extensive reforestation of cedar being carried out in the Mediterranean region, particularly in Lebanon and Turkey, where over 50 million young cedars are being planted annually.
The Lebanon Reforestation Initiative has been working with tree nurseries throughout Lebanon since 2012 to grow stronger seedlings with higher survival rates.
Turkey
Of the country's 78 million hectares of land in total, the Ministry of Agriculture and Forestry aims to increase Turkey's forest cover to 30% by 2023.
Four thousand years ago, Anatolia was 60% to 70% forested. Although the flora of Turkey remains more biodiverse than many European countries, deforestation occurred during both prehistoric and historic times, including the Roman and Ottoman periods.
Since the first forest code of 1937, the official government definition of 'forest' has varied. According to the current definition, 21 million hectares are forested, an increase of about 1 million hectares over the past thirty years, but only about half is 'productive'. However, according to the United Nations Food and Agriculture Organization definition of forest, about 12 million hectares was forested in 2015, about 15% of the land surface.
The amount of greenhouse gas emissions by Turkey removed by forests is very uncertain., however, a new assessment is being made with the help of satellites and new soil measurements and better information should be available by 2020. According to the World Resources Institute "Atlas of Forest Landscape Restoration Opportunities", 50 million hectares are potential forest land, a similar area to the ancient Anatolian forest mentioned above. This could help limit climate change in Turkey. To help preserve the biodiversity of Turkey, more sustainable forestry has been suggested. Improved rangeland management is also needed.
National Forestation Day is on 11 November but, according to the agriculture and forestry trade union, although volunteers planted a record number of trees in 2019, most had died by 2020 in part due to lack of rainfall.
North America
Canada
Natural Resources Canada (The Department of Natural Resources) states that the national forest cover was decreased by 0.34% from 1990 to 2015, and Canada has the lowest deforestation rate in the world. The forest industry is one of the main industries in Canada, which contributes about 7% of Canadian economy, and about 9% of the forests on Earth are in Canada. Therefore, Canada has many policies and laws to commit to sustainable forest management. For example, 94% of Canadian forests are public land, and the government obligates planting trees after harvesting to public forests.
United States
It is the stated goal of the United States Forest Service (USFS) to manage forest resources sustainably. This includes reforestation after timber harvest, among other programs.
United States Department of Agriculture (USDA) data shows that forest occupied about 46% of total U.S. land in 1630 (when European settlers began to arrive in large numbers), but had decreased to 34% by 1910. After 1910, forest area has remained almost constant although the U.S. population has increased substantially. In the late 19th century, the USFS was established in part to address the concern of natural disasters due to deforestation, and new reforestation programs and federal laws such as the Knutson-Vandenberg Act (1930) were implemented. The USFS states that human-directed reforestation is required to support natural regeneration and the agency engages in ongoing research into effective ways to restore forests.
As for the year 2020, the U.S. planted 2.5 billion trees per year. At the beginning of the year 2020, a bill that will increase the number to 3.3 billion, was proposed by the Republican Party, after President Donald Trump joined the Trillion Tree Campaign.
Latin America
Bolivia
Training in reforestation for young people in Bolivia has been provided by Oxfam Intermón.
Costa Rica
Through reforestation and environmental conservation, Costa Rica doubled its forest cover in 30 years.
Costa Rica has a long-standing commitment to the environment. The country is now one of the leaders of sustainability, biodiversity, and other protections. It wants to be completely fossil fuel free by 2050. The country has generated all of its electric power from renewable sources for three years as of 2019. It has committed to be carbon-free and plastic-free by 2021.
As of 2019, half of the country's land surface is covered with forests. They absorb a huge amount of carbon dioxide, combating climate change.
In the 1940s, more than 75% of the country was covered in mostly tropical rainforests and other indigenous woodlands. Between the 1940s and 1980s, extensive, uncontrolled logging led to severe deforestation. By 1983, only 26% of the country had forest cover. Realizing the devastation, policymakers took a stand. Through a continued environmental focus they were able to turn things around to the point that today forest cover has increased to 52%, two times more than 1983 levels.
An honorable world leader for ecotourism and conservation, Costa Rica has pioneered the development of payments for environmental services. Costa Rica's extensive system of environmental protection has been encouraging conservation and reforestation of the land by providing grants for environmental services. The system is not just advanced for its time but is also unparalleled in the world. It received great international attention.
Costa Rica doubled its forest cover in 30 years using its system of grants and other payments for environmental services, including compensation for landowners. One of the main programs established in Costa Rica was the Forest Promotion Certificate in 1979 and is funded by international donations and nationwide taxes. The initiative is helping to protect the forests in the country, and is now helped pass both the Forest Law in 1986 and FONAFIFO in 1990 which insures the continuity of the conservation programs.
Costa Rica's ambitious reforestation initiatives have transformed the landscape, fostering biodiversity, carbon sequestration, and sustainable land management practices.
Peru
Approximately 59% of Peru is covered by forest. A history of political turmoil and the government's inability to enforce environmental regulations has led to the degradation of the forest and environment in Peru. A military coup in 1968 caused a loss of economic mobility in the Talara region and sparked a boom in illegal logging due to the lack of alternative economic opportunities. Illegal mining and logging operations are responsible for a great deal of Peru's deforestation and environmental damage. The Peruvian government has not been able to enforce an environmentally conscious mining formalization plan to protect the Amazon forest in the Madre de Dios region. The 1980s were known in Peru as the "lost decade" due to a nationwide internal conflict and severe economic crisis almost destroying the country and resulting in the state losing control over several regions. Many areas in Peru, including Madre de Dios, had no state presence until the government initiated a movement to 'conquer and populate the Amazon,' with the hopes of minimizing illegal and informal mining operations that had expanded in the region and were polluting the Amazonian rivers and the destroying of its forests.
Reforestation initiatives have expanded in the country since. In Peru, reforestation is essential to preserving the livelihoods of rural communities because much of the population relies on the forest in some way. Deforestation also disproportionally affects indigenous communities in Peru, which is why reforestation efforts are essential for the protection of many communities' livelihoods.
Sub-Saharan Africa
One plan in this region, called Great Green Wall (Africa), involves planting a nine-mile width of trees on the Southern Border of the Sahara Desert for stopping its expansion to the south. However, this is more of an afforestation project than a reforestation one.
In 2019, Ethiopia begun a massive tree planting campaign "Green Legacy" with a target to plant 4 billion trees in one year. In one day only, over 350 million trees were planted.
Nigeria
Organizations and programs
Ecosia is a non-profit organization based in Berlin, Germany, that has planted over 100 million trees worldwide as of July 2020.
Trees for the Future has assisted more than 170,000 families, in 6,800 villages of Asia, Africa and the Americas, to plant over 35 million trees.
Ecologi is an organization that offers its members ways to support climate change solutions. This includes offsetting their carbon emissions and tree planting. So far over 50 million trees have been planted through Ecologi, as well a more than 2.2 million tonnes of CO2e reduced.
Wangari Maathai, 2004 Nobel Peace Prize recipient, founded the Green Belt Movement which planted over 47 million trees to restore the Kenyan environment.
Team Trees was a 2019 fundraiser with an initiative to plant 20 million trees. The initiative was started by American YouTubers MrBeast and Mark Rober, and was mostly supported by YouTubers. The Arbor Day Foundation will work with its local partners around the world to plant one tree for each dollar they raise.
Trees For Life (Brooklyn Park) is a state based organization, which was established back in 1981 and delivers conservation, revegetation and community training programs. It now has thousands of active supporters and energizes activity within communities.
Many companies are trying to achieve carbon offsets by nature-based solutions like reforestation, including mangrove forests and soil restoration. Among them are Microsoft and Eni. Increasing the forest cover of Earth by 25% will offset the human emissions in the last 20 years. In any case it will be necessary to pull from the atmosphere the that already have been emitted. However, this can work only if the companies will stop new emissions and stop deforestation.
The 2020 World Economic Forum, held in Davos, announced the creation of the Trillion Tree Campaign, which is an initiative aiming to plant 1 trillion trees across the globe. The implementation can have big environmental and societal benefits but needs to be tailored to local conditions.
The forest landscape restoration strategy seeks to rehabilitate landscapes and repair marginal and degraded areas in order to generate productive forest landscapes that are resilient and long-term. It aims to guarantee that diverse ecological and land-use functions are restored, safeguarded, and preserved over time.
See also
References
Reforest
Forest management
Habitat
Emissions reduction
Carbon dioxide removal | Reforestation | Chemistry | 7,075 |
31,277,685 | https://en.wikipedia.org/wiki/Minimum%20routing%20cost%20spanning%20tree | In computer science, the minimum routing cost spanning tree of a weighted graph is a spanning tree minimizing the sum of pairwise distances between vertices in the tree. It is also called the optimum distance spanning tree, shortest total path length spanning tree, minimum total distance spanning tree, or minimum average distance spanning tree. In an unweighted graph, this is the spanning tree of minimum Wiener index.
writes that the problem of constructing these trees was proposed by Francesco Maffioli.
It is NP-hard to construct it, even for unweighted graphs. However, it has a polynomial-time approximation scheme. The approximation works by choosing a number that depends on the approximation ratio but not on the number of vertices of the input graph, and by searching among all trees with internal nodes.
The minimum routing cost spanning tree of an unweighted interval graph can be constructed in linear time. A polynomial time algorithm is also known for distance-hereditary graphs, weighted so that the weighted distances are hereditary.
Fairness considerations
Several works assume that different people may have different preferences on edges in the graph, and the goal is to find a spanning tree that is "socially" best.
Darmann, Klamler and Pferschy present a greedy algorithm that finds such a spanning tree.
Escoffier, Gourvès and Monnot study the problem under the egalitarian rule - maximizing the smallest utility of an agent.
Galand, Perny and Spanjaard study the problem under the criterion of minimizing the Choquet integral.
See also
Optimal network design - the problem of finding a spanning set (not necessarily a tree) that minimizes the sum of shortest path lengths.
References
Spanning tree
NP-complete problems | Minimum routing cost spanning tree | Mathematics | 348 |
2,965,801 | https://en.wikipedia.org/wiki/Behavior-driven%20development | Behavior-driven development (BDD) involves naming software tests using domain language to describe the behavior of the code.
BDD involves use of a domain-specific language (DSL) using natural-language constructs (e.g., English-like sentences) that can express the behavior and the expected outcomes.
Proponents claim it encourages collaboration among developers, quality assurance experts, and customer representatives in a software project. It encourages teams to use conversation and concrete examples to formalize a shared understanding of how the application should behave. BDD is considered an effective practice especially when the problem space is complex.
BDD is considered a refinement of test-driven development (TDD). BDD combines the techniques of TDD with ideas from domain-driven design and object-oriented analysis and design to provide software development and management teams with shared tools and a shared process to collaborate on software development.
At a high level, BDD is an idea about how software development should be managed by both business interests and technical insight. Its practice involves use of specialized tools. Some tools specifically for BDD can be used for TDD. The tools automate the ubiquitous language.
Overview
BDD is a process by which DSL structured natural-language statements are converted into executable tests. The result are tests that read like acceptance criteria for a given function.
As such, BDD is an extension of TDD.
BDD focuses on:
Where to start in the process
What to test and what not to test
How much to test in one go
What to call the tests
How to understand why a test fails
At its heart, BDD is about rethinking the approach to automated testing (including unit testing and acceptance testing) in order to avoid issues that naturally arise. For example, BDD suggests that unit test names be whole sentences starting with a conditional verb ("should" in English for example) and should be written in order of business value. Acceptance tests should be written using the standard agile framework of a user story: "Being a [role/actor/stakeholder] I want a [feature/capability] yielding a [benefit]". Acceptance criteria should be written in terms of scenarios and implemented in classes: Given [initial context], when [event occurs], then [ensure some outcomes] .
Starting from this point, many people developed BDD frameworks over a period of years, finally framing it in terms of a communication and collaboration framework for developers, QA and non-technical or business participants in a software project.
Principles
BDD suggests that software tests should be named in terms of desired behavior. Borrowing from agile software development the "desired behavior" in this case consists of the requirements set by the business — that is, the desired behavior that has business value for whatever entity commissioned the software unit under construction. Within BDD practice, this is referred to as BDD being an "outside-in" activity.
TDD does not differentiate tests in terms of high-level software requirements, low-level technical details or anything in between. One way of looking at BDD therefore, is that it is an evolution of TDD which makes more specific choices.
Behavioral specifications
Another BDD suggestion relates to how the desired behavior should be specified. BDD suggests using a semi-formal format for behavioral specification which is borrowed from user story specifications from the field of object-oriented analysis and design. The scenario aspect of this format may be regarded as an application of Hoare logic to behavioral specification of software using the domain-specific language.
BDD suggests that business analysts and software developers should collaborate in this area and should specify behavior in terms of user stories, which are each explicitly documented. Each user story should, to some extent, follow the structure:
Title An explicit title.
Narrative A short introductory section with the following structure:
As a: the person or role who will benefit from the feature;
I want: the feature;
so that: the benefit or value of the feature.
Acceptance criteriaA description of each specific scenario of the narrative with the following structure:
Given: the initial context at the beginning of the scenario, in one or more clauses;
When: the event that triggers the scenario;
Then: the expected outcome, in one or more clauses.
BDD does not require how this information is formatted, but it does suggest that a team should decide on a relatively simple, standardized format with the above elements. It also suggests that the scenarios should be phrased declaratively rather than imperatively — in the business language, with no reference to elements of the UI through which the interactions take place. This format is referred to in Cucumber as the Gherkin language.
Specification as a ubiquitous language
BDD borrows the concept of the ubiquitous language from domain driven design. A ubiquitous language is a (semi-)formal language that is shared by all members of a software development team — both software developers and non-technical personnel. The language in question is both used and developed by all team members as a common means of discussing the domain of the software in question. In this way BDD becomes a vehicle for communication between all the different roles in a software project.
A common risk with software development includes communication breakdowns between Developers and Business Stakeholders. BDD uses the specification of desired behavior as a ubiquitous language for the project Team members. This is the reason that BDD insists on a semi-formal language for behavioral specification: some formality is a requirement for being a ubiquitous language. In addition, having such a ubiquitous language creates a domain model of specifications, so that specifications may be reasoned about formally. This model is also the basis for the different BDD-supporting software tools that are available.
The example given above establishes a user story for a software system under development. This user story identifies a stakeholder, a business effect and a business value. It also describes several scenarios, each with a precondition, trigger and expected outcome. Each of these parts is exactly identified by the more formal part of the language (the term Given might be considered a keyword, for example) and may therefore be processed in some way by a tool that understands the formal parts of the ubiquitous language.
Most BDD applications use text-based DSLs and specification approaches. However, graphical modeling of integration scenarios has also been applied successfully in practice, e.g., for testing purposes.
Specialized tooling
Much like TDD, BDD may involve using specialized tooling.
BDD requires not only test code as does TDD, but also a document that describes behavior in a more human-readable language. This requires a two-step process for executing the tests, reading and parsing the descriptions, and reading the test code and finding the corresponding test implementation to execute. This process makes BDD more laborious for developers. Proponents suggest that due to its human-readable nature the value of those documents extends to a relatively non-technical audience, and can hence serve as a communication means for describing requirements ("features").
Tooling principles
In principle, a BDD support tool is a testing framework for software, much like the tools that support TDD. However, where TDD tools tend to be quite free-format in what is allowed for specifying tests, BDD tools are linked to the definition of the ubiquitous language.
The ubiquitous language allows business analysts to document behavioral requirements in a way that will also be understood by developers. The principle of BDD support tooling is to make these same requirements documents directly executable as a collection of tests. If this cannot be achieved because of reasons related to the technical tool that enables the execution of the specifications, then either the style of writing the behavioral requirements must be altered or the tool must be changed. The exact implementation of behavioral requirements varies per tool, but agile practice has come up with the following general process:
The tooling reads a specification document.
The tooling directly understands completely formal parts of the ubiquitous language (such as the Given keyword in the example above). Based on this, the tool breaks each scenario up into meaningful clauses.
Each individual clause in a scenario is transformed into some sort of parameter for a test for the user story. This part requires project-specific work by the software developers.
The framework then executes the test for each scenario, with the parameters from that scenario.
Story versus specification
A separate subcategory of behavior-driven development is formed by tools that use specifications as an input language rather than user stories. Specification tools don't use user stories as an input format for test scenarios but rather use functional specifications for units that are being tested. These specifications often have a more technical nature than user stories and are usually less convenient for communication with business personnel than are user stories. An example of a specification for a stack might look like this:
Specification: Stack
When a new stack is created
Then it is empty
When an element is added to the stack
Then that element is at the top of the stack
When a stack has N elements
And element E is on top of the stack
Then a pop operation returns E
And the new size of the stack is N-1
Such a specification may exactly specify the behavior of the component being tested, but is less meaningful to a business user. As a result, specification-based testing is seen in BDD practice as a complement to story-based testing and operates at a lower level. Specification testing is often seen as a replacement for free-format unit testing.
The three amigos
The "three amigos", also referred to as a "Specification Workshop", is a meeting where the product owner discusses the requirement in the form of specification by example with different stakeholders like the QA and development team. The key goal for this discussion is to trigger conversation and identify any missing specifications. The discussion also gives a platform for QA, development team and product owner to converge and hear out each other's perspective to enrich the requirement and also make sure if they are building the right product.
The three amigos are:
Business - Role of the business user is to define the problem only and not venture into suggesting a solution
Development - Role of the developers involve suggesting ways to fix the problem
Testing - Role of testers is to question the solution, bring up as many as different possibilities for brain storming through what-if scenarios and help make the solution more precise to fix the problem.
See also
Specification by example
Behat (PHP framework)
Cynefin framework
Concordion (Java framework)
RSpec
Gauge
Jasmine (JavaScript testing framework)
Squish GUI Tester (BDD GUI Testing Tool for JavaScript, Python, Perl, Ruby and Tcl)
Use case
Fitnesse has been used to roll out BDD
References
Software design
Software development philosophies
Software testing
Articles with example Java code | Behavior-driven development | Engineering | 2,189 |
59,019,267 | https://en.wikipedia.org/wiki/Oligoflexia | The Oligoflexia are a class of the phylum Bdellovibrionota. All species of this group are all Gram-negative.
See also
List of bacterial orders
List of bacteria genera
References
Gram-negative bacteria | Oligoflexia | Biology | 48 |
29,920,367 | https://en.wikipedia.org/wiki/Swelling%20capacity | The swelling capacity of a polymer is the amount of a liquid that can be absorbed by it. This test can done by two methods:
Beaker test method
Tea bag test method
Beaker test method
In this method
A small amount of superabsorbent polymer material is taken (0.1g) and it is placed in the beaker.
100 ml of deionized water is poured into the beaker.
After 20 min the swollen polymer was separated by using [filter paper]
By weighing the polymer, one can find the swollen capacity of the SAP material.
Tea bag test method
In this method, 0.1 g of SAP material is placed into a permeable bag, which is suspended over excess water in a beaker.
Wait 20 min. and weigh the bag and then calculate the percentage of swelling through the following formula:
(w2-w1)/(w1) %
w1= weight of the polymer (Before swelling)
w2= weight of the polymer (After swelling)
Note: Filter paper only for removing water.
Schroeder's paradox
Some polymers exhibit larger experimentally measured swelling capacity when immersed in pure liquid compared to testing with saturated vapor. This phenomenon is known as the Schroeder's paradox.
References
Laboratory techniques | Swelling capacity | Chemistry | 260 |
27,137,205 | https://en.wikipedia.org/wiki/Journal%20of%20Automated%20Reasoning | The Journal of Automated Reasoning was established in 1983 by Larry Wos, who was its editor in chief until 1992. It covers research and advances in automated reasoning, mechanical verification of theorems, and other deductions in classical and non-classical logic.
The journal is published by Springer Science+Business Media. As of 2021, the editor-in-chief is Jasmin Blanchette, a professor of theoretical computer science at the Ludwig-Maximilians-Universität München. The journal's 2019 impact factor is 1.431, and it is indexed by several science indexing services, including the Science Citation Index Expanded and Scopus.
References
External links
Computer science journals
Logic journals
English-language journals
Academic journals established in 1983
Logic in computer science
Formal methods publications
Springer Science+Business Media academic journals | Journal of Automated Reasoning | Mathematics | 165 |
11,191,427 | https://en.wikipedia.org/wiki/Nine-segment%20display | A nine-segment display is a type of display based on nine segments that can be turned on or off according to the graphic pattern to be produced. It is an extension of the more common seven-segment display, having an additional two diagonal or vertical segments (one between the top and the middle, and the other between the bottom and the horizontal segments). It provides an efficient method of displaying alphanumeric characters.
The letters displayed by a nine-segment display are not consistently uppercase or lowercase in shape. A common compromise is to use a lower-case "n" instead of "N". Depending on the design of the display segments, the use of the extra two segments may be avoided whenever possible, as in the Nixxo X-Page "tall" lowercase "r" and "y".
Uses
In some Soviet digital calculators of the 1970s, such as the Elektronika 4-71b, 9-segment displays were used to provide basic alphanumerics and avoid confusions with representing numbers in Soviet postcodes.
The extra two bars were slanted forward, allowing for an appropriate-looking И, and to differentiate the numeral 3
from the letter З. The Sharp Compet calculator also uses a 9-segment display, allowing a small range of characters and symbols to be used.
Nine-segment displays are used in many Timex digital watches, and some pagers, such as the Nixxo XPage, the Arch BR502 pager, and the Scope Geo N8T. They are also used in some Epson Stylus printers, and Newport iSeries digital meters. The display used in the iSeries is unique in that it has a vertical extra segment at top, and a fully backwards-leaning slant for the extra segment at bottom. This allows for a somewhat more natural-appearing R and M.
A nine-segment display has been developed for displaying Bengali and Roman numerals.
See also
Seven-segment display
Eight-segment display
Fourteen-segment display
Sixteen-segment display
Dot matrix display
Nixie tube display
Vacuum fluorescent display
References
External links
Display technology | Nine-segment display | Engineering | 433 |
15,514,902 | https://en.wikipedia.org/wiki/Age%20of%20Oil | The Age of Oil, also known as the Oil Age, the Petroleum Age, or the Oil Boom, refers to the era in human history characterised by an increased use of petroleum in products and as fuel. Though unrefined petroleum has been used for various purposes since ancient times, it was during the 19th century that refinement techniques were developed and gasoline engines were created.
Although crude petroleum oil has been used for a variety of purposes for thousands of years, the Oil Age is considered to have started in the 1800s with the advance of drilling techniques, as well as the processing of products made use in internal combustion engines. Alternatively, the age of oil can be placed in the first period until the early 1900s, when oil consumption and combustion engines utilization increased. Contemporary industrial society is built largely on petroleum resources, but the future of the Oil Age has become increasingly controversial as the effects of climate change have become apparent, and use of alternative energy sources increases.
History
Since the beginning of the Industrial Revolution, fossil fuels have been used as sources of energy. Coal began to be widely used after 1800 and would continue to be the dominant source of fuel into the 20th century. However, two events set the stage for the Age of Oil: The first was in 1846, when Abraham Gesner invented kerosene making coal and petroleum practical raw materials for lighting fuel. The second was in 1859, when Edwin Drake invented the first modern drilling process for deep oil wells. John Davison Rockefeller founded the Standard Oil Company, which dominated the oil industry and was the first great U.S. business trust. He founded the company in 1870, and aggressively ran it until he officially retired in 1897. Karl Friedrich Benz developed petrol-powered automobiles by 1878 and, in 1879, obtained a patent for the practical automobile. The invention of the internal combustion engine was the major influence in the rise in the importance of petroleum.
The beginning of the contemporaneous age of oil is commonly thought of originating in 1901 with the strike at Spindletop by Croatian oil explorer Antun Lučić and Texan Patillo Higgins, near Beaumont, Texas in the United States which launched large-scale oil production and soon made the petroleum products widely available.
Powered by the increased use of petroleum, the post–World War II economic expansion was a period of economic prosperity in the mid-20th century which occurred, following the end of World War II in 1945, and lasted until the early 1970s. It ended with the 1973 oil crisis. In 1956, Geophysicist M. King Hubbert deduced that U.S. oil production would peak between 1965 and 1970 (peaked in 1971) and that oil production would peak "within half a century" on the basis of 1956 data. In 1989, another peak was predicted by Colin Campbell
Since the 1960s and 1970s, when petroleum production peaked in many industrialized nations, a frequent topic of speculation among scholars has been when worldwide production will peak, as well as when and how the oil age will ultimately end. According to some definitions the age is defined as ending at the point where consumption outstrips the decreasing production making its use unprofitable or impossible.
Contemporary oil
With the dawning of the so-called Atomic Age many observers in the mid-20th century believed that the Oil Age was rapidly coming to an end. The rapid change to atomic power envisioned during this period never materialized, in part due to environmental fears following high-profile accidents such as the 1979 Three Mile Island accident, the 1986 Chernobyl disaster and the 2011 Fukushima nuclear disaster.
Peak oil is the point in time when the maximum rate of petroleum extraction is reached, after which the rate of production is expected to enter terminal decline. Many believe that we are at or close to the peak, positioning us in the second half of the oil age. Some estimate, assuming current consumption rates, current oil reserves will last through at least the year 2040. In 2004, OPEC estimated, with substantial investments, it would nearly double oil output by 2025.
See also
General Wheeler No. 1 Oil Well, Edward L. Doheny, Texas Oil Boom, History of the petroleum industry in Canada, History of the Venezuelan oil industry
Fuels Fossil fuel, Unconventional oil, Oil sands, Oil shale reserves
Gluts and crisis Price of petroleum, 1980s oil glut, 1980–1989 world oil market chronology, 1979 energy crisis, Oil price increases since 2003, Oil depletion
Business Chronology of world oil market events (1970–2005), Company man, Drilling Fluids Engineer, Major Drilling Group International
Drilling Extraction of petroleum, Oil well (Oil well drilling, Oil Driller), Well drilling (Drilling), Drilling rig (Wellhead, Drill string), Oil platform, Drillship, Oil well Dog House, Submersible pump, Well logging, Wellbore, Relief well, Oil well control, Completion (oil and gas wells), Pore pressure gradient, Offshore drilling, Deepwater drilling, Drilling fluid
Other Resource curse, Oil reserves in Saudi Arabia, Problems in oil well drilling, Oil imperialism, Energy Slave
Alternatives Natural gas, Renewable energy, Renewable energy commercialization, History of renewable energy
References and notes
Citations
Further reading
Olien, Diana Davids, and Roger M. Olien. “Why Big Bad Oil?” OAH Magazine of History 11#1 (1996), pp. 22–27. online
Goodstein, D. L. (2005). Out of gas: The end of the age of oil. New York., NY: W.W. Norton.
Ash, R. Whitaker's World of Facts.
Petroleum politics
20th century
21st century | Age of Oil | Chemistry | 1,141 |
1,408,531 | https://en.wikipedia.org/wiki/Bdellovibrionales | Bdellovibrionales is an order of Pseudomonadota.
See also
List of bacterial orders
List of bacteria genera
References
Bacteria orders | Bdellovibrionales | Biology | 30 |
274,810 | https://en.wikipedia.org/wiki/Scientific%20instrument | A scientific instrument is a device or tool used for scientific purposes, including the study of both natural phenomena and theoretical research.
History
Historically, the definition of a scientific instrument has varied, based on usage, laws, and historical time period. Before the mid-nineteenth century such tools were referred to as "natural philosophical" or "philosophical" apparatus and instruments, and older tools from antiquity to the Middle Ages (such as the astrolabe and pendulum clock) defy a more modern definition of "a tool developed to investigate nature qualitatively or quantitatively." Scientific instruments were made by instrument makers living near a center of learning or research, such as a university or research laboratory. Instrument makers designed, constructed, and refined instruments for purposes, but if demand was sufficient, an instrument would go into production as a commercial product.
In a description of the use of the eudiometer by Jan Ingenhousz to show photosynthesis, a biographer observed, "The history of the use and evolution of this instrument helps to show that science is not just a theoretical endeavor but equally an activity grounded on an instrumental basis, which is a cocktail of instruments and techniques wrapped in a social setting within a community of practitioners. The eudiometer has been shown to be one of the elements in this mix that kept a whole community of researchers together, even while they were at odds about the significance and the proper use of the thing."
By World War II, the demand for improved analyses of wartime products such as medicines, fuels, and weaponized agents pushed instrumentation to new heights. Today, changes to instruments used in scientific endeavors — particularly analytical instruments — are occurring rapidly, with interconnections to computers and data management systems becoming increasingly necessary.
Scope
Scientific instruments vary greatly in size, shape, purpose, complication and complexity. They include relatively simple laboratory equipment like scales, rulers, chronometers, thermometers, etc. Other simple tools developed in the late 20th century or early 21st century are the Foldscope (an optical microscope), the SCALE(KAS Periodic Table), the MasSpec Pen (a pen that detects cancer), the glucose meter, etc. However, some scientific instruments can be quite large in size and significant in complexity, like particle colliders or radio-telescope antennas. Conversely, microscale and nanoscale technologies are advancing to the point where instrument sizes are shifting towards the tiny, including nanoscale surgical instruments, biological nanobots, and bioelectronics.
The digital era
Instruments are increasingly based upon integration with computers to improve and simplify control; enhance and extend instrumental functions, conditions, and parameter adjustments; and streamline data sampling, collection, resolution, analysis (both during and post-process), and storage and retrieval. Advanced instruments can be connected as a local area network (LAN) directly or via middleware and can be further integrated as part of an information management application such as a laboratory information management system (LIMS). Instrument connectivity can be furthered even more using internet of things (IoT) technologies, allowing for example laboratories separated by great distances to connect their instruments to a network that can be monitored from a workstation or mobile device elsewhere.
Examples of scientific instruments
List of scientific instruments manufacturers
List of scientific instruments designers
Jones, William
Kipp, Petrus Jacobus
Le Bon, Gustave
Roelofs, Arjen
Schöner, Johannes
Von Reichenbach, Georg Friedrich
History of scientific instruments
Museums
Collection of Historical Scientific Instruments (CHSI)
Boerhaave Museum
Chemical Heritage Foundation
Deutsches Museum
Royal Victoria Gallery for the Encouragement of Practical Science
Whipple Museum of the History of Science
Historiography
Paul Bunge Prize
Types of scientific instruments
Optical instrument
Electronic test equipment
See also
Instrumentation
Instrumentalism, a philosophic theory
List of collectibles
, a suffix to denote a complex scientific instrument, like in cyclotron, phytotron, synchrotron, ...
References
Science-related lists | Scientific instrument | Technology,Engineering | 811 |
5,096,405 | https://en.wikipedia.org/wiki/Dynameter | A dynameter is an instrument that measures the magnification of a telescope. It is usually a double-image micrometer used to measure the diameter of the image of the object glass. The magnifying power is found by comparing the actual diameter of the glass with the measured diameter of the image of the glass.
References
Dictionary entry for dynameter.
The DYNAMETER, archived from the original
Optical instruments
Measuring instruments
Astronomical imaging
Telescope instruments | Dynameter | Astronomy,Technology,Engineering | 92 |
1,573,046 | https://en.wikipedia.org/wiki/HD%20130322 | HD 130322 is a star with a close orbiting exoplanet in the constellation of Virgo. The distance to this system is 104 light years, as determined using parallax measurements. It is drifting closer to the Sun with a radial velocity of −12.4 km/s. With an apparent visual magnitude of 8.04, it is too dim to be visible to the naked eye; requiring binoculars or a small telescope to view. Being almost exactly on the celestial equator the star is visible everywhere in the world except for the North Pole. The star shows a high proper motion, traversing the celestial sphere at an angular rate of .
The spectrum of this star presents as a K-type main-sequence star, an orange dwarf, with a stellar classification of K0V. The star has 92% of the mass of the Sun and 85% of the Sun's radius. It is spinning with a rotation period of 26.5 days. HD 130322 is radiating 62% of the luminosity of the Sun from its photosphere at an effective temperature of 5,387 K. It is estimated to be around six billion years old.
The star HD 130322 is named Mönch and its companion is Eiger. The names were selected in the NameExoWorlds campaign by Switzerland, during the 100th anniversary of the IAU. Mönch and Eiger are prominent peaks of the Bernese Alps.
Planetary system
In 2000, an extrasolar planet was discovered orbiting the star using Doppler spectroscopy. As the inclination of the orbital plane is unknown, only a lower bound on the mass can be estimated. Most likely this is a hot Jupiter as it is orbiting close to the host star and has at least the mass of Jupiter.
The star rotates at an inclination of 76 degrees relative to Earth. It has been assumed that the planet shares that inclination. But several "hot Jupiters" are known to be oblique relative to the stellar axis.
See also
Lists of exoplanets
References
K-type main-sequence stars
Planetary systems with one confirmed planet
Virgo (constellation)
Durchmusterung objects
130322
072339 | HD 130322 | Astronomy | 443 |
1,796,414 | https://en.wikipedia.org/wiki/Linde%E2%80%93Buzo%E2%80%93Gray%20algorithm | The Linde–Buzo–Gray algorithm (named after its creators Yoseph Linde, Andrés Buzo and Robert M. Gray, who designed it in 1980) is an iterative vector quantization algorithm to improve a small set of vectors (codebook) to represent a larger set of vectors (training set), such that it will be locally optimal. It combines Lloyd's Algorithm with a splitting technique in which larger codebooks are built from smaller codebooks by splitting each code vector in two. The core idea of the algorithm is that by splitting the codebook such that all code vectors from the previous codebook are present, the new codebook must be as good as the previous one or better.
Description
The Linde–Buzo–Gray algorithm may be implemented as follows:
algorithm linde-buzo-gray is
input: set of training vectors training, codebook to improve old-codebook
output: codebook that is twice the size and better or as good as old-codebook
new-codebook ← {}
for each old-codevector in old-codebook do
insert old-codevector into new-codebook
insert old-codevector + into new-codebook where is a small vector
return lloyd(new-codebook, training)
algorithm lloyd is
input: codebook to improve, set of training vectors training
output: improved codebook
do
previous-codebook ← codebook
clusters ← divide training into |codebook| clusters, where each cluster contains all vectors in training who are best represented by the corresponding vector in codebook
for each cluster cluster in clusters do
the corresponding code vector in codebook ← the centroid of all training vectors in cluster
while difference in error representing training between codebook and previous-codebook >
return codebook
References
Cluster analysis algorithms
Machine learning algorithms
Artificial neural networks
Signal processing | Linde–Buzo–Gray algorithm | Technology,Engineering | 377 |
4,510,496 | https://en.wikipedia.org/wiki/Head%20gasket | In an internal combustion engine, a head gasket provides the seal between the engine block and cylinder head(s).
Its purpose is to seal the combustion gases within the cylinders and to avoid coolant or engine oil leaking into the cylinders. Leaks in the head gasket can cause poor engine running and/or overheating.
Purpose
Within a water-cooled internal combustion engine, there are three fluids which travel between the engine block and the cylinder head:
Combustion gases (unburned air/fuel mixture and exhaust gases) in each cylinder
Water-based coolant in the coolant passages
Lubricating oil in the oil galleries
Correct operation of the engine requires that each of these circuits do not leak or lose pressure at the junction of the engine block and the cylinder head. The head gasket is the seal that prevents these leaks and pressure losses.
Types
Multi-layer steel (MLS): Most modern engines are produced with MLS gaskets. These consist of two to five (typically three) thin layers of steel, interleaved with elastomer. The contact faces are usually coated with a rubber-like coating such as Viton which adheres to the engine block and cylinder head while the inner layers are optimized for resilience.
Solid copper: A solid sheet of copper, and typically requires special machining called O-ringing that places a piece of wire around the circumference of the cylinder to bite into the copper. When this is performed copper gaskets are very durable.
Composite: An older design which is more prone to blowouts than newer designs. Composite gaskets are traditionally made from asbestos or graphite. Asbestos gaskets are increasingly rare due to health concerns.
Elastomeric: Uses a steel core plate with molded in place silicone rubber beads to seal oil and coolant passages. The bores are sealed by rolled steel fire rings in a more conventional manner. This type of gasket was used in the Rover K-series engine.
O-ring: These gaskets are typically built from steel or copper. They are reusable and if used between correctly prepared flat surfaces will yield the highest clamping pressure, due to their much lower surface area compared with other gasket types.
Gasket failure
A leak in the head gasket - often called a "blown head gasket" - can result in a leak of coolant, the combustion gasses, or both.
Blue smoke from the exhaust suggests that excess oil is entering the combustion chambers (although there are other possible causes than a head gasket leak). White smoke from the exhaust suggests that coolant is entering the combustion chamber.
Head gasket leaks are classified as either external or internal. External leaks are visible as oil or coolant on the outside of the engine (typically underneath). Internal leaks are when the fluids enter another circuit and may result in changes to the coolant or oil. The former may be the presence of foam (caused by hydrocarbons) in the coolant expansion tank. Coolant leaking into the oil system may result in a mayonnaise- or milkshake-like substance in the oil, often to be seen on the dipstick, or oil filler cap. However, the presence of this substance is not conclusive proof of head gasket failure, since oil could mix with the coolant via other routes. Likewise, it is entirely possible for a head gasket to fail in such a way that oil never comes in contact with coolant. Therefore it is not possible to conclusively determine the head gasket condition by inspecting the oil.
Coolant leakage
If coolant enters a cylinder, the burning of the air/fuel mixture is compromised, reducing the engine's performance and often causing steam (white smoke) to be visible from the exhaust. This steam can damage the catalytic converter. If a very large amount of coolant leaks into the cylinders, then the engine can suffer from hydrolock, which can cause extensive engine damage.
Combustion gas leakage
When the combustion gasses leak out of a cylinder, this causes a loss of compression, leading to power reduction or rough running. If the combustion gases are leaking into the cooling system, this reduces the effectiveness of the cooling system and can cause the engine to overheat. In other occurrences the gases can leak into small spaces between the gasket and either the cylinder head or engine block traps those gases, and then released when the engine is turned off. These gases then escape into the coolant and create air pockets. Sometimes these air pockets can get trapped in the engine's coolant thermostat, causing it to stay closed and cause further overheating, thereby creating more voids between the gasket and the engine. Other times these air pockets can also cause the engine to expel coolant into the overflow or expansion tank, thereby reducing the amount of coolant available for cooling.
Diagnosis and repair
Common test methods for head gasket leaks are a compression test (using a pressure gauge), a leak-down test or a chemical test that identifies hydrocarbons in the coolant fluid.
The cost of the replacement component (i.e. the head gasket itself) is usually relatively low, however there are significant labor costs involved in the replacement process. This is because the process of removing and replacing the cylinder head is a time-consuming task.
Effect of engine knocking
Engine knocking (detonation) can be caused by poor quality fuel, an engine fault or if inappropriate fuel and/or ignition settings are trialled/chosen while engine tuning is taking place. If the detonation is severe, the cylinder pressure can increase to eight times above normal pressures, which can cause the cylinder head to lift away from the engine block, disrupting the seal between the two. Most gaskets used in standard production engines can be critically damaged by severe detonation.
See also
Internal combustion engine cooling
List of auto parts
Motor oil
Rocker cover gasket
References
Seals (mechanical)
Engine technology
Engine problems | Head gasket | Physics,Technology | 1,241 |
7,473,734 | https://en.wikipedia.org/wiki/Annual%20Review%20of%20Biomedical%20Engineering | Annual Review of Biomedical Engineering is an academic journal published by Annual Reviews. In publication since 1999, this journal covers the significant developments in the broad field of biomedical engineering with an annual volume of review articles. It is edited by Martin L. Yarmush and Mehmet Toner. As of 2024, Journal Citation Reports gave the journal has an impact factor of 12.8 ranking it fourth out of 122 journals in the category "Biomedical Engineering". As of 2021, Annual Review of Biomedical Engineering is being published as open access, under the Subscribe to Open model.
History
The Annual Review of Biomedical Engineering was first published in 1999 by the nonprofit publisher Annual Reviews. The inaugural editor was Martin L. Yarmush; Yarmush remained editor until 2021, at which point he was co-editor along with Mehmet Toner. Though it began with a physical edition, it is now only published electronically.
Scope and indexing
The Annual Review of Biomedical Engineering defines its scope as covering significant developments relevant to biomedical engineering. Included subfields are biomechanics; biomaterials; computational genomics; proteomics; healthcare, biochemical, and tissue engineering; biomonitoring; and medical imaging. As of 2022, Journal Citation Reports lists the journal's impact factor as 11.324, ranking it seventh of 98 journal titles in the category "Biomedical Engineering". It is abstracted and indexed in Scopus, Science Citation Index Expanded, MEDLINE, EMBASE, Inspec and Academic Search, among others.
Editorial processes
The Annual Review of Biomedical Engineering is helmed by the editor or the co-editors. The editor is assisted by the editorial committee, which includes associate editors, regular members, and occasionally guest editors. Guest members participate at the invitation of the editor, and serve terms of one year. All other members of the editorial committee are appointed by the Annual Reviews board of directors and serve five-year terms. The editorial committee determines which topics should be included in each volume and solicits reviews from qualified authors. Unsolicited manuscripts are not accepted. Peer review of accepted manuscripts is undertaken by the editorial committee.
Current editorial board
As of 2022, the editorial committee consists of the co-editors and the following members:
James S. Duncan
Martha L. Gray
Todd P. Coleman
Frances Ligler
Wendy M. Murray
Yaakov Nahmias
Eleftherios Terry Papoutsakis
Erkin Şeker
Marjolein C. H. van der Meulen
Jennifer L. West
George R. Wodicka
See also
List of engineering journals and magazines
References
Biomedical engineering journals
Biomedical engineering
Biomedical Engineering
Academic journals established in 1999
Annual journals
English-language journals | Annual Review of Biomedical Engineering | Engineering,Biology | 548 |
17,550,575 | https://en.wikipedia.org/wiki/Earthquake%20simulation | Earthquake simulation applies a real or simulated vibrational input to a structure that possesses the essential features of a real seismic event. Earthquake simulations are generally performed to study the effects of earthquakes on man-made engineered structures, or on natural features which may present a hazard during an earthquake.
Dynamic experiments on building and non-building structures may be physical – as with shake-table testing – or virtual (based on computer simulation). In all cases, to verify a structure's expected seismic performance, researchers prefer to deal with so called 'real time-histories' though the last cannot be 'real' for a hypothetical earthquake specified by either a building code or by some particular research requirements.
Shake-table testing
Studying a building's response to an earthquake is performed by putting a model of the structure on a shake-table that simulates the seismic loading. The earliest such experiments were performed more than a century ago.
Computational approaches
Another way is to evaluate the earthquake performance analytically.
The very first earthquake simulations were performed by statically applying some horizontal inertia forces, based on scaled peak ground accelerations, to a mathematical model of a building. With the further development of computational technologies, static approaches began to give way to dynamic ones.
Traditionally, numerical simulation and physical tests have been uncoupled and performed separately. So-called hybrid testing systems employ rapid, parallel analyses using both physical and computational tests.
See also
Seismic analysis
References
External links
Network for Earthquake Engineering Simulation (NEES)
AEM Earthquake Simulation
Building
Earthquake engineering | Earthquake simulation | Engineering | 307 |
67,558,583 | https://en.wikipedia.org/wiki/Time%20in%20Albania | In Albania, the standard time is Central European Time (CET; UTC+01:00). Daylight saving time, which moves one hour ahead to Central European Summer Time, is observed from the last Sunday in March (02:00 CET) to the last Sunday in October (03:00 CEST). Albania adopted CET in 1914.
IANA time zone database
In the IANA time zone database, Albania is given the zone Europe/Tirane.
See also
Time in Europe
Time in Bosnia and Herzegovina
Time in Kosovo
References
External links
Current time in Albania at Time.is
Albania
Albania
Geography of Albania | Time in Albania | Physics | 126 |
69,594,812 | https://en.wikipedia.org/wiki/PF-06260414 | PF-06260414 is a drug which acts as a selective androgen receptor modulator (SARM), and was developed for androgen replacement therapy.
See also
AC-262536
ACP-105
Enobosarm
JNJ-28330835
Ligandrol
References
Selective androgen receptor modulators
Isoquinolines
Thiadiazinanes
Nitriles
Sulfones
Sulfur–nitrogen compounds | PF-06260414 | Chemistry | 90 |
66,807,151 | https://en.wikipedia.org/wiki/Nitryl%20chloride | Nitryl chloride is a volatile inorganic compound with formula ClNO2. At standard conditions it is a gas.
Formation
Nitryl chloride can be formed in the reaction of dinitrogen pentoxide with chlorides or hydrogen chloride:
N2O5 + 2HCl → 2ClNO2 + H2O
N2O5 + NaCl → ClNO2 + NaNO3
Reactions
Nitryl chloride adds to olefins in a radical reaction.
References
Nitro compounds
Nitrogen oxohalides
Nitrogen(V) compounds
Oxychlorides
Inorganic chlorine compounds | Nitryl chloride | Chemistry | 119 |
1,461,205 | https://en.wikipedia.org/wiki/Argon%E2%80%93argon%20dating | Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. 40Ar/39Ar dating relies on neutron irradiation from a nuclear reactor to convert a stable form of potassium (39K) into the radioactive 39Ar. As long as a standard of known age is co-irradiated with unknown samples, it is possible to use a single measurement of argon isotopes to calculate the 40K/40Ar* ratio, and thus to calculate the age of the unknown sample. 40Ar* refers to the radiogenic 40Ar, i.e. the 40Ar produced from radioactive decay of 40K. 40Ar* does not include atmospheric argon adsorbed to the surface or inherited through diffusion and its calculated value is derived from measuring the 36Ar (which is assumed to be of atmospheric origin) and assuming that 40Ar is found in a constant ratio to 36Ar in atmospheric gases.
Method
The sample is generally crushed and single crystals of a mineral or fragments of rock are hand-selected for analysis. These are then irradiated to produce 39Ar from 39K via the (n-p) reaction 39K(n,p)39Ar. The sample is then degassed in a high-vacuum mass spectrometer via a laser or resistance furnace. Heating causes the crystal structure of the mineral (or minerals) to degrade, and, as the sample melts, trapped gases are released. The gas may include atmospheric gases, such as carbon dioxide, water, nitrogen, and radiogenic gases like argon and helium, generated from regular radioactive decay over geologic time. The abundance of 40Ar* increases with the age of the sample, though the rate of increase decays exponentially with the half-life of 40K, which is 1.248 billion years.
Age equation
The age of a sample is given by the age equation:
where λ is the radioactive decay constant of 40K (approximately 5.5 x 10−10 year−1, corresponding to a half-life of approximately 1.25 billion years), J is the J-factor (parameter associated with the irradiation process), and R is the 40Ar*/39Ar ratio. The J factor relates to the fluence of the neutron bombardment during the irradiation process; a denser flow of neutron particles will convert more atoms of 39K to 39Ar than a less dense one.
Relative dating only
The 40Ar/39Ar method only measures relative dates. In order for an age to be calculated by the 40Ar/39Ar technique, the J parameter must be determined by irradiating the unknown sample along with a sample of known age for a standard. Because this (primary) standard ultimately cannot be determined by 40Ar/39Ar, it must be first determined by another dating method. The method most commonly used to date the primary standard is the conventional K/Ar technique. An alternative method of calibrating the used standard is astronomical tuning (also known as orbital tuning), which arrives at a slightly different age.
Applications
The primary use for 40Ar/39Ar geochronology is dating metamorphic and igneous minerals. 40Ar/39Ar is unlikely to provide the age of intrusions of granite as the age typically reflects the time when a mineral cooled through its closure temperature. However, in a metamorphic rock that has not exceeded its closure temperature the age likely dates the crystallization of the mineral. Dating of movement on fault systems is also possible with the 40Ar/39Ar method. Different minerals have different closure temperatures; biotite is ~300°C, muscovite is about 400°C and hornblende has a closure temperature of ~550°C. Thus, a granite containing all three minerals will record three different "ages" of emplacement as it cools down through these closure temperatures. Thus, although a crystallization age is not recorded, the information is still useful in constructing the thermal history of the rock.
Dating minerals may provide age information on a rock, but assumptions must be made. Minerals usually only record the last time they cooled down below the closure temperature, and this may not represent all of the events which the rock has undergone, and may not match the age of intrusion. Thus, discretion and interpretation of age dating is essential. 40Ar/39Ar geochronology assumes that a rock retains all of its 40Ar after cooling past the closing temperature and that this was properly sampled during analysis.
This technique allows the errors involved in K-Ar dating to be checked. Argon–argon dating has the advantage of not requiring determinations of potassium. Modern methods of analysis allow individual regions of crystals to be investigated. This method is important as it allows crystals forming and cooling during different events to be identified.
Recalibration
One problem with argon-argon dating has been a slight discrepancy with other methods of dating. Work by Kuiper et al. reports that a correction of 0.65% is needed. Thus the Cretaceous–Paleogene extinction (when the dinosaurs died out)—previously dated at 65.0 or 65.5 million years ago—is more accurately dated to 66.0-66.1 Ma.
See also
Grenville Turner, inventor of the technique
Berkeley Geochronology Center
References
External links
WiscAr Geochronology Laboratory, University of Wisconsin-Madison
UC Berkeley press release: "Precise dating of the destruction of Pompeii proves argon-argon method can reliably date rocks as young as 2,000 years"
New Mexico Geochronology Research Laboratory
Argon Isotope Facility of the Scottish Universities Environmental Research Council
Open University Ar/Ar and Noble Gas Laboratory
Argon Laboratory / Australian National University
Radiometric dating
Argon | Argon–argon dating | Chemistry | 1,236 |
1,072,505 | https://en.wikipedia.org/wiki/Voice%20over%20WLAN | Voice over wireless LAN (VoWLAN), also voice over Wi‑Fi (VoWiFi), is the use of a wireless broadband network according to the IEEE 802.11 standards for the purpose of vocal conversation. In essence, it is voice over IP (VoIP) over a Wi-Fi network. In most cases, the Wi-Fi network and voice components supporting the voice system are privately owned.
VoWLAN can be conducted over any Internet accessible device, including a laptop, PDA or VoWLAN units which look and function like DECT and cellphones. Just like for IP-DECT, the VoWLAN's main advantages to consumers are cheaper local and international calls, free calls to other VoWLAN units and a simplified integrated billing of both phone and Internet service providers.
Although VoWLAN and 3G have certain feature similarities, VoWLAN is different in the sense that it uses a wireless internet network (typically 802.11) rather than a cellular network. Both VoWLAN and 3G are used in different ways, although with a femtocell the two can deliver similar service to users and can be considered alternatives.
Applications
For a single location organisation it enables use of existing Wi-Fi network for low (or no) cost of use VoIP (hence VoWLAN) communication in a similar manner to land mobile radio system or walkie-talkie systems with push to talk and emergency broadcast channels. They are also used across multiple locations for mobile workers such as delivery drivers, these workers need to take advantage of 3G type services whereby a cellular company provide data access between the handheld device and the companies back-end network.
Types
as an extension to cellular network using Generic Access Network or Unlicensed Mobile Access (the equivalent but more commercial term).
as a local network independent of cellular company.
Design considerations
A Wi-Fi network that supports voice telephony must be carefully designed in a way that maximizes performance and is able to support the applicable call density. A voice network includes call gateways in addition to the Wi-Fi access points. The gateways provide call handling among wireless IP phones and connections to traditional telephone systems. The Wi-Fi network supporting voice applications must provide much stronger signal coverage than what's needed for most data-only applications. In addition, the Wi-Fi network must provide seamless roaming between access points.
Alternatives
As noted above, in many contexts a femtocell, using cellular technology to connect to standard terminals, can be considered an alternative to VoWLAN.
See also
Local area network
Mobile VoIP
Voice over LTE
References
Wireless networking
Voice over IP | Voice over WLAN | Technology,Engineering | 529 |
63,630,286 | https://en.wikipedia.org/wiki/HII%20galaxy | An HII galaxy is a very luminous dwarf starburst galaxy. Generally, HII galaxies have a low metallicity and high percentage of neutral hydrogen. There is generally believed to be a relationship between luminosity and disturbed morphology, suggesting that the starburst activity in the galaxy is caused by tidal interactions. The distribution of luminosities tends to cluster around two different extremes: those with a high luminosity and highly disturbed morphology, and those with a low luminosity and fairly regular and symmetric morphology. Those with high luminosities are labelled by some as type I HII galaxies and those with lower luminosities as type II HII galaxies. There is also a general correlation between metallicity and mass of the galaxies. The name of HII galaxies comes from their spectroscopic properties which are more or less indistinguishable from that of HII regions.
References
Starburst galaxies | HII galaxy | Astronomy | 190 |
12,122,491 | https://en.wikipedia.org/wiki/C2H8N2 | {{DISPLAYTITLE:C2H8N2}}
The molecular formula C2H8N2 (molar mass: 60.10 g/mol, exact mass: 60.0688 u) may refer to:
Dimethylhydrazine
Unsymmetrical dimethylhydrazine
Symmetrical dimethylhydrazine
Ethylenediamine, or ethane-1,2-diamine | C2H8N2 | Chemistry | 90 |
27,114,298 | https://en.wikipedia.org/wiki/Isoclinism%20of%20groups | In mathematics, specifically group theory, isoclinism is an equivalence relation on groups which generalizes isomorphism. Isoclinism was introduced by to help classify and understand p-groups, although it is applicable to all groups. Isoclinism also has consequences for the Schur multiplier and the associated aspects of character theory, as described in and . The word "isoclinism" comes from the Greek ισοκλινης meaning equal slope.
Some textbooks discussing isoclinism include and and .
Definition
The isoclinism class of a group G is determined by the groups G/Z(G) (the inner automorphism group) and (the commutator subgroup) and the commutator map from G/Z(G) × G/Z(G) to (taking a, b to aba−1b−1).
In other words, two groups G1 and G2 are isoclinic if there are isomorphisms from G1/Z(G1) to G2/Z(G2) and from G1 to G2 commuting with the commutator map.
Examples
All Abelian groups are isoclinic since they are equal to their centers and their commutator subgroups are always the identity subgroup. Indeed, a group is isoclinic to an abelian group if and only if it is itself abelian, and G is isoclinic with G×A if and only if A is abelian. The dihedral, quasidihedral, and quaternion groups of order 2n are isoclinic for n≥3, in more detail.
Isoclinism divides p-groups into families, and the smallest members of each family are called stem groups. A group is a stem group if and only if Z(G) ≤ [G,G], that is, if and only if every element of the center of the group is contained in the derived subgroup (also called the commutator subgroup), . Some enumeration results on isoclinism families are given in .
Isoclinism is used in theory of projective representations of finite groups, as all Schur covering groups of a group are isoclinic, a fact already hinted at by Hall according to . This is used in describing the character tables of the finite simple groups .
References
Finite groups | Isoclinism of groups | Mathematics | 492 |
514,036 | https://en.wikipedia.org/wiki/Association%20for%20Progressive%20Communications | The Association for Progressive Communications (APC) is an international network of organizations that was founded in 1990 to provide communication infrastructure, including Internet-based applications, to groups and individuals who work for peace, human rights, protection of the environment, and sustainability. Pioneering the use of ICTs for civil society, especially in developing countries, APC were often the first providers of Internet in their member countries.
APC is a worldwide network of social activists who use the internet to make the world a better place. APC is both a network and an organisation. APC members are groups working in their own countries to advance the same mission as APC. APC has more than 59 members, mostly in Asia, Africa and Latina America, from five continents. This is a challenge and a strength, because members are at the two extremes of internet development (members in South Korea with incredible connectivity and members in rural Nigeria where they have to power computers using car batteries and solar power) and in between.
History
Background and creation
APC was founded in 1990 by:
Institute for Global Communications (IGC), San Francisco, USA
GreenNet, London, United Kingdom
IBASE, Rio de Janeiro, Brazil
Nicarao, Managua, Nicaragua
Pegasus Networks, Byron Bay, Australia
Web Networks, Toronto, Canada
NordNet, Sweden
The activists working with United Nations–sponsored data management NGO (IDOC) create a network of like-minded organisations working with information and alternative media. At this point they communicated mainly using fax and regular mail. People physically travelled around transporting and sharing databases of information and software on disks.
In 1988, on the verge of APC creation, Mitra Ardron describes the central characteristic of the future APC user, present operations and the history of APC precedents: PeaceNet, EcoNet and GreenNet. He also expresses a common commitment to global communication available to everyone.
UN status
Collaboration between APC and the United Nations began in 1992, in preparation for the UN Conference on Environment and Development (UNCED), more popularly known as the Earth Summit. As APC had the only international, civil society communications network in existence at that time, the UNCED secretariat published their information in APC conferences. They had no other way of distributing information so economically and so effectively. (The UN itself began distributing information by electronic means many years later).
Email links are set up between Cuba and APC networks. They call the Cuban servers three times a day to deliver and collect email.
The cooperation continues over the years. APC received consultative status to the UN with the several quadrennial reports submitted over the years. APC also cooperated with United Nations Development Programme. APC actively participate in UN initiatives such as Millennium Development Goals. The studies of violence against women and ICTs in ten countries and how legislation or lack of it hinders or helps women were conducted and published as a part of promoting gender equality and empowering women.
The APC Women's Networking Support Programme (APC - WNSP) co-coordinated a women's network to bring an NGO perspective to the UN Beijing +5 review. Official declarations promote ICT as a way of enhancing NGO participation in global media policy making. It also gives recommendations for women's portrayal, decision making and advocacy in media industry.
Late 1990s
APC made a significant impact in Africa, Asia, Central and Eastern Europe, and the Caribbean by providing civil society organisations with email and e-information using the Fidonet gateways. Fidonet protocol was used because it is store-and-forward technology enabling people to compose and read email offline which is very important in the countries with the pour infrastructure (phone lines, electrical supply and hardware).
APC's African networks faced with the strong competition from commercial providers, held an Africa Strategy Development Meeting from February 8–11, 1997 in Johannesburg, South Africa. The meeting attended 34 APC members and partner networks from all over Africa. The program areas, action framework and plan as well as women's program were discussed. A powerful statement from the meeting was published as The Holy Family Communiqué from African Electronic Communicators.
A legal threat to freedom of information online came from the company Biwater and involved APC member LabourNet, April 1997. Thirteen APC members mirrored the threatened content.
2000–2003
2000 was a turning point for APC. The new vision statement drafted at an APC council meeting held in Piriapolis, Uruguay hosted by the Third World Institute (ITeM): "APC works to achieve a world in which all people have easy, equal and affordable access to the creative potential of the internet to improve their lives and create more democratic and egalitarian societies.".
In May 2001, APC and partners started work on building a portal which collects training materials related to ICT for social change. This portal, named Itrain Online, is an entry point for finding the best computer training resources on the web for the social change and development.
The first APC Internet Rights Charter was published in three languages: English, French and Spanish. The themes: internet access for all, freedom of expression and association, access to knowledge, shared learning and creation, privacy, governance and rights were addressed.
APC started Gender, Agriculture and Rural Development in the Information Society (GenARDIS) in 2002. This project was launched to provide small grants for the agricultural initiatives by women. The access to new information and communication technologies affected rural men and women and improved agricultural production.
The ICT policy handbook for beginners was published in 2003 together with a tri-lingual ICT policy training for civil society curriculum which includes a special section on advocacy for positive policy change.
APC stimulated multi-stakeholder dialogue as part of the Catalysing Access to ICTs in Africa (CATIA) programme, and trained 100 technology enthusiasts in Africa to set up community wireless networks.
2004–2008
Take Back The Tech!, a 16 days of activism against gender-based violence (25 Nov - 10 Dec), started in 2006. This campaign engages information and communication technology in helping end gender-based violence.
APC joined Internet Governance Forum for the first time in 2008. A statement to IGF open consultations was submitted before the third IGF supporting regional IGF meetings and giving suggestions about themes and content of the meeting in Hyderabad.
The first edition of Global Information Society Watch was published, focused on citizen participation in ICT policy processes in the wake of the World Summit on the Information Society. These reports are accessible yearly and are a joint initiative with the Humanist Institute for Development Cooperation Hivos.
The other activities included replication of the community wireless training developed in Africa in Latin America and the Caribbean, forming an eighteen-country network connecting indigenous communities, rural backwaters and impulsing university networking courses, the first Feminist Tech Exchange, training people from 680 organisations in technology for social change and ICT policy from 2004-2008, organizing a press conference in Tunisia to address the host government's suppression of free speech in the wake of the second World Summit on the Information Society, launching GenderIT.org.
2009–2012 strategic plan and progress
APC priorities for 2009–2012 period were: advocate for affordable internet for all, make technology work to sustain environment, use emerging technology for social change, build collaborative open online space, secure and defend internet rights and improve internet and other governance.
The strategic plan was realized by
launching Internet Rights and Human Rights project,
starting research on the real lived experiences of women around the internet and sexuality,
publishing Global Information Society Watch: 2010 addressed the pressing issues of ICTs and climate change and e-waste, a dedicated edition on a defence of human rights and women's rights workers working online, GISWatch 2012 focused on the Internet and corruption, as well as 2 updates to GISWatch 2011: Update 1 and Update II,
designing a manual called "Communicating research for influence: Strategies and challenges for bringing about change" based on their success stories and challenges in communicating research for influence,
developing a practical guide to sustainable IT. It offers a detailed, "hands-on" introduction to thinking about sustainable computing holistically; starting with the choices you make when buying technology, through to the software and peripherals you use, how you store and work with information, manage your security, save power, and maintain and dispose of your old hardware.
The Dominican government chooses APC's Gender Evaluation Methodology (GEM) as a tool to design and evaluate their ICT policies.
The eleventh face-to-face APC council meeting is held on Panglao Island in the Philippines, hosted by the Foundation for Media Alternatives. Over one hundred communications activists also attend a Networking and Learning Forum to strategise for an open, fair and sustainable internet.
2013–2016 strategic plan and progress
The second strategic plan was released defining five priorities for 2013–2016: securing and defending internet access and rights, fostering good internet governance, strengthening use and development of transformative technology, ending technology-based violence against women and girls and strengthening APC community networks.
The realization of this plan included the following:
Global Information Society Watch was published on communication rights ten years after the World Summit on the Information Society (WSIS).
APC co-organised the second (2014) and third (2015) editions of the African School on Internet Governance, with graduates from more than 15 African countries.
Structure
APC is governed by the board of directors which include an executive director, a chair, a vice-chair, a treasurer and any other officers elected by APC council. The executive officer is a past board member and all other officers are elected for a three-year term during APC council meeting. The council is made up of the two representatives from each member organization and it is a secondary governing body that meets every three years. Besides, electing the board officers, it also sets strategic priorities.
APC board 2014–2016 was elected in Barcelona:
Julián Casabuenas, Colnodo, Colombia (Chair)
Valentina Pelizzer, OWPSEE, Bosnia-Herzegovina (Vice-chair)
Liz Probert, GreenNet, United Kingdom (Secretary)
Osama Manzar, Digital Empowerment Foundation, India (Treasurer)
John Dada, Fantsuam Foundation, Nigeria
Lillian Nalwoga, CIPESA, Uganda
Chim Manavy, Open Institute, Cambodia
Anriette Esterhuysen, APC, South Africa
Membership
North America
Alternatives, Action and Communication Network for International Development, Canada
Institute for Global Communications (IGC), United States of America
LaborNet, United States of America
LaNeta, Mexico
Web Networks, Canada
May First/People Link, United States of America
Latin America and the Caribbean
CEPES, Peru
Colnodo, Colombia
Fundación Escuela Latinoamericana de Redes (EsLaRed), Venezuela
Instituto del Tercer Mundo (ITeM), Uruguay
NODO TAU, Argentina
RITS (Information Network for the Third Sector), Brazil
Networks & Development Foundation - FUNREDES, Dominican Republic
Wamani, Argentina
Núcleo de Pesquisas, Estudos e Formação (Nupef), Brazil
ONG Derechos Digitales, Chile
Sulá Batsú, Costa Rica
Asociación Trinidad Comunicación, Cultura y Desarrollo, Paraguay
Europe
BlueLink Information Network, Bulgaria
Computer Aid International, United Kingdom
GreenNet, United Kingdom
Green Spider, Hungary
Metamorphosis Foundation, Macedonia
OWPSEE, Bosnia-Herzegovina
Pangea.org, Spain
StrawberryNet, Romania
ZaMirNet, Croatia
ComLink, Germany (See :de:CL-Netz for German article)
Africa
ArabDev, Egypt
Fantsuam Foundation, Nigeria
Arid Lands Information Network (East Africa), Kenya
Community Education Computer Society (CECS), South Africa
SANGONeT, South Africa
Ungana-Afrika, South Africa
Women'sNet, South Africa
WOUGNET - Women of Uganda Network, Uganda
AZUR Développement, Republic of the Congo
Kenya ICT Action Network (KICTANet), Kenya
Collaboration on International ICT Policy for East and Southern Africa (CIPESA), Uganda
Asia-Pacific
Bytes for All.org, South Asia
EngageMedia, Australia, Indonesia
Foundation for Media Alternatives (FMA), Philippines
JCA-NET, Japan
JCafe, Japan
Korean Progressive Network Center (Jinbonet), South Korea
Open Institute of Cambodia, Cambodia
WomensHub, Philippines
Bangladesh Friendship Education Society (BFES) - Bangladesh
Voices for Interactive Choice and Empowerment (VOICE), Bangladesh
Digital Empowerment Foundation (DEF), India
Society for Promotion of Alternative Computing and Employment (SPACE), India
Actions
Gender evaluation methodology (GEM)
The Gender Evaluation Methodology is an evaluation methodology that integrates a gender analysis into evaluations of initiatives that use information and communications technologies (ICTs) for social change. It is an evaluation tool for determining whether ICTs are really improving or worsening women’s lives and gender relations, as well as for promoting positive change at the individual, institutional, community and broader social levels. It was first developed in 2002 and was tried and tested by thirty community-based organisations. Since then hundreds of people have become involved in GEM's development including people who developed the tool, who train in how to use GEM, who are adapting GEM to increase its applicability to rural ICT4D projects, telecentres, software localisation and ICT policy advocacy and who are now offering GEM evaluations on a consultancy basis. The GEM manual was written in English and has been translated into French, Spanish, Brazilian Portuguese and Arabic). GEM was developed by the APC Women's Rights Programme (APC WRP
Global Information Society Watch
Global Information Society Watch is an annual report co-produced by APC and Hivos, a Dutch organization for development, which looks at the progress being made in creating an inclusive information society worldwide (particularly in implementing World Summit on the Information Society goals), encourages critical debate and strengthens networking and advocacy for a just, inclusive information society. The country reports are easy to read and offer a quick insight into a country situation. Contributors are primarily from civil society organisations active in ICT issues in their countries. Themes covered include environment and ICTs, human rights and the internet and internet infrastructure. There is a Giswatch book website.
GISWatch editions by year:
GIS Watch 2019 - Artificial intelligence: human rights, social justice and development
GISWatch 2018 - Community networks
GISWatch 2017 - National and Regional Internet Governance Forum Initiatives (NRIs)
GISWatch 2017 Special Issue - Internet governance from the edges - National and regional IGFs in their own words
GISWatch 2017 Special Issue - Unshackling expression - A study on laws criminalising expression online in Asia
GISWatch 2016 - Economic, Social and Cultural Rights and the Internet
GISWatch 2015 - Sexual Rights and the Internet
GISWatch 2014 - Communications surveillance in the digital age
GISWatch 2013 - Women's rights, gender and ICTs
GISWatch 2012 - The internet and corruption
GISWatch 2011 - Internet rights and democratisation
GISWatch 2010 - ICTs and Environmental Sustainability
GISWatch 2009 - Access to Online Information and Knowledge
GISWatch 2008 - Access to Infrastructure
GISWatch 2007 - Participation
ActionApps
ActionApps offer a low cost solution for content sharing that both increases the functionality of not-for-profit and NGO websites, and facilitates the creation of portals sites so as to improve the visibility of civil society information. They are driven by free software. ActionApps were first developed by APC and released to the free and open source software community. Development continues strongly in South America.
Evaluations, awards and criticism
FLOSS
APC is awarding Chris Nicol free/libre open source software award (FLOSS or FOSS). The criteria and 2014 and 2007 winners are published.
Awards to people
Karen Banks and the APC Women's Networking Support Programme are awarded the Anita Borg Prize for Social Impact (2004).
Valeria Betancourt, Communications and Information Policy Programme manager, wins LACNIC's Outstanding Achievement Award, honouring internet leaders in the LAC region
APC's Executive Director Anriette Esterhuysen and Finance Manager Karen Banks are inducted into the ISOC's Internet Hall of Fame (2013)
APC's Executive Director Anriette Esterhuysen and APC were awarded the Electronic Frontier Foundation's 2015 Pioneer Award.
Awards for programs
GISWatch wins WSIS Project Prize from the ITU
Take Back the Tech! (South Africa) won GEM Award 2014 in category 6: Efforts to Reduce Threats Online and Building Women's Confidence and Security in the Use of ICTs.
2013 DDoS Attack
Beginning at 10.15 BST on Thursday 1 August 2013 GreenNet, and consequently APC, suffered an extensive DDoS attack. The attack was later described as a "DNS reflection attack" also known as a spoofed attack Several sources linked the attack to the Zimbabwe Elections, held a day earlier. GreenNet's services were not fully operational again until 10.30 BST on Thursday 7 August. On the 9th of August there was a second attack, which, while affecting some systems, allowed GreenNet to discover the site which was being targeted. In October 2013, the target was revealed to be the site of British investigative reporter Andrew Jennings.
See also
References
External links
The Association for Progressive Communications (English, French, Spanish and Portuguese)
International Development Research Centre
Organizations established in 1990
Information technology organizations
Privacy organizations | Association for Progressive Communications | Technology | 3,591 |
72,244,439 | https://en.wikipedia.org/wiki/Deutschlandticket | The () often shorted to the D-Ticket, also known as the 49-Euro-Ticket, is a subscription public transport ticket for all local public transport, valid in the whole of Germany, that costs 49 euros per month. The Scholz cabinet introduced it in May 2023 as a permanent successor to the 9-Euro-Ticket which had been offered in Summer 2022. The German federation () and the federal states () initially participate in the financing with 1.5 billion euros per year until 2025.
At the beginning of January 2025, the price of the ticket was raised to 58 per month.
Ticket conditions
Validity
The ticket is valid on all local and regional buses, trams, metros, S-Bahn trains, and local and regional trains (RB/RE) across the whole of Germany, except on few RE trains operated by DB Fernverkehr.
It is usually valid on international eligible trains from/to end stations in a neighbour country, if operated by a German operator. Deutschlandticket holders can also go to a number of border tariff stations outside Germany using their passes including; Tønder () in Denmark, Wissembourg (Gare de Wissembourg) in France, Hengelo (over Oldenzaal), and Venlo in the Netherlands, Basel in Switzerland and Świnoujście () in Poland.
It is not valid on most of the long-distance trains (such as Intercity Express (ICE), Intercity (IC) and Eurocity (EC) trains operated by Deutsche Bahn) and on long-distance bus coaches (such as those operated by Flixbus). There are exceptions for long-distance trains, which are co-financed by cities and states.
The ticket is only valid for transportation in second class. Often it is possible to buy upgrades to first class (if available) from the concerned operator. Children under 6 years old travel for free, while older children need their own ticket. The Deutschlandticket does not include transportation for pets or for bicycles in cases where they require a separate ticket.
Sales
The Deutschlandticket was originally sold as a monthly subscription at a cost of 49 Euros per month which increased to 58 Euros in January 2025. The ticket is valid for a calendar month, and is automatically renewed, with payment taken by SEPA direct debit from the user's bank account or by credit card. The subscription can be cancelled by the 10th day of each month. Users wishing to purchase a new subscription for the current month on the 11th day of the month or later must pay for at least the current and the following calendar month. The mo.pla app allows users to cancel their Deutschlandticket subscription up to the second-last day of the month.
The Deutschlandticket is sold by participating local transit authorities. It is issued as a digital ticket via mobile apps offered by local transit authorities. It can also be issued on a chip smartcard using the "eTicket Deutschland" standard. Employers can subsidise the ticket for their employees, and university students can upgrade their "Semesterticket" to a Deutschlandticket. Some communities have additionally subsidised the ticket for those on low income, senior citizens and apprentices. The city of Tübingen has gone as far as subsidising the ticket for every resident, so they can get it for 34 euros per month. The local council in the city of Stuttgart has offered the Deutschlandticket to its employees as an employee benefit.
The BahnCard 100, a rail card offered by Deutsche Bahn allowing unlimited travel on its trains, includes a Deutschlandticket at no additional charge.
History
After the start of the Russian invasion of Ukraine, energy prices in Germany rose significantly. In response, the government introduced the heavily subsidized 9-Euro-Ticket, which allowed unlimited use of public local transportation across Germany at a cost of 9 euros per calendar month. It was available for June, July, and August 2022. After the end of this 3-month period, politicians called for a permanent successor ticket that would offer similar simplicity, though there was debate about the price.
At the end of November 2022, transport ministers reaffirmed their commitment to the monthly ticket for 49 euros, and it was planned to start in April 2023, as a start in January was considered too early for implementation. The start was delayed further by one month as there was opposition from the local and regional transportation services like the Munich MVV that wanted more funding from the federal and the state governments.
On 31 March 2023, the Bundesrat approved the bill passed by the Bundestag for a nationwide ticket for local and regional public transportation at a monthly price of 49 euros. The monthly tickets started in May 2023, but could only be purchased by subscription. There are no paper tickets for the subscription – with the possible exception at the start-up phase; the users have to authenticate digitally (either via smartphone app or chip card).
The ticket price is to be adjusted to inflation each year, although the 49 euro price is intended to be fixed for at least the first two years of operation of the ticket.
On 31 July, three months after the introduction of the Deutschlandticket, the transport ministry reported that 11 million people subscribed to the ticket, with 5 million being existing subscribers to monthly transport passes, 5 million new subscribers from existing public transport ticket holders and one million new users of public transport. On 13 September, the Hamburg transport agency reported that it had sold over a million subscriptions.
Since the summer of 2023, Federal Transport Minister Volker Wissing (FDP) had argued with the federal states about the financing of the ticket. The financing of the ticket is unclear. Both sides have so far contributed 1.5 billion euros annually. If there is not enough money, the federal and state governments currently share the additional costs. The federal government rejects further financial commitments from 2024.
At the beginning of December 2023, the Stendal district decided that the ticket will no longer be valid on its buses from January 1, 2024. This would have meant that the Deutschlandticket would no longer be valid across the board. However, the district council reverted its decision two weeks later and the Deutschlandticket remains a valid ticket in the Stendal district.
Interest outside Germany
Due to the popularity and interest in the Deutschlandticket in Germany, other countries expressed interest in introducing a similar scheme in their country.
Portugal
On 30 June 2023, influenced by Deutschlandticket, the eco-socialist LIVRE party proposed a monthly rail pass for the regional trains by the state-owned rail operator Comboios de Portugal in the country's annual budget. The proposal passed in parliament, and the Portuguese government said it was introducing a 49 euros per month regional rail pass called the Passe Ferroviário Nacional (National Train Pass) from 1 August 2023. It would allow unlimited travel on all regional trains, known as comboios regionais apart from the tourist trains like the , and suburban rail services in Lisbon, Porto and Coimbra.
Critics have said that due to the rules and exclusions of the pass, there are virtually no regional rail services in the middle of the country and frequent strikes by rail workers make the pass worthless.
France
On 9 June 2023, German federal transport minister Volker Wissing said in an interview with Berliner Morgenpost, that he was talking to his French counterpart Clément Beaune about the scheme in a meeting between the two ministers during a discussion about a Franco-German student travel scheme.
In an interview with French YouTuber Hugo Travers on 4 September 2023, French president Emmanuel Macron said his government is looking at a French equivalent of the Deutschlandticket. Later that week on 7 September, on France 2's breakfast programme Télématin, Beaune said the transport ministry was provisionally working on a similar scheme called "Pass Rail" which would come in the summer of 2024. The ticket would allow unlimited travel throughout France on the country's regional trains, the TERs and the regular Intercités for 49 euros per month. Beaune said the government was talking to local authorities about including local bus and trams as well.
Reactions to the proposal were mixed, with the region of Grand Est being supportive of the idea, while the region of Hauts-de-France was critical particularly over costs, pointing out that the region already subsidises its TER to the tune of 530 million euros. The president of the Île-de-France region Valérie Pécresse said in an interview on France 3 Paris Île-de-France, that the costs for such a scheme would be around 1.8 billion euros for the region, making it unaffordable. Wissing has said he would like to interlink the two schemes, so that persons could use either pass in each other's countries.
On 27 September, Beaune and the presidents of all regions came together in Saint-Malo to begin discussions on financing such a scheme, together with general rail finance such as track fees and rolling stock. It is hoped that such a subscription would be available by the summer of 2024.
United Kingdom
A report produced for Greenpeace by the Greengauge 21 think tank suggested that a similar scheme might increase usage of UK train routes and reduce the climate impact of fossil fuel powered vehicles. The Department for Transport responded to the report by stating that the UK Government has no plans to implement a similar scheme at the present time.
See also
Klimaticket in Austria
365-Euro-Ticket in Vienna
External links
Federal government's information on the Deutschlandticket
Deutsche Bahn's page on the Deutschlandticket
Rhein-Main-Verkehrsverbund's page on the Deutschlandticket
References
2022 in politics
Emissions reduction
Euro
Fare collection systems in Germany
Public transport in Germany
Scholz cabinet
Public transport tickets
Environmental policies approved in 2023 | Deutschlandticket | Chemistry | 2,025 |
19,342,760 | https://en.wikipedia.org/wiki/Seven%20Wonders%20of%20the%20Ancient%20World | The Seven Wonders of the Ancient World, also known as the Seven Wonders of the World or simply the Seven Wonders, is a list of seven notable structures present during classical antiquity. The first known list of seven wonders dates back to the 2nd–1st century BC.
While the entries have varied over the centuries, the seven traditional wonders are the Great Pyramid of Giza, the Colossus of Rhodes, the Lighthouse of Alexandria, the Mausoleum at Halicarnassus, the Temple of Artemis, the Statue of Zeus at Olympia, and the Hanging Gardens of Babylon. Using modern-day countries, two of the wonders were located in Greece, two in Turkey, two in Egypt, and one in Iraq. Of the seven wonders, only the Pyramid of Giza, which is also by far the oldest of the wonders, remains standing, while the others have been destroyed over the centuries. There is scholarly debate over the exact nature of the Hanging Gardens, and there is doubt as to whether they existed at all.
Background
Alexander the Great's conquest of much of the western world in the 4th century BC gave Hellenistic travellers access to the civilizations of the Egyptians, Persians, and Babylonians. Impressed and captivated by the landmarks and marvels of the various lands, these travellers began to list what they saw to remember them.
Instead of "wonders", the ancient Greeks spoke of "theamata" (θεάματα), which means "sights", in other words "things to be seen" (Τὰ ἑπτὰ θεάματα τῆς οἰκουμένης [γῆς] ). Later, the word for "wonder" ("thaumata" θαύματα, "wonders") was used. Hence, the list was meant to be the ancient world's counterpart of a travel guidebook.
The first reference to a list of seven such monuments was given by Diodorus Siculus. The epigrammist Antipater of Sidon, who lived around or before 100 BC, gave a list of seven "wonders", including six of the present list (substituting the walls of Babylon for the Lighthouse of Alexandria):
Another ancient writer, who, perhaps dubiously, identified himself as Philo of Byzantium, wrote a short account entitled The Seven Sights of the World. The surviving manuscript is incomplete, missing its last pages. Still, from the preamble text, it can be concluded that the list of seven sights exactly matches Antipater's (the preamble mentions the location of Halicarnassus, but the pages describing the seventh wonder, presumably the Mausoleum, are missing).
Earlier and later lists by the historian Herodotus ( BC– BC) and the poet Callimachus of Cyrene (–240 BC), housed at the Museum of Alexandria, survive only as references.
The Colossus of Rhodes was the last of the seven to be completed, after 280 BC, and the first to be destroyed, by an earthquake in 226/225 BC. It was therefore already in ruins by the time the list was compiled, and all seven wonders existed simultaneously for less than 60 years.
Scope
The list covered only the Mediterranean and Middle Eastern regions, which then comprised the known world for the Greeks. The primary accounts from Hellenistic writers also heavily influenced the places included in the wonders list. Five of the seven entries are a celebration of Greek accomplishments in construction, the exceptions being the Pyramids of Giza and the Hanging Gardens of Babylon.
Wonders
Influence
Arts and architecture
The seven wonders on Antipater's list won praises for their notable features, ranging from superlatives of the highest or largest of their types, to the artistry with which they were executed. Their architectural and artistic features were imitated throughout the Hellenistic world and beyond.
The Greek influence in Roman culture, and the revival of Greco-Roman artistic styles during the Renaissance caught the imagination of European artists and travellers. Paintings and sculptures alluding to Antipater's list were made, while significant numbers of adventurers travelled to the actual sites to personally witness the wonders. Legends circulated to further complement the superlatives of the wonders.
Modern lists
Of Antipater's wonders, the only one that has survived to the present day is the Great Pyramid of Giza. Its brilliant white stone facing had survived intact until around 1300 AD, when local communities removed most of the stonework for building materials. The existence of the Hanging Gardens has not been proven, though theories abound. Records and archaeology confirm the existence of the other five wonders. The Temple of Artemis and the Statue of Zeus were destroyed by fire, while the Lighthouse of Alexandria, the Colossus, and tomb of Mausolus were destroyed by earthquakes. Among the surviving artefacts are sculptures from the tomb of Mausolus and the Temple of Artemis, currently kept in the British Museum in London.
The listing of seven of the most marvellous architectural and artistic human achievements continued beyond the Ancient Greek times to the Roman Empire, the Middle Ages, the Renaissance and to the modern age. The Roman poet Martial and the Christian bishop Gregory of Tours had their versions. Reflecting the rise of Christianity and the factor of time, nature and the hand of man overcoming Antipater's seven wonders, Roman and Christian sites began to figure on the list, including the Colosseum, Noah's Ark, and Solomon's Temple. In the 6th century, a list of seven wonders was compiled by St. Gregory of Tours: the list included the Temple of Solomon, the Pharos of Alexandria, and Noah's Ark.
Modern historians, working on the premise that the original Seven Ancient Wonders List was limited in its geographic scope, also had their versions to encompass sites beyond the Hellenistic realm—from the Seven Wonders of the Ancient World to the Seven Wonders of the World. The "seven wonders" label has spawned innumerable versions among international organizations, publications and individuals based on different themes—works of nature, engineering masterpieces, constructions of the Middle Ages, etc. Its purpose has also changed from just a simple travel guidebook or a compendium of curious places to a list of sites to defend or preserve.
See also
New 7 Wonders of the World, a campaign for people to vote and choose Wonders of the World from a selection of 200 existing monuments.
Eighth Wonder of the World, about attempted additions to the famous ancient list.
Wonders of the World, about similar lists made throughout the ages.
Seven Wonders of the World (1956 film)
7 Wonders of the Ancient World (2007 video game)
7 Wonders (2010 board game)
Seven Wonders (2013 book series)
References
Further reading
Clayton, Peter and Price, Martin, 1988, The Seven Wonders of the Ancient World. Routledge.
External links
"Seven Ancient Wonders of the World" on The History Channel website. Also includes links to medieval, modern and natural wonders.
Parkin, Tim, Researching Ancient Wonders: A Research Guide, from the University of Canterbury, New Zealand. – a collection of books and Internet resources with information on seven ancient wonders.
"Eternal wonder of humanity's first great achievements", by Jonathan Glancey in The Guardian, 10 March 2007
Ancient history
Former buildings and structures
Cultural lists
Ancient technology
History of construction
de:Weltwunder#Die sieben Weltwunder der Antike | Seven Wonders of the Ancient World | Engineering | 1,505 |
5,392,262 | https://en.wikipedia.org/wiki/Shabaka%20Stone | The Shabaka Stone, sometimes Shabaqo, is a relic incised with an ancient Egyptian religious text, which dates from the Twenty-fifth Dynasty of Egypt. In later years, the stone was likely used as a millstone, which damaged the hieroglyphs. This damage is accompanied by other intentional defacements, leaving the hieroglyphic inscription in poor condition.
Provenance
Historical origins
Originally erected as a lasting monument at the Great Temple of Ptah in Memphis in the late eighth century BCE, the stone was at some point removed (for unknown reasons) to Alexandria. From there, it was transported by a navy vessel from Alexandria to England. It was brought back as ballast along with a capital of an Egyptian column, fragments of a Greco-Roman black basalt capital, two fragments of quartzite lintel of Senwosret III, and a black granite kneeling statue of Ramesses II. In 1805, the stone was donated to the British Museum by George Spencer, 2nd Earl Spencer (1758–1834), who was First Lord of the Admiralty and since 1794 the trustee of the museum. In 1901, the stone was deciphered, translated, and interpreted for the first time by the American Egyptologist, James Henry Breasted. The monument has remained at the museum to the present day.
Dating
The stone's dedicatory introduction claims that it is a copy of the surviving contents of a worm-ridden, decaying papyrus found by the pharaoh Shabaka in the Great Temple of Ptah. Homer W. Smith dates the original text to the First Dynasty, calling it "the oldest written record of human thought".
Breasted, Adolf Erman, Kurt Sethe, and Hermann Junker all dated the stone to the Old Kingdom. The stone is archaic, both linguistically (its language is similar to that used in the Pyramid Texts of the Old Kingdom) and politically (it alludes to the importance of Memphis as the first royal city). As such, Henri Frankfort, John Wilson, Miriam Lichtheim, and Erik Iversen have also assessed the stone to be from the Old Kingdom. However, Friedrich Junge and most other scholars since then have argued that the monument was produced in the Twenty-fifth Dynasty. Today, scholars feel it is clear that it cannot predate the Nineteenth Dynasty.
Composition
The stela is around wide, with the left side height estimated at and the right side about . The written surface is in width and on average, in height. The rectangular hole in the center is , with eleven radiating lines ranging in length from . The area of the surface which has been completely worn-out measures across.
In 1901, James Henry Breasted identified the stone as a rectangular slab of black granite. While other scholars postulated that the monument was a slab or basalt or a conglomerate stone, a recent analysis by a scientist of the British Museum revealed the stone to be green breccia originating from Wadi Hammamat.
Content
The text includes two main divisions with a short introduction and an ending summary. The first division relates the unification of Upper and Lower Egypt. Ptah works through Horus to accomplish this unification. The other is a creation myth, the "Memphite Theology" or "Memphite Drama", that establishes Ptah as the creator of all things, including gods.
The text stresses that it is in Memphis that the unification of Egypt took place. The inscription also states that this town was the burial-place of Osiris, after he drifted ashore.
Introduction and titulary of the King
The first line of the stone presents the fivefold royal titulary of the king: "The living Horus: Who prospers the Two Lands; the Two Ladies: Who prospers the Two Lands; the King of Upper and Lower Egypt: Neferkare; the Son of Re: [Shabaka], beloved of Ptah-South-of-His-Wall, who lives like Re forever." The first three names emphasize the king's manifestation as a living god (especially of the falcon-headed Horus, patron god to the Egyptian kings), while the latter two names (the king's throne name and birth name) refer to Egypt's division and unification.
The second line, a dedicatory introduction, states that the stone is a copy of the surviving contents of a worm-eaten papyrus Shabaka found as he was inspecting the Great Temple of Ptah.
The Unification of Egypt
Lines 3 to 47 describe the unification of Upper and Lower Egypt under the god Horus at Memphis. The text first declares the political and theological supremacy of the Memphite god Ptah, the king of both Upper and Lower Egypt, and the creator of the Ennead. The inscription then describes how Horus, as a manifestation of Ptah, initially rules Lower Egypt while his rival Set rules Upper Egypt. However, Horus receives Upper Egypt from Geb, becoming the sole ruler of the land.
The Memphite Theology
Lines 48 to 64 recount the creation myth known as the Memphite Theology. Ptah, the patron god of craftsmen, metalworkers, artisans, and architects was viewed as a creator-god, a divine craftsman of the universe who was responsible for all existence. Creation was first a spiritual and intellectual activity, facilitated by the divine heart (thought) and tongue (speech/word) of Ptah. Then, creation became a physical activity carried out by Atum, who, created by Ptah's teeth and lips, produced the Ennead from his seed and hands.
Summary
Lines 61 through 64 summarize the text as a whole.
Purpose
According to Ragnhild Bjerre Finnestad, there are three theories on the possible purpose of the Shabaka text:
To assert the supremacy of the Memphite theological system over the Heliopolitan
To claim the hegemony of the Memphis and its priesthood over Heliopolis and its priesthood
To present an ontology.
As a temple text written down and set up in the temple of Ptah, it is likely that the Shabaka Stone served a religious, cultic-theological purpose, placing its subject matter within a cultic frame of reference.
Damage
Projecting from the rectangular hole in the center of the stone are radial rough stripes, which destroyed the inscription within a radius of 78 cm, measured from the middle of the stone. According to the secondary literature on the monument, this damage occurred because the stone was re-used as a millstone. The oldest reference speculating the stone's use as a millstone is found in the display of the British Museum of 1821. However, the stone could instead have been the foundation of something round, possibly a column or a pillar.
Some parts of the stone were intentionally cut out during the Dynastic Period. This included the name of Seth (line 7), a god which was condemned during this time. Additionally, Psamtik II or Psamtik III erased the proper name and throne name of Shabaka from the stone. Psamtik III then engraved his name onto the stone, but his name was in turn erased by the Persians during their conquest.
See also
List of individual rocks
References
Sources
External links
The Shabaka Stone, English translation by M. Lichtheim
8th-century BC steles
1805 archaeological discoveries
Ancient Egyptian stelas
Stones
Twenty-fifth Dynasty of Egypt
Ancient Egyptian objects in the British Museum
Ptah
Creation myths | Shabaka Stone | Physics,Astronomy | 1,531 |
15,587,739 | https://en.wikipedia.org/wiki/Haplotype%20convergence | Haplotype convergence is the unrelated appearance of identical haplotypes in separate populations, through either convergent evolution or random chance.
Description
Haplotype convergence is rare, due to the sheer odds involved of two unrelated individuals independently evolving exactly the same genetic sequence in the site of interest. Thus, haplotypes are shared mainly between very closely related individuals, as the genetic information in two related individuals will be much more similar than between unrelated individuals. Substitution bias further increases the likelihood of haplotype convergence, as this increases the probability of mutations occurring at the same site. Sequences may also diverge from the same original sequence and then revert, converging in this manner. Convergence through convergent evolution in two unrelated groups is much less common, as derived traits may arise through dramatically different pathways.
Erroneously determining two individuals to be identical due to haplotype convergence becomes much less likely when more genetic markers are tested, since that would require a larger amount of extremely rare coincidences. With modern high-throughput sequencing approaches, sequencing a large set of markers, or even the entire genome, is much more feasible and greatly minimizes these issues.
Examples
In some regions, due to low diversity in the Y-STR gene (often used to study surname origin), haplotype convergence may confuse analyses, concluding unrelated individuals to be very closely related.
Similarly, a study of New World mitochondrial DNA haplogroups observed that similarities in haplotypes between Native Americans and Asians were a result of the hypervariability of the HVSI region in mitochondrial DNA, rather than common ancestry.
As an example of haplotype convergence due to convergent evolution in more distantly related groups, threespine stickleback in blackwater environments similar to that of the ancient bluefin killifish and black bream independently evolved the same haplotype in the SWS2 gene, which promotes better eyesight in those conditions.
References
Evolutionary biology
Genetic genealogy | Haplotype convergence | Biology | 402 |
39,064,863 | https://en.wikipedia.org/wiki/Stephen%20Liddle | Stephen T. Liddle FRSE FRSC is a British professor of inorganic chemistry at the University of Manchester. He is Head of Inorganic Chemistry and Co-Director of the Centre for Radiochemistry Research at the University of Manchester since 2015.
Early life and education
Liddle was born near Sunderland, in the North East of England, in 1974. In 1997 he graduated with a BSc(Hons) in chemistry with applied chemistry from Newcastle University. His degree included a year working as a research scientist for ICI Performance Chemicals at Wilton, Teesside. Alongside a stint in the Territorial Army, Liddle continued his studies at the university and received his PhD in 2000. His PhD supervisor was Professor W. Clegg.
Career and research
After postdoctoral fellowships with P. J. Bailey at the University of Edinburgh, Keith Izod at Newcastle University as the Wilfred Hall Research Fellow, and Polly Arnold at the University of Nottingham, Liddle began his independent academic career at the University of Nottingham with a Royal Society University Research Fellowship (2007–2015) held with a proleptic Lectureship. He was promoted to Associate Professor and Reader in 2010 and Professor of Inorganic Chemistry in 2013.
He moved to the University of Manchester in 2015 as Head of Inorganic Chemistry and Co-Director of the Centre for Radiochemistry Research. He held an Engineering and Physical Sciences Research Council Established Career Fellowship (2015–2021).
He was Chairman of COST Action CM1006, a 22 country, research network of over 120 research groups in f-block chemistry (2011–2015), is an advisor to the Commonwealth Scholarship Commission (2013–), and was an elected category 3 member of Senate, the University of Manchester (2016–2019).
Liddle's research is focused on synthetic inorganic chemistry, particularly making early transition metal, lanthanide, and actinide complexes to explore their structure, bonding, reactivity, and magnetism. In 2011 he reported a single-molecule magnet based on depleted uranium. In 2012 his research group was the first to synthesize a molecular terminal uranium(V) nitride.
In 2013 he reported the isolation of a terminal uranium(VI) nitride akin to examples previously restricted to cryogenic matrix isolation experiments. Also in 2013, his research group disclosed the first f-element cyclobutadienyl complexes. In 2015 he reported a uranium(IV)-arsenido complex containing uranium-arsenic triple bonds. In 2019 his research group isolated a uranium(V)-dinitrogen complex. In 2021, Liddle reported a tri-thorium cluster featuring σ-aromatic actinide metal-metal bonding. Before the synthesis of this complex, examples of actinide-actinide bonding had been restricted to matrix isolation experiments and fullerene-encapsulated species.
In 2022, he reported a terminal neptunium(V)-mono(oxo) complex. Before the synthesis of this complex all transuranium-ligand multiple bond complexes required two or more metal-ligand multiple bonds to be stable.
Honours and awards
Liddle was elected Fellow of the Royal Society of Chemistry (FRSC) in 2011 and is Vice President to the Executive Committee of the European Rare Earth and Actinide Society (2012–).
He was elected to the Fellowship of the Royal Society of Edinburgh, Scotland’s National Academy of Science and Letters in 2022.
He was awarded the RSC Sir Edward Frankland Fellowship (2011), the RSC Radiochemistry Group Bill Newton Award (2011), the RSC Corday-Morgan Prize (2015), and the RSC Tilden Prize (2020).
He was a recipient of a Rising Star Award at the 41st International Conference on Coordination Chemistry (2014).
He was awarded an Alexander von Humboldt Foundation Friedrich Wilhelm Bessel Research award (2019).
He was awarded a European Research Council (ERC) Starter Grant (2009) and Consolidator Grant (2014).
He was one of the Periodic Videos team awarded the IChemE Petronas award for excellence in education and training (2008).
Popular science
Liddle is known for his work on The Periodic Table of Videos, a series of videos from the University of Nottingham presented on YouTube, which feature educational vignettes on the periodic table.
He is executive producer for Chemistry at Manchester Explains Research Advances (CAMERA), a series of videos from the University of Manchester presented on YouTube, which feature videos explaining chemistry research papers published from the University of Manchester.
He is a National Co-ordinating Centre for Public Engagement Ambassador (2013–).
References
British chemists
Academics of the University of Nottingham
Living people
Academics of the University of Manchester
Alumni of Newcastle University
Inorganic chemists
Year of birth missing (living people)
Rare earth scientists | Stephen Liddle | Chemistry | 973 |
7,186,688 | https://en.wikipedia.org/wiki/Trestolone%20acetate | Trestolone acetate (; developmental code names CDB-903, NSC-69948, U-15614; also known as 7α-methyl-19-nortestosterone 17β-acetate (MENT acetate) and 7α-methylestr-4-en-17β-ol-3-one 17β-acetate) is a synthetic and injected anabolic–androgenic steroid (AAS) and a derivative of nandrolone (19-nortestosterone) which was never marketed. It is an androgen ester – specifically, the C17 acetate ester of trestolone (7α-methyl-19-nortestosterone; MENT). The medication was first described in 1963.
See also
List of androgen esters
References
Abandoned drugs
Acetate esters
Androgen esters
Anabolic–androgenic steroids
Estranes
Ketones
Sex hormone esters and conjugates
Progestogens
Synthetic estrogens | Trestolone acetate | Chemistry | 213 |
9,938,270 | https://en.wikipedia.org/wiki/Roland%20MS-1 | The Roland MS-1 digital sampler was a compact, 16-bit digital audio phrase sampler produced by Roland in 1994 as a straightforward, inexpensive, entry-level sampler. In 1998, the MS-1 was succeeded by the Boss SP-202 sampler.
Overview
The MS-1 was what Roland refers to as a "phrase sampler" and featured eight rubber pads that triggered individual samples assigned to them. The eight pads were arranged into five banks for a total of 40 sampled sounds - 16 sounds (banks A & B) with the built-in flash memory and up to 24 (banks C, D & E) expanded with the insertion of a PCMCIA memory card. Without a card, only banks A & B could be used. Programming of the MS-1 was possible through the use of a small LCD display and menu-driven settings entered with left and right directional buttons which increased or decreased numerical values and controlled a text editing cursor.
Sample time depended on the sample-rate quality that was selected during recording. The settings were simply called "High", "Standard," "Long-1," or "Long 2." The internal flash memory held approximately 20 seconds on the High setting, or nearly a minute on the Long-2 setting. Typically, Sandisk 2.5, 5 and 10 mega-byte memory cards were used with the MS-1 which increased sampling time and expanded its capabilities.
There were no built-in audio effects, but samples could be pitch controlled, playback start-and-end points could be edited, samples could be truncated allowing the deletion of audio bits that were not desired, samples could be divided and the split parts assigned to separate pads, and samples could be looped and loop start-and-end points could be edited. It also featured MIDI in and out, but no thru.
For recording audio, the MS-1 used left/right RCA jack audio inputs and two microphone jacks. It could sample in either mono or stereo and sampling quality could be reduced to allow more sampling time and the lower the setting, the grittier the digitized sounds became. Audio output was provided through a pair of left/right RCA output jacks and a headphone jack.
The MS-1 also featured a simple, single-track sequencer which triggered only the internal sounds. Up to four sequence patterns could be stored in memory to a total of 900 pad operations.
The machine was also portable and powered either by AC adapter or batteries.
Features
16-bit stereo phrase sampler
R-DAC (Roland digital audio coding)
AD/DA conversion
8 onboard trigger pads
4 sampling frequencies
• (High: 44.1–32.07 kHz)
• (Standard: 32–23.27 kHz)
• (Long-1: 22.05–16.04 kHz)
• (Long-2: 16–11.64 kHz)
Single-track sequencer
RPS (real-time phrase sequencer)
MIDI in/out
Battery operation possible
Flash ROM feature
Bundled sampling CD
See also
Boss SP-202
External links
Sonicstate review of the MS-1
Harmony Central review of the MS-1
Sound on Sound Magazine - Roland MS1 Digital Sampler - March 1995
MS-1
Samplers (musical instrument)
Grooveboxes
Music sequencers
Sound modules
Music workstations
Hip-hop production
Japanese inventions | Roland MS-1 | Engineering | 687 |
56,966,379 | https://en.wikipedia.org/wiki/Markarian%201034 | Markarian 1034 (Mrk 1034) is a pair of spiral galaxies comprising PGC 9074 and PGC 9071, located in the constellation Triangulum. They are located at a distance of 465 million light-years from Earth and are classified as luminous infrared galaxies.
PGC 9074
PGC 9074 known as Mrk 1034a, is classified as a type Sa galaxy. It has two spiral arms around its nucleus with a bright galactic bulge. These spiral arms are shown to have dust obscuring background light of stars behind its regions. These are mixed together with star clusters containing a stellar population of hot, recently formed stars. In the central region of PGC 9074, older stars are found surrounded by a faint halo of another group of old stars, some inside globular clusters.
The nucleus of PGC 9074 is active and it has been classified as a Seyfert 1 galaxy. It is categorized as a Markarian galaxy because when, compared to other galaxies, its nucleus emits large amounts of ultraviolet rays. It is on the verge of gravitationally interacting with its neighbor, PGC 9071 since the two of them are at close proximity.
PGC 9071
PGC 9071 known as Mrk 1034b, is classified as a type Sb galaxy. It has almost the same appearance and size to PGC 9074, but with a fainter bulge and a slight altered spiral arm structure: its coils are further away. In addition, it contains a young stellar popular of hot stars combined with obscured dust, with a central region of older star populations.
The nucleus of PGC 9071 is active and it is also a Seyfert 1 galaxy. It has a high surface brightness and contains a one-sided jet measured to be 0.144 arcsecs or 103 pc, with a 'kidney-bean' shaped structure located within its optical core. The galaxy is also interacting with PGC 9074, in which eventually they will merge together to form a larger entity in hundreds of millions of years.
References
1034
Interacting galaxies
Principal Galaxies Catalogue objects
Seyfert galaxies
Luminous infrared galaxies
Active galaxies
Triangulum
Spiral galaxies | Markarian 1034 | Astronomy | 457 |
2,732,140 | https://en.wikipedia.org/wiki/GeoGebra | GeoGebra (a portmanteau of geometry and algebra) is an interactive geometry, algebra, statistics and calculus application, intended for learning and teaching mathematics and science from primary school to university level. GeoGebra is available on multiple platforms, with apps for desktops (Windows, macOS and Linux), tablets (Android, iPad and Windows) and web. It is presently owned by Indian edutech firm Byju's.
History
GeoGebra's creator, Markus Hohenwarter, started the project in 2001 as part of his master's thesis at the University of Salzburg. After a successful Kickstarter campaign, GeoGebra expanded its offering to include an iPad, an Android and a Windows Store app version. In 2013, GeoGebra incorporated Bernard Parisse's Xcas into its CAS view. The project is now freeware (with open-source portions) and multi-lingual, and Hohenwarter continues to lead its development at the University of Linz.
GeoGebra includes both commercial and not-for-profit entities that work together from the head office in Linz, Austria, to expand the software and cloud services available to users.
In December 2021, GeoGebra was acquired by edtech conglomerate Byju's for approximately $100 million USD.
On January 25, 2024, lenders began bankruptcy proceedings against GeoGebra's parent company Byju's in an effort to repay its loans. On February 1, 2024, Byju's U.S. division filed for Chapter 11 bankruptcy in Delaware. Byju's would raise around $200 million in an effort to clear "immediate liabilities" and for other operational costs.
Features
GeoGebra is an interactive mathematics software suite for learning and teaching science, technology, engineering, and mathematics from primary school up to the university level. Constructions can be made with points, vectors, segments, lines, polygons, conic sections, inequalities, implicit polynomials and functions, all of which can be edited dynamically later. Elements can be entered and modified using mouse and touch controls, or through an input bar. GeoGebra can store variables for numbers, vectors and points, calculate derivatives and integrals of functions, and has a full complement of commands like Root or Extremum. Teachers and students can use GeoGebra as an aid in formulating and proving geometric conjectures.
GeoGebra's main features are:
Interactive geometry environment (2D and 3D)
Built-in spreadsheet
Built-in computer algebra system (CAS)
Built-in statistics and calculus tools
Scripting hooks
Large number of interactive learning and teaching resources at GeoGebra Materials.
GeoGebra Materials platform
The GeoGebra Materials platform is a cloud service that allows users to upload and share GeoGebra applets with others. GeoGebra Materials was originally launched as GeoGebraTube in June 2011, and was renamed in 2016. As of April 2016 the service hosts more than 1 million resources, 400,000+ of which are public. "Materials" include interactive worksheets, simulations, games and e-books created using GeoGebraBook.
GeoGebra Materials can be also exported in several formats, including SVG, Animated GIF, Windows Metafile, PNG, PDF and EPS, as well as copied directly to the clipboard. GeoGebra can also generate code for use in LaTeX files.
Licensing
Before version 4.2, GeoGebra was published under the GNU General Public License (GPL-3.0-or-later).
After version 4.2 the licensing was changed. GeoGebra's source code, except the installers, web services, user interface image and style files, and documentation and language files, is licensed under the GNU General Public License (GPL-3.0-or-later). The installers and web services are released under GeoGebra's own proprietary license. User interface image and style files, and documentation and language files are published under the Creative Commons NonCommercial license (CC BY-NC-SA 3.0). Commercial use is subject to a special license and collaboration agreement.
Since parts of GeoGebra not licensed under a GPL compatible license are required to build the program, and since GeoGebra includes GPL licensed libraries, some users, including a maintainer of one of the libraries used by GeoGebra, consider the license invalid. In response, the International
GeoGebra Institute, and GeoGebra's creator, Markus Hohenwarter, have provided a license FAQ.
Community
The International GeoGebra Institute (IGI) is the nonprofit arm of the GeoGebra Group. The institute coordinates research, development, translation and deployment efforts of the GeoGebra system across a global network of user groups at universities and non-profit organizations, as well as provide certification to GeoGebra experts and trainers.
Awards
Archimedes 2016: MNU Award in category Mathematics (Hamburg, Germany)
Microsoft Partner of the Year Award 2015: Finalist, Public Sector: Education (Redmond, WA, USA)
MERLOT Award for Exemplary Online Learning Resources – MERLOT Classics 2013 (Las Vegas, Nevada, USA)
NTLC Award 2010: National Technology Leadership Award 2010 (Washington D.C., USA)
Tech Award 2009: Laureate in the Education Category (San Jose, California, USA)
BETT Award 2009: Finalist in London for British Educational Technology Award
SourceForge.net Community Choice Awards 2008: Finalist, Best Project for Educators
AECT Distinguished Development Award 2008: Association for Educational Communications and Technology (Orlando, USA)
Learnie Award 2006: Austrian Educational Software Award for "Wurfbewegungen mit GeoGebra" (Vienna, Austria)
eTwinning Award 2006: 1st prize for "Crop Circles Challenge" with GeoGebra (Linz, Austria)
Les Trophées du Libre 2005: International Free Software Award, category Education (Soisson, France)
Comenius 2004: German Educational Media Award (Berlin, Germany)
Learnie Award 2005: Austrian Educational Software Award for "Spezielle Relativitätstheorie mit GeoGebra" (Vienna, Austria)
digita 2004: German Educational Software Award (Cologne, Germany)
Learnie Award 2003: Austrian Educational Software Award (Vienna, Austria)
EASA 2002: European Academic Software Award (Ronneby, Sweden)
See also
C.a.R.
DrGeo
Graphmatica
Kig
Xcas
References
External links
Development coordination site
Creative Commons-licensed works
Educational math software
Interactive geometry software
Java platform software
Companies that filed for Chapter 11 bankruptcy in 2024
Byju's | GeoGebra | Mathematics | 1,372 |
11,569,073 | https://en.wikipedia.org/wiki/Schizopora%20flavipora | Schizopora flavipora is a plant pathogen infecting tea.
References
External links
Index Fungorum
USDA ARS Fungal Database
Fungal plant pathogens and diseases
Tea diseases
Hymenochaetales
Fungus species | Schizopora flavipora | Biology | 48 |
432,213 | https://en.wikipedia.org/wiki/15%20puzzle | The 15 puzzle (also called Gem Puzzle, Boss Puzzle, Game of Fifteen, Mystic Square and more) is a sliding puzzle. It has 15 square tiles numbered 1 to 15 in a frame that is 4 tile positions high and 4 tile positions wide, with one unoccupied position. Tiles in the same row or column of the open position can be moved by sliding them horizontally or vertically, respectively. The goal of the puzzle is to place the tiles in numerical order (from left to right, top to bottom).
Named after the number of tiles in the frame, the 15 puzzle may also be called a "16 puzzle", alluding to its total tile capacity. Similar names are used for different sized variants of the 15 puzzle, such as the 8 puzzle, which has 8 tiles in a 3×3 frame.
The n puzzle is a classical problem for modeling algorithms involving heuristics. Commonly used heuristics for this problem include counting the number of misplaced tiles and finding the sum of the taxicab distances between each block and its position in the goal configuration. Note that both are admissible. That is, they never overestimate the number of moves left, which ensures optimality for certain search algorithms such as A*.
Mathematics
Solvability
used a parity argument to show that half of the starting positions for the n puzzle are impossible to resolve, no matter how many moves are made. This is done by considering a binary function of the tile configuration that is invariant under any valid move and then using this to partition the space of all possible labelled states into two mutually inaccessible equivalence classes of the same size. This means that half of all positions are unsolvable, although it says nothing about the remaining half.
The invariant is the parity of the permutation of all 16 squares plus the parity of the taxicab distance (number of rows plus number of columns) of the empty square from the lower right corner. This is an invariant because each move changes both the parity of the permutation and the parity of the taxicab distance. In particular, if the empty square is in the lower right corner, then the puzzle is solvable only if the permutation of the remaining pieces is even.
also showed that on boards of size m × n, where m and n are both larger or equal to 2, all even permutations are solvable. It can be proven by induction on m and n, starting with m = n = 2. This means that there are exactly two equivalency classes of mutually accessible arrangements, and that the parity described is the only non-trivial invariant, although equivalent descriptions exist.
gave another proof, based on defining equivalence classes via a Hamiltonian path.
studied the generalization of the 15 puzzle to arbitrary finite graphs, the original problem being the case of a 4×4 grid graph. The problem has some degenerate cases where the answer is either trivial or a simple combination of the answers to the same problem on some subgraphs. Namely, for paths and polygons, the puzzle has no freedom; if the graph is disconnected, only the connected component of the vertex with the "empty space" is relevant; and if there is an articulation vertex, the problem reduces to the same puzzle on each of the biconnected components of that vertex. Excluding these cases, Wilson showed that other than one exceptional graph on 7 vertices, it is possible to obtain all permutations unless the graph is bipartite, in which case exactly the even permutations can be obtained. The exceptional graph is a regular hexagon with one diagonal and a vertex at the center added; only of its permutations can be attained, which gives an instance of the exotic embedding of S5 into S6.
For larger versions of the n puzzle, finding a solution is easy. But, the problem of finding the shortest solution is NP-hard. It is also NP-hard to approximate the fewest slides within an additive constant, but there is a polynomial-time constant-factor approximation. For the 15 puzzle, lengths of optimal solutions range from 0 to 80 single-tile moves (there are 17 configurations requiring 80 moves) or 43 multi-tile moves; the 8 Puzzle always can be solved in no more than 31 single-tile moves or 24 multi-tile moves (integer sequence A087725). The multi-tile metric counts subsequent moves of the empty tile in the same direction as one.
The number of possible positions of the 24 puzzle is ≈ , which is too many to calculate God's number feasibly using brute-force methods. In 2011, lower bounds of 152 single-tile moves or 41 multi-tile moves had been established, as well as upper bounds of 208 single-tile moves or 109 multi-tile moves. In 2016, the upper bound was improved to 205 single-tile moves.
Group theory
The transformations of the 15 puzzle form a groupoid (not a group, as not all moves can be composed); this groupoid acts on configurations.
Because the combinations of the 15 puzzle can be generated by 3-cycles, it can be proved that the 15 puzzle can be represented by the alternating group . In fact, any sliding puzzle with square tiles of equal size can be represented by .
History
The puzzle was "invented" by Noyes Palmer Chapman, a postmaster in Canastota, New York, who is said to have shown friends, as early as 1874, a precursor puzzle consisting of 16 numbered blocks that were to be put together in rows of four, each summing to 34 (see magic square). Copies of the improved 15 puzzle made their way to Syracuse, New York, by way of Chapman's son, Frank, and from there, via sundry connections, to Watch Hill, Rhode Island, and finally to Hartford, Connecticut, where students in the American School for the Deaf started manufacturing the puzzle. By December 1879, these were sold both locally and in Boston, Massachusetts. Shown one of these, Matthias Rice, who ran a woodworking business in Boston, started manufacturing the puzzle sometime in December 1879 and convinced a "Yankee Notions" fancy goods dealer to sell them under the name of "Gem Puzzle." In late January 1880, Charles Pevey, a dentist in Worcester, Massachusetts, garnered some attention by offering a cash reward for a solution to the 15 Puzzle.
The game became a craze in the U.S. in 1880.
Chapman applied for a patent on his "Block Solitaire Puzzle" on February 21, 1880. However, this patent was rejected, likely because it was not sufficiently different from the August 20, 1878 "Puzzle-Blocks" patent (US 207124) granted to Ernest U. Kinsey.
Sam Loyd
From 1891 until his death in 1911, Sam Loyd claimed that he had invented the puzzle. However, Loyd had no connection to the invention or initial popularity of the puzzle. Loyd's first article about the puzzle was published in 1886, and it was not until 1891 that he first claimed to be the inventor.
Some later interest was fueled by Loyd's offer of a $1,000 prize () to anyone who could provide a solution for achieving a particular combination specified by Loyd, namely reversing the 14 and 15, which Loyd called the 14-15 puzzle. This is impossible, as had been shown over a decade earlier by , because it requires a transformation from an even to an odd permutation.
Varieties of the 15 puzzle
The Minus Cube, manufactured in the USSR, is a 3D puzzle with similar operations to the 15 Puzzle.
Versions of the 15 puzzle include a different number of tiles, such as the 8-puzzle or 24-puzzle.
Pop culture
Chess world champion Bobby Fischer was an expert at solving the 15 puzzle. He had been timed to be able to solve it within 25 seconds; Fischer demonstrated this on November 8, 1972, on The Tonight Show Starring Johnny Carson.
See also
Combination puzzles
Jeu de taquin, an operation on skew Young tableaux similar to the moves of the 15 puzzle
Klotski
Mechanical puzzles
Pebble motion problems
Rubik's Cube
Three cups problem
Notes
References
Edward Kasner & James Newman (1940) Mathematics and the Imagination, pp 177–80, Simon & Schuster.
External links
The history of the 15 puzzle
15 Puzzle Game
Fifteen Puzzle Solution
Maximal number of moves required for the m X n generalization of the 15 puzzle
15-Puzzle Optimal Solver with download (from Herbert Kociemba)
Mechanical puzzles
Combination puzzles
NP-complete problems
Permutations
19th-century fads and trends | 15 puzzle | Mathematics | 1,762 |
40,826,054 | https://en.wikipedia.org/wiki/Job%20characteristic%20theory | Job characteristics theory is a theory of work design. It provides “a set of implementing principles for enriching jobs in organizational settings”. The original version of job characteristics theory proposed a model of five “core” job characteristics (i.e. skill variety, task identity, task significance, autonomy, and feedback) that affect five work-related outcomes (i.e. motivation, satisfaction, performance, and absenteeism and turnover) through three psychological states (i.e. experienced meaningfulness, experienced responsibility, and knowledge of results).
History
Work redesign first got its start in the 1960s. Up until then, the prevailing attitude was that jobs should be simplified in order to maximize production, however it was found that when subjected to highly routinized and repetitive tasks, the benefits of simplification sometimes disappeared due to worker dissatisfaction. It was proposed that jobs should be enriched in ways that boosted motivation, instead of just simplified to a string of repetitive tasks. It is from this viewpoint that Job Characteristics Theory emerged.
In 1975, Greg R. Oldham and J. Richard Hackman constructed the original version of the Job Characteristics Theory (JCT), which is based on earlier work by Turner and Lawrence and Hackman and Lawler. Turner and Lawrence, provided a foundation of objective characteristics of jobs in work design. Further, Hackman and Lawler indicated the direct effect of job characteristics on employee's work related attitudes and behaviors and, more importantly, the individual differences in need for development, which is called Growth Need Strength in Job Characteristics Theory.
In 1980, Hackman and Oldham presented the final form of the Job Characteristics Theory in their book Work Redesign. The main changes included the addition of two more moderators- Knowledge and Skill and Context Satisfaction, removal of the work outcomes of absenteeism and turnover, and increased focus on Internal Work Motivation. Several of the outcome variables were removed or renamed as well. Concentration was shifted to the affective outcomes following results from empirical studies that showed weak support for the relationship between the psychological states and behavioral outcomes.
In addition to the theory, Oldham and Hackman also created two instruments, the Job Diagnostic Survey (JDS) and the Job Rating Form (JRF), for assessing constructs of the theory. The JDS directly measures jobholders' perceptions of the five core job characteristics, their experienced psychological states, their Growth Need Strength, and outcomes. The JRF was designed to obtain the assessments from external observers, such as supervisors or researchers, of the core job characteristics.
Important variables
According to the final version of the theory, five core job characteristics should prompt three critical psychological states, which lead to many favorable personal and work outcomes. The moderators Growth Need Strength, Knowledge and Skill, and Context Satisfaction should moderate the links between the job characteristics and the psychological states, and the psychological states and the outcomes.
Core job characteristics
Skill Variety: The degree to which a job requires various activities, requiring the worker to develop a variety of skills and talents. Jobholders can experience more meaningfulness in jobs that require several different skills and abilities than when the jobs are elementary and routine.
Task Identity: The degree to which the job requires the jobholders to identify and complete a workpiece with a visible outcome. Workers experience more meaningfulness in a job when they are involved in the entire process rather than just being responsible for a part of the work.
Task Significance: The degree to which the job affects other people's lives. The influence can be either in the immediate organization or in the external environment. Employees feel more meaningfulness in a job that substantially improves either psychological or physical well-being of others than a job that has limited effect on anyone else.
Autonomy: The degree to which the job provides the employee with significant freedom, independence, and discretion to plan out the work and determine the procedures in the job. For jobs with a high level of autonomy, the outcomes of the work depend on the workers’ own efforts, initiatives, and decisions; rather than on the instructions from a manager or a manual of job procedures. In such cases, the jobholders experience greater personal responsibility for their own successes and failures at work.
Feedback: The degree to which the worker has knowledge of results. This is clear, specific, detailed, actionable information about the effectiveness of his or her job performance. When workers receive clear, actionable information about their work performance, they have better overall knowledge of the effect of their work activities, and what specific actions they need to take (if any) to improve their productivity.
Critical psychological states
Experienced Meaningfulness of the Work: The degree to which the jobholder experiences the work as intrinsically meaningful and can present his or her value to other people and/or the external environment.
Experienced Responsibility for Outcome of the Work: The degree to which the worker feels he or she is accountable and responsible for the results of the work.
Knowledge of Results of the Work Activities: The degree to which the jobholder knows how well he or she is performing.
Outcomes
Adopted from earlier work the personal and work outcomes of the initial theory were: Internal Work Motivation, Job Satisfaction, Absenteeism and Turnover, and Performance Quality. However, the 1980 revisions to the original model included removing absenteeism and turnover, and breaking performance into Quality of Work and Quantity of Work.
Moderators
Growth Need Strength (GNS): GNS is the strength of a person's need for personal accomplishment, learning, and development”. The theory posits that Growth Need Strength moderates both the relationship of core job characteristics and psychological states, and the relationship between psychological states and outcomes.
Knowledge and Skill: The level of knowledge and skill the worker possesses can moderate the relationship between the mediators and the job characteristics and outcomes. For motivating jobs, adequate knowledge and skill lead to experiencing the critical psychological states and better outcomes, while insufficient knowledge and skill discourage the psychological states and result in more negative outcomes. Unmotivating jobs don't allow the worker to experience the psychological states at all, thus knowledge and skill have no effect.
Context Satisfaction: The context of the job also affects employees’ experience. The authors suggest that when workers are satisfied with things like their managers, pay, co-workers, and job security they respond more positively to highly motivating jobs and less positively when they are not satisfied. The reason being that they must use attentional resources to handle the undesirable work context, which distracts from the richness otherwise inherent in the job.
Propositions
The three critical psychological states of job characteristic theory (JCT) draw upon cognitive motivation theory and some previous work on identifying the presence of certain psychological states could lead to favorable outcomes. JCT provided the chance to systematically assess the relationship between the previously discovered psychological states ('Experienced Meaningfulness, 'Experienced Responsibility, and Knowledge of Results) and outcomes. More importantly, previous work on work design showed job characteristics can predict individual performance, but did not provide “why” and “how” this relationship existed. Job Characteristics Theory filled this gap by building a bridge between job characteristics and work-related outcomes through the use of the three critical psychological states.
The three psychological states, which are also the conceptual core of the theory, include (1) Experienced Meaningfulness of the Work, (2) Experienced Responsibility for the Outcomes of the Work, and (3) Knowledge of the Results of Work Activities. These psychological states are theorized to mediate the relationship between job characteristics and work-related outcomes. According to the theory, these three critical psychological states are noncompensatory conditions, meaning jobholders have to experience all three critical psychological states to achieve the outcomes proposed in the model. For example, when workers experience the three psychological states, they feel good about themselves when they perform well. These positive feelings, in turn, reinforce the workers to keep performing well.
According to the theory, certain core job characteristics are responsible for each psychological state: skill variety, task identity, and task significance shape the experienced meaningfulness; autonomy affects experienced responsibility, and feedback contributes to the knowledge of results. Previous research found that four job characteristics (autonomy, variety, identity, and feedback) could increase workers’ performance, satisfaction, and attendance. Task significance was derived from Greg Oldham's own work experience as an assembly line worker. Though his job did not provide task variety or identity, he still experienced meaningfulness through the realization that others depended on his work. This realization led to the inclusion of task significance as another job characteristic that would influence experienced meaningfulness of the job. Thus, job characteristics theory proposed the five core job characteristics that could predict work related outcomes.
Motivating potential score
When a job has a high score on the five core characteristics, it is likely to generate three psychological states, which can lead to positive work outcomes, such as high internal work motivation, high satisfaction with the work, high quality work performance, and low absenteeism and turnover. This tendency for high levels of job characteristics to lead to positive outcomes can be formulated by the motivating potential score (MPS). Hackman and Oldham explained that the MPS is an index of the “degree to which a job has an overall high standing on the person's degree of motivation...and, therefore, is likely to prompt favorable personal and work outcomes”:
The motivating potential score (MPS) can be calculated, using the core dimensions discussed above, as follows:
Jobs that are high in motivating potential must be also high on at least one of the three factors that lead to experienced meaningfulness, and also must be high on both Autonomy and Feedback. If a job has a high MPS, the job characteristics model predicts that motivation, performance and job satisfaction will be positively affected and the likelihood of negative outcomes, such as absenteeism and turnover, will be reduced.
According to the equation above, a low standing on either autonomy or feedback will substantially compromise a job's MPS, because autonomy and feedback are the only job characteristics expected to foster experienced responsibility and knowledge of results, respectively. On the contrary, a low score on one of the three job characteristics that lead to experienced meaningfulness may not necessarily reduce a job's MPS, because a strong presence of one of those three attributes can offset the absence of the others.
Individual difference factor
In response to one of the disadvantages of Motivator–Hygiene Theory, Job Characteristics Theory added an individual difference factor into the model. While Herzberg et al. took into account the importance of intrinsically and extrinsically motivating job characteristics there was no consideration of individual differences. The importance of individual differences had been demonstrated by previous work showing that some individuals are more likely to positively respond to an enriched job environment than others. Thus, the original version of the theory posits an individual difference characteristic, Growth Need Strength (GNS), that moderates the effect of the core job characteristics on outcomes. Jobholders with high Growth Need Strength should respond more positively to the opportunities provided by jobs with high levels of the five core characteristics compared to low GNS jobholders.
Alternative theories of work design
Scientific management
Taylor's theory of scientific management emphasized efficiency and productivity through the simplification of tasks and division of labor.
Motivator–hygiene theory
Herzberg et al.’s Motivator–Hygiene Theory, aka Two-factor Theory, an influence on Job Characteristics Theory, sought to increase motivation and satisfaction through enriching jobs. The theory predicts changes in “motivators”, which are intrinsic to the work, (such as recognition, advancement, and achievement) will lead to higher levels of employee motivation and satisfaction; while “hygiene factors”, which are extrinsic to the work itself, (such as company policies and salary) can lead to lower levels of dissatisfaction, but will not actually effect satisfaction or motivation.
Sociotechnical systems theory
Sociotechnical systems theory predicts an increase in satisfaction and productivity through designing work that optimized person-technology interactions.
Quality improvement theory
Quality improvement theory is based on the idea that jobs can be improved through the analysis and optimized of work processes.
Adaptive structuration theory
Adaptive structuration theory provides a way to look at the interaction between technology's intended and actual use in an organization, and how it can influence different work-related outcomes.
Variations
Reverse scoring correction
Idaszak and Drasgow provided a corrected version of the Job Diagnostic Survey that corrected for one of the measurement errors in the instrument. It had been suggested that reverse scoring on several of the questions was to blame for the inconsistent studies looking at the factors involved in the Job Diagnostic Survey. Following a factor analysis, Idaszak and Drasgow found six factors rather than the theorized five characteristics proposed by the Job Characteristics Theory. Upon further investigation, they were able to show that the sixth factor was made up of the reverse coded items. The authors rephrased the questions, ran the analysis again, and found it removed the measurement error.
GN–GO model
Due to the inconsistent findings about the validity of Growth Need Strength as a moderator of the Job characteristic-outcomes relationship, Graen, Scandura, and Graen proposed the GN–GO model, which added Growth Opportunity as another moderator. They suggested there isn't a simple positive relationship between motivation and Growth Need Strength, but instead there is an underlying incremental (stairstep) relationship with various levels of Growth Opportunity. Growth Opportunity increments are described as “events that change either the characteristics of the job itself or the understanding of the job itself”. It was hypothesized that as people high in Growth Need Strength met each level of Growth Opportunity they could be motivated to increase their performance, but when people low on Growth Need Strength met these same increments their performance would either maintain or degrade. Field studies found more support for the GN–GO model than the original Growth Need Strength moderation.
Extension of characteristics and outcomes
Humphrey, Nahrgang, and Morgeson extended the original model by incorporating many different outcomes and job characteristics. The authors divided the revised set of Job Characteristics into three sections- Motivational, Social, and Work Context Characteristics; and the outcomes were portioned out into four parts- Behavioral, Attitudinal, Role Perception, and Well-being Outcomes. Results showed strong relationships between some of the expanded characteristics and outcomes, suggesting that there are more options for enriching jobs than the original theory would suggest.
Psychological ownership
Taking from earlier empirical research on Job Characteristics Theory and Psychological Ownership, researchers developed a model that combined the two theories. They replaced the psychological states of the Job Characteristics Theory with Psychological Ownership of the job as the mediator between job characteristics and outcomes. In addition to the positive personal and work outcomes of Job Characteristics Theory, negative outcomes (e.g. Territorial Behaviors, Resistance to Change, and Burden of Responsibility) were added.
Empirical tests
Since its inception, Job Characteristics Theory has been scrutinized extensively. The first empirical tests of the theory came from Hackman and Oldham themselves. The authors found the “internal consistency reliability of the scales and the discriminant validity of the items” to be “satisfactory”. They also tried to assess the objectivity of the measure by having the supervisors and the researchers evaluate the job in addition to the jobholders. More importantly, the authors reported the relationships predicted by the model were supported by their analysis.
Following these publications, over 200 empirical articles were published examining Job Characteristics Theory over the next decade. Fried and Ferris summarized the research on Job Characteristics Theory and found “modest support” overall. Fried and Ferris mentioned seven general areas of criticism in their review, which are discussed below:
Relation of objective and perceived job characteristics: Whether or not there is accuracy in the worker's perceptions of job characteristics is an important topic of concern for Job Characteristics Theory. Inaccurate ratings of the five job characteristics can be detrimental to the job enrichment process because the Job Diagnostic Survey, which is instrumental in determining what enrichment needs to take place, relies on jobholders' perceptions.
Influential forces on job perceptions: Social cues, personal factors, and what order the portions of the Job Diagnostic Survey is given can influence job perceptions. These “irrelevant cues” could color one's perception of the job characteristics.
Perceived versus objective job characteristics-outcomes relationships: Researchers have also been concerned about the objectivity of jobholders’ assessment of job characteristics and work outcomes, however studies have tended to show that this fear is largely unfounded.
Factors of the Job Diagnostic Survey: The support for the five dimensions of job characteristics in Job Characteristics Theory have mixed support among the studies examining the factor solutions of the Job Diagnostic Survey.
The job characteristics-outcomes relationships: Researchers have argued job characteristics have a stronger relationship with personal outcomes, than with work outcomes. More importantly, it was found that the Motivating Potential Score was not as predictive as adding up rater's assessment of the five job characteristics.
Mediator effects of critical psychological states: Researchers have found support for the mediating role of psychological states between job characteristics and personal outcomes, but didn't find similar evidence for the mediation on work outcomes.
Growth Need Strength's use as a moderator: There have been several studies investigating the validity of Growth Need Strength as a moderator. Many of the studies reported the moderating effect of Growth Need Strength to be low.
New developments
Over the years since Job Characteristics Theory's introduction into the organizational literature, there have been many changes to the field and to work itself. Oldham and Hackman suggest that the areas more fruitful for development in work design are social motivation, job crafting, and teams.
Social sources of motivation are becoming more important due to the changing nature of work in this country. More jobs are requiring higher levels of client-employee interaction, as well as increasing interdependence among employees. With this in mind, it would make sense to investigate the effect the social aspects have on affective and behavioral outcomes.
While Job Characteristics Theory was mainly focused on the organization's responsibility for manipulating job characteristics to enrich jobs there has been a considerable buzz in the literature regarding job crafting. In job crafting the employee has some control over their role in the organization. Hackman and Oldham point out there are many avenues of inquiry regarding job crafting such as: what are the benefits of job crafting, are the benefits due to the job crafting process itself or the actual changes made to the job, and what are the negative effects of job crafting?
Finally, they brought up the potential research directions relevant to team work design. Specifically, they discuss the need to understand when to use work-design aimed at the individual or team level in order to increase performance, and what type of team is best suited to particular tasks.
Practical implications
Job Characteristics Theory is firmly entrenched within the work design (also called job enrichment) literature, moreover the theory has become one of the most cited in all of the organizational behavior field. In practical terms, Job Characteristics Theory provides a framework for increasing employees’ motivation, satisfaction, and performance through enriching job characteristics.
Job Characteristics Theory has been embraced by researchers and used in a multitude of professions and organizations. In the applied domain, Hackman and Oldham have reported that a number of consulting firms have employed their model or modified it to meet their needs.
See also
Core self-evaluations
Industrial and organizational psychology
Job satisfaction
Motivation
Positive psychology in the workplace
Work design
Work motivation
References
Organizational theory
Organizational behavior
Industrial and organizational psychology
Motivational theories
Sociological theories
Psychological theories
Engineering management | Job characteristic theory | Engineering,Biology | 3,980 |
1,839,990 | https://en.wikipedia.org/wiki/Crypton%20%28particle%29 | In particle physics, the crypton is a hypothetical superheavy particle, thought to exist in a hidden sector of string theory. It has been proposed as a candidate particle to explain the dark matter content of the universe. Cryptons arising in the hidden sector of a superstring-derived flipped SU(5) GUT model have been shown to be metastable with a lifetime exceeding the age of the universe. Their slow decays may provide a source for the ultra-high-energy cosmic rays (UHECR).
References
Hypothetical elementary particles
String theory | Crypton (particle) | Physics,Astronomy | 114 |
1,085,308 | https://en.wikipedia.org/wiki/Candlepower | Candlepower (abbreviated as cp or CP) is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents. The historical candlepower is equal to 0.981 candelas. In modern usage, candlepower is sometimes used as a synonym for candla.
History
The term candlepower was originally defined in the United Kingdom, by the Metropolitan Gas Act 1860, as the light produced by a pure spermaceti candle that weighs and burns at a rate of . Spermaceti is a material from the heads of sperm whales, and was once used to make high-quality candles.
At the time the UK established candlepower as a unit, the French standard of light was based on the illumination from a Carcel burner, which defined the illumination that emanates from a lamp burning pure colza oil (obtained from the seed of the plant Brassica campestris) at a defined rate. Ten standard candles equaled about one Carcel burner.
In 1909, several agencies met to establish an international standard. It was attended by representatives of the Laboratoire Central de l’Electricité (France), the National Physical Laboratory (UK), the Bureau of Standards (United States), and the Physikalische Technische Reichsanstalt (Germany). The majority redefined the candle in term of an electric lamp with a carbon filament. The Germans, however, dissented and decided to use a definition equal to 9/10 of the output of a Hefner lamp.
In 1921, the Commission Internationale de l'Eclairage (International Commission for Illumination, commonly referred to as the CIE) redefined the international candle again in terms of a carbon filament incandescent lamp.
In 1937, the international candle was redefined again—against the luminous intensity of a blackbody at the freezing point of liquid platinum which was to be 58.9 international candles per square centimetre.
In 1948, the international unit (SI) candela replaced candlepower. One candlepower unit is about 0.981 candela. In general modern use, a candlepower now equates directly (1:1) to the number of candelas—an implicit increase from its old value.
Calibration of lamps
To measure the candlepower of a lamp, a person judged by eye the relative brightness of adjacent surfaces—one illuminated only by a standard lamp (or candle) and the other only by the lamp under test. They adjusted the distance of one of the lamps until the two surfaces appeared to be of equal brightness. Then they calculated the candlepower of the lamp under test from the two distances and the inverse square law.
Modern use
"Candlepower" is largely an obsolete term. However, people still sometimes use it to describe the luminous intensity of high powered flashlights and spotlights. Narrow-beamed lights of all sorts can have very high candlepower specifications, because candlepower measures the intensity of the light on a target, rather than the total amount of light it emits. A given lamp has a higher candlepower rating if its light is more tightly focused.
Candlepower is still used today in law. For example, it is presently used in the California Vehicle Code to define the legal requirements for headlamps and other lamps, including accessory lamps.
Only a few artificial light sources, such as military photoflash bombs, have the very high candlepower ratings characteristic of narrow-beamed spotlights but, simultaneously, a wide unfocused distribution of light.
See also
Candela
List of obsolete units of measurement
Lumen (unit)
Notes and references
Further reading
International candle at Sizes.com Last revised: 27 June 2007. Accessed July 2007
Candle History - Candlepower 2003 Bob Sherman at Craftcave. Accessed July 2007.
Brief History Of Lighting 2004 by The Wolfstone Group. Accessed July 2007.
A History of Light and Lighting by Bill Williams Edition: 2.3 - (2005) Accessed July 2007.
Candles
Units of luminous intensity
Lighting
Obsolete units of measurement | Candlepower | Mathematics | 834 |
916,340 | https://en.wikipedia.org/wiki/Type%20I%20keratin | Type I keratins (or Type I cytokeratins) are cytokeratins that constitute the Type I intermediate filaments (IFs) of the intracytoplasmatic cytoskeleton, which is present in all mammalian epithelial cells. Most of the type I keratins consist of acidic, low molecular weight proteins which in vivo are arranged in pairs of heterotypic Type I and Type II keratin chains, coexpressed during differentiation of simple and stratified epithelial tissues.
Type I keratins are encoded on chromosome 17q and encompasses: K9, K10, K11, K12, K13, K14, K15, K16, K17, K18, K19 and K20. Their molecular weight ranges from 40 kDa (K19) to 64 kDa (K9).
See also
Type II keratin
External links
Proteopedia page on keratins
Keratins | Type I keratin | Chemistry | 205 |
74,440,694 | https://en.wikipedia.org/wiki/ODE/IM%20correspondence | In mathematical physics, the ODE/IM correspondence is a link between ordinary differential equations (ODEs) and integrable models. It was first found in 1998 by Patrick Dorey and Roberto Tateo. In this original setting it relates the spectrum of a certain integrable model of magnetism known as the XXZ-model to solutions of the one-dimensional Schrödinger equation with a specific choice of potential, where the position coordinate is considered as a complex coordinate.
Since then, such a correspondence has been found for many more ODE/IM pairs.
See also
Bethe ansatz
WKB approximation
References
Integrable systems
Spin models
Ordinary differential equations | ODE/IM correspondence | Physics | 136 |
1,821,329 | https://en.wikipedia.org/wiki/2M1207b | 2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth. It is one of the first candidate exoplanets to be directly observed (by infrared imaging). It was discovered in April 2004 by the Very Large Telescope (VLT) at the Paranal Observatory in Chile by a team from the European Southern Observatory led by Gaël Chauvin. It is believed to be from 5 to 6 times the mass of Jupiter and may orbit 2M1207 at a distance roughly as far from the brown dwarf as Pluto is from the Sun.
The object is a very hot gas giant; the estimated surface temperature is roughly 1200 K (930 °C or 1700 °F), mostly due to gravitational contraction. Its mass is well below the calculated limit for deuterium fusion in brown dwarfs, which is 13 Jupiter masses. The projected distance between 2M1207b and its primary is around 40 AU (similar to the mean distance between Pluto and the Sun). Its infrared spectrum indicates the presence of water molecules in its atmosphere. The object is not a likely candidate to support life, either on its surface or on any satellites.
Discovery and identification
2M1207b is around 100 times fainter in the sky than its companion. It was first spotted as a "faint reddish speck of light" in 2004 by the VLT. After the initial observation, there was some question as to whether the objects might be merely an optical double, but subsequent observations by the Hubble Space Telescope and the VLT have shown that the objects move together and are therefore presumably a binary system.
An initial photometric estimate for the distance to 2M1207b was 70 parsecs. In December 2005, American astronomer Eric Mamajek reported a more accurate distance () to 2M1207b using the moving-cluster method. Recent trigonometric parallax results have confirmed this moving-cluster distance, leading to a distance estimate of 52.75 parsecs or 172 ± 3 light years.
Properties
Estimates for the mass, size, and temperature of 2M1207b are still uncertain. Although spectroscopic evidence is consistent with a mass of 8 ± 2 Jupiter masses and a surface temperature of 1600 ± 100 kelvins, theoretical models for such an object predict a luminosity 10 times greater than observed. Because of this, lower estimates for the mass and temperature have been proposed. Alternatively, 2M1207b might be dimmed by a surrounding disk of dust and gas. As an unlikely possibility, Mamajek and Michael Meyer have suggested that the planet is actually much smaller, but is radiating away heat generated by a recent collision.
JWST observations of 2M1207B with NIRSpec did not detect any methane (CH4) and only weak carbon monoxide (CO) in the atmosphere of this object. The best-fit models show stronger methane and carbon monoxide bands than observed. A weaker methane band is a sign for nonequilibrium chemistry for young low-mass objects. The weakness of carbon monoxide could be attributed to other effects, such as temperature gradient or cloud thickness. The researchers used cloudless models that show some inconsistency with the temperature and absorption of methane and carbon monoxide, which might be resolved in the future with models that include clouds.
The JWST observations were also able to detect emission of hydrogen (Paschen transitions) and the Helium I triplet at 1.083 μm. This is a sign of active accretion from a small circumstellar disk or circumplanetary disk. For now this disk remains undetected, but it might be detected in future observations by JWST at longer wavelengths.
Status as an exoplanet
Although the mass of 2M1207b is less than that required for deuterium fusion to occur, some 13 times the mass of Jupiter, and the image of 2M1207b has been widely hailed as the first direct image of an exoplanet, it may be questioned whether 2M1207b is actually a planet. , the International Astronomical Union's (IAU) official definition of an exoplanet requires that the mass ratio of the orbiting object to the central object be below the L4/L5 instability, which is given by the equation M/Mcentral < 2/(25+) ≈ 1/25. The mass ratio of 2M1207b and 2M1207 is approximately 0.22, which exceeds the L4/L5 instability threshold and therefore means 2M1207b does not qualify as an exoplanet under the IAU's definition.
Some other definitions of the term planet require a planet to have formed in the same way as the planets in the Solar System did, by secondary accretion in a protoplanetary disk. With such a definition, if 2M1207b formed by direct gravitational collapse of a gaseous nebula, it would be a sub-brown dwarf rather than a planet. A similar debate exists regarding the identity of GQ Lupi b, also first imaged in 2004. On the other hand, the discovery of marginal cases like Cha 110913-773444—a free-floating, planetary-mass object—raises the question of whether distinction by formation is a reliable dividing line between stars/brown dwarfs and planets.In 2006, the IAU's Working Group on Extrasolar Planets described 2M1207b as a "possible planetary-mass companion to a brown dwarf."
See also
Extrasolar moon
HD 172555
Rogue planet
References
External links
ESO Press Release 12/05:Yes, it is the Image of an Exoplanet
BBC: Planet 'seen' around distant sun
Space.com – Astronomers Confident: Planet Beyond Solar System Has Been Photographed
Space.com article on the discovery
"A Giant Planet Candidate Near a Young Brown Dwarf" (PDF) from the European Southern Observatory.
Space.com: Fresh Debate over First Photo of Extrasolar Planet
"A Moving Cluster Distance to the Exoplanet 2M1207 B in the TW Hydrae Association"
"The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk"
"Planet collision could explain alien world's heat"
Catalog views: Aladin Lite
DSS color
DSS near IR
sDSS red (high res)
b
Centaurus
TW Hydrae association
Giant planets
Exoplanets discovered in 2004
Exoplanets detected by direct imaging | 2M1207b | Astronomy | 1,373 |
12,670,711 | https://en.wikipedia.org/wiki/Scyllo-Inositol | scyllo-Inositol, also called scyllitol, cocositol, or quercinitol, is a chemical compound with formula , one of the nine inositols, the stereoisomers of cyclohexane-1,2,3,4,5,6-hexol. The molecule has a ring of six carbon atoms, each bound to one hydrogen atom and one hydroxyl group (–OH); if the ring is assumed horizontal, the hydroxyls lie alternately above and below the respective hydrogens.
scyllo-Inositol is a naturally occurring carbohydrate, specifically a sugar alcohol. It occurs in small amounts in the tissues of humans and other animals, certain bacteria, and more abundantly in some plants.
Around 2000, scyllo-inositol attracted attention as a possible treatment for neurodegenerative disorders such as Alzheimer's. For this use it received the codes AZD-103 and ELND005.
Chemical and physical properties
Crystal structure
Anhydrous scyllo-inositol exists in at least two polymorphs (crystal forms). In both forms the molecules have symmetry and are in the chair conformation, that puts all the hydroxyls in nearly equatorial positions.
The "A" form readily crystallizes from water. It has a lower density 1.57 g/ml and decomposes at 358 °C. It crystallizes in the monoclinic system with group is . The cell parameters are a = 508.9 pm, b = 664.5 pm, c = 1194.8 pm, β = 116.98°, Z = 2. The ring puckering parameter Q is 58.1 pm.
The "B" form is hard to obtain in pure form, as it often crystallizes mixed with the "A" form. Its density is 1.66 g/ml and decomposes at about 360 °C. Its crystal system is triclinic with group . The cell parameters are a = 672.5 pm, b = 679.7 pm, c = 863.5 pm, α = 95.45°, β = 99.49°, γ = 99.19°, Z = 2. The puckering Q is 56.6 pm.
The density of the "A" form is similar to that of myo-inositol but about 0.05 to 0.10 g/mL lower than that of the other inositol stereoisomers, and of the "B" form. The melting (decomposition) point of both forms is the highest among all inositols. Like all of them, the crystals feature infinite chains of hydrogen bonds.
Synthesis
Scyllitol and other stereo isomers can be synthesized from para-benzoquinone via a conduritol intermediate. It can also be obtained from myo-inositol by the Mitsunobu reaction.
Various animals, plants, insects, and bacteria have been found to convert myo-inositol to scyllo-inositol, including Streptomyces griseus, where that conversion is part of the synthesis of streptomycin.
Scyllitol was known to be a facultative intermediate in the metabolism of myo-inositol by the bacterium Bacillus subtilis. In 2011 a genetically engineered strain of this organism was developed which interrupted that pathway and converted part of the myo-inositol in the medium to scyllo-inositol in 48 hours. Eventually the process was able to produce 27.6 g/L of scyllo-inositol in the medium, from 50 g/L of myo-inositol, in 48 h.
In 2021 another process was developed using the bacterium Corynebacterium glutamicum, producing 1.8 g/L of scyllitol from 20 g/L glucose and 4.4 g/L from 20 g/L sucrose in 72 h. The conversion involves NAD+-dependent oxidation of myo-inositol to 2-keto-myo-inositol (scyllo-inosose), followed by NADPH-dependent reduction to scyllitol.
Derivatives
Several derivatives of scyllo-inositol have been synthesized and studied in the laboratory, such as phosphates (variants of phytic acid) and orthoformates with an adamantane structure.
Biochemistry
Natural occurrence
Scyllitol is widely distributed in nature in fish, insects, mammalian tissues and urine, certain bacteria, and plants such as Calycanthus occidentalis. It is particularly abundant in coconut milk.
The scyllitol derivative O-methyl-scyllo-inositol is one of the predominant soluble carbohydrate derivatives in the root nodules of the pea plant created bythe bacterium Rhizobium leguminosarum, together with the isomer ononitol (4-O-methyl-myo-inositol), which are not found elsewhere in the plant.
Scyllitol hexakis dihydrogenphosphate, the scyllo isomer of phytic acid (but not lower phosphates) has been detected in pasture soils from England and Wales at concentrations up to 130 mg of phosphorus per kg of soil, accounting for up to 15% of the soil organic phosphorus. The ratio of the scyllo isomer to the myo isomer ranged between 0.29 and 0.79.
The concentration of scyllo-inositol in coconut milk (the fluid inside the fruit of Cocos nucifera) is 0.5 g/L, five times that of myo-inositol.
Physiology
The concentration of scyllo-inositol in human brain can be measured by NMR; typical values are 0.35 mM for white matter, 0.4 mM for grey matter and 0.5 mM for cerebellum Another study compared the concentrations of myo and scyllo-inositol in brains of 24 healthy volunteers. Averages were about 0.36 mM for scyllo and 4.31 mM for myo, with large deviations. The study found a significant increase of both isomers in the older 14 (46-71 yrs) compared to the younger 10 (26-29 yrs), namely about 40% for scyllo, 20% for myo; and a weak correlation between the two values. However a concentration of scyllo-inositol 300% higher than normal was measured in a healthy volunteer, without a corresponding increase in myo-inositol; suggesting that metabolism of the two isomers are independently regulated.
Researchers at the Harvard Medical School-affiliated McLean Hospital found that chronic users of anabolic steroids had lower levels of brain scyllo-inositol levels than non-users.
Brain concentration of scyllo-inositol was found to be about 75% lower than average in patients with hepatic encephalopathy, which also lowers the levels of myo-inositol.
Scyllitol was found to inhibit in vitro the aggregation of α-synuclein into fibrils, a phenomenon implicated in Parkinson's disease.
Previous intravenous administration of either myo- or scyllo-inositol was found to reduce the duration and intensity of chemically-induced seizures in rats.
Since the 1940s, 5–20% of coconut milk has been used as a growth-promoting agent in formulations of plant cell culture medium. Part of its effectiveness in this application is due to its myo- and scyllo-inositol contents.
Clinical evaluation
Alzheimer's disease
In the early 2000s it was reported that scyllo–inositol crossed blood-brain barrier and, when given to mice (TgCRND8) that were genetically engineered to exhibit Alzheimers-like symptoms, it inhibited cognitive deficits and significantly improved the disease pathology. The compound was found to decrease the amount of insoluble amyloid proteins Aβ40, Aβ42 and amyloid plaque accumulation in the brain, without interfering with the synthesis of phosphatidylinositol lipids from myo-inositol. More recently, it has also been found to inhibit the binding of Aβ oligomers to plasma membranes and interfering with synaptic function.
Motivated by these and other results, in about 2008 Transition Therapeutics set to investigate scyllo-inositol as a disease-modifying therapy for Alzheimer's disease, under the designation AZD-103. Transition partnered with Elan Corporation for the development of the compound, relabeled ELND005, and a patent for this use () was issued on April 21, 2009. In 2014, ELND005 reverted to Transition Therapeutics, which was acquired by OPKO Health in 2016.
A clinical investigation of ELND005 with approximately 353 patients, planned to take 18 months, was started in 2008 and received fast track designation from the U.S. Food and Drug Administration. The study initially used daily doses of 500, 2000, and 4000 mg; however, the last two were discontinued by December 2009, due to suspected adverse effects, including 9 deaths. Results of this trial were not positive but considered inconclusive. A new 12-week fast-track trial with 296 moderate to advanced Alzheimer's was started in November 2012, to investigate the effect of a single dose of ELND005 on the NPI-C agitation and aggression scores. In June 2015, the results of this trial were reported as negative, and the company abandoned plans to extend the trial further.
Bipolar disorder
In 2012, Elan started a Phase 2 study of AZD-103 as an add-on therapy in 400 patients with bipolar disorder; this program was discontinued in 2014.
Down's syndrome
In 2013, a four-week Phase 2 trial began evaluating 250 and 500 mg daily of AZD-103 in 23 young adults with Down's syndrome. This trial was completed in November 2014, without significant positive results, and was considered inconclusive.
See also
allo-Inositol
cis-Inositol
D-chiro-Inositol
epi-Inositol
L-chiro-Inositol
muco-Inositol
neo-Inositol
References
Inositol | Scyllo-Inositol | Chemistry | 2,211 |
19,347,046 | https://en.wikipedia.org/wiki/HD%20118889 | HD 118889 is a binary star system in the northern constellation of Boötes. It is faintly visible to the naked eye as a point of light with an apparent visual magnitude of 5.57. The system is located at a distance of approximately 196 light years from the Sun based on stellar parallax, but is drifting closer with a radial velocity of −26 km/s.
The binary components of this system were first measured by S. W. Burnham in 1878 and it was given the discovery code BU 612. The pair are orbiting each other with a period of 22.46 years with an eccentricity (ovalness) of 0.545. The primary component is a magnitude 6.35 star with a stellar classification of F0V, matching an F-type main-sequence star. It is an estimated 718 million years old and is spinning rapidly with a projected rotational velocity of 144 km/s. The star has 1.4–1.9 times the mass of the Sun. The secondary is slightly fainter at magnitude 6.47.
References
External links
HR 5138
CCDM J13395+1045
Image HD 118889
F-type main-sequence stars
Binary stars
Boötes
Durchmusterung objects
118889
066640
5138 | HD 118889 | Astronomy | 265 |
26,849,987 | https://en.wikipedia.org/wiki/Differential%20phase | Differential phase is a kind of linearity distortion which affects the color hue in TV broadcasting.
Composite color video signal
Composite color video signal (CCVS) consists of three terms:
Monochrome (luminance) signal
Auxiliary signals (sync pulse and blanking signals)
Color signal, which is actually a subcarrier modulated by chroma information
The first two terms are usually called composite video signal (CVS)
The modulation technique of the color subcarrier is quadrature amplitude modulation (QAM) both in PAL and NTSC systems. The amplitude of the color signal represents the saturation of the color and the phase lag of the color signal with respect to a certain reference which is called colorburst represents the hue; i.e., each phase lag is assigned for a different color hue. So, in order to reproduce the original color in the receiver, the phase difference between the colorburst and the color signal must be kept constant throughout the broadcasting.
The colorburst
The colorburst is a 10 period signal of color carrier (3.58 MHz in System M and 4.43 MHz in System B and System G). It is superimposed on the back porch of the CVS. The peak to peak amplitude is about 300 mV. That means that, when the color signal has a low luminance, its DC component is comparable to that of the colorburst. All dark colors have more or less the same DC component as the colorburst. But light colors have a higher luminance and hence a higher DC component.
Differential phase distortion
During broadcasting, the inherent non linearity in electronic devices may cause a level dependent phase shift. Differential phase distortion (DP or dP) is the shift of color signal phase with respect to the colorburst phase. When DC (brightness / luminance) levels of light colors and the colorburst are different, the hue of the light colors may change. Especially a slight change in skin color may be irritating to viewers (too yellow or too red skin color depending on whether shift is positive or negative).
PAL system
To solve the problem of differential phase distortion in PAL system, the polarity of both the colorburst and the color signal are reversed in each consecutive lines. So in odd lines the phase of the colorburst leads and in the even lines the phase of the color signal leads. However, if there is DP distortion in the system, the shift caused by DP has always the same polarity, thus the overall shift is more than the original in even line and less than the original in the odd line by the same amount. The average of two lines yields the original phase difference and thus the color.
The mathematics involved is as follows:
Let be the phase difference of the color signal with respect to colorburst and be the extra shift introduced by DP.
The original signal is
If there is a DP distortion, the received signal for the first line is
In the second line (after multiplying by -1)
The average is
So while the effect of diminishes on the color hue, the amplitude of the color signal is reduced by which means that color saturation is reduced.
See also
Differential gain
References
Broadcasting
Television technology | Differential phase | Technology | 664 |
3,931 | https://en.wikipedia.org/wiki/Binary%20relation | In mathematics, a binary relation associates elements of one set called the domain with elements of another set called the codomain. Precisely, a binary relation over sets and is a set of ordered pairs where is in and is in . It encodes the common concept of relation: an element is related to an element , if and only if the pair belongs to the set of ordered pairs that defines the binary relation.
An example of a binary relation is the "divides" relation over the set of prime numbers and the set of integers , in which each prime is related to each integer that is a multiple of , but not to an integer that is not a multiple of . In this relation, for instance, the prime number is related to numbers such as , , , , but not to or , just as the prime number is related to , , and , but not to or .
Binary relations, and especially homogeneous relations, are used in many branches of mathematics to model a wide variety of concepts. These include, among others:
the "is greater than", "is equal to", and "divides" relations in arithmetic;
the "is congruent to" relation in geometry;
the "is adjacent to" relation in graph theory;
the "is orthogonal to" relation in linear algebra.
A function may be defined as a binary relation that meets additional constraints. Binary relations are also heavily used in computer science.
A binary relation over sets and is an element of the power set of Since the latter set is ordered by inclusion (), each relation has a place in the lattice of subsets of A binary relation is called a homogeneous relation when . A binary relation is also called a heterogeneous relation when it is not necessary that .
Since relations are sets, they can be manipulated using set operations, including union, intersection, and complementation, and satisfying the laws of an algebra of sets. Beyond that, operations like the converse of a relation and the composition of relations are available, satisfying the laws of a calculus of relations, for which there are textbooks by Ernst Schröder, Clarence Lewis, and Gunther Schmidt. A deeper analysis of relations involves decomposing them into subsets called concepts, and placing them in a complete lattice.
In some systems of axiomatic set theory, relations are extended to classes, which are generalizations of sets. This extension is needed for, among other things, modeling the concepts of "is an element of" or "is a subset of" in set theory, without running into logical inconsistencies such as Russell's paradox.
A binary relation is the most studied special case of an -ary relation over sets , which is a subset of the Cartesian product
Definition
Given sets and , the Cartesian product is defined as and its elements are called ordered pairs.
A over sets and is a subset of The set is called the or of , and the set the or of . In order to specify the choices of the sets and , some authors define a or as an ordered triple , where is a subset of called the of the binary relation. The statement reads " is -related to " and is denoted by . The or of is the set of all such that for at least one . The codomain of definition, , or of is the set of all such that for at least one . The of is the union of its domain of definition and its codomain of definition.
When a binary relation is called a (or ). To emphasize the fact that and are allowed to be different, a binary relation is also called a heterogeneous relation. The prefix hetero is from the Greek ἕτερος (heteros, "other, another, different").
A heterogeneous relation has been called a rectangular relation, suggesting that it does not have the square-like symmetry of a homogeneous relation on a set where Commenting on the development of binary relations beyond homogeneous relations, researchers wrote, "... a variant of the theory has evolved that treats relations from the very beginning as or , i.e. as relations where the normal case is that they are relations between different sets."
The terms correspondence, dyadic relation and two-place relation are synonyms for binary relation, though some authors use the term "binary relation" for any subset of a Cartesian product without reference to and , and reserve the term "correspondence" for a binary relation with reference to and .
In a binary relation, the order of the elements is important; if then can be true or false independently of . For example, divides , but does not divide .
Operations
Union
If and are binary relations over sets and then is the of and over and .
The identity element is the empty relation. For example, is the union of < and =, and is the union of > and =.
Intersection
If and are binary relations over sets and then is the of and over and .
The identity element is the universal relation. For example, the relation "is divisible by 6" is the intersection of the relations "is divisible by 3" and "is divisible by 2".
Composition
If is a binary relation over sets and , and is a binary relation over sets and then (also denoted by ) is the of and over and .
The identity element is the identity relation. The order of and in the notation used here agrees with the standard notational order for composition of functions. For example, the composition (is parent of)(is mother of) yields (is maternal grandparent of), while the composition (is mother of)(is parent of) yields (is grandmother of). For the former case, if is the parent of and is the mother of , then is the maternal grandparent of .
Converse
If is a binary relation over sets and then is the , also called , of over and .
For example, is the converse of itself, as is , and and are each other's converse, as are and . A binary relation is equal to its converse if and only if it is symmetric.
Complement
If is a binary relation over sets and then (also denoted by ) is the of over and .
For example, and are each other's complement, as are and , and , and , and for total orders also and , and and .
The complement of the converse relation is the converse of the complement:
If the complement has the following properties:
If a relation is symmetric, then so is the complement.
The complement of a reflexive relation is irreflexive—and vice versa.
The complement of a strict weak order is a total preorder—and vice versa.
Restriction
If is a binary homogeneous relation over a set and is a subset of then is the of to over .
If is a binary relation over sets and and if is a subset of then is the of to over and .
If a relation is reflexive, irreflexive, symmetric, antisymmetric, asymmetric, transitive, total, trichotomous, a partial order, total order, strict weak order, total preorder (weak order), or an equivalence relation, then so too are its restrictions.
However, the transitive closure of a restriction is a subset of the restriction of the transitive closure, i.e., in general not equal. For example, restricting the relation " is parent of " to females yields the relation " is mother of the woman "; its transitive closure does not relate a woman with her paternal grandmother. On the other hand, the transitive closure of "is parent of" is "is ancestor of"; its restriction to females does relate a woman with her paternal grandmother.
Also, the various concepts of completeness (not to be confused with being "total") do not carry over to restrictions. For example, over the real numbers a property of the relation is that every non-empty subset with an upper bound in has a least upper bound (also called supremum) in However, for the rational numbers this supremum is not necessarily rational, so the same property does not hold on the restriction of the relation to the rational numbers.
A binary relation over sets and is said to be a relation over and , written if is a subset of , that is, for all and if , then . If is contained in and is contained in , then and are called written . If is contained in but is not contained in , then is said to be than , written For example, on the rational numbers, the relation is smaller than , and equal to the composition .
Matrix representation
Binary relations over sets and can be represented algebraically by logical matrices indexed by and with entries in the Boolean semiring (addition corresponds to OR and multiplication to AND) where matrix addition corresponds to union of relations, matrix multiplication corresponds to composition of relations (of a relation over and and a relation over and ), the Hadamard product corresponds to intersection of relations, the zero matrix corresponds to the empty relation, and the matrix of ones corresponds to the universal relation. Homogeneous relations (when ) form a matrix semiring (indeed, a matrix semialgebra over the Boolean semiring) where the identity matrix corresponds to the identity relation.
Examples
Types of binary relations
Some important types of binary relations over sets and are listed below.
Uniqueness properties:
Injective (also called left-unique): for all and all if and then . In other words, every element of the codomain has at most one preimage element. For such a relation, is called a primary key of . For example, the green and blue binary relations in the diagram are injective, but the red one is not (as it relates both and to ), nor the black one (as it relates both and to ).
Functional (also called right-unique or univalent): for all and all if and then . In other words, every element of the domain has at most one image element. Such a binary relation is called a or . For such a relation, is called of . For example, the red and green binary relations in the diagram are functional, but the blue one is not (as it relates to both and ), nor the black one (as it relates to both and ).
One-to-one: injective and functional. For example, the green binary relation in the diagram is one-to-one, but the red, blue and black ones are not.
One-to-many: injective and not functional. For example, the blue binary relation in the diagram is one-to-many, but the red, green and black ones are not.
Many-to-one: functional and not injective. For example, the red binary relation in the diagram is many-to-one, but the green, blue and black ones are not.
Many-to-many: not injective nor functional. For example, the black binary relation in the diagram is many-to-many, but the red, green and blue ones are not.
Totality properties (only definable if the domain and codomain are specified):
Total (also called left-total): for all there exists a such that . In other words, every element of the domain has at least one image element. In other words, the domain of definition of is equal to . This property, is different from the definition of (also called by some authors) in Properties. Such a binary relation is called a . For example, the red and green binary relations in the diagram are total, but the blue one is not (as it does not relate to any real number), nor the black one (as it does not relate to any real number). As another example, is a total relation over the integers. But it is not a total relation over the positive integers, because there is no in the positive integers such that . However, is a total relation over the positive integers, the rational numbers and the real numbers. Every reflexive relation is total: for a given , choose .
Surjective (also called right-total): for all , there exists an such that . In other words, every element of the codomain has at least one preimage element. In other words, the codomain of definition of is equal to . For example, the green and blue binary relations in the diagram are surjective, but the red one is not (as it does not relate any real number to ), nor the black one (as it does not relate any real number to ).
Uniqueness and totality properties (only definable if the domain and codomain are specified):
A function (also called mapping): a binary relation that is functional and total. In other words, every element of the domain has exactly one image element. For example, the red and green binary relations in the diagram are functions, but the blue and black ones are not.
An injection: a function that is injective. For example, the green relation in the diagram is an injection, but the red one is not; the black and the blue relation is not even a function.
A surjection: a function that is surjective. For example, the green relation in the diagram is a surjection, but the red one is not.
A bijection: a function that is injective and surjective. In other words, every element of the domain has exactly one image element and every element of the codomain has exactly one preimage element. For example, the green binary relation in the diagram is a bijection, but the red one is not.
If relations over proper classes are allowed:
Set-like (also called local): for all , the class of all such that , i.e. , is a set. For example, the relation is set-like, and every relation on two sets is set-like. The usual ordering < over the class of ordinal numbers is a set-like relation, while its inverse > is not.
Sets versus classes
Certain mathematical "relations", such as "equal to", "subset of", and "member of", cannot be understood to be binary relations as defined above, because their domains and codomains cannot be taken to be sets in the usual systems of axiomatic set theory. For example, to model the general concept of "equality" as a binary relation , take the domain and codomain to be the "class of all sets", which is not a set in the usual set theory.
In most mathematical contexts, references to the relations of equality, membership and subset are harmless because they can be understood implicitly to be restricted to some set in the context. The usual work-around to this problem is to select a "large enough" set , that contains all the objects of interest, and work with the restriction instead of . Similarly, the "subset of" relation needs to be restricted to have domain and codomain (the power set of a specific set ): the resulting set relation can be denoted by Also, the "member of" relation needs to be restricted to have domain and codomain to obtain a binary relation that is a set. Bertrand Russell has shown that assuming to be defined over all sets leads to a contradiction in naive set theory, see Russell's paradox.
Another solution to this problem is to use a set theory with proper classes, such as NBG or Morse–Kelley set theory, and allow the domain and codomain (and so the graph) to be proper classes: in such a theory, equality, membership, and subset are binary relations without special comment. (A minor modification needs to be made to the concept of the ordered triple , as normally a proper class cannot be a member of an ordered tuple; or of course one can identify the binary relation with its graph in this context.) With this definition one can for instance define a binary relation over every set and its power set.
Homogeneous relation
A homogeneous relation over a set is a binary relation over and itself, i.e. it is a subset of the Cartesian product It is also simply called a (binary) relation over .
A homogeneous relation over a set may be identified with a directed simple graph permitting loops, where is the vertex set and is the edge set (there is an edge from a vertex to a vertex if and only if ).
The set of all homogeneous relations over a set is the power set which is a Boolean algebra augmented with the involution of mapping of a relation to its converse relation. Considering composition of relations as a binary operation on , it forms a semigroup with involution.
Some important properties that a homogeneous relation over a set may have are:
: for all . For example, is a reflexive relation but > is not.
: for all not . For example, is an irreflexive relation, but is not.
: for all if then . For example, "is a blood relative of" is a symmetric relation.
: for all if and then For example, is an antisymmetric relation.
: for all if then not . A relation is asymmetric if and only if it is both antisymmetric and irreflexive. For example, > is an asymmetric relation, but is not.
: for all if and then . A transitive relation is irreflexive if and only if it is asymmetric. For example, "is ancestor of" is a transitive relation, while "is parent of" is not.
: for all if then or .
: for all or .
: for all if then some exists such that and .
A is a relation that is reflexive, antisymmetric, and transitive. A is a relation that is irreflexive, asymmetric, and transitive. A is a relation that is reflexive, antisymmetric, transitive and connected. A is a relation that is irreflexive, asymmetric, transitive and connected.
An is a relation that is reflexive, symmetric, and transitive.
For example, " divides " is a partial, but not a total order on natural numbers "" is a strict total order on and " is parallel to " is an equivalence relation on the set of all lines in the Euclidean plane.
All operations defined in section also apply to homogeneous relations.
Beyond that, a homogeneous relation over a set may be subjected to closure operations like:
the smallest reflexive relation over containing ,
the smallest transitive relation over containing ,
the smallest equivalence relation over containing .
Calculus of relations
Developments in algebraic logic have facilitated usage of binary relations. The calculus of relations includes the algebra of sets, extended by composition of relations and the use of converse relations. The inclusion meaning that implies , sets the scene in a lattice of relations. But since the inclusion symbol is superfluous. Nevertheless, composition of relations and manipulation of the operators according to Schröder rules, provides a calculus to work in the power set of
In contrast to homogeneous relations, the composition of relations operation is only a partial function. The necessity of matching target to source of composed relations has led to the suggestion that the study of heterogeneous relations is a chapter of category theory as in the category of sets, except that the morphisms of this category are relations. The of the category Rel are sets, and the relation-morphisms compose as required in a category.
Induced concept lattice
Binary relations have been described through their induced concept lattices:
A concept satisfies two properties:
The logical matrix of is the outer product of logical vectors logical vectors.
is maximal, not contained in any other outer product. Thus is described as a non-enlargeable rectangle.
For a given relation the set of concepts, enlarged by their joins and meets, forms an "induced lattice of concepts", with inclusion forming a preorder.
The MacNeille completion theorem (1937) (that any partial order may be embedded in a complete lattice) is cited in a 2013 survey article "Decomposition of relations on concept lattices". The decomposition is
, where and are functions, called or left-total, functional relations in this context. The "induced concept lattice is isomorphic to the cut completion of the partial order that belongs to the minimal decomposition of the relation ."
Particular cases are considered below: total order corresponds to Ferrers type, and identity corresponds to difunctional, a generalization of equivalence relation on a set.
Relations may be ranked by the Schein rank which counts the number of concepts necessary to cover a relation. Structural analysis of relations with concepts provides an approach for data mining.
Particular relations
Proposition: If is a surjective relation and is its transpose, then where is the identity relation.
Proposition: If is a serial relation, then where is the identity relation.
Difunctional
The idea of a difunctional relation is to partition objects by distinguishing attributes, as a generalization of the concept of an equivalence relation. One way this can be done is with an intervening set of indicators. The partitioning relation is a composition of relations using relations Jacques Riguet named these relations difunctional since the composition involves functional relations, commonly called partial functions.
In 1950 Riguet showed that such relations satisfy the inclusion:
In automata theory, the term rectangular relation has also been used to denote a difunctional relation. This terminology recalls the fact that, when represented as a logical matrix, the columns and rows of a difunctional relation can be arranged as a block matrix with rectangular blocks of ones on the (asymmetric) main diagonal. More formally, a relation on is difunctional if and only if it can be written as the union of Cartesian products , where the are a partition of a subset of and the likewise a partition of a subset of .
Using the notation , a difunctional relation can also be characterized as a relation such that wherever and have a non-empty intersection, then these two sets coincide; formally implies
In 1997 researchers found "utility of binary decomposition based on difunctional dependencies in database management." Furthermore, difunctional relations are fundamental in the study of bisimulations.
In the context of homogeneous relations, a partial equivalence relation is difunctional.
Ferrers type
A strict order on a set is a homogeneous relation arising in order theory.
In 1951 Jacques Riguet adopted the ordering of an integer partition, called a Ferrers diagram, to extend ordering to binary relations in general.
The corresponding logical matrix of a general binary relation has rows which finish with a sequence of ones. Thus the dots of a Ferrer's diagram are changed to ones and aligned on the right in the matrix.
An algebraic statement required for a Ferrers type relation R is
If any one of the relations is of Ferrers type, then all of them are.
Contact
Suppose is the power set of , the set of all subsets of . Then a relation is a contact relation if it satisfies three properties:
The set membership relation, "is an element of", satisfies these properties so is a contact relation. The notion of a general contact relation was introduced by Georg Aumann in 1970.
In terms of the calculus of relations, sufficient conditions for a contact relation include
where is the converse of set membership ().
Preorder R\R
Every relation generates a preorder which is the left residual. In terms of converse and complements, Forming the diagonal of , the corresponding row of and column of will be of opposite logical values, so the diagonal is all zeros. Then
, so that is a reflexive relation.
To show transitivity, one requires that Recall that is the largest relation such that Then
(repeat)
(Schröder's rule)
(complementation)
(definition)
The inclusion relation Ω on the power set of can be obtained in this way from the membership relation on subsets of :
Fringe of a relation
Given a relation , its fringe is the sub-relation defined as
When is a partial identity relation, difunctional, or a block diagonal relation, then . Otherwise the operator selects a boundary sub-relation described in terms of its logical matrix: is the side diagonal if is an upper right triangular linear order or strict order. is the block fringe if is irreflexive () or upper right block triangular. is a sequence of boundary rectangles when is of Ferrers type.
On the other hand, when is a dense, linear, strict order.
Mathematical heaps
Given two sets and , the set of binary relations between them can be equipped with a ternary operation where denotes the converse relation of . In 1953 Viktor Wagner used properties of this ternary operation to define semiheaps, heaps, and generalized heaps. The contrast of heterogeneous and homogeneous relations is highlighted by these definitions:
See also
Abstract rewriting system
Additive relation, a many-valued homomorphism between modules
Allegory (category theory)
Category of relations, a category having sets as objects and binary relations as morphisms
Confluence (term rewriting), discusses several unusual but fundamental properties of binary relations
Correspondence (algebraic geometry), a binary relation defined by algebraic equations
Hasse diagram, a graphic means to display an order relation
Incidence structure, a heterogeneous relation between set of points and lines
Logic of relatives, a theory of relations by Charles Sanders Peirce
Order theory, investigates properties of order relations
Notes
References
Bibliography
Ernst Schröder (1895) Algebra der Logik, Band III, via Internet Archive
External links
Binary relations | Binary relation | Mathematics | 5,253 |
1,659,646 | https://en.wikipedia.org/wiki/Initiation%20%28chemistry%29 | In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Initiation creates a reactive centre on a molecule which produces a chain reaction. The reactive centre generated by initiation is usually a radical, but can also be cations or anions. Once the reaction is initiated, the species goes through propagation where the reactive species reacts with stable molecules, producing stable species and reactive species. This process can produce very long chains of molecules called polymers, which are the building blocks for many materials. After propagation, the reaction is then terminated. There are different types of initiation, with the two main ways being thermal initiation and photo-initiation (light).
Thermal initiation
Thermal initiation involves initiating a reaction in the presence of heat, usually at very high temperatures. Heating a reaction can result in radical initiation of the substrate(s). In the presence of heat, a monomer can self-initiate and react with other monomers or pairs of monomers. This process is called spontaneous polymerization and requires a lot of heat to occur (up to 200°C). For monomers to initiate and polymerize with the same type of monomer (called Homopolymerization), ~180°C is needed for the monomers to initiate. Copolymerization, which is when different kinds of monomers are initiated and react with each other, is more stable and can happen at lower temperatures than Homopolymerization. Self-initiation between homo-monomers is a difficult mechanism to observe because species that are initiated aren't always the same kind of monomer. Sometimes impurities found in the reaction flask with the monomers get initiated and polymerize with monomers, instead of the monomer getting initiated.
Photoinitiation (light)
Photo-initiation occurs when monomers get initiated by light irradiation. LED light passes through the reaction flask which excites the monomers turning them into reactive species, mainly radicals and ions, which can then polymerize. There are two mechanistic classifications of photo-initiation reactions, being either a photoredox process or intramolecular photochemical process. This type of initiation can happen at much lower temperatures, mainly room temperature, then thermal initiation. This makes photo-initiation much more practical than thermal initiation. Photo-initiation also produces less side reactions than thermal and has less impurities. Though thermal initiation is hard to maintain, photo-initiation provides an easy way to initiate monomers to polymerize. Photo-initiation is even used in application such as making various coatings, adhesives, inks, and microelectronics.
See also
Free radical addition
References
Sources
R. G., Compton.1992. Mechanism and Kinetics of Addition Polymerizations, 30, 75-162.
Britannica, The Editors of Encyclopaedia. "chain reaction". Encyclopedia Britannica, 2 May. 2017, https://www.britannica.com/science/chain-reaction. Accessed 29 March 2023.
Britannica, The Editors of Encyclopaedia. "polymer". Encyclopedia Britannica, 2 Jan. 2023, https://www.britannica.com/science/polymer. Accessed 31 March 2023.
Graeme, Moad and David H., Solomon. 1989. Comprehensive Polymer Science and Supplements. 141-146.
Yagçi, Y., Jockusch, S., Turro, N.J. Photoinitiated Polymerization: Advances, Challenges, and Opportunities. Macromolecules 2010, 43, 6245–6260.
Gijsman, P., Hensen, G., Manon, M. Thermal initiation of the oxidation of thermoplastic polymers (Polyamides, Polyesters and UHMwPE). Polymer Degradation and Stability 2021, 183.
Chen, M., Zhong, M., Johnson, J. A. Light-Controlled Radical Polymerization: Mechanisms, Methods, and Applications. Chemical Reviews, 2016,116(17), 10167–1021.
Khojczyk (2011-20-09), English: Hofmann-Löffler-Freytag reaction mechanism, retrieved 2023-03-31.
Reaction mechanisms | Initiation (chemistry) | Chemistry | 875 |
3,834,818 | https://en.wikipedia.org/wiki/Comparability | In mathematics, two elements x and y of a set P are said to be comparable with respect to a binary relation ≤ if at least one of x ≤ y or y ≤ x is true. They are called incomparable if they are not comparable.
Rigorous definition
A binary relation on a set is by definition any subset of Given is written if and only if in which case is said to be to by
An element is said to be , or (), to an element if or
Often, a symbol indicating comparison, such as (or and many others) is used instead of in which case is written in place of which is why the term "comparable" is used.
Comparability with respect to induces a canonical binary relation on ; specifically, the induced by is defined to be the set of all pairs such that is comparable to ; that is, such that at least one of and is true.
Similarly, the on induced by is defined to be the set of all pairs such that is incomparable to that is, such that neither nor is true.
If the symbol is used in place of then comparability with respect to is sometimes denoted by the symbol , and incomparability by the symbol .
Thus, for any two elements and of a partially ordered set, exactly one of and is true.
Example
A totally ordered set is a partially ordered set in which any two elements are comparable. The Szpilrajn extension theorem states that every partial order is contained in a total order. Intuitively, the theorem says that any method of comparing elements that leaves some pairs incomparable can be extended in such a way that every pair becomes comparable.
Properties
Both of the relations and are symmetric, that is is comparable to if and only if is comparable to and likewise for incomparability.
Comparability graphs
The comparability graph of a partially ordered set has as vertices the elements of and has as edges precisely those pairs of elements for which .
Classification
When classifying mathematical objects (e.g., topological spaces), two are said to be comparable when the objects that obey one criterion constitute a subset of the objects that obey the other, which is to say when they are comparable under the partial order ⊂. For example, the T1 and T2 criteria are comparable, while the T1 and sobriety criteria are not.
See also
, a partial ordering in which incomparability is a transitive relation
References
External links
Binary relations
Order theory | Comparability | Mathematics | 501 |
31,954,755 | https://en.wikipedia.org/wiki/WASP-44 | WASP-44 is a G-type star about away in the constellation Cetus that is orbited by the Jupiter-size planet WASP-44b. The star is slightly less massive and slightly smaller than the Sun; it is also slightly cooler, but is more metal-rich. The star was observed by SuperWASP, an organization searching for exoplanets, starting in 2009; manual follow-up observations using WASP-44's spectrum and measurements of its radial velocity led to the discovery of the transiting planet WASP-44b. The planet and its star were presented along with WASP-45b and WASP-46b on May 17, 2011 by a team of scientists testing the idea that hot Jupiters tend to have circular orbits, an assumption that is made when the orbital eccentricity of such planets are not well-constrained.
Observational history
WASP-44 was observed between July and November 2009 by WASP-South, a station of the SuperWASP planet-searching program based at the South African Astronomical Observatory. Observations of the star revealed a periodic decrease in its brightness. WASP-South, along with the SuperWASP-North station at the Roque de los Muchachos Observatory on the Canary Islands, collected 15,755 photometric observations, allowing scientists to produce a more accurate light curve. Another set of observations yielded a 6,000 point photometric data set, but the light curve was prepared late and was not considered in the discovery paper.
In 2010, a European science team investigated the star using the CORALIE spectrograph and collected seventeen spectra of WASP-44. From the spectra, radial velocity measurements were extrapolated. Analysis of collected CORALIE data ruled out the possibility that the detected radial velocity was caused by the blended spectrum of a spectroscopic binary star, supporting the possibility that the body orbiting WASP-44 was indeed a planet, designated WASP-44b.
The Leonhard Euler Telescope at La Silla Observatory in Chile was used to follow up on the planet circling WASP-44, searching for a point at which the planet transited, or crossed in front of, its host star. One transit was detected.
WASP-44, its recently discovered planet, the planets orbiting WASP-45 and WASP-46, and a discussion exploring the validity of the common assumption amongst scientists that closely orbiting hot Jupiter planets have highly circular orbits unless proven otherwise, were reported in a single discovery paper that was published on May 17, 2011 by the Royal Astronomical Society. The paper was submitted to the Monthly Notices of the Royal Astronomical Society on May 16, 2011.
Characteristics
WASP-44 is a G-type star (the same class of star as the Sun) that is located in the Cetus constellation. WASP-44 has a mass that is 0.951 times that of the Sun. In terms of size, WASP-44 has a radius that is 0.927 times that of the Sun. WASP-44 has an effective temperature of 5410 K (cooler than the Sun). However, the star is metal-rich with relation to the Sun. Its measured metallicity is [Fe/H] = 0.06, or 1.148 times that the amount of iron found in the Sun. WASP-44's chromosphere (outermost layer) is not active. The star also does not rotate at a high velocity.
The star has an apparent magnitude of 12.9. It cannot be seen from Earth with the naked eye.
Planetary system
There is one known planet in the orbit of WASP-44: WASP-44b. The planet is a hot Jupiter with a mass of 0.889 times that of Jupiter. Its radius is 1.14 times that of Jupiter. WASP-44b orbits its host star every 2.4238039 days at a distance of 0.03473 AU, approximately 3.47% the mean distance between the Earth and Sun. With an orbital inclination of 86.02º, WASP-44b has an orbit that exists almost edge-on to its host star with respect to Earth. WASP-44b's orbital eccentricity is fit to 0.036, indicating a mostly circular orbit. An analysis of transit timing variations to search for additional planets was negative.
References
Planetary systems with one confirmed planet
Cetus
Planetary transit variables
G-type main-sequence stars
J00153675-1156172
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44 | WASP-44 | Astronomy | 904 |
24,094,910 | https://en.wikipedia.org/wiki/C21H20O12 | {{DISPLAYTITLE:C21H20O12}}
The molecular formula C21H20O12 (molar mass: 464.37 g/mol, exact mass: 464.095476 u) may refer to:
Hyperoside
Isoquercetin
Myricitrin, a flavonol
Spiraeoside, a flavonol
Molecular formulas | C21H20O12 | Physics,Chemistry | 84 |
1,616,204 | https://en.wikipedia.org/wiki/Network%20Load%20Balancing%20Services | Network Load Balancing Services (NLBS) is a Microsoft implementation of clustering and load balancing that is intended to provide high availability and high reliability, as well as high scalability. NLBS is intended for applications with relatively small data sets that rarely change (one example would be web pages), and do not have long-running in-memory states. These types of applications are called stateless applications, and typically include Web, File Transfer Protocol (FTP), and virtual private networking (VPN) servers. Every client request to a stateless application is a separate transaction, so it is possible to distribute the requests among multiple servers to balance the load.
One attractive feature of NLBS is that all servers in a cluster monitor each other with a heartbeat signal, so there is no single point of failure.
In its current incarnation in Windows Server 2003, NLBS does not support automatic removal of a failed server from a cluster unless the server is completely offline, or if its NLBS service is stopped. For example, if a web server is returning an error page instead of correct content, it is still perceived as "alive" by NLBS. As such, a monitoring script is typically required on every participating node, which checks the correctness of local web page delivery, and calls the nlb.exe utility to add or remove itself from the cluster as needed.
History
Windows NT Load Balancing Service (WLBS) is a feature of Windows NT that provides load balancing and clustering for applications. WLBS dynamically distributes IP traffic across multiple cluster nodes, and provides automatic failover in the event of node failure. WLBS was replaced by Network Load Balancing Services in Windows 2000.
Auto fail over is also a part in this frame.
Internet Protocol based network software
Microsoft server technology
Load balancing (computing) | Network Load Balancing Services | Technology | 370 |
25,061,146 | https://en.wikipedia.org/wiki/Project%20management%20information%20system | A project management information system (PMIS) is the logical organization of the information required for an organization to execute projects successfully. A PMIS is typically one or more software applications and a methodical process for collecting and using project information. These electronic systems "help [to] plan, execute, and close project management goals."
PMIS systems differ in scope, design and features depending upon an organisation's operational requirements.
PMIS PMBOK 5th edition definition
The project management information system, which is part of the environmental factors, provides access to tools, such as a scheduling tool, a work authorization system, a configuration management system, an information collection and distribution system, or interfaces to other online automated systems. Automated gathering and reporting on key performance indicators (KPI) can be part of this system.
Project management information system software
At the center of any modern PMIS is a software. Project management information system can vary from something as simple as a File system containing Microsoft Excel documents, to a full blown enterprise PMIS software.
Characteristics of a PMIS
The methodological process used to collect and organize project information can match normalized methodologies such as PRINCE2.
A PMIS Software supports all Project management knowledge areas such as Integration Management, Project Scope Management, Project Time Management, Project Cost Management, Project Quality Management, Project Human Resource Management, Project Communications Management, Project Risk Management, Project Procurement Management, and Project Stakeholder Management.
A PMIS Software is a multi-user application, and can be cloud based or hosted on-premises.
Relationship between a PMS and PMIS
A project management system (PMS) could be a part of a PMIS or sometimes an external tool beside project management information system. PMS is basically an aggregation of the processes, tools, techniques, methodologies, resources, and procedures to manage a project. What a PMIS does is to manage all stakeholders in a project such as the project owner, client, contractors, sub-contractors, in-house staff, workers, managers etc.
References
External links
Project Management Institute
Project management information systems By Donald E. Forbes
Guides for managing projects
Agiles Projektmanagement
Project management software
Information management | Project management information system | Technology | 441 |
58,693,880 | https://en.wikipedia.org/wiki/Aspergillus%20thesauricus | Aspergillus thesauricus is a species of fungus in the genus Aspergillus. It is from the Usti section. The species was first described in 2012.
Growth and morphology
A. thesauricus has been cultivated on both Czapek yeast extract agar (CYA) plates and Malt Extract Agar Oxoid® (MEAOX) plates. The growth morphology of the colonies can be seen in the pictures below.
References
thesauricus
Fungi described in 2012
Fungus species | Aspergillus thesauricus | Biology | 107 |
23,920,929 | https://en.wikipedia.org/wiki/C5H7NO2 | {{DISPLAYTITLE:C5H7NO2}}
The molecular formula C5H7NO2 may refer to:
Ethyl cyanoacetate
Piperidinediones
2,3-Piperidinedione
2,4-Piperidinedione
2,5-Piperidinedione
2,6-Piperidinedione
3,4-Piperidinedione
3,5-Piperidinedione
1-Pyrroline-5-carboxylic acid | C5H7NO2 | Chemistry | 108 |
12,193,926 | https://en.wikipedia.org/wiki/IMUnified | IMUnified, formed in 2000, is a coalition of companies that intend to develop open standards for instant messaging (IM). The founding members are AT&T, Excite@Home, iCAST, Microsoft, Odigo, Phone.com, Prodigy, Tribal Voice and Yahoo!. Notably absent from the list of members is AOL, who was not invited to join the coalition. Some analysts believe the goal of the coalition was to try to force AOL toward a more open IM standard.
See also
IMUnited
External links
AOL not invited to IMUnified alliance , ZDNet (July 26, 2000).
Leading Technology and Instant Messaging Companies for IMUnited, mobile.com.
Trillian restores AOL IM connection , CNN (February 26, 2002).
Instant messaging
Microsoft
Yahoo! | IMUnified | Technology | 168 |
57,185,399 | https://en.wikipedia.org/wiki/Pawl | A pawl is a movable lever that engages a fixed component to either prevent movement in one direction or restrain it altogether. As such, it is a type of latch and can also be considered a type of dog. It typically consists of a spring-loaded lever that engages a mating component at a steep enough angle to restrain it. Pawls are often tapered, being widened at their pivot for anchoring and narrow at their tip.
Applications
Anchor windlass A pawl is used in an anchor windlass to prevent a free-spooling chain by grabbing and snubbing an individual link. Similar mechanisms include a Devil's claw, or a claw and dog.
Ratchet A pawl is used in combination with a ratchet gear in socket wrenches, bicycle freehubs, winches, ratchet reels for diving, fishing, and many other applications.
Ladder Dogs (in the form of pawls) are used on extension ladders to temporarily anchor their sections to one-another.
Table saw Pawls are used on table saws to prevent a workpiece being sawn from kicking back.
Transmission A parking pawl is a device in an automobile automatic transmission which prevents it from moving when the vehicle is parked .
Revolvers The hand (pawl) indexes the cylinder.
References
Mechanisms (engineering)
Fasteners
de:Sperrklinke | Pawl | Engineering | 280 |
72,245,879 | https://en.wikipedia.org/wiki/Data%20ecosystem | A data ecosystem is the complex environment of co-dependent networks and actors that contribute to data collection, transfer and use. It can span multiple sectors – such as healthcare or finance, to inform one another's practices. A data ecosystem often consists of numerous data assemblages. Research into data ecosystems has developed in response to the rapid proliferation and availability of information through the web, which has contributed to the commodification of data.
Data
Data refers to digitized information that is compressed for efficient transmission. Data is constituted of binary values, expressed as 1 or 0, which allows complex thoughts, images, videos and more to be abstracted. The level of data production and exchange has exploded in recent decades, with government and public agencies freely publishing vast swaths of data, particularly in environmental, cultural, scientific and statistical fields. It has also led to a highly profitable industry for companies that collect, categorize and disseminate data as a tradable resource and operate within the newly defined data ecosystems.
Data ecosystems
The nature of an ecosystem denotes a symbiotic relationship between elements. Thus, when describing a data environment as an ecosystem, it describes a co-constitutive relationship. Their primary purpose is to create, manage and sustain the sharing of data across platforms and disciplines. Key to this initiative are data intermediaries, which facilitate access to the data, and are categorized into seven types, including data trusts, data exchanges and data platforms. A data ecosystem also comprises data providers and consumers, who as their titles denote, provide and consume the data through the intermediaries.
A common example of data ecosystem exists within the realm of web browser. A third-party tracking app on a website (referred to as cookies) acts as an intermediary by collecting and organizing data. The web browser becomes the data provider, as it shares a user's information as they navigate through different websites. The websites themselves become consumers as they utilize the tracking information to tailor content based on user behaviour.
As mentioned, data ecosystems can span multiple sectors, for example, a client's medical data is shared with an insurance company to calculate a premium. The point of an ecosystem is that all actors within the shared environment are contributing to a common resource or knowledge-base.
Mapping
Data ecosystems possess three major characteristics: network, platform, and co-evolution. Network loosely refers to the groups of data and technology developers, providers, and resellers. The platform, then, is the service, tool or platform that is collaboratively used by the network of actors. The platform provides the interface for the actors to produce their shared product or service. The final characteristic refers to how the different actors and platform enable one another to evolve or improve upon itself. The metaphorical use of the term "ecosystem" intrinsically demands that all parties involved are mutually benefited by their engagement. That would be the betterment or evolution of their own functioning, which leads to positive outcomes for the larger ecosystem. Again, to use the example of a web browser – the third-party tracking app collects data to help websites evolve their content strategies, which then provide more accurate user data to third-party trackers in an endless feedback loop.
Data assemblages
Within the broad landscape of a data ecosystem are numerous data assemblages. An assemblage is described as interconnected socio-technical systems that work in tandem with one another for a common purpose. These systems encompass the technological, political, financial and best practices that sustain the collection, transfer, and dispersion of data. The below table demonstrates the common elements of a data assemblage which facilitate and govern datafication.
A data ecosystem contains numerous data assemblages, as each actor within the system have their own sets of tangible and non-tangible elements for their operation. Web browsers as data providers have their own assemblages of hardware, software, servers, finances, infrastructure, practices, etc. Each website that consumes the data and the broader companies that they represent similarly present an assemblage of systems. And the intermediary tracking sites which collect and sell the data operate within their own assemblage. It is possible that different assemblages may share elements within the broader ecosystem, or have individual elements, such as opposing hardware or platforms, that come into conflict. For example, a web browser may include ad blockers which conflict with the third-party trackers that attempt to scrape a user's data.
Big data
The rise of data ecosystems is part and parcel with the development of big data. Big data is an emerging trend in science and technology that tracks and defines almost all human engagement. It is defined by the following five properties:
Volume
Big data consists of massive amounts of information, which could be terabytes or petabytes.
Velocity
Big data is produced rapidly, and exchanged in real-time.
Variety
Big Data are extremely diverse, constituting numerous fields of study, and with extensive practical applications.
Value
Big data has inherent value due to the potential application of the data and the political economy in which it operates.
Veracity
Big data must be considered accurate and of high-quality. This can be difficult, as information may be incomplete or wrong, but there should be a level of trust that the collection of the data was done with the intention of being truthful.
Concerns
The main concern or critique of data ecosystems relates to privacy. Who has access to the data, either implicitly or explicitly? How is that data secured? How is it being used, and perhaps monetized? The non-profit organization Cloud Secure Alliance (CSA) categorizes the security challenges of Big Data Ecosystems into four groups; infrastructure security, data privacy, data management, and integrity and relative security.
In the case of a web browser, website and third-party tracking operation, there is a clear financial incentive for why data is collected and how it is used. But there is also a level of surveillance that occurs in this scenario, that perhaps goes unnoticed. Rob Kitchin terms this as 'dataveillance,' a result of the datafication of everyday life which allows for highly accurate and continuous tracking of our locations and activities. Who else, besides those trackers and websites, has access to the data being collected, and is it used for more nefarious purposes? In the case of US states that have banned access to abortions, there's concern that these data ecosystems can be harnessed to penalize citizens that seek services out of state.
References
Data
Data collection
Information | Data ecosystem | Technology | 1,335 |
27,741,322 | https://en.wikipedia.org/wiki/Eiji%20Osawa | is a former professor of computational chemistry, noted for his prediction of the C60 molecule in 1970.
Osawa received his Master's of Engineering in chemistry from Kyoto University's Department of Industrial Chemistry and then became an engineer at Teijin Co., Ltd. In 1964, he returned to Kyoto University and earned a Doctorate of Engineering in chemistry under Professor M. Yoshida. After three years of postdoctoral work at the University of Wisconsin, Princeton University, and the State University of New York at Stony Brook, in 1970 he became an assistant professor at Hokkaido University. In 1990, Osawa became a full professor at Toyahashi University of Technology, where he retired in 2001. Upon his retirement, assisted by Futaba, Co., Ltd., headquartered in Chiba, Osawa started the research and development company Nano-Carbon Research Institute, Ltd.
C60 molecule prediction
The icosahedral C60H60 cage was mentioned in 1965 as a possible topological structure. Eiji Osawa predicted the existence of C60 in 1970. He noticed that the structure of a corannulene molecule was a subset of a football shape, and he hypothesised that a full ball shape could also exist. Japanese scientific journals reported his idea, but it did not reach Europe or the Americas.
In 1996, Harold Kroto, Robert Curl and Richard Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of molecules. C60 and other fullerenes were later noticed occurring outside the laboratory.
References
Japanese chemists
1935 births
People from Toyama Prefecture
Living people
Toyohashi University of Technology people
Computational chemists | Eiji Osawa | Chemistry | 332 |
13,653,971 | https://en.wikipedia.org/wiki/Littelfuse | Littelfuse, Inc. is an American electronics manufacturing company headquartered in Chicago, Illinois. The company primarily produces circuit protection products (fuses) but also manufactures a variety of switches, automotive sensors and, through its subsidiary Zilog, microprocessors. Littelfuse was founded in 1927. In addition to its Chicago, Illinois, world headquarters, Littelfuse has more than 40 sales, distribution, manufacturing and engineering facilities in the Americas, Europe and Asia. Littelfuse is the developer of AutoFuse, the first blade-type automotive fuse.
History
Early history
Edward V. Sundt founded Littelfuse in 1927 in Chicago Illinois as Littelfuse Laboratories. Prior to founding Littelfuse, Sundt had worked for General Electric and Stewart-Warner, where he found diagnostic equipment frequently experienced electrical failure. Sundt developed Littelfuse's first product, a small protective fuse, to regulate current in diagnostic equipment and prevent electrical failure. When the US government refused Sundt a trademark for Little fuse (the small protective fuse) on the grounds that the words were too common, Sundt compromised by reversing the l and the e to form Littelfuse.
Littelfuse was incorporated and renamed Littelfuse, Inc. in 1938.
Littelfuse became a public company in 1962. The company retained founder Edward V. Sundt as the chairman of its board. In 1963, Littelfuse moved its headquarters from Chicago to Des Plaines, Illinois. Sundt retired in 1965 and was succeeded by Thomas Blake. Tracor purchased the company in 1968. Blake was made president of Littelfuse, which operated as a wholly owned subsidiary of Tracor.
1970–1991
The company expanded its manufacturing base in the 1970s with new factories opening in Watseka, Illinois and Piedras Negras, Mexico. In 1974, the company also introduced Littelites, electronic indicator lights used in industrial and office machinery, household appliances and computers.
In 1976, Littelfuse developed Autofuse, which was the first blade-type fuse used in automobiles. The Autofuse brand was counterfeited heavily and in 1983 the company obtained an exclusionary order from the United States International Trade Commission, which barred the importation of counterfeit blade-type fuses.
In 1987, Westmark Systems purchased Tracor and its Littelfuse subsidiary in leveraged buyout. Tracor filed for bankruptcy in 1991 and spun off Littelfuse.
Modern history
Littelfuse reincorporated in November 1991 with Howard Witt as its president and CEO. Witt had worked for Littelfuse since 1979 and had been president and CEO of Littelfuse since February 1990, when the company was still owned by Tracor. In 1991, Littelfuse offered its second IPO in company history. The company's profits rose throughout the 1990s and the company expanded its operations in Europe and Asia. Littelfuse also expanded into South America with a distribution and engineering center in São Paulo, Brazil.
Gordon Hunter replaced Witt as president and CEO of Littelfuse at the end of 2004. In 2008, Littelfuse restructured its manufacturing operations, closing 16 small manufacturing plants and opening 6 new, larger plants. The company moved its headquarters from Des Plaines, Illinois, to Chicago, Illinois, the same year.
The company was recognized as Product of the Year by Consulting-Specifying Engineer in 2010, 2011, 2012 and 2013. Arrow Electronics recognized Littelfuse with an award for Supplier Excellence in 2011. The company received TTI Supplier's Excellence Award in 2010, 2011, 2012 and 2013. Littelfuse received the Chicago Innovation Award in 2012. In 2013, the company received Processing Magazine's Breakthrough Product of the Year. Littelfuse was recognized as one of the Best Places to Work in Illinois in 2012, 2013 and 2014.
The company announced in November 2016 that COO Dave Heinzmann would succeed Hunter as president and CEO in January 2017.
Products
Littelfuse designs and manufactures circuit protection products for the electronics, automotive and electrical industries. The company operates between three business unit segments: Electronics, Industrial, and Automotive. Products include: fuses and protectors, suppressors, gas discharge tubes, electronic switches, solenoids, battery management devices, and protective relays.
With the acquisition of Hamlin, Inc. in 2013, Littelfuse expanded its product offering to include sensors for the automotive, industrial and consumer industries.
Acquisitions
Littelfuse has acquired multiple companies since 1999, including:
1999 – Harris Suppression Products.
2002 – Semitron.
2003 – Teccor, a manufacturer of circuit and overvoltage protection products.
2004 – Heinrich Industrie, a German manufacturer of circuit protection products, including the WICKMANN Group, Efen and Pudenz brands.
2006 – Taiwan-based silicon manufacturer Concord Semiconductor, Inc. and Catalina Performance Accessories, which manufactures and distributes blade-type automotive fuses.
2008 – Shock Block Corporation that develop and manufacture ground fault protection technology.
2008 – Startco Engineering, maker of ground-fault protection products and custom-power distribution centers that are used in industrial manufacturing and mining applications.
2010 – Cole Hersee, a maker of power management products, heavy duty electromechanical and switches for commercial vehicles.
2011 – Selco A/S, a Danish company, which produces electrical equipment for use in maritime and industrial environments.
2012 – Accel AB, a Swedish company that manufactures advanced automotive switches and sensors, and Terra Power Systems, which manufactures electrical components for heavy-duty vehicles and trucks.
2013 – Hamlin Inc., an automotive sensors manufacturer.
2014 – SymCom, a power, voltage, and current monitor developer and manufacturer.
2015 – JRS MFG. LTD., a custom engineered products developer and manufacturer, such as metal-clad, metal-enclosed, and arc-resistant switchgear, E-Houses, mine power centers and mining substations.
2016 – TE Connectivity's circuit protection business.
2016 – IGBT and TVS divisions of ON Semiconductor, a semiconductors supplier company.
2017 – U.S. Sensor, Manufacturer of Temperature Sensors.
2017 – IXYS Corp., a power semiconductor manufacturer, thereby also acquiring Zilog
2018 – Monolith Semiconductor Inc., a silicon carbide switch developer and manufacturer.
2021 – Carling Technologies Inc., a switch and electromechanical circuit breaker manufacturer.
2022 – C&K Switches, an electromechanical switch manufacturer
2023 – Western Automation Research and Development Limited, a designer and manufacturer of electrical shock protection devices.
References
1927 establishments in Illinois
1960s initial public offerings
Companies listed on the Nasdaq
Manufacturing companies based in Chicago
Electronics companies established in 1927
Electrical engineering companies
Companies in the S&P 400 | Littelfuse | Engineering | 1,415 |
55,585,798 | https://en.wikipedia.org/wiki/Samsung%20Bio%20Processor | The Samsung Bio Processor is an advanced system logic chip designed by Samsung Electronics in December 2015 that integrates five AFEs including bioelectrical impedance analysis (BIA), photoplethysmogram (PPG), electrocardiogram (ECG), skin temperature, and galvanic skin response (GSR) into a single chip that measures body fat, and skeletal muscle mass, heart rate, heart rhythm, skin temperature and stress level. It is designed for future fitness wearable devices. The chip is also designed to be included in "patches" that track health, and the chip design is available for other companies to use. The chip is designed for low power usage to allow it to be used in small devices with small batteries.
See also
Apple motion coprocessors
References
Samsung Electronics | Samsung Bio Processor | Technology | 167 |
27,190,089 | https://en.wikipedia.org/wiki/Vinay%20V.%20Deodhar | Vinay Vithal Deodhar (3 December 1948 – 18 January 2015) was a Professor Emeritus in the Department of Mathematics at Indiana University. He worked in the area of algebraic groups and representation theory.
Early life
Deodhar was born in Mumbai (Bombay), India in 1948.
Career
Deodhar earned his Ph.D. from the University of Mumbai in 1974 for his work On Central Extensions of Rational Points of Algebraic Groups done under the supervision of M. S. Raghunathan.
After his doctorate, he was invited to join the School of Mathematics of the Tata Institute of Fundamental Research. Simultaneously he was a visiting scholar at the Institute for Advanced Study (IAS) in Princeton during 1975-77 and then a visiting professor at the Australian National University in Canberra. In 1981 he was appointed to a professorship at Indiana University, Bloomington, Indiana, where he remained until his death in 2015. He spent a further period as a visiting scholar at the IAS in 1992-93.
References
External links
20th-century Indian mathematicians
Algebraists
University of Mumbai alumni
Scientists from Mumbai
Tata Institute of Fundamental Research alumni
Institute for Advanced Study visiting scholars
1948 births
2015 deaths | Vinay V. Deodhar | Mathematics | 234 |
21,713,216 | https://en.wikipedia.org/wiki/Jumble%20ice | Jumble ice is a phenomenon that occurs when ice atop a river or other flowing body of water fractures due to the different flow rates beneath the ice. On a lake, pond, or other stationary body of water, ice forms undisturbed and generally does not move as long as the entire surface of the body of water is frozen. When a river freezes, water flow typically continues beneath the ice, exerting pressure on it. If the ice fractures, pieces of ice torn free by the river's current will collide with stationary or slower-moving pieces. After becoming stuck in place, the loosened pieces of ice refreeze irregularly, causing a rough, or jumbled, surface.
In general, the faster a body of water flows beneath ice, the more likely it is to develop jumble ice. Temperatures near the freezing point also tend to cause jumble ice, as the higher temperatures weaken the ice structure, allowing for more pieces to be torn free before refreezing. The Yukon River in Alaska often exhibits jumble ice during the winter.
Jumble ice is a hazard for winter travelers, as the broken "ground" formed by the jumble ice can cause snowmachine accidents or injuries to sled dogs.
See also
Ice jacking
Ice dam
References
Saari, Matias. "Jumble ice a jarring experience for some mushers, dog teams", Fairbanks Daily News-Miner. February 13, 2008. Accessed February 25, 2009.
Saari, Matias. "Yukon River a jumble of problems for Quest mushers", Fairbanks Daily News-Miner. January 29, 2009. Accessed February 25, 2009.
External links
YouTube video of a musher encountering jumble ice
Precipitation
Snow or ice weather phenomena
Water ice
Weather hazards | Jumble ice | Physics | 362 |
54,700,310 | https://en.wikipedia.org/wiki/NGC%207087 | NGC 7087 is a barred spiral galaxy located about 215 million light-years away in the constellation of Grus. NGC 7087 was discovered by astronomer John Herschel on September 4, 1834.
NGC 7087 is a member of a group of galaxies known as the NGC 7087 group.
See also
NGC 1300
References
External links
Barred spiral galaxies
Grus (constellation)
7087
66988
Astronomical objects discovered in 1834 | NGC 7087 | Astronomy | 91 |
77,394,414 | https://en.wikipedia.org/wiki/Skin%20lightening%20in%20the%20Middle%20East | Skin lightening is a common practice in several Middle Eastern countries, particularly among women. The use of skin lightening products among Middle Eastern women has been attributed to the perceived association between light skin and beauty, as well as marriage and employment opportunities. Furthermore, the portrayal of light skin as the beauty ideal in popular media has contributed to the use of skin lightening products among Middle Eastern women.
History
Palestinian scholar Sonia Nimr has stated that the preference for lighter skin can be found in old Arabic and pre-Islamic poetry, stating: For centuries there’s been an image that if you’re pale or whiter, it means you’re a lady. You don’t have to go out of the tent to do hard work.
By country
Jordan
In a 2010 study conducted among 318 Jordanian women at selected pharmacy stores, 60.7% of the women reported using skin lightening products at some point in their lives.
Palestine
In 2009, a correspondent from The Christian Science Monitor investigated the use of skin lightening products among women in the city of Ramallah, by interviewing users of skin lightening products, as well as businesses which sold these products.
When interviewed, an employee at a beauty salon expressed the following sentiment:Palestinians believe that white skin is beautiful. In the West, they sunbathe to get darker skin, but here, people like to lighten their skin and they hide from the sun at all costs.A 2023 study found that Palestinian women from urban areas and those with a bachelor's degree were more likely to use skin lightening products.
Saudi Arabia
Skin lightening is prevalent among Saudi women, as indicated by several studies.
A 2019 study conducted among 760 Saudi female students found that 56.2% of the participants had used skin lightening products at some point in their lives. Women with lower socioeconomic status were more likely to use skin lightening products.
In another 2019 study, 605 Saudi women were asked about their use of skin lightening products. 63.1% of the participants reported using skin lightening products at some point in their lives.
Media
The portrayal of light skin as the beauty ideal in Middle Eastern popular media has contributed to the use of skin lightening products among Middle Eastern women. An investigation by a correspondent from The Christian Science Monitor conducted in the Palestinian city of Ramallah found that Lebanese singers with European features, including Haifa Wehbe and Nancy Ajram are widely considered beauty icons. Furthermore, Sudanese-born writer Nesrine Malik stated Lebanese standards of beauty and complexion have taken the Arab world by storm since the resurgence of the Lebanese in media ... further limiting the accepted definition of beauty as light-skinned, catty-eyed and slim-nosed.
See also
Human skin color
Colorism
References
Physical attractiveness
Human skin color
Skin whitening | Skin lightening in the Middle East | Biology | 565 |
9,617,836 | https://en.wikipedia.org/wiki/Broadcast%20Television%20Systems%20Inc. | Broadcast Television Systems (BTS) was a joint venture between Robert Bosch GmbH's Fernseh Division and Philips Broadcast in Breda, Netherlands, formed in 1986.
History
Philips had been in the broadcast market for many years with a line of PC- and LDK- Norelco professional video cameras and other video products. By the 1980s, the Norelco name was dropped in favour of Philips. Robert Bosch GmbH's Fernseh Division also had a long history going back to the early days of television (1929).
BTS's North America headquarters was at first located in Salt Lake City, Utah. This was later moved to Simi Valley, California, in 1991, later returning to Salt Lake City. Also in 1991, BTS Latin America entered into an agreement to provide Televisa SA of Mexico what was believed to be until that time, the largest equipment sale in history.
In 1995 Philips Electronics North America Corp. fully acquired BTS Inc., renaming it Philips Broadcast-Philips Digital Video Systems. The BTS Inc.'s Darmstadt factory in Germany was near the Darmstadt Train Station and European Space Operations Centre this was later moved a short distance to Weiterstadt, Germany.
In March 2001, Philips' broadcast video division was sold to Thomson SA, the current owner; the division was called Thomson Multimedia. In 2002, the French electronics giant Thomson SA also acquired the Grass Valley Group from Terry Gooding of San Diego, CA, USA. Grass Valley, Inc., the Thomson, Grass Valley, a Thomson Brand is headquartered in Nevada City, California.
The Thomson Film Division, located in Weiterstadt, including the product line of Spirit DataCine, Bones Work station and LUTher 3D Color Space converter, was sold to Parter Capital Group. The sale was made public on Sept. 9, 2008 and completed on Dec. 1, 2008. The new headquarters is in Weiterstadt, in the former Bosch Fernseh - BTS factory. Parter Capital Group will continue to have worldwide offices to support products from Weiterstadt, Germany. The new name of the company is Digital Film Technology. On October 1, 2012, Precision Mechatronics and DFT were acquired by Prasad Corp, part of Prasad Studios. In 2013 DFT moved from Weiterstadt to Arheilgen-Darmstadt, Germany.
Grass Valley operated offices in the cities of all the former acquisitions:
Cergy, France (Thomson World Headquarters)
Salt Lake City, Utah, USA – from TeleMation Inc. – Bell and Howell – BTS
Beaverton, Oregon, USA – from Tektronix
Nevada City, California, USA – from Grass Valley Group
Breda, Netherlands – from Philips – Norelco – BTS
After the financial crisis of 2008, Thomson became upside-down in its financial covenants and was forced by its creditors to divest itself of Grass Valley and other manufacturing entities. On January 29, 2009, Thomson announced that they were putting the Grass Valley division up for sale.
In 2010, the Grass Valley business unit, not including the head-end and transmission businesses, was acquired by private equity firm Francisco Partners and resumed operating as an independent company on January 1, 2011. Grass Valley still maintains offices worldwide.
Grass Valley was sold to Belden on February 6, 2014, Belden also owns Miranda.
Products
See:
Fernseh - for German-made products
TeleMation Inc. for SLC products.
Philips invented the plumbicon pick up video camera tube in 1965; almost all of their color cameras used this award-winning tube. Starting with the LDK 90 camera, Philips used their Frame transfer CCD - Charge-coupled device. Philips' patented Dynamic Pixel Management (DPM) FT-17 CCD technology won awards and was first used in the 1994 LDK10 and LDK10p camera.
Philips-BTS product from Breda, Netherlands, professional video camera products:
EL-8020 B&W Studio 5 fixed lens
LDK2 1970s Norelco
LDH10 Norelco
LDH20 Norelco
LDH-0200 Studio Norelco
LDK3 Studio PC-80 Norelco
LDK4800 ? Triax repeater ? Camera ?
LDK5 1971 Studio 3 tubes Philips
LDK6 1982 Studio 3 tubes Norelco/BTS
LDK9P BTS CCD 1993 HandHeld
LDK10 BTS DPM CCD 1994
LDK10P BTS DPM CCD 1994
LDK11 1976 ENG Backpack Norelco
LDK12 ENG
LDK13 1971 ENG Backpack Norelco
LDK14 1977 ENG 3 tubes Philips
LDK15 1974? ENG Norelco
LDK20 ~1997 BTS CCD
LDK23HS BTS CCD Super slow mo
LDK25 Studio
LDK26 1982 Studio
LDK33 Early Handheld
LDK44 1984 Studio/ENG 3 tubes
LDK54 Handheld 3 tubes
LDK63
LDK65
LDK90 1987 BTS CCD HandHeld
LDK91 BTS CCD HandHeld
LDK93 BTS CCD HandHeld
LDK491 ENG Philips DIODE GUN PLUMBICONS
LDK614 LDK6 handheld
LDK700 BTS CCD
LDK910 BTS CCD Studio
LDK9000 BTS CCD HDTV
LDM42 B&W 1968 Studio
LDM53 B&W Studio
PC60 1965 Studio 3 tubes Norelco
PC70 1967 Studio 3 tubes Norelco
PC80 Studio Norelco LDK3
PC100 Studio Norelco
PCP70 Handheld Norelco
PCP90 1968 Handheld Norelco
VIDEO 80 Handheld
Current:
LDK 300 CCD Thomson Grassvalley
LDK 400 CCD Thomson Grassvalley
LDK 500 CCD Thomson Grassvalley 2003
LDK23HS Mk2 CCD Super slow mo Thomson Grassvalley
LDK 5000 CCD Thomson Grassvalley
TTV 1657D CCD Thomson Grassvalley
LDK 20S CCD Thomson Grassvalley
LDK 1707 CCD Thomson Grassvalley
LDK 4000 CCD HDTV Thomson Grassvalley
LDK 5000 CCD HDTV Thomson Grassvalley
LDK 6000 CCD HDTV Thomson Grassvalley
LDK 6200 CCD HDTV Super SloMo
LDK 8000 CCD HDTV/SDTV
Philips early VTRs:
LDL110 Portable
NL1500 cassette
LDL110 Portable 1977
NL1702
VR202
VR2350
Awards
Outstanding Achievement in Technical/Engineering Development Awards from National Academy of Television Arts & Sciences.
1966-1967 PLUMBICON TUBE - N.V. Philips -Breda
1987-1988 FGS 4000 computer animation system CGI- BTS -SLC, UT
1991-1992 Triaxial cable Technology for Color Television Cameras -N.V. Philips -Breda
1992-1993 Prism Technology for Color Television Cameras -N.V. Philips -Breda
1993-1994 Controlled Edge Enhancement Utilizing Skin Hue KeyingBTS and Ikegami (Joint Award) -Breda
1997-1998 Development of a High Resolution Digital Film Scanner Eastman Kodak and Philips Germany. See Spirit DataCine
2000-2001 Pioneering developments in shared video-data storage systems for use in television video servers - BTS/Philips/Thomson/ - SLC, UT
2002-2003 Technology to simultaneously encode multiple video qualities and the corresponding metadata to enable real-time conformance and / or playout of the higher quality video (nominally broadcast) based on the decisions made using the lower quality proxies Montage. Philips and Thomson.
Photo gallery
See also
Fernseh
TeleMation Inc.
Philips
Robert Bosch GmbH
Norelco
Grass Valley (company)
Thomson SA
Professional video camera
References
tmquest.com onBTS Product
thefreelibrary.com On BTS
thefreelibrary.com On BTS, ABC'S KGO-TV Picks BTS Video Server to Go All Digital; Also Pilot Program For ABC-OWNED Stations
patentmaps.com BTS Patents
electronics.zibb.com BTS Trademarks
business.highbeam.com BC plans playback for disk-based server; its San Francisco O&O also plots Media Pool project. (owned-and-operated television station; BTS Broadcast Television Systems Inc. Media Pool server), Article from: Broadcasting & Cable | May 15, 1995 | McConnell, Chris
business.highbeam.com New cable networks going digital. (includes related article on Game Show Network) Article from: Broadcasting & Cable | January 9, 1995 | McConnell, Chris
business.highbeam.com Media Pool tests the tapeless waters. (BTS digital disk-based recorder), Article from: Broadcasting & Cable | July 18, 1994 | McConnell, Chris
allbusiness.com KGO-TV picks BTS' Media Pool Video Server to provide all-digital system of the future. Las Vegas, Nev.--(Business Wire)--April 11, 1995—KGO-TV,
smpte.org 138th SMPTE Technical Conference Technical Papers Program, October 10–11, 1996, Los Angeles, Calif., Media Pool — Flexible Video Server Design for Television Broadcasting, by Charlie Bernstein1
patentstorm.us BTS, System and method for enabling a data/video server]
trademarks.justia.com Compositor I - Trademark Details
trademarkia.com Compositor I By: BTS-Broadcast Television Systems, Inc.
emmyonline.tv National Academy of Television Arts and Sciences, Outstanding Achievement in Technical/Engineering Development Awards, BTS Broadcast Television Systems, Inc. To BTS in recognition of their engineering contribution in 3D computer graphic technology and for development of the FGS 4000 computer animation system.
trademarks.justia.com MACH ONE - Trademark Details.
trademarkia.com MACH ONE By: BTS-Broadcast Television Systems, Inc.
The History of Television, 1942 to 2000, By Albert Abramson, Christopher H. Sterling, Page 304]
trademarkia.com PIXELERATOR, By: BTS-Broadcast Television Systems, Inc., High-Speed Rendering Computer Processor For Use In Computer Graphics Application.
broadcasting101.ws BTS Logo
www.broadcasting101.ws LDK91 Camera
broadcasting101.ws LDK910 camera
broadcasting101.ws LDK-9000
www.broadcasting101.ws BTS OB Van *tvcameramuseum.org List of BTS cameras
tvcameramuseum.org LDK614
tvcameramuseum.org XQ3427B Plumbicon camera tube.
tvcameramuseum.org LDK 6
tvcameramuseum.org LDH 200
tvcameramuseum.org LDK 11
tvcameramuseum.org LDK 12
tvcameramuseum.org LDK 13
tvcameramuseum.org LDK 14
tvcameramuseum.org LDK 15
tvcameramuseum.org LDK 2
tvcameramuseum.org LDK 25
tvcameramuseum.org LDK 26
tvcameramuseum.org LDK 3
tvcameramuseum.org LDK 44
tvcameramuseum.org LDK 54
tvcameramuseum.org PC 60
[tvcameramuseum.org] LDK 54
tvcameramuseum.org List of cameras
tvcameramuseum.org EL 8000 cam
External links
BTS Awards Page 8 and 11
Thomson Grassvalley Cameras
Camera Museum
The Museum of the Broadcast TV camera
Philips Cameras, Photos and Specs
Fernseh Museum
BTS/Thomson/Grass valley Hi-res Photo Archive
Cameras:
EL-8020
PC-60
PC-70
PC-72
PCP-90
LDH-1
LDK-5
LDK-6
LDK-300
LDK-6200
Electronics companies of the Netherlands
Philips
Film and video technology
Cameras
Video storage
Film production
Technicolor SA | Broadcast Television Systems Inc. | Technology | 2,437 |
58,157,092 | https://en.wikipedia.org/wiki/Claudia%20Sagastiz%C3%A1bal | Claudia Alejandra Sagastizábal is an applied mathematician known for her research in convex optimization and energy management, and for her co-authorship of the book Numerical Optimization: Theoretical and Practical Aspects. She is a researcher at the University of Campinas in Brazil. Since 2015 she has been editor-in-chief of the journal Set-Valued and Variational Analysis.
Education and career
Sagastizábal earned a degree in mathematics, astronomy and physics from the National University of Córdoba in Argentina in 1984. She completed a PhD in 1993 at Pantheon-Sorbonne University in France; her dissertation, Quelques methodes numeriques d'optimization: Application en gestion de stocks, was supervised by Claude Lemaréchal.
While in France, she worked with Électricité de France on optimization problems involving electricity generation, a topic that has continued in her research since that time.
She moved to Brazil in 1997. Before joining the University of Campinas in 2017, she has also been affiliated with the Instituto Nacional de Matemática Pura e Aplicada and French Institute for Research in Computer Science and Automation, among other institutions.
Recognition
Sagastizábal was an invited speaker at the 8th International Congress on Industrial and Applied Mathematics in 2015.
She was also an invited speaker on control theory and mathematical optimization at the 2018 International Congress of Mathematicians.
She is a SIAM Fellow, in the 2024 class of fellows, elected "for contributions to non-smooth optimization and applications to engineering, and numerical methods for optimization".
References
External links
Year of birth missing (living people)
Living people
Argentine mathematicians
Brazilian mathematicians
Brazilian women mathematicians
Argentine women mathematicians
Applied mathematicians
National University of Córdoba alumni
Fellows of the Society for Industrial and Applied Mathematics | Claudia Sagastizábal | Mathematics | 345 |
13,774,593 | https://en.wikipedia.org/wiki/Differential%20capacitance | Differential capacitance in physics, electronics, and electrochemistry is a measure of the voltage-dependent capacitance of a nonlinear capacitor, such as an electrical double layer or a semiconductor diode. It is defined as the derivative of charge with respect to potential.
Description
In electrochemistry differential capacitance is a parameter introduced for characterizing electrical double layers:
where is surface charge and is electric surface potential.
Capacitance is usually defined as the stored charge between two conducting surfaces separated by a dielectric divided by the voltage between the surfaces. Another definition is the rate of change of the stored charge or surface charge () divided by the rate of change of the voltage between the surfaces or the electric surface potential (). The latter is called the "differential capacitance", but usually the stored charge is directly proportional to the voltage, making the capacitances given by the two definitions equal.
This type of differential capacitance may be called "parallel plate capacitance", after the usual form of the capacitor. However, the term is meaningful when applied to any two conducting bodies such as spheres, and not necessarily ones of the same size, for example, the elevated terminals of a Tesla wireless system and the earth. These are widely spaced insulated conducting bodies positioned over a spherically conducting ground plane.
"The differential capacitance between the spheres is obtained by assuming opposite charges on them ..."
Another form of differential capacitance refers to single isolated conducting bodies. It is usually discussed in books under the topic of "electrostatics". This capacitance is best defined as the rate of change of charge stored in the body divided by the rate of change of the potential of the body. The definition of the absolute potential of the body depends on what is selected as a reference. This is sometimes referred to as the "self-capacitance" of a body. If the body is a conducting sphere, the self-capacitance is proportional to its radius, and is roughly 1 pF per centimetre of radius.
See also
Capacitive coupling
Electric displacement field
References
External links
McGraw-Hill Dictionary of Scientific and Technical Terms definition of "differential capacitance"
Electrochemistry
Colloidal chemistry
Telecommunications engineering
Power electronics | Differential capacitance | Chemistry,Engineering | 479 |
33,994,239 | https://en.wikipedia.org/wiki/SailTimer | SailTimer is a technology for sailboat navigation, which calculates optimal tacking angles, distances and times.
Seafarers have had a dilemma for as long as sailboats could use lift to sail upwind. Should you head off the wind more, to get more speed (but at a longer distance)? Or should you sail upwind more, to lessen the distance (but at slower speed)?
Different sailboats have varying capabilities for sailing upwind because of the condition of their sails, the type of rigging, and the ability to track in the water based on their keel or centerboard design. That means there is not a single rule for everyone; each vessel has its own individual polar plot of boat speed for all of the possible wind angles. The mathematical calculations for determining the tacking angles and times with polar plots would not be practical to do mentally.
Rationale
Civilian access to GPS navigation became available circa 1989. Estimated time of arrival (ETA) is a standard GPS chartplotter parameter, based on the assumption that the route will be a straight line to the destination. However, sailboats typically tack back and forth, creating a longer distance than a straight line.
SailTimer evaluates tacking distances and boat speeds on different points of sail to determine optimal tacking headings. During the original development of the SailTimer software in 2005–2006, the term TTD (tm) was coined for "Tacking Time to Destination".
Safe Navigation
Sailboats can be pushed downwind by the wind, or can use lift to move across or into the wind. However, for most sailboats the boat speed drops if sailing closer than 45 degrees to the wind. The highest speed for most sailboats is reaching with the wind from the side or the aft quarter (a beam reach or a broad reach).
If the destination is upwind but the sailboat goes fastest heading away from this direction, this poses a significant problem: how to choose tack headings with the best tradeoff between maximimizing speed and minimizing distance. The ability to define an efficient tacking route is an important issue in sailboat racing, and for recreational sailing. It is also an important issue of navigational safety, so that the sailboat is able to arrive before dark. Being able to accurately calculate the Tacking Time to Destination also allows a skipper to select a course that avoids bad weather or shipping traffic.
Versions
Given the widespread growth of smartphones, a version of SailTimer is available from the App Store (iOS) for iPhone, iPod and iPad tablets.
SailTimer also runs on a dedicated handheld device called The Sailing GPS. An artificial intelligence algorithm allows it to learn the polar plots for an individual sailboat, which it then uses for making decisions on the optimal tacking route and Tacking Time to Destination.
References
External links
www.SailTimerApp.com
www.TheSailingGPS.com
Sailing
Marine electronics
Navigational equipment
Global Positioning System | SailTimer | Technology,Engineering | 607 |
43,871 | https://en.wikipedia.org/wiki/Fatal%20insomnia | Fatal insomnia is an extremely rare neurodegenerative prion disease that results in trouble sleeping as its hallmark symptom. The majority of cases are familial (fatal familial insomnia [FFI]), stemming from a mutation in the PRNP gene, with the remainder of cases occurring sporadically (sporadic fatal insomnia [sFI]). The problems with sleeping typically start out gradually and worsen over time. Eventually, the patient will succumb to total insomnia (agrypnia excitata), most often leading to other symptoms such as speech problems, coordination problems, and dementia. It results in death within a few months to a few years, and there is no known disease-modifying treatment.
Signs and symptoms
The disease has four stages:
Characterized by worsening insomnia, resulting in panic attacks, paranoia, and phobias. This stage lasts for about four months.
Hallucinations and panic attacks become noticeable, continuing for about five months.
Complete inability to sleep is followed by rapid loss of weight. This lasts for about three months.
Dementia, during which the person becomes unresponsive or mute over the course of six months, is the final stage of the disease, after which death follows.
Clinically, FFI manifests with a disordered sleep-wake cycle, dysautonomia, motor disturbances, and neuropsychiatric disorders.
Other symptoms include profuse sweating, miosis (pinpoint pupils), sudden entrance into menopause or impotence, neck stiffness, and elevation of blood pressure and heart rate. The sporadic form of the disease often presents with double vision. Prolonged constipation is common as well. As the disease progresses, the person becomes stuck in a state of pre-sleep limbo, or hypnagogia, which is the state just before sleep in healthy individuals. During these stages, people commonly and repeatedly move their limbs as if they were dreaming.
The age of onset is variable, ranging from 13 to 60 years, with an average of 50. The disease can be detected prior to onset by genetic testing. Death usually occurs between 6–36 months from onset. The presentation of the disease varies considerably from person to person, even among people within the same family; in the sporadic form, for example, sleep problems are not commonly reported and early symptoms are ataxia, cognitive impairment, and double vision.
Cause
Fatal familial insomnia is a rare hereditary prion disease that is associated with a mutation in PRNP. The gene, which provides instructions for making the prion protein PrPC, is located on the short arm of chromosome 20 at position p13. Individuals with FFI or familial Creutzfeldt–Jakob disease (fCJD) both carry a mutation at codon 178 of the prion protein gene. FFI is also invariably linked to the presence of the methionine codon at position 129 of the mutant allele, whereas fCJD is linked to the presence of the valine codon at that position. The disease occurs when there is a change of amino acid at position 178 in which asparagine is found instead of the normal aspartic acid. This has to be accompanied with a methionine at position 129.
FFI is an autosomal dominant disease caused by a missense GAC-to-AAC mutation at codon 178 of the PRNP prion protein gene located on chromosome 20, along with the presence of the methionine polymorphism at position 129 of the mutant allele. Pathologically, FFI is characterized predominantly by thalamic degenerationespecially in the medio-dorsal and anteroventral nuclei. Phenotypic variability is a perplexing feature of FFI.
Pathophysiology
Given its striking clinical and neuropathologic similarities with fatal familial insomnia (FFI), a genetic prion disease linked to a point mutation at codon 178 (D178N) in the PRNP coupled with methionine at codon 129, the MM2T subtype is also known as sporadic FI (sFI). Transmission studies using susceptible transgenic mice have consistently demonstrated that the same prion strain is associated with both sFI and FFI. In contrast to what has been the rule for the most common neurodegenerative disorders, sFI is rarer than its genetic counterpart. Whereas the recognized patients with FFI are numerous and belong to >50 families worldwide, only about 30 cases of CJD MM2T and a few cases with mixed MM2T and MM2C features (MM2T+C) have been recorded to date.
In itself the presence of prions causes reduced glucose to be used by the thalamus and a mild hypo-metabolism of the cingulate cortex. The extent of this symptom varies between two variations of the disease, these being those presenting methionine homozygotes at codon 129 and methionine/valine heterozygotes, with some evidence that hypo-metabolism is more severe in the latter. Given the relationship between the involvement of the thalamus in regulating sleep and alertness, a causal relationship can be drawn and is often mentioned as the cause of insomnia.
Diagnosis
Diagnosis is based on symptoms and can be supported by a sleep study, a PET scan and genetic testing if the patient's family has a history of the disease. As with other prion diseases, the diagnosis can be confirmed only by a brain autopsy post-mortem.
The real-time quaking-induced conversion (RT-QuIC), a highly sensitive assay that detects minute amounts of PrPSc in the cerebrospinal fluid (CSF), has been reported to have a sensitivity of 50% in FFI and sFI.[Cracco et al. Handb Clin Neurol 2018][Mock et al. Sci Rep. 2021] However, this low sensitivity may change since the examination was based on a low number of cases, and the RT-QuIC technology is continuously evolving.
A test that measures the cerebral metabolic rate of glucose by positron emission tomography (PET), referred to as [18F]-FDG-PET, has demonstrated severe hypometabolism of the thalamus bilaterally in FFI and sFI, also in the earliest stages of the disease. This hypometabolism then spreads, eventually impacting most cortical regions.[Cortelli et al. Brain 2006] The complexity and cost of this test currently impede its use in routine diagnosis.
Differential diagnosis
Other diseases involving the mammalian prion protein are known. Some are transmissible (TSEs, including FFI) such as kuru, bovine spongiform encephalopathy (BSE, also known as mad cow disease) in cattle and chronic wasting disease in American deer and American elk in some areas of the United States and Canada, as well as Creutzfeldt–Jakob disease (CJD). Until recently prion diseases were thought to be transmissible only by direct contact with infected tissue, such as from eating infected tissue, transfusion or transplantation; research suggests that prions can be transmitted by aerosols but that the general public is not at risk of airborne infection.
Treatments
Treatment involves palliative care. There is conflicting evidence over the use of sleeping pills, including barbiturates, as a treatment for the disease. Symptoms of fatal familial insomnia may be treated with medications.
Clonazepam may be prescribed to treat muscle spasms, and eszopiclone or zolpidem may be prescribed to help treat insomnia. However these drugs do not work in the long term.
Prognosis
Like all prion diseases, the disease is invariably fatal. Life expectancy ranges from seven months to six years, with an average of 18 months.
Epidemiology and history
Fatal insomnia was first described by Elio Lugaresi et al. in 1986.
In 1998 40 families were known to carry the gene for FFI globally: eight German, five Italian, four American, two French, two Australian, two British, one Japanese and one Austrian. In the Basque Country of Spain, 16 family cases of the 178N mutation were seen between 1993 and 2005 related to two families with a common ancestor in the 18th century. In 2011, another family was added to the list when researchers found the first man in the Netherlands to be diagnosed with FFI. Whilst he had lived in the Netherlands for 19 years, he was of Egyptian descent. Other prion diseases are similar to FFI and may be related but are missing the D178N gene mutation.
, 37 cases of sporadic fatal insomnia have been diagnosed. Unlike in FFI, those with sFI do not have the D178N mutation in the PRNP-prion gene; they all have a different mutation in the same gene causing methionine homozygosity at codon 129.
Nonetheless, the methionine presence in lieu of the valine (Val129) is what causes the sporadic form of disease. The targeting of this mutation has been suggested as a strategy for treatment, or possibly as a cure for the disease.
Silvano, 1983, Bologna, Italy
In late 1983 Italian neurologist/sleep expert Dr Ignazio Roiter received a patient at the University of Bologna hospital's sleep institute. The man, known only as Silvano, decided in a rare moment of consciousness to be recorded for future studies and to donate his brain for research in hopes of finding a cure for future victims.
In 1986, Lugaresi and colleagues first named and described in detail the clinical and histopathological features of fatal familial insomnia (FFI) [Lugaresi et al. NEJM]. This report was mostly based on a patient referred to as Silvano, who was diagnosed with sleep impairment in 1983 by Dr. Ignazio Roiter. Dr. Roiter referred the case to Prof. Elio Lugaresi, a well-known sleep expert, who, along with his colleagues, carried out advanced sleep analyses. As Silvano's condition quickly deteriorated, Lugaresi arranged for a postmortem neuropathological examination of the brain to be carried out by Dr. Gambetti, Lugaresi's former trainee. The collaboration of these two groups led to the 1986 publication [27]. At the time, a prion disease was not suspected due to a lack of prion-related histpathology and frozen brain tissue for advanced analysis. However, due to the devotion of Dr. Roiter and Silvano's family, more cases were obtained, resulting in the classification of FFI as a familial prion disease tied to the 178Asn genetic mutation. [Medori et al. NEJM, 1992]
Unnamed American patient, 2001
In an article published in 2006, Schenkein and Montagna wrote of a 52-year-old American man who was able to exceed the average survival time by nearly one year with various strategies that included vitamin therapy and meditation, different stimulants and hypnotics and even complete sensory deprivation in an attempt to induce sleep at night and increase alertness during the day. He managed to write a book and drive hundreds of miles in this time, but nonetheless, over the course of his trials, the man succumbed to the classic four-stage progression of the illness.
Egyptian man, 2011, Netherlands
In 2011, the first reported case in the Netherlands was of a 57-year-old man of Egyptian descent. The man came in with symptoms of double vision and progressive memory loss, and his family also noted he had recently become disoriented, paranoid and confused. Whilst he tended to fall asleep at random during daily activities, he experienced vivid dreams and random muscular jerks during normal slow-wave sleep. After four months of these symptoms, he began to have convulsions in his hands, trunk and lower limbs while awake. The person died at age 58, seven months after the onset of symptoms. An autopsy revealed mild atrophy of the frontal cortex and moderate atrophy of the thalamus. The latter is one of the most common signs of FFI.
Research
Still with unclear benefit in humans, a number of treatments have had tentative success in slowing disease progression in animal models, including pentosan polysulfate, mepacrine, and amphotericin B. , a study investigating doxycycline is being carried out.
In 2009, a mouse model was made for FFI. These mice expressed a humanized version of the PrP protein that also contains the D178N FFI mutation. These mice appear to have progressively fewer and shorter periods of uninterrupted sleep, damage in the thalamus, and early deaths, similar to humans with FFI.
The Prion Alliance was established by husband and wife duo Eric Minikel and Sonia Vallabh after Vallabh's mother was diagnosed with the fatal disease. They conduct research at the Broad Institute to develop therapeutics for human prion diseases. Other research interests involve identifying biomarkers to track the progression of prion disease in living people.
References
External links
Neurodegenerative disorders
Transmissible spongiform encephalopathies
Unsolved problems in neuroscience
Sleep disorders
Rare diseases
Sleeplessness and sleep deprivation | Fatal insomnia | Biology | 2,823 |
11,552 | https://en.wikipedia.org/wiki/Frederick%20Abel | Sir Frederick Augustus Abel, 1st Baronet (17 July 18276 September 1902) was an English chemist who was recognised as the leading British authority on explosives. He is best known for the invention of cordite as a replacement for gunpowder in firearms.
Education
Born in London as son of Johann Leopold Abel, Abel studied chemistry at the Royal Polytechnic Institution and in 1845 became one of the original 26 students of A. W. von Hofmann at the Royal College of Chemistry (now a constituent of Imperial College London). In 1852 he was appointed lecturer in chemistry at the Royal Military Academy, Woolwich, succeeding Michael Faraday, who had held that post since 1829.
Early career
From 1854 until 1888 Abel served as ordnance chemist at the Chemical Establishment of the Royal Arsenal at Woolwich, establishing himself as the leading British authority on explosives. Three years later was appointed chemist to the War Department and chemical referee to the government. During his tenure of this office, which lasted until 1888, he carried out a large amount of work in connection with the chemistry of explosives.
Notable work
One of the most important of his investigations had to do with the manufacture of guncotton, and he developed a process, consisting essentially of reducing the nitrated cotton to fine pulp, which enabled it to be safely manufactured and at the same time yielded the product in a form that increased its usefulness. This work to an important extent prepared the way for the "smokeless powders" which came into general use towards the end of the 19th century; cordite, the type adopted by the British government in 1891, was invented jointly by him and Sir James Dewar. He and Dewar were unsuccessfully sued by Alfred Nobel over infringement of Nobel's patent for a similar explosive called ballistite, the case finally being resolved in the House of Lords in 1895. He also extensively researched the behaviour of black powder when ignited, with the Scottish physicist Sir Andrew Noble. At the request of the British government, he devised the Abel test, a means of determining the flash point of petroleum products. His first instrument, the open-test apparatus, was specified in an Act of Parliament in 1868 for officially specifying petroleum products. It was superseded in August 1879 by the much more reliable Abel close-test instrument. Under his leadership, first, guncotton was developed at Waltham Abbey Royal Gunpowder Mills, patented in 1865, then, the propellant cordite, patented in 1889. In electricity, Abel studied the construction of electrical fuses and other applications of electricity to warlike purposes.
Leadership and honours
He was elected a Fellow of the Royal Society in 1860 and received their Royal Medal in 1887. He was president of the Chemical Society (1875–77), of the Institution of Electrical Engineers (then the Society of Telegraph Engineers) (1877), of the Institute of Chemistry (1881–82) and of the Society of Chemical Industry (1882–83). He was also president of the Iron and Steel Institute in 1891 and was awarded the Bessemer Gold Medal in 1897 for his work on problems of steel manufacture. He was awarded the Telford Medal by the Institution of Civil Engineers in 1879.
He was made a Commander of the Order of the Bath (CB) in 1877. and knighted on 20 April 1883
He took an important part in the work of the Inventions Exhibition (London) in 1885, and in 1887 became organizing secretary and first director of the Imperial Institute, a position he held till his death in 1902. He was Rede Lecturer and received an honorary doctorate from Cambridge University in 1888. He was upgraded Knight Commander of the Order of the Bath (KCB) on 3 February 1891, created a baronet, of Cadogan Place in the Parish of Chelsea in the County of London, on 25 May 1893 and made a Knight Grand Cross of the Royal Victorian Order (GCVO) on 8 March 1901.
Abel died at his residence in Whitehall Court, London, on 6 September 1902, aged 75, and was buried in Nunhead Cemetery, London. The baronetcy became extinct on his death.
Family
Abel married twice; first to Sarah Blanch, daughter of James Blanch, of Bristol; secondly after his first wife's death to Giulietta de La Feuillade. He left no children.
Books
Handbook of Chemistry (with C. L. Bloxam)
The Modern History of Gunpowder (1866)
Gun-cotton (1866)
On Explosive Agents (1872)
Researches in Explosives (1875)
Electricity applied to Explosive Purposes (1898)
He also wrote several articles in the ninth edition of the Encyclopædia Britannica.
See also
Internal ballistics
References
Attribution
Further reading
External links
1827 births
1902 deaths
19th-century English chemists
Cordite
Ballistics experts
Fellows of the Royal Society
Knights Commander of the Order of the Bath
Knights Grand Cross of the Royal Victorian Order
Presidents of the Smeatonian Society of Civil Engineers
Alumni of Imperial College London
Scientists from London
Knights Bachelor
Baronets in the Baronetage of the United Kingdom
Burials at Nunhead Cemetery
Royal Medal winners
Bessemer Gold Medal | Frederick Abel | Chemistry | 1,025 |
17,672,510 | https://en.wikipedia.org/wiki/Polyptychodon | Polyptychodon (meaning 'many-folded tooth') is a genus of pliosaurid found in Middle-Late Cretaceous marine deposits in southern England, France and Argentina. It has been considered a nomen dubium in a 2016 review.
History of discovery
The type species, P. interruptus is known from an isolated tooth from the Late Cretaceous Chalk Group of southern England. Owen described a second nominal species of the genus, P. continuus, from an isolated tooth collected in the Hythe Formation of Maidstone, Kent. (The macronarian sauropod Dinodocus was mistakenly thought to be conspecific with P. continuus before it was correctly recognized as a dinosaur and not a plesiosaur.)
Numerous pliosaurid teeth and vertebrae from England and eastern France have been previously assigned to Polyptychodon, including isolated vertebrae from France which were misidentified as a sauropod. Comparison between Albian-age isolated vertebrae from marine deposits in France and Kronosaurus suggested a size of approximately for a Polyptychodon-like brachaucheniine pliosaurid. However, a 2016 re-evaluation found Polyptychodon and its types species to be dubious, and that numerous remains from the Chalk Group in England that had been referred to the genus most likely represent different species of plesiosaurs, with some teeth possibly being referable to Polycotylidae. Similar fossils of pliosaurs were found also in Czech Republic.
The species Polyptychodon patagonicus (Ameghino, 1893), based on crocodile teeth discovered in Argentina, shares the same genus name. According to a 2010 study, P. patagonicus is a nomen vanum and a nomen dubium.
Polyptychodon hudsoni (holotytpe, SMU 60313) was described from the Turonian-age Eagle Ford Formation of Dallas, Texas. It probably belongs to a different genus.
See also
Timeline of plesiosaur research
References
External links
Polyptychodon in the Paleobiology Database
Late Cretaceous plesiosaurs of Europe
Cenomanian genus first appearances
Turonian genus extinctions
Fossil taxa described in 1841
Taxa named by Richard Owen
Nomina dubia
Sauropterygian genera | Polyptychodon | Biology | 479 |
56,428,662 | https://en.wikipedia.org/wiki/Robot%20Monk%20Xian%27er | Robot Monk Xian'er () is a humanoid robot based on the cartoon character Xian'er. It was developed by a team of monks, volunteers and AI experts from Beijing Longquan Monastery in Beijing, China.
He can follow human instructions to make body movements, read scriptures and play Buddhist music. He can chat and respond to people's emotional and spiritual questions with Buddhist wisdom. As a chatbot, Robot Monk Xian'er is available on certain public platforms including WeChat and Facebook. Over the years, master Xuecheng, the abbot of Beijing Longquan Monastery, replied to thousands of questions on Sina Weibo. These questions and their answers become the data source of the chatbot.
References
External links
Robot Monk Xian’er Facebook Page
Chatbots
Robots | Robot Monk Xian'er | Physics,Technology | 163 |
48,740 | https://en.wikipedia.org/wiki/Henri%20Poincar%C3%A9 | Jules Henri Poincaré (, ; ; 29 April 185417 July 1912) was a French mathematician, theoretical physicist, engineer, and philosopher of science. He is often described as a polymath, and in mathematics as "The Last Universalist", since he excelled in all fields of the discipline as it existed during his lifetime. He has further been called "the Gauss of modern mathematics". Due to his success in science, along with his influence and philosophy, he has been called "the philosopher par excellence of modern science."
As a mathematician and physicist, he made many original fundamental contributions to pure and applied mathematics, mathematical physics, and celestial mechanics. In his research on the three-body problem, Poincaré became the first person to discover a chaotic deterministic system which laid the foundations of modern chaos theory. Poincaré is regarded as the creator of the field of algebraic topology, and is further credited with introducing automorphic forms. He also made important contributions to algebraic geometry, number theory, complex analysis and Lie theory. He famously introduced the concept of the Poincaré recurrence theorem, which states that a state will eventually return arbitrarily close to its initial state after a sufficiently long time, which has far-reaching consequences. Early in the 20th century he formulated the Poincaré conjecture, which became, over time, one of the famous unsolved problems in mathematics. It was eventually solved in 2002–2003 by Grigori Perelman. Poincaré popularized the use of non-Euclidean geometry in mathematics as well.
Poincaré made clear the importance of paying attention to the invariance of laws of physics under different transformations, and was the first to present the Lorentz transformations in their modern symmetrical form. Poincaré discovered the remaining relativistic velocity transformations and recorded them in a letter to Hendrik Lorentz in 1905. Thus he obtained perfect invariance of all of Maxwell's equations, an important step in the formulation of the theory of special relativity, for which he is also credited with laying down the foundations for, further writing foundational papers in 1905. He first proposed gravitational waves (ondes gravifiques) emanating from a body and propagating at the speed of light as being required by the Lorentz transformations, doing so in 1905. In 1912, he wrote an influential paper which provided a mathematical argument for quantum mechanics. Poincaré also laid the seeds of the discovery of radioactivity through his interest and study of X-rays, which influenced physicist Henri Becquerel, who then discovered the phenomena. The Poincaré group used in physics and mathematics was named after him, after he introduced the notion of the group.
Poincaré was considered the dominant figure in mathematics and theoretical physics during his time, and was the most respected mathematician of his time, being described as "the living brain of the rational sciences" by mathematician Paul Painlevé. Philosopher Karl Popper regarded Poincaré as the greatest philosopher of science of all time, with Poincaré also originating the conventionalist view in science. Poincaré was a public intellectual in his time, and personally, he believed in political equality for all, while wary of the influence of anti-intellectual positions that the Catholic Church held at the time. He served as the president of the French Academy of Sciences (1906), the president of Société astronomique de France (1901–1903), and twice the president of Société mathématique de France (1886, 1900).
Life
Poincaré was born on 29 April 1854 in Cité Ducale neighborhood, Nancy, Meurthe-et-Moselle, into an influential French family. His father Léon Poincaré (1828–1892) was a professor of medicine at the University of Nancy. His younger sister Aline married the spiritual philosopher Émile Boutroux. Another notable member of Henri's family was his cousin, Raymond Poincaré, a fellow member of the Académie française, who was President of France from 1913 to 1920, and three-time Prime Minister of France between 1913 and 1929.
Education
During his childhood he was seriously ill for a time with diphtheria and received special instruction from his mother, Eugénie Launois (1830–1897).
In 1862, Henri entered the Lycée in Nancy (now renamed the in his honour, along with Henri Poincaré University, also in Nancy). He spent eleven years at the Lycée and during this time he proved to be one of the top students in every topic he studied. He excelled in written composition. His mathematics teacher described him as a "monster of mathematics" and he won first prizes in the concours général, a competition between the top pupils from all the Lycées across France. His poorest subjects were music and physical education, where he was described as "average at best". Poor eyesight and a tendency towards absentmindedness may explain these difficulties. He graduated from the Lycée in 1871 with a baccalauréat in both letters and sciences.
During the Franco-Prussian War of 1870, he served alongside his father in the Ambulance Corps.
Poincaré entered the École Polytechnique as the top qualifier in 1873 and graduated in 1875. There he studied mathematics as a student of Charles Hermite, continuing to excel and publishing his first paper (Démonstration nouvelle des propriétés de l'indicatrice d'une surface) in 1874. From November 1875 to June 1878 he studied at the École des Mines, while continuing the study of mathematics in addition to the mining engineering syllabus, and received the degree of ordinary mining engineer in March 1879.
As a graduate of the École des Mines, he joined the Corps des Mines as an inspector for the Vesoul region in northeast France. He was on the scene of a mining disaster at Magny in August 1879 in which 18 miners died. He carried out the official investigation into the accident.
At the same time, Poincaré was preparing for his Doctorate in Science in mathematics under the supervision of Charles Hermite. His doctoral thesis was in the field of differential equations. It was named Sur les propriétés des fonctions définies par les équations aux différences partielles. Poincaré devised a new way of studying the properties of these equations. He not only faced the question of determining the integral of such equations, but also was the first person to study their general geometric properties. He realised that they could be used to model the behaviour of multiple bodies in free motion within the Solar System. He graduated from the University of Paris in 1879.
First scientific achievements
After receiving his degree, Poincaré began teaching as junior lecturer in mathematics at the University of Caen in Normandy (in December 1879). At the same time he published his first major article concerning the treatment of a class of automorphic functions.
There, in Caen, he met his future wife, Louise Poulain d'Andecy (1857–1934), granddaughter of Isidore Geoffroy Saint-Hilaire and great-granddaughter of Étienne Geoffroy Saint-Hilaire and on 20 April 1881, they married. Together they had four children: Jeanne (born 1887), Yvonne (born 1889), Henriette (born 1891), and Léon (born 1893).
Poincaré immediately established himself among the greatest mathematicians of Europe, attracting the attention of many prominent mathematicians. In 1881 Poincaré was invited to take a teaching position at the Faculty of Sciences of the University of Paris; he accepted the invitation. During the years 1883 to 1897, he taught mathematical analysis in the École Polytechnique.
In 1881–1882, Poincaré created a new branch of mathematics: qualitative theory of differential equations. He showed how it is possible to derive the most important information about the behavior of a family of solutions without having to solve the equation (since this may not always be possible). He successfully used this approach to problems in celestial mechanics and mathematical physics.
Career
He never fully abandoned his career in the mining administration to mathematics. He worked at the Ministry of Public Services as an engineer in charge of northern railway development from 1881 to 1885. He eventually became chief engineer of the Corps des Mines in 1893 and inspector general in 1910.
Beginning in 1881 and for the rest of his career, he taught at the University of Paris (the Sorbonne). He was initially appointed as the maître de conférences d'analyse (associate professor of analysis). Eventually, he held the chairs of Physical and Experimental Mechanics, Mathematical Physics and Theory of Probability, and Celestial Mechanics and Astronomy.
In 1887, at the young age of 32, Poincaré was elected to the French Academy of Sciences. He became its president in 1906, and was elected to the Académie française on 5 March 1908.
In 1887, he won Oscar II, King of Sweden's mathematical competition for a resolution of the three-body problem concerning the free motion of multiple orbiting bodies. (See three-body problem section below.)
In 1893, Poincaré joined the French Bureau des Longitudes, which engaged him in the synchronisation of time around the world. In 1897 Poincaré backed an unsuccessful proposal for the decimalisation of circular measure, and hence time and longitude. It was this post which led him to consider the question of establishing international time zones and the synchronisation of time between bodies in relative motion. (See work on relativity section below.)
In 1904, he intervened in the trials of Alfred Dreyfus, attacking the spurious scientific claims regarding evidence brought against Dreyfus.
Poincaré was the President of the Société Astronomique de France (SAF), the French astronomical society, from 1901 to 1903.
Students
Poincaré had two notable doctoral students at the University of Paris, Louis Bachelier (1900) and Dimitrie Pompeiu (1905).
Death
In 1912, Poincaré underwent surgery for a prostate problem and subsequently died from an embolism on 17 July 1912, in Paris. He was 58 years of age. He is buried in the Poincaré family vault in the Cemetery of Montparnasse, Paris, in section 16 close to the gate Rue Émile-Richard.
A former French Minister of Education, Claude Allègre, proposed in 2004 that Poincaré be reburied in the Panthéon in Paris, which is reserved for French citizens of the highest honour.
Work
Summary
Poincaré made many contributions to different fields of pure and applied mathematics such as: celestial mechanics, fluid mechanics, optics, electricity, telegraphy, capillarity, elasticity, thermodynamics, potential theory, Quantum mechanics, theory of relativity and physical cosmology.
Among the specific topics he contributed to are the following:
algebraic topology (a field that Poincaré virtually invented)
the theory of analytic functions of several complex variables
the theory of abelian functions
algebraic geometry
the Poincaré conjecture, proven in 2003 by Grigori Perelman.
Poincaré recurrence theorem
hyperbolic geometry
number theory
the three-body problem
the theory of diophantine equations
electromagnetism
special relativity
the fundamental group
In the field of differential equations Poincaré has given many results that are critical for the qualitative theory of differential equations, for example the Poincaré sphere and the Poincaré map.
Poincaré on "everybody's belief" in the Normal Law of Errors (see normal distribution for an account of that "law")
Published an influential paper providing a novel mathematical argument in support of quantum mechanics.
Three-body problem
The problem of finding the general solution to the motion of more than two orbiting bodies in the Solar System had eluded mathematicians since Newton's time. This was known originally as the three-body problem and later the n-body problem, where n is any number of more than two orbiting bodies. The n-body solution was considered very important and challenging at the close of the 19th century. Indeed, in 1887, in honour of his 60th birthday, Oscar II, King of Sweden, advised by Gösta Mittag-Leffler, established a prize for anyone who could find the solution to the problem. The announcement was quite specific:
Given a system of arbitrarily many mass points that attract each according to Newton's law, under the assumption that no two points ever collide, try to find a representation of the coordinates of each point as a series in a variable that is some known function of time and for all of whose values the series converges uniformly.
In case the problem could not be solved, any other important contribution to classical mechanics would then be considered to be prizeworthy. The prize was finally awarded to Poincaré, even though he did not solve the original problem. One of the judges, the distinguished Karl Weierstrass, said, "This work cannot indeed be considered as furnishing the complete solution of the question proposed, but that it is nevertheless of such importance that its publication will inaugurate a new era in the history of celestial mechanics." (The first version of his contribution even contained a serious error; for details see the article by Diacu and the book by Barrow-Green). The version finally printed contained many important ideas which led to the theory of chaos. The problem as stated originally was finally solved by Karl F. Sundman for n = 3 in 1912 and was generalised to the case of n > 3 bodies by Qiudong Wang in the 1990s. The series solutions have very slow convergence. It would take millions of terms to determine the motion of the particles for even very short intervals of time, so they are unusable in numerical work.
Work on relativity
Local time
Poincaré's work at the Bureau des Longitudes on establishing international time zones led him to consider how clocks at rest on the Earth, which would be moving at different speeds relative to absolute space (or the "luminiferous aether"), could be synchronised. At the same time Dutch theorist Hendrik Lorentz was developing Maxwell's theory into a theory of the motion of charged particles ("electrons" or "ions"), and their interaction with radiation. In 1895 Lorentz had introduced an auxiliary quantity (without physical interpretation) called "local time"
and introduced the hypothesis of length contraction to explain the failure of optical and electrical experiments to detect motion relative to the aether (see Michelson–Morley experiment). Poincaré was a constant interpreter (and sometimes friendly critic) of Lorentz's theory. Poincaré as a philosopher was interested in the "deeper meaning". Thus he interpreted Lorentz's theory and in so doing he came up with many insights that are now associated with special relativity. In The Measure of Time (1898), Poincaré said, "A little reflection is sufficient to understand that all these affirmations have by themselves no meaning. They can have one only as the result of a convention." He also argued that scientists have to set the constancy of the speed of light as a postulate to give physical theories the simplest form.
Based on these assumptions he discussed in 1900 Lorentz's "wonderful invention" of local time and remarked that it arose when moving clocks are synchronised by exchanging light signals assumed to travel with the same speed in both directions in a moving frame.
Principle of relativity and Lorentz transformations
In 1881 Poincaré described hyperbolic geometry in terms of the hyperboloid model, formulating transformations leaving invariant the Lorentz interval , which makes them mathematically equivalent to the Lorentz transformations in 2+1 dimensions. In addition, Poincaré's other models of hyperbolic geometry (Poincaré disk model, Poincaré half-plane model) as well as the Beltrami–Klein model can be related to the relativistic velocity space (see Gyrovector space).
In 1892 Poincaré developed a mathematical theory of light including polarization. His vision of the action of polarizers and retarders, acting on a sphere representing polarized states, is called the Poincaré sphere. It was shown that the Poincaré sphere possesses an underlying Lorentzian symmetry, by which it can be used as a geometrical representation of Lorentz transformations and velocity additions.
He discussed the "principle of relative motion" in two papers in 1900
and named it the principle of relativity in 1904, according to which no physical experiment can discriminate between a state of uniform motion and a state of rest.
In 1905 Poincaré wrote to Lorentz about Lorentz's paper of 1904, which Poincaré described as a "paper of supreme importance". In this letter he pointed out an error Lorentz had made when he had applied his transformation to one of Maxwell's equations, that for charge-occupied space, and also questioned the time dilation factor given by Lorentz.
In a second letter to Lorentz, Poincaré gave his own reason why Lorentz's time dilation factor was indeed correct after all—it was necessary to make the Lorentz transformation form a group—and he gave what is now known as the relativistic velocity-addition law.
Poincaré later delivered a paper at the meeting of the Academy of Sciences in Paris on 5 June 1905 in which these issues were addressed. In the published version of that he wrote:
The essential point, established by Lorentz, is that the equations of the electromagnetic field are not altered by a certain transformation (which I will call by the name of Lorentz) of the form:
and showed that the arbitrary function must be unity for all (Lorentz had set by a different argument) to make the transformations form a group. In an enlarged version of the paper that appeared in 1906 Poincaré pointed out that the combination is invariant. He noted that a Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing as a fourth imaginary coordinate, and he used an early form of four-vectors. Poincaré expressed a lack of interest in a four-dimensional reformulation of his new mechanics in 1907, because in his opinion the translation of physics into the language of four-dimensional geometry would entail too much effort for limited profit. So it was Hermann Minkowski who worked out the consequences of this notion in 1907.
Mass–energy relation
Like others before, Poincaré (1900) discovered a relation between mass and electromagnetic energy. While studying the conflict between the action/reaction principle and Lorentz ether theory, he tried to determine whether the center of gravity still moves with a uniform velocity when electromagnetic fields are included. He noticed that the action/reaction principle does not hold for matter alone, but that the electromagnetic field has its own momentum. Poincaré concluded that the electromagnetic field energy of an electromagnetic wave behaves like a fictitious fluid (fluide fictif) with a mass density of E/c2. If the center of mass frame is defined by both the mass of matter and the mass of the fictitious fluid, and if the fictitious fluid is indestructible—it's neither created or destroyed—then the motion of the center of mass frame remains uniform. But electromagnetic energy can be converted into other forms of energy. So Poincaré assumed that there exists a non-electric energy fluid at each point of space, into which electromagnetic energy can be transformed and which also carries a mass proportional to the energy. In this way, the motion of the center of mass remains uniform. Poincaré said that one should not be too surprised by these assumptions, since they are only mathematical fictions.
However, Poincaré's resolution led to a paradox when changing frames: if a Hertzian oscillator radiates in a certain direction, it will suffer a recoil from the inertia of the fictitious fluid. Poincaré performed a Lorentz boost (to order v/c) to the frame of the moving source. He noted that energy conservation holds in both frames, but that the law of conservation of momentum is violated. This would allow perpetual motion, a notion which he abhorred. The laws of nature would have to be different in the frames of reference, and the relativity principle would not hold. Therefore, he argued that also in this case there has to be another compensating mechanism in the ether.
Poincaré himself came back to this topic in his St. Louis lecture (1904). He rejected the possibility that energy carries mass and criticized his own solution to compensate the above-mentioned problems:
In the above quote he refers to the Hertz assumption of total aether entrainment that was falsified by the Fizeau experiment but that experiment does indeed show that that light is partially "carried along" with a substance. Finally in 1908 he revisits the problem and ends with abandoning the principle of reaction altogether in favor of supporting a solution based in the inertia of aether itself.
He also discussed two other unexplained effects: (1) non-conservation of mass implied by Lorentz's variable mass , Abraham's theory of variable mass and Kaufmann's experiments on the mass of fast moving electrons and (2) the non-conservation of energy in the radium experiments of Marie Curie.
It was Albert Einstein's concept of mass–energy equivalence (1905) that a body losing energy as radiation or heat was losing mass of amount m = E/c2 that resolved Poincaré's paradox, without using any compensating mechanism within the ether. The Hertzian oscillator loses mass in the emission process, and momentum is conserved in any frame. However, concerning Poincaré's solution of the Center of Gravity problem, Einstein noted that Poincaré's formulation and his own from 1906 were mathematically equivalent.
Gravitational waves
In 1905 Poincaré first proposed gravitational waves (ondes gravifiques) emanating from a body and propagating at the speed of light. He wrote:
Poincaré and Einstein
Einstein's first paper on relativity was published three months after Poincaré's short paper, but before Poincaré's longer version. Einstein relied on the principle of relativity to derive the Lorentz transformations and used a similar clock synchronisation procedure (Einstein synchronisation) to the one that Poincaré (1900) had described, but Einstein's paper was remarkable in that it contained no references at all. Poincaré never acknowledged Einstein's work on special relativity. However, Einstein expressed sympathy with Poincaré's outlook obliquely in a letter to Hans Vaihinger on 3 May 1919, when Einstein considered Vaihinger's general outlook to be close to his own and Poincaré's to be close to Vaihinger's. In public, Einstein acknowledged Poincaré posthumously in the text of a lecture in 1921 titled "Geometrie und Erfahrung (Geometry and Experience)" in connection with non-Euclidean geometry, but not in connection with special relativity. A few years before his death, Einstein commented on Poincaré as being one of the pioneers of relativity, saying "Lorentz had already recognized that the transformation named after him is essential for the analysis of Maxwell's equations, and Poincaré deepened this insight still further ....".
Assessments on Poincaré and relativity
Poincaré's work in the development of special relativity is well recognised, though most historians stress that despite many similarities with Einstein's work, the two had very different research agendas and interpretations of the work. Poincaré developed a similar physical interpretation of local time and noticed the connection to signal velocity, but contrary to Einstein he continued to use the ether-concept in his papers and argued that clocks at rest in the ether show the "true" time, and moving clocks show the local time. So Poincaré tried to keep the relativity principle in accordance with classical concepts, while Einstein developed a mathematically equivalent kinematics based on the new physical concepts of the relativity of space and time.
While this is the view of most historians, a minority go much further, such as E. T. Whittaker, who held that Poincaré and Lorentz were the true discoverers of relativity.
Algebra and number theory
Poincaré introduced group theory to physics, and was the first to study the group of Lorentz transformations. He also made major contributions to the theory of discrete groups and their representations.
Topology
The subject is clearly defined by Felix Klein in his "Erlangen Program" (1872): the geometry invariants of arbitrary continuous transformation, a kind of geometry. The term "topology" was introduced, as suggested by Johann Benedict Listing, instead of previously used "Analysis situs". Some important concepts were introduced by Enrico Betti and Bernhard Riemann. But the foundation of this science, for a space of any dimension, was created by Poincaré. His first article on this topic appeared in 1894.
His research in geometry led to the abstract topological definition of homotopy and homology. He also first introduced the basic concepts and invariants of combinatorial topology, such as Betti numbers and the fundamental group. Poincaré proved a formula relating the number of edges, vertices and faces of n-dimensional polyhedron (the Euler–Poincaré theorem) and gave the first precise formulation of the intuitive notion of dimension.
Astronomy and celestial mechanics
Poincaré published two now classical monographs, "New Methods of Celestial Mechanics" (1892–1899) and "Lectures on Celestial Mechanics" (1905–1910). In them, he successfully applied the results of their research to the problem of the motion of three bodies and studied in detail the behavior of solutions (frequency, stability, asymptotic, and so on). They introduced the small parameter method, fixed points, integral invariants, variational equations, the convergence of the asymptotic expansions. Generalizing a theory of Bruns (1887), Poincaré showed that the three-body problem is not integrable. In other words, the general solution of the three-body problem can not be expressed in terms of algebraic and transcendental functions through unambiguous coordinates and velocities of the bodies. His work in this area was the first major achievement in celestial mechanics since Isaac Newton.
These monographs include an idea of Poincaré, which later became the basis for mathematical "chaos theory" (see, in particular, the Poincaré recurrence theorem) and the general theory of dynamical systems.
Poincaré authored important works on astronomy for the equilibrium figures of a gravitating rotating fluid. He introduced the important concept of bifurcation points and proved the existence of equilibrium figures such as the non-ellipsoids, including ring-shaped and pear-shaped figures, and their stability. For this discovery, Poincaré received the Gold Medal of the Royal Astronomical Society (1900).
Differential equations and mathematical physics
After defending his doctoral thesis on the study of singular points of the system of differential equations, Poincaré wrote a series of memoirs under the title "On curves defined by differential equations" (1881–1882). In these articles, he built a new branch of mathematics, called "qualitative theory of differential equations". Poincaré showed that even if the differential equation can not be solved in terms of known functions, yet from the very form of the equation, a wealth of information about the properties and behavior of the solutions can be found. In particular, Poincaré investigated the nature of the trajectories of the integral curves in the plane, gave a classification of singular points (saddle, focus, center, node), introduced the concept of a limit cycle and the loop index, and showed that the number of limit cycles is always finite, except for some special cases. Poincaré also developed a general theory of integral invariants and solutions of the variational equations. For the finite-difference equations, he created a new direction – the asymptotic analysis of the solutions. He applied all these achievements to study practical problems of mathematical physics and celestial mechanics, and the methods used were the basis of its topological works.
Character
Poincaré's work habits have been compared to a bee flying from flower to flower. Poincaré was interested in the way his mind worked; he studied his habits and gave a talk about his observations in 1908 at the Institute of General Psychology in Paris. He linked his way of thinking to how he made several discoveries.
The mathematician Darboux claimed he was un intuitif (an intuitive), arguing that this is demonstrated by the fact that he worked so often by visual representation. Jacques Hadamard wrote that Poincaré's research demonstrated marvelous clarity and Poincaré himself wrote that he believed that logic was not a way to invent but a way to structure ideas and that logic limits ideas.
Toulouse's characterisation
Poincaré's mental organisation was interesting not only to Poincaré himself but also to Édouard Toulouse, a psychologist of the Psychology Laboratory of the School of Higher Studies in Paris. Toulouse wrote a book entitled Henri Poincaré (1910). In it, he discussed Poincaré's regular schedule:
He worked during the same times each day in short periods of time. He undertook mathematical research for four hours a day, between 10 a.m. and noon then again from 5 p.m. to 7 p.m.. He would read articles in journals later in the evening.
His normal work habit was to solve a problem completely in his head, then commit the completed problem to paper.
He was ambidextrous and nearsighted.
His ability to visualise what he heard proved particularly useful when he attended lectures, since his eyesight was so poor that he could not see properly what the lecturer wrote on the blackboard.
These abilities were offset to some extent by his shortcomings:
He was physically clumsy and artistically inept.
He was always in a rush and disliked going back for changes or corrections.
He never spent a long time on a problem since he believed that the subconscious would continue working on the problem while he consciously worked on another problem.
In addition, Toulouse stated that most mathematicians worked from principles already established while Poincaré started from basic principles each time (O'Connor et al., 2002).
His method of thinking is well summarised as:
Publications
Legacy
Poincaré is credited with laying the foundations of special relativity, with some arguing that he should be credited with its creation. He is said to have "dominated the mathematics and the theoretical physics of his time", and that "he was without a doubt the most admired mathematician while he was alive, and he remains today one of the world's most emblematic scientific figures." Poincaré is regarded as a "universal specialist", as he refined celestial mechanics, he progressed nearly all parts of mathematics of his time, including creating new subjects, is a father of special relativity, participated in all the great debates of his time in physics, was a major actor in the great epistemological debates of his day in relation to philosophy of science, and Poincaré was the one who investigated the 1879 Magny shaft firedamp explosion as an engineer. Due to the breadth of his research, Poincaré was the only member to be elected to every section of the French Academy of Sciences of the time, those being geometry, mechanics, physics, astronomy and navigation.
Physicist Henri Becquerel nominated Poincaré for a Nobel Prize in 1904, as Becquerel took note that "Poincaré's mathematical and philosophical genius surveyed all of physics and was among those that contributed most to human progress by giving researchers a solid basis for their journeys into the unknown." After his death, he was praised by many intellectual figures of his time, as the author Marie Bonaparte wrote to his widowed wife Louise that "He was – as you know better than anyone – not only the greatest thinker, the most powerful genius of our time – but also a deep and incomparable heart; and having been close to him remains the precious memory of a whole life."
Mathematician E.T. Bell titled Poincaré as "The Last Universalist", and noted his prowess in many fields, stating that:
When philosopher and mathematician Bertrand Russell was asked who was the greatest man that France had produced in modern times, he instantly replied "Poincaré". Bell noted that if Poincaré had been as strong in practical science as he was in theoretical, he might have "made a fourth with the incomparable three, Archimedes, Newton, and Gauss."
Bell further noted his powerful memory, one that was even superior to Leonhard Euler's, stating that:
Bell notes the terrible eyesight of Poincaré, he almost completely remembered formulas and theorems by ear, and "unable to see the board distinctly when he became a student of advanced mathematics, he sat back and listened, following and remembering perfectly without taking notes - an easy feat for him, but one incomprehensible to most mathematicians."
Honours
Awards
Oscar II, King of Sweden's mathematical competition (1887)
Foreign member of the Royal Netherlands Academy of Arts and Sciences (1897)
American Philosophical Society (1899)
Gold Medal of the Royal Astronomical Society of London (1900)
Commander of the Legion of Honour (1903)
Bolyai Prize (1905)
Matteucci Medal (1905)
French Academy of Sciences (1906)
Académie française (1909)
Bruce Medal (1911)
Named after him
Institut Henri Poincaré (mathematics and theoretical physics centre)
Maison Poincaré, a mathematics museum in the 5th arrondissement of Paris
Poincaré Prize (Mathematical Physics International Prize)
Annales Henri Poincaré (Scientific Journal)
Poincaré Seminar (nicknamed "Bourbaphy")
The crater Poincaré on the Moon
Asteroid 2021 Poincaré
List of things named after Henri Poincaré
Henri Poincaré did not receive the Nobel Prize in Physics, but he had influential advocates like Henri Becquerel or committee member Gösta Mittag-Leffler. The nomination archive reveals that Poincaré received a total of 51 nominations between 1904 and 1912, the year of his death. Of the 58 nominations for the 1910 Nobel Prize, 34 named Poincaré. Nominators included Nobel laureates Hendrik Lorentz and Pieter Zeeman (both of 1902), Marie Curie (of 1903), Albert Michelson (of 1907), Gabriel Lippmann (of 1908) and Guglielmo Marconi (of 1909).
The fact that renowned theoretical physicists like Poincaré, Boltzmann or Gibbs were not awarded the Nobel Prize is seen as evidence that the Nobel committee had more regard for experimentation than theory. In Poincaré's case, several of those who nominated him pointed out that the greatest problem was to name a specific discovery, invention, or technique.
Philosophy
Poincaré had philosophical views opposite to those of Bertrand Russell and Gottlob Frege, who believed that mathematics was a branch of logic. Poincaré strongly disagreed, claiming that intuition was the life of mathematics. Poincaré gives an interesting point of view in his 1902 book Science and Hypothesis:
Poincaré believed that arithmetic is synthetic. He argued that Peano's axioms cannot be proven non-circularly with the principle of induction (Murzi, 1998), therefore concluding that arithmetic is a priori synthetic and not analytic. Poincaré then went on to say that mathematics cannot be deduced from logic since it is not analytic. His views were similar to those of Immanuel Kant (Kolak, 2001, Folina 1992). He strongly opposed Cantorian set theory, objecting to its use of impredicative definitions.
However, Poincaré did not share Kantian views in all branches of philosophy and mathematics. For example, in geometry, Poincaré believed that the structure of non-Euclidean space can be known analytically. Poincaré held that convention plays an important role in physics. His view (and some later, more extreme versions of it) came to be known as "conventionalism". Poincaré believed that Newton's first law was not empirical but is a conventional framework assumption for mechanics (Gargani, 2012). He also believed that the geometry of physical space is conventional. He considered examples in which either the geometry of the physical fields or gradients of temperature can be changed, either describing a space as non-Euclidean measured by rigid rulers, or as a Euclidean space where the rulers are expanded or shrunk by a variable heat distribution. However, Poincaré thought that we were so accustomed to Euclidean geometry that we would prefer to change the physical laws to save Euclidean geometry rather than shift to non-Euclidean physical geometry.
Free will
Poincaré's famous lectures before the Société de Psychologie in Paris (published as Science and Hypothesis, The Value of Science, and Science and Method) were cited by Jacques Hadamard as the source for the idea that creativity and invention consist of two mental stages, first random combinations of possible solutions to a problem, followed by a critical evaluation.
Although he most often spoke of a deterministic universe, Poincaré said that the subconscious generation of new possibilities involves chance.
It is certain that the combinations which present themselves to the mind in a kind of sudden illumination after a somewhat prolonged period of unconscious work are generally useful and fruitful combinations... all the combinations are formed as a result of the automatic action of the subliminal ego, but those only which are interesting find their way into the field of consciousness... A few only are harmonious, and consequently at once useful and beautiful, and they will be capable of affecting the geometrician's special sensibility I have been speaking of; which, once aroused, will direct our attention upon them, and will thus give them the opportunity of becoming conscious... In the subliminal ego, on the contrary, there reigns what I would call liberty, if one could give this name to the mere absence of discipline and to disorder born of chance.
Poincaré's two stages—random combinations followed by selection—became the basis for Daniel Dennett's two-stage model of free will.
Bibliography
Poincaré's writings in English translation
Popular writings on the philosophy of science:
; reprinted in 1921; this book includes the English translations of Science and Hypothesis (1902), The Value of Science (1905), Science and Method (1908).
1905. "", The Walter Scott Publishing Co.
1906. "", Athenæum
1913. "The New Mechanics", The Monist, Vol. XXIII.
1913. "The Relativity of Space", The Monist, Vol. XXIII.
1913.
1956. Chance. In James R. Newman, ed., The World of Mathematics (4 Vols).
1958. The Value of Science, New York: Dover.
On algebraic topology:
1895. . The first systematic study of topology.
On celestial mechanics:
1890.
1892–99. New Methods of Celestial Mechanics, 3 vols. English trans., 1967. .
1905. "The Capture Hypothesis of J. J. See", The Monist, Vol. XV.
1905–10. Lessons of Celestial Mechanics.
On the philosophy of mathematics:
Ewald, William B., ed., 1996. From Kant to Hilbert: A Source Book in the Foundations of Mathematics, 2 vols. Oxford Univ. Press. Contains the following works by Poincaré:
1894, "On the Nature of Mathematical Reasoning", 972–981.
1898, "On the Foundations of Geometry", 982–1011.
1900, "Intuition and Logic in Mathematics", 1012–1020.
1905–06, "Mathematics and Logic, I–III", 1021–1070.
1910, "On Transfinite Numbers", 1071–1074.
1905. "The Principles of Mathematical Physics", The Monist, Vol. XV.
1910. "The Future of Mathematics", The Monist, Vol. XX.
1910. "Mathematical Creation", The Monist, Vol. XX.
Other:
1904. Maxwell's Theory and Wireless Telegraphy, New York, McGraw Publishing Company.
1905. "The New Logics", The Monist, Vol. XV.
1905. "The Latest Efforts of the Logisticians", The Monist, Vol. XV.
Exhaustive bibliography of English translations:
1892–2017. .
See also
Concepts
Poincaré–Andronov–Hopf bifurcation
Poincaré complex – an abstraction of the singular chain complex of a closed, orientable manifold
Poincaré duality
Poincaré disk model
Poincaré expansion
Poincaré gauge
Poincaré group
Poincaré half-plane model
Poincaré homology sphere
Poincaré inequality
Poincaré lemma
Poincaré map
Poincaré residue
Poincaré series (modular form)
Poincaré space
Poincaré metric
Poincaré plot
Poincaré polynomial
Poincaré series
Poincaré sphere
Poincaré–Einstein synchronisation
Poincaré–Lelong equation
Poincaré–Lindstedt method
Poincaré–Lindstedt perturbation theory
Poincaré–Steklov operator
Euler–Poincaré characteristic
Neumann–Poincaré operator
Reflecting Function
Theorems
Here is a list of theorems proved by Poincaré:
Poincaré's recurrence theorem: certain systems will, after a sufficiently long but finite time, return to a state very close to the initial state.
Poincaré–Bendixson theorem: a statement about the long-term behaviour of orbits of continuous dynamical systems on the plane, cylinder, or two-sphere.
Poincaré–Hopf theorem: a generalization of the hairy-ball theorem, which states that there is no smooth vector field on a sphere having no sources or sinks.
Poincaré–Lefschetz duality theorem: a version of Poincaré duality in geometric topology, applying to a manifold with boundary
Poincaré separation theorem: gives the upper and lower bounds of eigenvalues of a real symmetric matrix B'AB that can be considered as the orthogonal projection of a larger real symmetric matrix A onto a linear subspace spanned by the columns of B.
Poincaré–Birkhoff theorem: every area-preserving, orientation-preserving homeomorphism of an annulus that rotates the two boundaries in opposite directions has at least two fixed points.
Poincaré–Birkhoff–Witt theorem: an explicit description of the universal enveloping algebra of a Lie algebra.
Poincaré–Bjerknes circulation theorem: theorem about a conservation of quantity for the rotating frame.
Poincaré conjecture (now a theorem): Every simply connected, closed 3-manifold is homeomorphic to the 3-sphere.
Poincaré–Miranda theorem: a generalization of the intermediate value theorem to n dimensions.
Other
French epistemology
History of special relativity
List of things named after Henri Poincaré
Institut Henri Poincaré, Paris
Brouwer fixed-point theorem
Relativity priority dispute
Epistemic structural realism
References
Footnotes
Sources
Bell, Eric Temple, 1986. Men of Mathematics (reissue edition). Touchstone Books. .
Belliver, André, 1956. Henri Poincaré ou la vocation souveraine. Paris: Gallimard.
Bernstein, Peter L, 1996. "Against the Gods: A Remarkable Story of Risk". (pp. 199–200). John Wiley & Sons.
Boyer, B. Carl, 1968. A History of Mathematics: Henri Poincaré, John Wiley & Sons.
Grattan-Guinness, Ivor, 2000. The Search for Mathematical Roots 1870–1940. Princeton Uni. Press.
. Internet version published in Journal of the ACMS 2004.
Folina, Janet, 1992. Poincaré and the Philosophy of Mathematics. Macmillan, New York.
Gray, Jeremy, 1986. Linear differential equations and group theory from Riemann to Poincaré, Birkhauser
Gray, Jeremy, 2013. Henri Poincaré: A scientific biography. Princeton University Press
Kolak, Daniel, 2001. Lovers of Wisdom, 2nd ed. Wadsworth.
Gargani, Julien, 2012. Poincaré, le hasard et l'étude des systèmes complexes, L'Harmattan.
Murzi, 1998. "Henri Poincaré".
O'Connor, J. John, and Robertson, F. Edmund, 2002, "Jules Henri Poincaré". University of St. Andrews, Scotland.
Peterson, Ivars, 1995. Newton's Clock: Chaos in the Solar System (reissue edition). W H Freeman & Co. .
Sageret, Jules, 1911. Henri Poincaré. Paris: Mercure de France.
Toulouse, E., 1910. Henri Poincaré – (Source biography in French) at University of Michigan Historic Math Collection.
–
Verhulst, Ferdinand, 2012 Henri Poincaré. Impatient Genius. N.Y.: Springer.
Henri Poincaré, l'œuvre scientifique, l'œuvre philosophique, by Vito Volterra, Jacques Hadamard, Paul Langevin and Pierre Boutroux, Felix Alcan, 1914.
Henri Poincaré, l'œuvre mathématique, by Vito Volterra.
Henri Poincaré, le problème des trois corps, by Jacques Hadamard.
Henri Poincaré, le physicien, by Paul Langevin.
Henri Poincaré, l'œuvre philosophique, by Pierre Boutroux.
Further reading
Secondary sources to work on relativity
Non-mainstream sources
External links
Henri Poincaré's Bibliography
Internet Encyclopedia of Philosophy: "Henri Poincaré " – by Mauro Murzi.
Internet Encyclopedia of Philosophy: "Poincaré’s Philosophy of Mathematics" – by Janet Folina.
Henri Poincaré on Information Philosopher
A timeline of Poincaré's life University of Nantes (in French).
Henri Poincaré Papers University of Nantes (in French).
Bruce Medal page
Collins, Graham P., "Henri Poincaré, His Conjecture, Copacabana and Higher Dimensions," Scientific American, 9 June 2004.
BBC in Our Time, "Discussion of the Poincaré conjecture," 2 November 2006, hosted by Melvyn Bragg.
Poincare Contemplates Copernicus at MathPages
High Anxieties – The Mathematics of Chaos (2008) BBC documentary directed by David Malone looking at the influence of Poincaré's discoveries on 20th Century mathematics.
1854 births
1912 deaths
19th-century French essayists
19th-century French male writers
19th-century French mathematicians
19th-century French non-fiction writers
19th-century French philosophers
20th-century French essayists
20th-century French male writers
20th-century French mathematicians
20th-century French philosophers
Algebraic geometers
Burials at Montparnasse Cemetery
Chaos theorists
Continental philosophers
Corps des mines
Corresponding members of the Saint Petersburg Academy of Sciences
Deaths from embolism
Determinists
Dynamical systems theorists
École Polytechnique alumni
French fluid dynamicists
Foreign associates of the National Academy of Sciences
Foreign members of the Royal Society
French male essayists
French male non-fiction writers
French male writers
French military personnel of the Franco-Prussian War
French mining engineers
French geometers
Hyperbolic geometers
French lecturers
French mathematical analysts
Members of the Académie Française
Members of the Royal Netherlands Academy of Arts and Sciences
Mines Paris - PSL alumni
Officers of the French Academy of Sciences
Scientists from Nancy, France
Philosophers of logic
Philosophers of mathematics
Philosophers of psychology
French philosophers of science
French philosophy academics
Philosophy writers
Recipients of the Bruce Medal
Recipients of the Gold Medal of the Royal Astronomical Society
French relativity theorists
Thermodynamicists
Topologists
Academic staff of the University of Paris
Recipients of the Matteucci Medal | Henri Poincaré | Physics,Chemistry,Mathematics | 9,885 |
45,598,981 | https://en.wikipedia.org/wiki/Gaseous%20signaling%20molecules | Gaseous signaling molecules are gaseous molecules that are either synthesized internally (endogenously) in the organism, tissue or cell or are received by the organism, tissue or cell from outside (say, from the atmosphere or hydrosphere, as in the case of oxygen) and that are used to transmit chemical signals which induce certain physiological or biochemical changes in the organism, tissue or cell. The term is applied to, for example, oxygen, carbon dioxide, sulfur dioxide, nitrous oxide, hydrogen cyanide, ammonia, methane, hydrogen, ethylene, etc.
Select gaseous signaling molecules behave as neurotransmitters and are called gasotransmitters. These include nitric oxide, carbon monoxide, and hydrogen sulfide.
Historically, the study of gases and physiological effects was categorized under factitious airs.
The biological roles of each of the gaseous signaling molecules are outlined below.
Gasotransmitters
Gasotransmitters are a class of neurotransmitters. Only three gases are accepted to be classified as gasotransmitters including nitric oxide, carbon monoxide, and hydrogen sulfide.
Gaseous Signaling Molecules
Oxygen
Oxygen, O2, is an essential gaseous signaling molecule & biological messenger important in many physiological and pathological processes, acting via cellular gasoreceptor proteins and other signaling pathways. The levels of O2 in cells or organisms must be tighly regulated to ensure normoxic and not uncontrolled hypoxic or anoxic or hyperoxic states. In mammals, specialized tissues such as carotid body sense O2 levels.
Carbon dioxide
Carbon dioxide, CO2, is one of the mediators of local autoregulation of blood supply. If its levels are high, the capillaries expand to allow a greater blood flow to that tissue.
Mosquitoes are attracted to humans by sensing the CO2 via gustatory receptors, a type of gasoreceptor.
Although the body requires oxygen for metabolism, low oxygen levels normally do not stimulate breathing. Rather, breathing is stimulated by higher carbon dioxide levels.
The respiratory centers try to maintain an arterial CO2 pressure of 40 mm Hg. With intentional hyperventilation, the CO2 content of arterial blood may be lowered to 10–20 mm Hg (the oxygen content of the blood is little affected), and the respiratory drive is diminished. This is why one can hold one's breath longer after hyperventilating than without hyperventilating. This carries the risk that unconsciousness may result before the need to breathe becomes overwhelming, which is why hyperventilation is particularly dangerous before free diving.
Nitric oxide
Nitric oxide, NO, is a key vertebrate biological messenger important in many physiological and pathological processes, acting, for instance, as a powerful vasodilator in humans (see Biological functions of nitric oxide). Mammalian cells have a specialized gasoreceptor soluble guanylyl cyclase that bind to NO and trigger NO-dependent cellular signaling.
Nitrous oxide
Nitrous oxide, N2O, in biological systems can be formed by an enzymatic or non-enzymatic reduction of nitric oxide. In vitro studies have shown that endogenous nitrous oxide can be formed by the reaction between nitric oxide and thiol. Some authors have shown that this process of NO reduction to N2O takes place in hepatocytes, specifically in their cytoplasm and mitochondria, and suggested that the N2O can possibly be produced in mammalian cells. It is well known that N2O is produced by some bacteria during process called denitrification.
In 1981, it was first suggested from clinical work with nitrous oxide (N2O) that a gas had a direct action at pharmacological receptors and thereby acted as a neurotransmitter. In vitro experiments confirmed these observations which were replicated at NIDA later.
Apart from its direct and indirect actions at opioid receptors, it was also shown that N2O inhibits NMDA receptor-mediated activity and ionic currents and diminishes NMDA receptor-mediated excitotoxicity and neurodegeneration. Nitrous oxide also inhibits methionine synthase and slows the conversion of homocysteine to methionine, increases homocysteine concentration and decreases methionine concentration. This effect was shown in lymphocyte cell cultures and in human liver biopsy samples.
Nitrous oxide does not bind as a ligand to the heme and does not react with thiol-containing proteins. Nevertheless, studies have shown that nitrous oxide can reversibly and non-covalently "insert" itself into the inner structures of some heme-containing proteins such as hemoglobin, myoglobin, cytochrome oxidase and alter their structure and function. The ability of nitrous oxide to alter the structure and function of these proteins was demonstrated by shifts in infrared spectra of cysteine thiols of hemoglobin and by partial and reversible inhibition of cytochrome oxidase.
Endogenous nitrous oxide can possibly play a role in modulating endogenous opioid and NMDA systerosclerosis, severe sepsis, severe malaria, or autoimmunity. Clinical tests involving humans have been performed, but the results have not yet been released.
Carbon suboxide
Carbon suboxide, C3O2, can be produced in small amounts in any biochemical process that normally produces carbon monoxide, CO, for example, during heme oxidation by heme oxygenase-1. It can also be formed from malonic acid. It has been shown that carbon suboxide in an organism can quickly polymerize into macrocyclic polycarbon structures with the common formula (C3O2)n (mostly (C3O2)6 and (C3O2)8), and that those macrocyclic compounds are potent inhibitors of Na+/K+-ATP-ase and Ca-dependent ATP-ase, and have digoxin-like physiological properties and natriuretic and antihypertensive actions. Those macrocyclic carbon suboxide polymer compounds are thought to be endogenous digoxin-like regulators of Na+/K+-ATP-ases and Ca-dependent ATP-ases, and endogenous natriuretics and antihypertensives. Other than that, some authors think also that those macrocyclic compounds of carbon suboxide can possibly diminish free radical formation and oxidative stress and play a role in endogenous anticancer protective mechanisms, for example in the retina.
Sulfur dioxide
The role of sulfur dioxide, SO2, in mammalian biology is not well understood. Sulfur dioxide blocks nerve signals from the pulmonary stretch receptors and abolishes the Hering–Breuer inflation reflex.
Sulfur dioxide plays a role in diminishing an experimental lung damage caused by oleic acid. Endogenous sulfur dioxide lowered lipid peroxidation, free radical formation, oxidative stress and inflammation during an experimental lung damage. Conversely, a successful lung damage caused a significant lowering of endogenous sulfur dioxide production, and an increase in lipid peroxidation, free radical formation, oxidative stress and inflammation. Moreover, blockade of an enzyme that produces endogenous SO2 significantly increased the amount of lung tissue damage in the experiment. Conversely, adding acetylcysteine or glutathione to the rat diet increased the amount of endogenous SO2 produced and decreased the lung damage, the free radical formation, oxidative stress, inflammation and apoptosis.
Endogenous sulfur dioxide may play a role in regulating cardiac and blood vessel function, and aberrant or deficient sulfur dioxide metabolism can contribute to several different cardiovascular diseases, such as arterial hypertension, atherosclerosis, pulmonary arterial hypertension, stenocardia.
In children with pulmonary arterial hypertension due to congenital heart diseases, the level of homocysteine is higher and the level of endogenous sulfur dioxide is lower than in normal control children. Moreover, these biochemical parameters strongly correlated to the severity of pulmonary arterial hypertension. Authors considered homocysteine to be one of useful biochemical markers of disease severity and sulfur dioxide metabolism to be one of potential therapeutic targets in those patients.
Endogenous sulfur dioxide also lowers the proliferation rate of endothelial smooth muscle cells in blood vessels, via lowering the MAPK activity and activating adenylyl cyclase and protein kinase A. Smooth muscle cell proliferation is one of important mechanisms of hypertensive remodeling of blood vessels and their stenosis, so it is an important pathogenetic mechanism in arterial hypertension and atherosclerosis.
Endogenous sulfur dioxide in low concentrations causes endothelium-dependent vasodilation. In higher concentrations it causes endothelium-independent vasodilation and has a negative inotropic effect on cardiac output function, thus effectively lowering blood pressure and myocardial oxygen consumption. The vasodilating effects of sulfur dioxide are mediated via ATP-dependent calcium channels and L-type ("dihydropyridine") calcium channels. Endogenous sulfur dioxide is also a potent antiinflammatory, antioxidant and cytoprotective agent. It lowers blood pressure and slows hypertensive remodeling of blood vessels, especially thickening of their intima. It also regulates lipid metabolism.
Endogenous sulfur dioxide also diminishes myocardial damage, caused by isoproterenol adrenergic hyperstimulation, and strengthens the myocardial antioxidant defense reserve.
Hydrogen cyanide
Some authors have shown that neurons can produce hydrogen cyanide, HCN, upon activation of their opioid receptors by endogenous or exogenous opioids. They have also shown that neuronal production of HCN activates NMDA receptors and plays a role in signal transduction between neuronal cells (neurotransmission). Moreover, increased endogenous neuronal HCN production under opioids was seemingly needed for adequate opioid analgesia, as analgesic action of opioids was attenuated by HCN scavengers. They considered endogenous HCN to be a neuromodulator.
It was also shown that, while stimulating muscarinic cholinergic receptors in cultured pheochromocytoma cells increases HCN production, in a living organism (in vivo) muscarinic cholinergic stimulation actually decreases HCN production.
Leukocytes generate HCN during phagocytosis.
The vasodilatation, caused by sodium nitroprusside, has been shown to be mediated not only by NO generation, but also by endogenous cyanide generation, which adds not only toxicity, but also some additional antihypertensive efficacy compared to nitroglycerine and other non-cyanogenic nitrates which do not cause blood cyanide levels to rise.
Ammonia
Ammonia, NH3, also plays a role in both normal and abnormal animal physiology. It is biosynthesised through normal amino acid metabolism, but is toxic in high concentrations. The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia. Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy, as well as the neurologic disease common in people with urea cycle defects and organic acidurias.
Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine, α-ketoglutarate may be degraded to produce two molecules of bicarbonate, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules, combine with a hydrogen ion, and thus allow for further acid excretion.
Methane
Some authors have shown that endogenous methane, CH4, is produced not only by the intestinal flora and then absorbed into the blood, but also is produced - in small amounts - by eukaryotic cells (during process of lipid peroxidation). And they have also shown that the endogenous methane production rises during an experimental mitochondrial hypoxia, for example, sodium azide intoxication. They thought that methane could be one of intercellular signals of hypoxia and stress.
Other authors have shown that cellular methane production also rises during sepsis or bacterial endotoxemia, including an experimental imitation of endotoxemia by lipopolysaccharide (LPS) administration.
Some other researchers have shown that methane, produced by the intestinal flora, is not fully "biologically neutral" to the intestine, and it participates in the normal physiologic regulation of peristalsis. And its excess causes not only belching, flatulence and belly pain, but also functional constipation.
Ethylene
Ethylene, H2C=CH2, serves as a hormone in plants. It acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves.
Commercial ripening rooms use "catalytic generators" to make ethylene gas from a liquid supply of ethanol. Typically, a gassing level of 500 to 2,000 ppm is used, for 24 to 48 hours. Care must be taken to control carbon dioxide levels in ripening rooms when gassing, as high temperature ripening () has been seen to produce CO2 levels of 10% in 24 hours.
Ethylene has been used since the ancient Egyptians, who would gash figs in order to stimulate ripening (wounding stimulates ethylene production by plant tissues). The ancient Chinese would burn incense in closed rooms to enhance the ripening of pears. In 1864, it was discovered that gas leaks from street lights led to stunting of growth, twisting of plants, and abnormal thickening of stems. In 1901, a Russian scientist named Dimitry Neljubow showed that the active component was ethylene. Sarah Doubt discovered that ethylene stimulated abscission in 1917. It wasn't until 1934 that Gane reported that plants synthesize ethylene. In 1935, Crocker proposed that ethylene was the plant hormone responsible for fruit ripening as well as senescence of vegetative tissues.
Ethylene is produced from essentially all parts of higher plants, including leaves, stems, roots, flowers, fruits, tubers, and seeds.
Ethylene production is regulated by a variety of developmental and environmental factors. During the life of the plant, ethylene production is induced during certain stages of growth such as germination, ripening of fruits, abscission of leaves, and senescence of flowers. Ethylene production can also be induced by a variety of external aspects such as mechanical wounding, environmental stresses, and certain chemicals including auxin and other regulators.
Ethylene is biosynthesized from the amino acid methionine to S-adenosyl-L-methionine (SAM, also called Adomet) by the enzyme Met Adenosyltransferase. SAM is then converted to 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase (ACS). The activity of ACS determines the rate of ethylene production, therefore regulation of this enzyme is key for the ethylene biosynthesis. The final step requires oxygen and involves the action of the enzyme ACC-oxidase (ACO), formerly known as the ethylene forming enzyme (EFE). Ethylene biosynthesis can be induced by endogenous or exogenous ethylene. ACC synthesis increases with high levels of auxins, especially indole acetic acid (IAA) and cytokinins.
Ethylene is perceived by a family of five transmembrane protein dimers such as the ETR1 gasoreceptor protein in Arabidopsis. The gene encoding an ethylene receptor has been cloned in Arabidopsis thaliana and then in tomato. Ethylene receptors are encoded by multiple genes in the Arabidopsis and tomato genomes. Mutations in any of the gene family, which comprises five receptors in Arabidopsis and at least six in tomato, can lead to insensitivity to ethylene. DNA sequences for ethylene receptors have also been identified in many other plant species and an ethylene binding protein has even been identified in Cyanobacteria.
Environmental cues such as flooding, drought, chilling, wounding, and pathogen attack can induce ethylene formation in plants. In flooding, roots suffer from lack of oxygen, or anoxia, which leads to the synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC). ACC is transported upwards in the plant and then oxidized in leaves. The ethylene produced causes nastic movements (epinasty) of the leaves, perhaps helping the plant to lose water.
Ethylene in plant induces such responses:
Seedling triple response, thickening and shortening of hypocotyl with pronounced apical hook.
In pollination, when the pollen reaches the stigma, the precursor of the ethene, ACC, is secreted to the petal, the ACC releases ethylene with ACC oxidase.
Stimulates leaf and flower senescence
Stimulates senescence of mature xylem cells in preparation for plant use
Induces leaf abscission
Induces seed germination
Induces root hair growth — increasing the efficiency of water and mineral absorption through rhizosheath formation
Induces the growth of adventitious roots during flooding
Stimulates survival under low-oxygen conditions (hypoxia) in submerged plant tissues
Stimulates epinasty — leaf petiole grows out, leaf hangs down and curls into itself
Stimulates fruit ripening
Induces a climacteric rise in respiration in some fruit which causes a release of additional ethylene.
Affects gravitropism
Inhibits root growth in response to soil compaction, shade and flooding
Stimulates nutational bending
Inhibits stem growth and stimulates stem and cell broadening and lateral branch growth outside of seedling stage (see Hyponastic response)
Interference with auxin transport (with high auxin concentrations)
Inhibits shoot growth and stomatal closing except in some water plants or habitually flooded ones such as some rice varieties, where the opposite occurs (conserving and )
Induces flowering in pineapples
Inhibits short day induced flower initiation in Pharbitus nil and Chrysanthemum morifolium
Small amounts of endogenous ethylene are also produced in mammals, including humans, due to lipid peroxidation. Some of endogenous ethylene is then oxidized to ethylene oxide, which is able to alkylate DNA and proteins, including hemoglobin (forming a specific adduct with its N-terminal valine, N-hydroxyethyl-valine). Endogenous ethylene oxide, just as like environmental (exogenous) one, can alkylate guanine in DNA, forming an adduct 7-(2-hydroxyethyl)-guanine, and this poses an intrinsic carcinogenic risk. It is also mutagenic.
See also
Gas sensor protein (Gasoreceptor)
References
External links
Biochemistry
Molecular biology
Molecules
Signal transduction | Gaseous signaling molecules | Physics,Chemistry,Biology | 4,219 |
32,566,545 | https://en.wikipedia.org/wiki/Converged%20network%20adapter | A converged network adapter (CNA), also called a converged network interface controller (C-NIC), is a computer input/output device that combines the functionality of a host bus adapter (HBA) with a network interface controller (NIC). In other words, it "converges" access to, respectively, a storage area network and a general-purpose computer network.
Support
Some products were marketed around 2005 with the term C-NIC which combined iSCSI storage functionality with Gigabit Ethernet.
Later products used the marketing term converged network adapter (CNA), combining Fibre Channel over Ethernet with 10 Gigabit Ethernet, for example.
Brocade
Brocade Communications Systems offers two types of CNAs, with PCI Express generation 2.0 interfaces. The only difference between the two models are the number of interfaces on the cards: one or two. The two port model will allow connection to two different switches to create a redundant configuration without having to use two PCI slots.
Broadcom
In 2009 Broadcom entered the CNA market. Broadcom offers their CNAs under their own brand name but also sell the application-specific integrated circuits and other related components to others. Their intended customers are the larger builders of server systems such as Dell and HP. These vendors can then include the ten Gigabit CNA with their servers: as embedded interface on the motherboard (LOM or LAN on motherboard), via a mezzanine card in blade servers or as PCI extension-card.
Emulex
Emulex offers CNAs under the Emulex brand name as the OneConnect ten Gigabit series of dual port optical and copper adapters. They also OEM their adapters for Cisco, Dell, EMC, Fujitsu, HDS, HP, IBM and NetApp.
QLogic
QLogic offers CNAs via their QLogic 8200 & 8300 series Converged Network Adapters. They offer single and dual port PCI cards with copper or optical fibre interfaces. QLogic CNAs are available under the QLogic brandname and as OEM cards. The QME CNA and drivers were supported by Citrix, NetApp, EMC and IBM.
Hewlett-Packard
HP claims that their BL460c G7 was the first blade server that offers FCoE via a LOM (LAN on motherboard) instead of using a PCI slot or mezzanine card.
Dell
Dell uses the QLogic 8100 series in their PowerEdge servers. For the M-series, blade-servers for the M1000e use the custom made dual-port mezzanine card QME8142. For the normal tower and rack servers Dell offers an OEM version of the standard QME8152.
Cisco
Cisco Systems offered Fibre Channel over Ethernet in their Unified Computing System product line via Virtual Interface Cards (VICs). These cards make it possible to create multiple virtual HBAs or NICs within each physical VIC.
Intel
Intel demonstrates how the term Converged Network Adapter is really a marketing term, as they sell the X710-DA2/DA4 adapters that don't actually support FCoE.
References
Fibre Channel
Networking hardware
Ethernet
Computer storage buses | Converged network adapter | Engineering | 665 |
40,621,922 | https://en.wikipedia.org/wiki/Cantharellus%20zangii | Cantharellus zangii is a species of fungus in the family Cantharellaceae. Described as new to science in 2012, it is found only in a small area in northwestern Yunnan, China. The fungus produces small, ochre to ochre-yellow fruit bodies (mushrooms) with thin flesh and a long tapering stipe. Microscopically, the mushroom features thin-walled hyphae with clamp connections, and large ellipsoid-shaped spores.
Taxonomy
Cantharellus zangii was described in 2012 in the scientific journal Mycotaxon by Xiao-Fei Tian and colleagues. The type collection was made in August 2008 in the Bitahai National Natural Reserve, located in Shangri-La County, Yunnan, China. The authors classify the fungus in Parvocantharellus, a subgenus of Craterellus that was originally proposed by Guillaume Eyssartier and Bart Buyck in 2001. The specific epithet zangii honors Chinese mycologist Zang Mu, founder of the Cryptogamic Herbarium in the Kunming Institute of Botany.
Description
Fruit bodies have caps ranging in shape from umbonate to flat to slightly concave, reaching a diameter of . The cap is smooth with an ochre to yellow colour. Initially curved inward, the cap margin eventually straightens in maturity. The golden-colored gills, which have a decurrent attachment to the stipe, are up to 2 mm high with a 1–2 mm spacing between them. They are connected by transverse cross-veins. There are short, branched gills near the cap edge. The dark orange-yellow to orange stipe measures long by 0.3–0.4 cm thick. It is hollow and sometimes slightly curved. The thin flesh has a mild taste and an odor similar to Osmanthus flowers.
Spores are ellipsoid, thin-walled, and hyaline (translucent), measuring 8.5–11 by 5–6.5 μm. They sometimes have multiple tiny oil droplets. Basidia (spore-bearing cells) are slender and club-shaped, usually five-spored (sometimes six) with sterigmata 5–6 μm long, and dimensions of 75–85 by 6–9 μm. All hyphae have distinct clamp connections.
Similar species
Similar species include the European Cantharellus queletii, but this mushroom can be distinguished by its solid stipe and the lack of cross-veins between the gills. Another European species, Craterellus tubaeformis, has a horn-shaped fruit body with depressed caps, and grey or greyish-white gills.
Habitat and distribution
The fruit bodies of Cantharellus zangii grow on the ground singly or in groups in mixed forests. The predominant trees are Larix potaninii var. macrocarpa and Picea likiangensis. The species has been collected from only the type locality and from nearby locales in Shangri-La County (northwestern Yunnan). The habitat is subalpine, at elevations of about . The type locality, Bitahai National Natural Reserve, is a highly biodiverse area and has the highest elevation and highest latitude of all wetland reserves in Yunnan.
References
External links
zangii
Fungi described in 2012
Fungi of Asia
Fungus species | Cantharellus zangii | Biology | 678 |
31,404 | https://en.wikipedia.org/wiki/Tietze%20extension%20theorem | In topology, the Tietze extension theorem (also known as the Tietze–Urysohn–Brouwer extension theorem or Urysohn-Brouwer lemma) states that any real-valued, continuous function on a closed subset of a normal topological space can be extended to the entire space, preserving boundedness if necessary.
Formal statement
If is a normal space and
is a continuous map from a closed subset of into the real numbers carrying the standard topology, then there exists a of to that is, there exists a map
continuous on all of with for all Moreover, may be chosen such that
that is, if is bounded then may be chosen to be bounded (with the same bound as ).
Proof
The function is constructed iteratively. Firstly, we define
Observe that and are closed and disjoint subsets of . By taking a linear combination of the function obtained from the proof of Urysohn's lemma, there exists a continuous function such that
and furthermore
on . In particular, it follows that
on . We now use induction to construct a sequence of continuous functions such that
We've shown that this holds for and assume that have been constructed. Define
and repeat the above argument replacing with and replacing with . Then we find that there exists a continuous function such that
By the inductive hypothesis, hence we obtain the required identities and the induction is complete. Now, we define a continuous function as
Given ,
Therefore, the sequence is Cauchy. Since the space of continuous functions on together with the sup norm is a complete metric space, it follows that there exists a continuous function such that converges uniformly to . Since
on , it follows that on . Finally, we observe that
hence is bounded and has the same bound as .
History
L. E. J. Brouwer and Henri Lebesgue proved a special case of the theorem, when is a finite-dimensional real vector space. Heinrich Tietze extended it to all metric spaces, and Pavel Urysohn proved the theorem as stated here, for normal topological spaces.
Equivalent statements
This theorem is equivalent to Urysohn's lemma (which is also equivalent to the normality of the space) and is widely applicable, since all metric spaces and all compact Hausdorff spaces are normal. It can be generalized by replacing with for some indexing set any retract of or any normal absolute retract whatsoever.
Variations
If is a metric space, a non-empty subset of and is a Lipschitz continuous function with Lipschitz constant then can be extended to a Lipschitz continuous function with same constant
This theorem is also valid for Hölder continuous functions, that is, if is Hölder continuous function with constant less than or equal to then can be extended to a Hölder continuous function with the same constant.
Another variant (in fact, generalization) of Tietze's theorem is due to H.Tong and Z. Ercan:
Let be a closed subset of a normal topological space If is an upper semicontinuous function, a lower semicontinuous function, and a continuous function such that for each and for each , then there is a continuous
extension of such that for each
This theorem is also valid with some additional hypothesis if is replaced by a general locally solid Riesz space.
Dugundji (1951) extends the theorem as follows: If is a metric space, is a locally convex topological vector space, is a closed subset of and is continuous, then it could be extended to a continuous function defined on all of . Moreover, the extension could be chosen such that
See also
References
External links
Weisstein, Eric W. "Tietze's Extension Theorem." From MathWorld
Mizar system proof: http://mizar.org/version/current/html/tietze.html#T23
.
Theory of continuous functions
Theorems in topology | Tietze extension theorem | Mathematics | 790 |
24,008,469 | https://en.wikipedia.org/wiki/Eudysmic%20ratio | The eudysmic ratio (also spelled eudismic ratio) represents the difference in pharmacologic activity between the two enantiomers of a drug. In most cases where a chiral compound is biologically active, one enantiomer is more active than the other. The eudysmic ratio is the ratio of activity between the two. A eudysmic ratio significantly differing from 1 means that they are statistically different in activity. Eudisimic ratio (ER) reflects the degree of enantioselectivity of the biological systems. For example, (S)-propranolol (ER = 130) meaning that (S)-propranolol is 130 times more active than its (R)-enantiomer.
Terminology
The eutomer is the enantiomer having the desired pharmacological activity, e.g., as an active ingredient in a drug.
The distomer, on the other hand, is the enantiomer of the eutomer which may have undesired bioactivity or may be bio-inert.
A racemic mixture is an equal mixture of both enantiomers, which may be easier to manufacture than a single enantiomeric form.
It is often the case that only a single one of the enantiomers contains all of the wanted bioactivity, the distomer is often less active, has no desired activity or may even be toxic. In some cases, the eudysmic ratio is so high, that it is desired to separate out the two enantiomers instead of leaving it as a racemic product. It is also possible that the distomer is not simply completely inactive but actually antagonizes the effects of the eutomer. There are a few examples of chiral drugs where both the enantiomers contribute, in different ways, to the overall desired effect. An interesting situation is that in which the distomer antagonizes a side-effect of the eutomer for the desired action, mutually beneficial action form therapeutic standpoint. This is convincingly demonstrated by the diuretic indacrinone.
The (R)-(+)-isomer, the eutomer, is responsible for the diuretic action and undesired uric acid retention, a side-effect common to many diuretics. The (S)-(-)-isomer, the distomer, acts as a uricosuric agent and thus antagonizes the side-effect caused by the (R)-isomer. A superficial examination of these facts might suggest the marketing of this product as a racemate (1:1 mixture of both enantiomers) to be desirable, since both enantiomers are complementing each other, but for optimal action, the ideal eutomer to distomer ratio for indacrinone has been determined to be 9:1. This is a classical case of a non-racemic drug. Alternatively, it is possible that in the body the distomer converts, at least in part, into the eutomer.
Calculation
One way the eudysmic ratio is computed is by dividing the EC50 or the IC50 of the eutomer by the same measurement of the distomer. Whether one chooses to use the EC50 or IC50 depends on the drug in question.
Examples
Citalopram: steps were taken to separate the more potent enantiomer, escitalopram.
Thalidomide is a drug whose two enantiomers cause distinctly different effects from one another. The unforeseen teratogenicity of the (R)-(+)-isomer caused it to become an important case study of stereochemistry in medicine. Although it is possible to chemically isolate just the desired (S)-(−)-isomer from the racemic mixture, the two enantiomers rapidly interconvert in vivo; thus rendering their separation to be of little use.
Methorphan is another drug whose two enantiomers possess very different binding profiles, with the L enantiomer being a potent opioid analgesic, and the D enantiomer being a commonly used over-the-counter cough suppressant which acts as an NMDA-antagonist but possesses nearly no opioid activity. In the case of morphinan, the eudysmic ratio is preserved after metabolism as the D and L metabolites possess the same pharmacological targets as the corresponding methorphan enantiomers, but are considerably more potent than their parent compounds.
Amino acids are also an example of eudysmic ratio. Nearly all of the amino acids in the human body are called "L" amino acids; despite being chiral, the body almost exclusively creates and uses amino acids in this one configuration. D amino acids, the enantiomers — or "mirror images" — of the amino acids in the human body cannot be incorporated into proteins. D-aspartate and D-serine are two notable counterexamples, since they do not appear to ever be incorporated into proteins, but instead act individually as signalling molecules. However, mammals can metabolize significant amount of D amino acids by oxidizing them to alpha-ketoacids (most of which are non-chiral) and then transaminases can create L amino acids. There are no reasons to believe that humans are exceptional, they have all required enzymes (DDO, DAO). Some common foods contain near-racemic mixtures of amino acids.
See also
Enantiopure drug
References
Pharmacodynamics
Stereochemistry | Eudysmic ratio | Physics,Chemistry | 1,188 |
51,564,601 | https://en.wikipedia.org/wiki/Microbial%20synergy | Microbial synergy is a phenomenon in which aerobic and anaerobic microbes support each other's growth and proliferation. In this process aerobes invade and destroy host tissues, reduce tissue oxygen concentration and redox potential, thus creating favorable conditions for anaerobic growth and proliferation. Anaerobes grow and produce short chain fatty acids such as butyric acid, propionic acid. These short chain fatty acids inhibit phagocytosis of aerobes. Thus aerobes grow, proliferate and destroy more tissues. Microbial synergy complicates and delays the healing of surgical and other chronic wounds or ulcers such as diabetic foot ulcers, venous ulcers, pressure ulcers etc. Microbial synergy also helps with eliminating oxygen redox. This allows the growth of organisms without the effects of oxygen reacting negatively. As a result, Microbial growth increases because other organisms can grow in the absence of Oxygen redox.
References
Rotstein, O. D., T. L. Pruett, and R. L. Simmons. "Mechanisms of Microbial Synergy in Polymicrobial Surgical Infections." Reviews of Infectious Diseases. U.S. National Library of Medicine, n.d. Web. 19 Apr. 2017.
Microbial growth and nutrition
Microbiology | Microbial synergy | Chemistry,Biology | 272 |
27,340,479 | https://en.wikipedia.org/wiki/Red%20Hat%20Virtualization | Red Hat Virtualization (RHV) formerly known as Red Hat Enterprise Virtualization, is an x86 virtualization product developed by Red Hat, and is based on the KVM hypervisor. Red Hat Virtualization uses the SPICE protocol and VDSM (Virtual Desktop Server Manager) with a RHEL-based centralized management server. The platform can access user and group information from either an Active Directory or FreeIPA domain which enables it to allocate resources effectively based on permissions. Built for use in enterprise datacenters, RHV can support up to 400 hosts in a single cluster and no upper limit on the total number of hosts it can support. Development of RHV has ceased and as of August 2020 the product is now only receiving maintenance updates, with extended life phase updates provided until 2026. The successor to RHV is Red Hat's OpenShift container platform.
References
External links
Red Hat software
Virtualization
Virtualization software for Linux | Red Hat Virtualization | Engineering | 200 |
52,719,386 | https://en.wikipedia.org/wiki/Testosterone%20acetate%20butyrate | Testosterone acetate butyrate, or testosterone 3β-acetate 17β-butanoate, also known as 4-androstenediol acetate butyrate, as well as androst-4-ene-3β,17β-diol 3β-acetate 17β-butanoate, is a synthetic anabolic-androgenic steroid and an androgen ester which was never marketed. It is the 3β-acetate, 17β-butyrate (butanoate) diester of testosterone (androst-4-en-17β-ol-3-one), or, more accurately, of 4-androstenediol (androst-4-ene-3β,17β-diol).
See also
Testosterone acetate propionate
Testosterone diacetate
Testosterone dipropionate
Bolandiol dipropionate
Methandriol bisenanthoyl acetate
Methandriol diacetate
Methandriol dipropionate
References
Abandoned drugs
Acetate esters
Anabolic–androgenic steroids
Androstanes
Butyrate esters
Testosterone esters | Testosterone acetate butyrate | Chemistry | 246 |
34,382,650 | https://en.wikipedia.org/wiki/Sarah%20Salmond | Sarah Salmond (7 August 1864 – 18 October 1956 in Dunedin, New Zealand) was a notable New Zealand governess and astronomer.
Early life
Salmond was born in Abbey St Bathans, Berwickshire, Scotland, the youngest of seven children of John Cockburn and Elizabeth Cockburn née Liddle. Cockburn was a farm labourer, and the family emigrated to New Zealand to escape poverty. They arrived in Dunedin on 4 January 1873 aboard the Zealandia. Eldest son George had emigrated earlier and was farming in Cromwell, where they joined him initially, but within a year the Cockburns had moved thirty miles to Queenstown. Salmond was nine when the family arrived in Queenstown, and her two years of schooling at the local school there were her only formal education. Her schooling was cut short to run the house due to her mother's frequent absence as a local midwife.
Interest in Astronomy
In 1874, at age 10 years, Sarah Cockburn (who would become Sarah Salmond upon her marriage) had a passion for astronomy, and was present in Queenstown during a visit by a United States Naval Observatory expedition to observe the transit of Venus. The expedition, headed by CHF Peters, resulted in a number of photographs of the event. Peters presented a "stirring public lecture" but it is not known if Salmond attended.
At the age of 15, Salmond became the first female settler in the Rees River Valley area, as she took up housekeeping duties for her brothers George and David, who had decided to establish a farm there. The farm was remote and the clear skies allowed for good observations. George Salmond was an enthusiastic sky-watcher, and his sister joined him in his hobby. It seems Salmond did not leave any written records of her interest.
At the age of around 18, Salmond became governess to three children on a sheep station. In Queenstown to fetch supplies, Salmond met John Salmond, from Torpichen, West Lothian, and the two were married in 1886, and had eight children together. Three of her children were leading figures in the New Zealand Presbyterian church.
As an adult Salmond campaigned for a memorial to this event, which was finally unveiled in 1953, when at age 88 she unveiled the plaque reading "From this site a transit of the planet Venus across the solar disc was observed on 1874 December 9 by an American scientific expedition which came to Otago in the ship "Swatara""Salmond died in 1856 in Ross Home in Dunedin. During her final illness she read both the Bible and a religious astronomical text The Heavens Declare by Hector Carsewell MacPherson. Her son, James David Salmond included some of her reminiscences in his book Hearts of Gold, published in 1961.
References
1864 births
1956 deaths
20th-century New Zealand astronomers
Women astronomers
Scottish emigrants to New Zealand
People from Berwickshire
19th-century New Zealand astronomers
Immigrants to former British colonies and protectorates in Oceania | Sarah Salmond | Astronomy | 602 |
3,117,887 | https://en.wikipedia.org/wiki/Grassmann%20number | In mathematical physics, a Grassmann number, named after Hermann Grassmann (also called an anticommuting number or supernumber), is an element of the exterior algebra of a complex vector space. The special case of a 1-dimensional algebra is known as a dual number. Grassmann numbers saw an early use in physics to express a path integral representation for fermionic fields, although they are now widely used as a foundation for superspace, on which supersymmetry is constructed.
Informal discussion
Grassmann numbers are generated by anti-commuting elements or objects. The idea of anti-commuting objects arises in multiple areas of mathematics: they are typically seen in differential geometry, where the differential forms are anti-commuting. Differential forms are normally defined in terms of derivatives on a manifold; however, one can contemplate the situation where one "forgets" or "ignores" the existence of any underlying manifold, and "forgets" or "ignores" that the forms were defined as derivatives, and instead, simply contemplate a situation where one has objects that anti-commute, and have no other pre-defined or presupposed properties. Such objects form an algebra, and specifically the Grassmann algebra or exterior algebra.
The Grassmann numbers are elements of that algebra. The appellation of "number" is justified by the fact that they behave not unlike "ordinary" numbers: they can be added, multiplied and divided: they behave almost like a field. More can be done: one can consider polynomials of Grassmann numbers, leading to the idea of holomorphic functions. One can take derivatives of such functions, and then consider the anti-derivatives as well. Each of these ideas can be carefully defined, and correspond reasonably well to the equivalent concepts from ordinary mathematics. The analogy does not stop there: one has an entire branch of supermathematics, where the analog of Euclidean space is superspace, the analog of a manifold is a supermanifold, the analog of a Lie algebra is a Lie superalgebra and so on. The Grassmann numbers are the underlying construct that make this all possible.
Of course, one could pursue a similar program for any other field, or even ring, and this is indeed widely and commonly done in mathematics. However, supermathematics takes on a special significance in physics, because the anti-commuting behavior can be strongly identified with the quantum-mechanical behavior of fermions: the anti-commutation is that of the Pauli exclusion principle. Thus, the study of Grassmann numbers, and of supermathematics, in general, is strongly driven by their utility in physics.
Specifically, in quantum field theory, or more narrowly, second quantization, one works with ladder operators that create multi-particle quantum states. The ladder operators for fermions create field quanta that must necessarily have anti-symmetric wave functions, as this is forced by the Pauli exclusion principle. In this situation, a Grassmann number corresponds immediately and directly to a wave function that contains some (typically indeterminate) number of fermions.
When the number of fermions is fixed and finite, an explicit relationship between anticommutation relations and spinors is given by means of the spin group. This group can be defined as the subset of unit-length vectors in the Clifford algebra, and naturally factorizes into anti-commuting Weyl spinors. Both the anti-commutation and the expression as spinors arises in a natural fashion for the spin group. In essence, the Grassmann numbers can be thought of as discarding the relationships arising from spin, and keeping only the relationships due to anti-commutation.
General description and properties
Grassmann numbers are individual elements or points of the exterior algebra generated by a set of Grassmann variables or Grassmann directions or supercharges , with possibly being infinite. The usage of the term "Grassmann variables" is historic; they are not variables, per se; they are better understood as the basis elements of a unital algebra. The terminology comes from the fact that a primary use is to define integrals, and that the variable of integration is Grassmann-valued, and thus, by abuse of language, is called a Grassmann variable. Similarly, the notion of direction comes from the notion of superspace, where ordinary Euclidean space is extended with additional Grassmann-valued "directions". The appellation of charge comes from the notion of charges in physics, which correspond to the generators of physical symmetries (via Noether's theorem). The perceived symmetry is that multiplication by a single Grassmann variable swaps the grading between fermions and bosons; this is discussed in greater detail below.
The Grassmann variables are the basis vectors of a vector space (of dimension ). They form an algebra over a field, with the field usually being taken to be the complex numbers, although one could contemplate other fields, such as the reals. The algebra is a unital algebra, and the generators are anti-commuting:
Since the are elements of a vector space over the complex numbers, they, by definition, commute with complex numbers. That is, for complex , one has
The squares of the generators vanish:
since
In other words, a Grassmann variable is a non-zero square-root of zero.
Formal definition
Formally, let be an -dimensional complex vector space with basis . The Grassmann algebra whose Grassmann variables are is defined to be the exterior algebra of , namely
where is the exterior product and is the direct sum. The individual elements of this algebra are then called Grassmann numbers. It is standard to omit the wedge symbol when writing a Grassmann number once the definition is established. A general Grassmann number can be written as
where are strictly increasing -tuples with , and the are complex, completely antisymmetric tensors of rank . Again, the , and the (subject to ), and larger finite products, can be seen here to be playing the role of a basis vectors of subspaces of .
The Grassmann algebra generated by linearly independent Grassmann variables has dimension ; this follows from the binomial theorem applied to the above sum, and the fact that the -fold product of variables must vanish, by the anti-commutation relations above. The dimension of is given by choose , the binomial coefficient. The special case of is called a dual number, and was introduced by William Clifford in 1873.
In case is infinite-dimensional, the above series does not terminate and one defines
The general element is now
where is sometimes referred to as the body and as the soul of the supernumber .
Properties
In the finite-dimensional case (using the same terminology) the soul is nilpotent, i.e.
but this is not necessarily so in the infinite-dimensional case.
If is finite-dimensional, then
and if is infinite-dimensional
Finite vs. countable sets of generators
Two distinct kinds of supernumbers commonly appear in the literature: those with a finite number of generators, typically = 1, 2, 3 or 4, and those with a countably-infinite number of generators. These two situations are not as unrelated as they may seem at first. First, in the definition of a supermanifold, one variant uses a countably-infinite number of generators, but then employs a topology that effectively reduces the dimension to a small finite number.
In the other case, one may start with a finite number of generators, but in the course of second quantization, a need for an infinite number of generators arises: one each for every possible momentum that a fermion might carry.
Involution, choice of field
The complex numbers are usually chosen as the field for the definition of the Grassmann numbers, as opposed to the real numbers, as this avoids some strange behaviors when a conjugation or involution is introduced. It is common to introduce an operator * on the Grassmann numbers such that:
when is a generator, and such that
One may then consider Grassmann numbers z for which , and term these (super) real, while those that obey are termed (super) imaginary. These definitions carry through just fine, even if the Grassmann numbers use the real numbers as the base field; however, in such a case, many coefficients are forced to vanish if the number of generators is less than 4. Thus, by convention, the Grassmann numbers are usually defined over the complex numbers.
Other conventions are possible; the above is sometimes referred to as the DeWitt convention; Rogers employs for the involution. In this convention, the real supernumbers always have real coefficients; whereas in the DeWitt convention, the real supernumbers may have both real and imaginary coefficients. Despite this, it is usually easiest to work with the DeWitt convention.
Analysis
Products of an odd number of Grassmann variables anti-commute with each other; such a product is often called an a-number. Products of an even number of Grassmann variables commute (with all Grassman numbers); they are often called c-numbers. By abuse of terminology, an a-number is sometimes called an anticommuting c-number. This decomposition into even and odd subspaces provides a grading on the algebra; thus Grassmann algebras are the prototypical examples of supercommutative algebras. Note that the c-numbers form a subalgebra of , but the a-numbers do not (they are a subspace, not a subalgebra).
The definition of Grassmann numbers allows mathematical analysis to be performed, in analogy to analysis on complex numbers. That is, one may define superholomorphic functions, define derivatives, as well as defining integrals. Some of the basic concepts are developed in greater detail in the article on dual numbers.
As a general rule, it is usually easier to define the super-symmetric analogs of ordinary mathematical entities by working with Grassmann numbers with an infinite number of generators: most definitions become straightforward, and can be taken over from the corresponding bosonic definitions. For example, a single Grassmann number can be thought of as generating a one-dimensional space. A vector space, the -dimensional superspace, then appears as the -fold Cartesian product of these one-dimensional It can be shown that this is essentially equivalent to an algebra with generators, but this requires work.
Spinor space
The spinor space is defined as the Grassmann or exterior algebra of the space of Weyl spinors (and anti-spinors ), such that the wave functions of n fermions belong in .
Integration
Integrals over Grassmann numbers are known as Berezin integrals (sometimes called Grassmann integrals). In order to reproduce the path integral for a Fermi field, the definition of Grassmann integration needs to have the following properties:
linearity
partial integration formula
Moreover, the Taylor expansion of any function terminates after two terms because , and quantum field theory additionally require invariance under the shift of integration variables such that
The only linear function satisfying this condition is a constant (conventionally 1) times , so Berezin defined
This results in the following rules for the integration of a Grassmann quantity:
Thus we conclude that the operations of integration and differentiation of a Grassmann number are identical.
In the path integral formulation of quantum field theory the following Gaussian integral of Grassmann quantities is needed for fermionic anticommuting fields, with A being an N × N matrix:
.
Conventions and complex integration
An ambiguity arises when integrating over multiple Grassmann numbers. The convention that performs the innermost integral first yields
Some authors also define complex conjugation similar to Hermitian conjugation of operators,
With the additional convention
we can treat and as independent Grassmann numbers, and adopt
Thus a Gaussian integral evaluates to
and an extra factor of effectively introduces a factor of , just like an ordinary Gaussian,
After proving unitarity, we can evaluate a general Gaussian integral involving a Hermitian matrix with eigenvalues ,
Matrix representations
Grassmann numbers can be represented by matrices. Consider, for example, the Grassmann algebra generated by two Grassmann numbers and . These Grassmann numbers can be represented by 4×4 matrices:
In general, a Grassmann algebra on n generators can be represented by 2n × 2n square matrices. Physically, these matrices can be thought of as raising operators acting on a Hilbert space of n identical fermions in the occupation number basis. Since the occupation number for each fermion is 0 or 1, there are 2n possible basis states. Mathematically, these matrices can be interpreted as the linear operators corresponding to left exterior multiplication on the Grassmann algebra itself.
Generalisations
There are some generalisations to Grassmann numbers. These require rules in terms of N variables such that:
where the indices are summed over all permutations so that as a consequence:
for some N > 2. These are useful for calculating hyperdeterminants of N-tensors where N > 2 and also for calculating discriminants of polynomials for powers larger than 2. There is also the limiting case as N tends to infinity in which case one can define analytic functions on the numbers. For example, in the case with N = 3 a single Grassmann number can be represented by the matrix:
so that . For two Grassmann numbers the matrix would be of size 10×10.
For example, the rules for N = 3 with two Grassmann variables imply:
so that it can be shown that
and so
which gives a definition for the hyperdeterminant of a 2×2×2 tensor as
See also
Grassmannian
Hermann Grassmann (linguist and mathematician)
Superspace
Exterior algebra
Notes
References
Hypercomplex numbers
Supersymmetry
Quantum field theory | Grassmann number | Physics,Mathematics | 2,846 |
5,364,886 | https://en.wikipedia.org/wiki/Kolliphor%20EL | Kolliphor EL, formerly known as Cremophor EL, is the registered trademark of BASF Corp. for its version of polyethoxylated castor oil. It is prepared by reacting 35 moles of ethylene oxide with each mole of castor oil. The resulting product is a mixture (CAS number 61791-12-6): the major component is the material in which the hydroxyl groups of the castor oil triglyceride have been ethoxylated with ethylene oxide to form polyethylene glycol ethers. Minor components are the polyethyelene glycol esters of ricinoleic acid, polyethylene glycols and polyethylene glycol ethers of glycerol. Kolliphor EL is a synthetic, nonionic surfactant used to stabilize emulsions of nonpolar materials in water.
Kolliphor EL is an excipient or additive in drugs. Therapeutically, modern drugs are rarely given in a pure chemical state, so most active ingredients are combined with excipients or additives such as Kolliphor EL.
Uses
Miconazole, anti-fungal
Paclitaxel (Taxol), anti-cancer
Aci-Jel (acetic acid / oxyquinoline / ricinoleic acid - vaginal)
Sandimmune (cyclosporine injection, USP)
Nelfinavir mesylate, HIV protease inhibitor
Propofol, intravenous anaesthetic agent, originally solublized with Cremophor EL in trials; later approved with a lipid emulsion
Diazepam injection; superseded by lipid emulsion alternative (Diazemuls)
Vitamin K injection
Ixabepilone, anti-cancer
Side effects
Allergic reactions to Taxol are most often allergic reactions to Kolliphor EL; symptoms include tightness in the chest, shortness of breath, and similar reactions consistent with severe anaphylactic reactions. Although many anti-allergens including corticosteroids and Benadryl may be administered before chemotherapy, they are not always sufficient to prevent the severe reaction to Kolliphor EL.
Allergic reaction should not be confused with the normal side effects of Taxol. The allergic reaction is usually immediate, similar to severe allergic reactions typical of other allergens.
BASF offers a purified, injectable version of Kolliphor EL, known as Kolliphor ELP.
See also
Castor oil
References
Excipients | Kolliphor EL | Chemistry | 539 |
40,428,588 | https://en.wikipedia.org/wiki/Dynamical%20pictures | In quantum mechanics, dynamical pictures (or representations) are the multiple equivalent ways to mathematically formulate the dynamics of a quantum system.
The two most important ones are the Heisenberg picture and the Schrödinger picture. These differ only by a basis change with respect to time-dependency, analogous to the Lagrangian and Eulerian specification of the flow field: in short, time dependence is attached to quantum states in the Schrödinger picture and to operators in the Heisenberg picture.
There is also an intermediate formulation known as the interaction picture (or Dirac picture) which is useful for doing computations when a complicated Hamiltonian has a natural decomposition into a simple "free" Hamiltonian and a perturbation.
Equations that apply in one picture do not necessarily hold in the others, because time-dependent unitary transformations relate operators in one picture to the analogous operators in the others. Not all textbooks and articles make explicit which picture each operator comes from, which can lead to confusion.
Schrödinger picture
Background
In elementary quantum mechanics, the state of a quantum-mechanical system is represented by a complex-valued wavefunction . More abstractly, the state may be represented as a state vector, or ket, |ψ⟩. This ket is an element of a Hilbert space, a vector space containing all possible states of the system. A quantum-mechanical operator is a function which takes a ket |ψ⟩ and returns some other ket |ψ′⟩.
The differences between the Schrödinger and Heiseinberg pictures of quantum mechanics revolve around how to deal with systems that evolve in time: the time-dependent nature of the system must be carried by some combination of the state vectors and the operators. For example, a quantum harmonic oscillator may be in a state |ψ⟩ for which the expectation value of the momentum, , oscillates sinusoidally in time. One can then ask whether this sinusoidal oscillation should be reflected in the state vector |ψ⟩, the momentum operator , or both. All three of these choices are valid; the first gives the Schrödinger picture, the second the Heisenberg picture, and the third the interaction picture.
The Schrödinger picture is useful when dealing with a time-independent Hamiltonian , that is, .
The time evolution operator
Definition
The time-evolution operator U(t, t0) is defined as the operator which acts on the ket at time t0 to produce the ket at some other time t:
For bras, we instead have
Properties
Unitarity
The time evolution operator must be unitary. This is because we demand that the norm of the state ket must not change with time. That is,
Therefore,
Identity
When t = t0, U is the identity operator, since
Closure
Time evolution from t0 to t may be viewed as a two-step time evolution, first from t0 to an intermediate time t1, and then from t1 to the final time t. Therefore,
Differential equation for time evolution operator
We drop the t0 index in the time evolution operator with the convention that and write it as U(t). The Schrödinger equation is
where H is the Hamiltonian. Now using the time-evolution operator U to write , we have
Since is a constant ket (the state ket at ), and since the above equation is true for any constant ket in the Hilbert space, the time evolution operator must obey the equation
If the Hamiltonian is independent of time, the solution to the above equation is
Since H is an operator, this exponential expression is to be evaluated via its Taylor series:
Therefore,
Note that is an arbitrary ket. However, if the initial ket is an eigenstate of the Hamiltonian, with eigenvalue E, we get:
Thus we see that the eigenstates of the Hamiltonian are stationary states: they only pick up an overall phase factor as they evolve with time.
If the Hamiltonian is dependent on time, but the Hamiltonians at different times commute, then the time evolution operator can be written as
If the Hamiltonian is dependent on time, but the Hamiltonians at different times do not commute, then the time evolution operator can be written as
where T is time-ordering operator, which is sometimes known as the Dyson series, after Freeman Dyson.
The alternative to the Schrödinger picture is to switch to a rotating reference frame, which is itself being rotated by the propagator. Since the undulatory rotation is now being assumed by the reference frame itself, an undisturbed state function appears to be truly static. This is the Heisenberg picture (below).
Heisenberg picture
The Heisenberg picture is a formulation (made by Werner Heisenberg while on Heligoland in the 1920s) of quantum mechanics in which the operators (observables and others) incorporate a dependency on time, but the state vectors are time-independent.
Definition
In the Heisenberg picture of quantum mechanics the state vector, , does not change with time, and an observable A satisfies
where H is the Hamiltonian and [•,•] denotes the commutator of two operators (in this case H and A). Taking expectation values yields the Ehrenfest theorem featured in the correspondence principle.
By the Stone–von Neumann theorem, the Heisenberg picture and the Schrödinger picture are unitarily equivalent. In some sense, the Heisenberg picture is more natural and convenient than the equivalent Schrödinger picture, especially for relativistic theories. Lorentz invariance is manifest in the Heisenberg picture. This approach also has a more direct similarity to classical physics: by replacing the commutator above by the Poisson bracket, the Heisenberg equation becomes an equation in Hamiltonian mechanics.
Derivation of Heisenberg's equation
The expectation value of an observable A, which is a Hermitian linear operator for a given state , is given by
In the Schrödinger picture, the state at time t is related to the state at time 0 by a unitary time-evolution operator, :
If the Hamiltonian does not vary with time, then the time-evolution operator can be written as
where H is the Hamiltonian and ħ is the reduced Planck constant. Therefore,
Define, then,
It follows that
Differentiation was according to the product rule, while ∂A/∂t
is the time derivative of the initial A, not the A(t) operator defined. The last equation holds since exp(−iHt/ħ) commutes with H.
Thus
whence the above Heisenberg equation of motion emerges, since the convective functional dependence on x(0) and p(0) converts to the same dependence on x(t), p(t), so that the last term converts to ∂A(t)/∂t . [X, Y] is the commutator of two operators and is defined as .
The equation is solved by the A(t) defined above, as evident by use of the standard operator identity,
which implies
This relation also holds for classical mechanics, the classical limit of the above, given the correspondence between Poisson brackets and commutators,
In classical mechanics, for an A with no explicit time dependence,
so, again, the expression for A(t) is the Taylor expansion around t = 0.
Commutator relations
Commutator relations may look different from in the Schrödinger picture, because of the time dependence of operators. For example, consider the operators and . The time evolution of those operators depends on the Hamiltonian of the system. Considering the one-dimensional harmonic oscillator,
,
the evolution of the position and momentum operators is given by:
,
.
Differentiating both equations once more and solving for them with proper initial conditions,
leads to
,
.
Direct computation yields the more general commutator relations,
,
,
.
For , one simply recovers the standard canonical commutation relations valid in all pictures.
Interaction picture
The interaction Picture is most useful when the evolution of the observables can be solved exactly, confining any complications to the evolution of the states. For this reason, the Hamiltonian for the observables is called "free Hamiltonian" and the Hamiltonian for the states is called "interaction Hamiltonian".
Definition
Operators and state vectors in the interaction picture are related by a change of basis (unitary transformation) to those same operators and state vectors in the Schrödinger picture.
To switch into the interaction picture, we divide the Schrödinger picture Hamiltonian into two parts,
Any possible choice of parts will yield a valid interaction picture; but in order for the interaction picture to be useful in simplifying the analysis of a problem, the parts will typically be chosen so that is well understood and exactly solvable, while contains some harder-to-analyze perturbation to this system.
If the Hamiltonian has explicit time-dependence (for example, if the quantum system interacts with an applied external electric field that varies in time), it will usually be advantageous to include the explicitly time-dependent terms with , leaving time-independent. We proceed assuming that this is the case. If there is a context in which it makes sense to have be time-dependent, then one can proceed by replacing by the corresponding time-evolution operator in the definitions below.
State vectors
A state vector in the interaction picture is defined as
where is the same state vector as in the Schrödinger picture.
Operators
An operator in the interaction picture is defined as
Note that will typically not depend on t, and can be rewritten as just . It only depends on t if the operator has "explicit time dependence", for example due to its dependence on an applied, external, time-varying electric field.
Hamiltonian operator
For the operator itself, the interaction picture and Schrödinger picture coincide,
This is easily seen through the fact that operators commute with differentiable functions of themselves. This particular operator then can be called H0 without ambiguity.
For the perturbation Hamiltonian H1,I, however,
where the interaction picture perturbation Hamiltonian becomes a time-dependent Hamiltonian—unless [H1,s, H0,s] = 0 .
It is possible to obtain the interaction picture for a time-dependent Hamiltonian H0,s(t) as well, but the exponentials need to be replaced by the unitary propagator for the evolution generated by H0,s(t), or more explicitly with a time-ordered exponential integral.
Density matrix
The density matrix can be shown to transform to the interaction picture in the same way as any other operator. In particular, let and be the density matrix in the interaction picture and the Schrödinger picture, respectively. If there is probability to be in the physical state , then
Time-evolution equations
States
Transforming the Schrödinger equation into the interaction picture gives:
This equation is referred to as the Schwinger–Tomonaga equation.
Operators
If the operator is time independent (i.e., does not have "explicit time dependence"; see above), then the corresponding time evolution for is given by:
In the interaction picture the operators evolve in time like the operators in the Heisenberg picture with
the Hamiltonian .
Density matrix
Transforming the Schwinger–Tomonaga equation into the language of the density matrix (or equivalently, transforming the von Neumann equation into the interaction picture) gives:
Existence
The interaction picture does not always exist. In interacting quantum field theories, Haag's theorem states that the interaction picture does not exist. This is because the Hamiltonian cannot be split into a free and an interacting part within a superselection sector. Moreover, even if in the Schrödinger picture the Hamiltonian does not depend on time, e.g. , in the interaction picture it does, at least, if does not commute with , since
.
Comparison of pictures
The Heisenberg picture is closest to classical Hamiltonian mechanics (for example, the commutators appearing in the above equations directly correspond to classical Poisson brackets).
The Schrödinger picture, the preferred formulation in introductory texts, is easy to visualize in terms of Hilbert space rotations of state vectors, although it lacks natural generalization to Lorentz invariant systems. The Dirac picture is most useful in nonstationary and covariant perturbation theory, so it is suited to quantum field theory and many-body physics.
Summary comparison of evolutions
Equivalence
It is evident that the expected values of all observables are the same in the Schrödinger, Heisenberg, and Interaction pictures,
as they must.
See also
Hamilton–Jacobi equation
Bra-ket notation
Notes
References
Albert Messiah, 1966. Quantum Mechanics (Vol. I), English translation from French by G. M. Temmer. North Holland, John Wiley & Sons.
Merzbacher E., Quantum Mechanics (3rd ed., John Wiley 1998) p. 430-1
Online copy
R. Shankar (1994); Principles of Quantum Mechanics, Plenum Press, .
J. J. Sakurai (1993); Modern Quantum Mechanics (Revised Edition), .
External links
Pedagogic Aides to Quantum Field Theory Click on the link for Chap. 2 to find an extensive, simplified introduction to the Heisenberg picture.
Quantum mechanics | Dynamical pictures | Physics | 2,784 |
25,193,231 | https://en.wikipedia.org/wiki/Benjamin%20Martin%20%28lexicographer%29 | Benjamin Martin (baptized 1705; died 1782) was a lexicographer who compiled one of the early English dictionaries, the Lingua Britannica Reformata (1749). He also was a lecturer on science and maker of scientific instruments.
Life
Martin was born in Worplesdon, Surrey and began life as a ploughboy, but graduated to become a teacher. A legacy of £500 enabled him to buy books and instruments, and he became a lecturer and instrument maker. He was an early champion for the Newtonian system. In 1737, he published the Bibliotheca Technologica - a survey of natural philosophy in 25 sub-headings.
In 1740, he moved to Fleet Street, near the Royal Society where his admired Newton would often lecture. He began manufacturing Hadley's quadrant (a predecessor to the sextant) and optical instruments, and also published a book A New and Compendious System of Optics, where he introduced to English the concept of fundamental science (from Neo-Latin scientia fundamentalis). His business prospered, and he also became known as a spectacle maker. He continued to lecture on natural philosophy, and from 1755 to 1764, he also published Martin's Magazine. The periodical, formally known as the General Magazine of Arts and Sciences, set out to provide subscribers with an encyclopedia's worth of knowledge "one Half-sheet upon a Science" at a time. He intended readers eventually to reorganize and rebind the separate parts of individual numbers into one large reference work. He was also the author of The Natural History of England, or, A description of each particular county, in regard to the curious productions of nature and art; 2 vols. London: Printed and sold by W. Owen, Temple-Bar, and by the author, at his house in Fleet-Street, 1759-63.
In 1781, the seventy-seven-year-old Martin went bankrupt; a few years earlier he had handed over his business to several managers who proved inept. He attempted suicide, and while it was not immediately successful, the wound (nature unknown) was grievous enough and he failed to recover, and died on 9 February 1782.
The Dictionary
In 1749, he published the Lingua Britannica Reformata, Or, A New English Dictionary. His dictionary incorporated a largely intact copy of Nathan Bailey's Universal Dictionary of 1721, which Benjamin Martin described as "the best English dictionary hitherto published". Bailey's dictionary in turn had copied heavily from the 1706 Phillips-Kersey English dictionary. A second edition of Martin's dictionary was published in 1754, a year before Samuel Johnson's dictionary.
In compiling his 24,500 word dictionary, he gave up on trying to "fix" the language:
The pretence of fixing a standard to the purity and perfection of any language is utterly vain and impertinent, because no language as depending on arbitrary use and custom, can ever be permanently the same, but will always be in a mutable and fluctuating state; and what is deem’d polite and elegant in one age, may be counted uncouth and barbarous in another.
This dynamic view of language was also adopted by Johnson and has become the accepted view in modern lexicography. His dictionary also pre-saged Johnson in that he laid out a detailed set of objectives (that it should be universal, explain the etymologies, etc.).
While his etymologies are often inconsistent and tended to err in favour of Latin origins, his work was an improvement on earlier dictionaries in that it had a simpler system of spelling and a clearer guide to pronunciation.
References
External links
1700s births
1782 deaths
18th-century English scientists
English lexicographers
Microscopists
English scientific instrument makers
18th-century lexicographers | Benjamin Martin (lexicographer) | Chemistry | 796 |
480,130 | https://en.wikipedia.org/wiki/Index%20of%20wave%20articles | This is a list of wave topics.
0–9
21 cm line
A
Abbe prism
Absorption spectroscopy
Absorption spectrum
Absorption wavemeter
Acoustic wave
Acoustic wave equation
Acoustics
Acousto-optic effect
Acousto-optic modulator
Acousto-optics
Airy disc
Airy wave theory
Alfvén wave
Alpha waves
Amphidromic point
Amplitude
Amplitude modulation
Animal echolocation
Antarctic Circumpolar Wave
Antiphase
Aquamarine Power
Arrayed waveguide grating
Artificial wave
Atmospheric diffraction
Atmospheric wave
Atmospheric waveguide
Atom laser
Atomic clock
Atomic mirror
Audience wave
Autowave
Averaged Lagrangian
B
Babinet's principle
Backward wave oscillator
Bandwidth-limited pulse
beat
Berry phase
Bessel beam
Beta wave
Black hole
Blazar
Bloch's theorem
Blueshift
Boussinesq approximation (water waves)
Bow wave
Bragg diffraction
Bragg's law
Breaking wave
Bremsstrahlung, Electromagnetic radiation
Brillouin scattering
Bullet bow shockwave
Burgers' equation
Business cycle
C
Capillary wave
Carrier wave
Cherenkov radiation
Chirp
Ernst Chladni
Circular polarization
Clapotis
Closed waveguide
Cnoidal wave
Coherence (physics)
Coherence length
Coherence time
Cold wave
Collimated light
Collimator
Compton effect
Comparison of analog and digital recording
Computation of radiowave attenuation in the atmosphere
Continuous phase modulation
Continuous wave
Convective heat transfer
Coriolis frequency
Coronal mass ejection
Cosmic microwave background radiation
Coulomb wave function
Cutoff frequency
Cutoff wavelength
Cymatics
D
Damped wave
Decollimation
Delta wave
Dielectric waveguide
Diffraction
Direction finding
Dispersion (optics)
Dispersion (water waves)
Dispersion relation
Dominant wavelength
Doppler effect
Doppler radar
Douglas Sea Scale
Draupner wave
Droplet-shaped wave
Duhamel's principle
E
E-skip
Earthquake
Echo (phenomenon)
Echo sounding
Echolocation (animal)
Echolocation (human)
Eddy (fluid dynamics)
Edge wave
Eikonal equation
Ekman layer
Ekman spiral
Ekman transport
El Niño–Southern Oscillation
Electroencephalography
Electromagnetic electron wave
Electromagnetic radiation
Electromagnetic wave
Electromagnetic wave cut-off
Electron
Elliott wave
Elliptical polarization
Emission spectrum
Envelope (waves)
Equatorial Rossby wave
Equatorial waves
Essential bandwidth
Evanescent wave
Extratropical cyclone
Extremely low frequency
F
F wave
Fabry–Pérot interferometer
Faraday wave
Fetch (geography)
Fourier series
Fraunhofer diffraction
Fraunhofer distance
Freak wave
Frequency
Frequency modulation
Fresnel diffraction
Fresnel equations
Fresnel integral
Fresnel lens
Fresnel number
Fresnel rhomb
Fresnel zone
Fresnel–Arago laws
Fundamental frequency
G
Gamma ray
Gamma ray burst
Gamma wave
Gaussian beam
Geometric optics, Geometrical optics
Geostrophic current
Gravitational radiation
Gravity wave
Groundwave
Group delay
Group velocity
H
Harmonic
Heat wave
Holography
Human echolocation
Hundred-year wave
Hurricane
Huygens' principle
Hydraulic jump
Hydrography
Hydropower
Hyperbolic partial differential equation
I
In phase
Inertial wave
Infragravity wave
Infrared gas analyzer
Inhomogeneous electromagnetic wave equation
Interference (wave propagation)
Interferometry
Internal wave
Inverse scattering transform
Ion acoustic wave
Irradiance
K
Kelvin wave
Kinematic wave
Knife-edge effect
Kondratiev wave
L
Lamb waves
Landau damping
Lee wave
Linear elasticity
Linear polarization
List of waves named after people
Long wavelength limit
Longitudinal mode
Longitudinal wave
Longwave
Love wave
M
Mach wave
Mach–Zehnder interferometer
Maelstrom (disambiguation)
Magnetometer
Magnetosonic wave
Matter wave
Maxwell's equations
Mayer waves
Mechanical wave
Medical ultrasonography
Mediumwave
Megatsunami
Microbarom
Microwave
Microwave auditory effect
Microwave oven
Microwave plasma
Microwaving
Mie scattering
Millimeter cloud radar
Modulation
Monochromatic electromagnetic plane wave
Monochromator
Moonlight
Morning Glory cloud
Mu wave
Multipath propagation
N
Neural oscillation
Neutron
Nondispersive infrared sensor
Nonlinear Schrödinger equation
Nonlinear wave
Nonlinear X-wave
Normal mode
O
Ocean surface wave
One-Way Wave Equation
Optical fiber
Optical waveguide
Oscillon
Out of phase
Outgoing longwave radiation
Overtone
Oyster wave energy converter
P
P-wave
Parabolic reflector
Periodic function
Periodic travelling wave
Phase (waves)
Phase difference
Phase modulation
Phase velocity
Phonon
Photon
Pitch shifter (audio processor)
Planck constant
Planck's law
Plane wave
Polarization (waves)
Ponto-geniculo-occipital waves, PGO waves
Power standing wave ratio
pp-wave spacetime
Pressure wave
Prism
Proton
Pulsar
Pulsar wind nebula
Pulse wave velocity
Pulse-density modulation
Q
QT interval
quadrature
Quadrature amplitude modulation
Quantum optics
Quantum tunneling
Quantum Zeno effect
R
Radar
Radar astronomy
Radar cross section
Radar gun
Radio propagation
Radio waves
Radiosity (heat transfer)
Rayleigh scattering
Rayleigh wave
Rayleigh–Jeans law
Redshift
Reflection coefficient
Reflection seismology
Refraction
Relativistic Doppler effect
Resonance
Resonator
Ring laser gyroscope
Ring modulation
Ring wave guide
Rip current
ripple
Ripple tank
Rogue wave (oceanography)
Rossby wave
Rossby-gravity waves
Rydberg constant
Rydberg formula
S
S-wave
Sampling (signal processing)
Sawtooth wave
Schrödinger equation
Sea state
Seiche
Seismic wave
Seismograph
Seismology
Sellmeier equation
Shallow water equations
Shive wave machine
Shock wave
Shortwave radio
Signal velocity
Significant wave height
Sine wave
Single-sideband modulation
Sinusoidal plane-wave solutions of the electromagnetic wave equation
Skywave
Slow-wave potential
Slow-wave sleep
Sneaker wave
Solitary wave
Soliton
Sonar
Sonic anemometers
Sound wave
Spark-gap transmitter
Spectroscopy
Speed of gravity
Speed of light
Speed of sound
Spike-and-wave
Spin wave
Square wave
Standing wave
Standing wave ratio
Stefan–Boltzmann law
Stokes drift
Stokes wave
Subharmonic
Super low frequency
Superharmonic
Superposition principle
Supersonic Wave Filter
Surface acoustic wave
Surface wave
Surface wave inversion
Surface-wave magnitude
Surface-wave-sustained discharge
Surfing
Sverdrup wave
Swell (ocean)
Synthetic-aperture radar
T
T wave
Terrestrial gamma-ray flash
Terrestrial stationary waves
Theta wave
Tidal bore
Tidal power
Tidal resonance
Tide
Tired light theory
Transverse mode
Transverse wave
Traveling plane wave
Traveling wave antenna
Traveling wave reactor
Traveling-wave tube
Triangle wave
Trigonometric function
Trojan wave packet
Tropical wave
Tsunami
Turbidity current
U
Ultra low frequency
Ultrasound
Ultraviolet catastrophe
Undertow (wave action)
Underwater wave
Undular bore
V
Velocity factor
Vestigial-sideband modulation
Vibrating string
Voltage standing wave ratio
Vortex
Vorticity
W
Wake
Wave (audience)
Wave base
Wave disk engine
Wave drag
Wave equation
Wave farm
Wave field synthesis
Wave function
Wave function collapse
Wave height
Wave impedance
Wave loading
Wave motor
Wave packet
Wave period
Wave plate
Wave pool
Wave pounding
Wave power
Wave propagation
Wave shoaling
Wave surface
Wave tank
Wave turbulence
Wave vector
Wave velocity
Wave–current interaction
Wave-cut platform
Wave-making resistance
Waveform
Waveform monitor
Wave-formed ripple
Wavefront
Wavefunction
Wavefunction collapse
Waveguide
Waveguide (acoustics)
Waveguide (electromagnetism)
Waveguide (optics)
Waveguide flange
Wavelength
Wavelength selective switching
Wavelength-division multiplexing
Wavelet
Wavelet transform
Wavenumber
Zonal wavenumber
Wavenumber-frequency diagram
Wave–particle duality
Waverider
Waves and shallow water
Waves in plasmas
Whitham's method
Wien approximation
Wien's displacement law
Wien's law
Wind wave
Windsurfing
X
X-band radar
X-ray
X-wave
Z
Zero-dispersion slope
Zero-dispersion wavelength
Zigzag
Zodiacal light
Zone plate
Wave topics
Wave topics | Index of wave articles | Physics | 1,550 |
56,650,665 | https://en.wikipedia.org/wiki/Air-liquid%20interface%20cell%20culture | Air liquid interface cell culture (ALI) is a method of cell culture by which basal stem cells are grown with their basal surfaces in contact with media, and the top of the cellular layer is exposed to the air. The cells are then lifted and media is changed until the development of a mucociliary phenotype of a pseudostratified epithelium, similar to the tracheal epithelium.
This method of cell culture aims to be used to study fundamental aspects of the respiratory epithelium, such as cell-to-cell signaling, disease modeling, and respiratory regeneration.
Air-liquid interface cell culture compares to standard cell culture practices by specifically aiming to restore the pseudostratified striation of the respiratory airway in vitro, and aiming to maintain the respiratory airway-niche of (from top to bottom) 1) air, 2) pseudostratified epithelium, and 3) liquid media. Standard cell culture processes are either non-airway specific or revolve around an organ system that requires other means of cellular maintenance in vitro.
Protocol
The protocol for air-liquid interface culture relies on two key steps: isolation of the epithelial cells from an organism, and culture of those cells.
Isolation
Organs with epithelial cells are isolated (dissected) and placed in PBS to clean any impurities and these isolated organs are digested using trypsin. After the digest, ROCK inhibitor (Rho-associated kinase inhibitor) is added to prevent cellular apoptosis of isolated cells. What is left is digested cellular content mixed with tissue; pronase/DNAse is added to clean up dead cellular material as well as any remaining protein material. The resulting material is chopped finely in media and individual isolated cell samples are placed in respectively marked microcentrifuge tubes, and shaken at 37 °C for 30 – 40 minutes. Once the cells have been incubated, they are plated onto transwell membranes for growth.
Culture
Plate cells with SABM (Small Airway Basal Media) to enrich the cells with nutrients for growth and eventual differentiation. Once the cells are plated, they are grown for 3–7 days under careful observation (while changing media each day) until desired confluence is reached.
More recently, a study on In vitro generation of type-II pneumocytes initiated from human CD34(+) stem cells has been demonstrated the air-liquid interface cell culture method precisely.
Uses in scientific study
Air-liquid interface cultures are used in many stem cell studies that aim to recreate a pseudostratified epithelium in vitro. These studies can contribute to new findings on various topics:
Cancer
In modeling cancer and various other diseases, the stem cells in the basal layer of the tracheal epithelium (basal stem cells) were isolated and used in developing 3D organoids that could be used for various studies, including tumor studies. The cell culture method used involves the isolation of cells into culturing with growth factors to grow over time. Once the cells had been grown, they were mixed with Matrigel and cultured to form 3D organoids.
Cell growth/differentiation
In modeling the pseudostratified epithelium in vitro, more cellular studies have been performed in order to determine the nature of the cells – their differentiation pathways, their growth mechanism, and their repair/response mechanism in the state of post-injury.
One recent study has shown that differentiated cells in the respiratory epithelium (secretory cells and ciliated cells primarily) can dedifferentiate into their naive status, and become stem-like again.
Adapted protocol: maintenance of stem-like properties in basal stem cells
As an adaptation to the air-liquid interface culture protocol, auxiliary protocols have been developed using the ALI framework to maintain naive stem cell properties for extensive periods of time.
References
Cell culture | Air-liquid interface cell culture | Biology | 793 |
64,042,964 | https://en.wikipedia.org/wiki/Redundancy%20principle%20%28biology%29 | The redundancy principle in biology expresses the need of many copies of the same entity (cells, molecules, ions) to fulfill a biological function. Examples are numerous: disproportionate numbers of spermatozoa during fertilization compared to one egg, large number of neurotransmitters released during neuronal communication compared to the number of receptors, large numbers of released calcium ions during transient in cells, and many more in molecular and cellular transduction or gene activation and cell signaling. This redundancy is particularly relevant when the sites of activation are physically separated from the initial position of the molecular messengers. The redundancy is often generated for the purpose of resolving the time constraint of fast-activating pathways. It can be expressed in terms of the theory of extreme statistics to determine its laws and quantify how the shortest paths are selected. The main goal is to estimate these large numbers from physical principles and mathematical derivations.
When a large distance separates the source and the target (a small activation site), the redundancy principle explains that this geometrical gap can be compensated by large number. Had nature used less copies than normal, activation would have taken a much longer time, as finding a small target by chance is a rare event and falls into narrow escape problems.
Molecular rate
The time for the fastest particles to reach a target in the context of redundancy depends on the numbers and the local geometry of the target. In most of the time, it is the rate of activation. This rate should be used instead of the classical Smoluchowski's rate describing the mean arrival time, but not the fastest. The statistics of the minimal time to activation set kinetic laws in biology, which can be quite different from the ones associated to average times.
Physical models
Stochastic process
The motion of a particle located at position can be described by the Smoluchowski's limit of the Langevin equation:
where is the diffusion coefficient of the particle, is the friction coefficient per unit of mass, the force per unit of mass, and is a Brownian motion. This model is classically used in molecular dynamics simulations.
Jump processes
, which is for example a model of telomere length dynamics. Here , with .
Directed motion process
where is a unit vector chosen from a uniform distribution. Upon hitting an obstacle at a boundary point , the velocity changes to where is chosen on the unit sphere in the supporting half space at from a uniform distribution, independently of . This rectilinear with constant velocity is a simplified model of spermatozoon motion in a bounded domain . Other models can be diffusion on graph, active graph motion.
Mathematical formulation: Computing the rate of arrival time for the fastest
The mathematical analysis of large numbers of molecules, which are obviously redundant in the traditional activation theory, is used to compute the in vivo time scale of stochastic chemical reactions. The computation relies on asymptotics or probabilistic approaches to estimate the mean time of the fastest to reach a small target in various geometries.
With N non-interacting i.i.d. Brownian trajectories (ions) in a bounded domain Ω that bind at a site, the shortest arrival time is by definition
where are the independent arrival times of the N ions in the medium. The survival distribution of arrival time of the fastest is expressed in terms of a single particle, . Here is the survival probability of a single particle prior to binding at the target.This probability is computed from the solution of the diffusion equation in a domain :
where the boundary contains NR binding sites (). The single particle survival probability is
so that where
and .
The probability density function (pdf) of the arrival time is
which gives the MFPT
The probability can be computed using short-time asymptotics of the diffusion equation as shown in the next sections.
Explicit computation in dimension 1
The short-time asymptotic of the diffusion equation is based on the ray method approximation. For an semi-interval , the survival pdf is solution of
that is
The survival probability with D=1 is . To compute the MFPT, we expand the complementary error function
which gives,
leading (the main contribution of the integral is near 0) to
This result is reminiscent of using the Gumbel's law. Similarly, escape from the interval [0,a] is computed from the infinite sum
.The conditional survival probability is approximated by
, where the maximum occurs at min[y,a-y] for 0<y<a (the shortest ray from y to the boundary). All other integrals can be computed explicitly, leading to
Arrival times of the fastest in higher dimensions
The arrival times of the fastest among many Brownian motions are expressed in terms of the shortest distance from the source S to the absorbing window A, measured by the distance where d is the associated Euclidean distance. Interestingly, trajectories followed by the fastest are as close as possible from the optimal trajectories. In technical language, the associated trajectories of the fastest among N, concentrate near the optimal trajectory (shortest path) when the number N of particles increases. For a diffusion coefficient D and a window of size a, the expected first arrival times of N identically independent distributed Brownian particles initially positioned at the source S are expressed in the following asymptotic formulas :
These formulas show that the expected arrival time of the fastest particle is in dimension 1 and 2, O(1/\log(N)). They should be used instead of the classical forward rate in models of activation in biochemical reactions. The method to derive formulas is based on short-time asymptotic and the Green's function representation of the Helmholtz equation. Note that other distributions could lead to other decays with respect N.
Optimal Paths
Minimizing The optimal path in large N
The optimal paths for the fastest can be found using the Wencell-Freidlin functional in the Large-deviation theory. These paths correspond to the short-time asymptotics of the diffusion equation from a source to a target. In general, the exact solution is hard to find, especially for a space containing various distribution of obstacles.
The Wiener integral representation of the pdf for a pure Brownian motion is obtained for a zero drift and diffusion tensor constant, so that it is given by the probability of a sampled path until it exits at the small window at the random time T
where
in the product and T is the exit time in the narrow absorbing window Finally,
where is the ensemble of shortest paths selected among n Brownian trajectories, starting at point y and exiting between time t and t+dt from the domain . The probability is used to show that the empirical stochastic trajectories of concentrate near the shortest paths starting from y and ending at the small absorbing window , under the condition that . The paths of can be approximated using discrete broken lines among a finite number of points and we denote the associated ensemble by . Bayes' rule leads to where is the probability that a path of exits in m-discrete time steps. A path made of broken lines (random walk with a time step) can be expressed using Wiener path-integral. The probability of a Brownian path x(s) can be expressed in the limit of a path-integral with the functional:
The Survival probability conditioned on starting at y is given by the Wiener representation:
where is the limit Wiener measure: the exterior integral is taken over all end points x and the path integral is over all paths starting from x(0). When we consider n-independent paths (made of points with a time step that exit in m-steps, the probability of such an event is
.Indeed, when there are n paths of m steps, and the fastest one escapes in m-steps, they should all exit in m steps. Using the limit of path integral, we get heuristically the representation
where the integral is taken over all paths starting at y(0) and exiting at time . This formula suggests that when n is large, only the paths that minimize the integrant will contribute. For large n, this formula suggests that paths that will contribute the most are the ones that will minimize the exponent, which allows selecting the paths for which the energy functional is minimal, that is
where the integration is taken over the ensemble of regular paths inside starting at y and exiting in , defined as
This formal argument shows that the random paths associated to the fastest exit time are concentrated near the shortest paths. Indeed, the Euler-Lagrange equations for the extremal problem are the classical geodesics between y and a point in the narrow window .
Fastest escape from a cusp in two dimensions
The formula for the fastest escape can generalize to the case where the absorbing window is located in funnel cusp and the initial particles are distributed outside the cusp. The cusp has a size in the opening and a curvature R. The diffusion coefficient is D. The shortest arrival time, valid for large n is given by Hereand c is a constant that depends on the diameter of the domain. The time taken by the first arrivers is proportional to the reciprocal of the size of the narrow target . This formula is derived for fixed geometry and large n and not in the opposite limit of large n and small epsilon.
Concluding remarks
How nature sets the disproportionate numbers of particles remain unclear, but can be found using the theory of diffusion. One example is the number of neurotransmitters around 2000 to 3000 released during synaptic transmission, that are set to compensate the low copy number of receptors, so the probability of activation is restored to one.
In natural processes these large numbers should not be considered wasteful, but are necessary for generating the fastest possible response and make possible rare events that otherwise would never happen. This property is universal, ranging from the molecular scale to the population level.
Nature's strategy for optimizing the response time is not necessarily defined by the physics of the motion of an individual particle, but rather by the extreme statistics, that select the shortest paths. In addition, the search for a small activation site selects the particle to arrive first: although these trajectories are rare, they are the ones that set the time scale. We may need to reconsider our estimation toward numbers when punctioning nature in agreement with the redundant principle that quantifies the request to achieve the biological function.
References
Biology terminology | Redundancy principle (biology) | Biology | 2,143 |
13,357,973 | https://en.wikipedia.org/wiki/Ofeq-7 | Ofeq-7 (also known as Ofek 7 or Offek-7) is part of the Ofeq family of Earth observation satellites designed and built by Israel Aerospace Industries (IAI) for the Israel Ministry of Defense.
Launch
The Ofeq-7 was launched by a Shavit 2 space launch vehicle on 10 June 2007 at 23:40 UTC. Equipped with advanced technology and a series of new enhancements to provide improved imagery, it is placed into an elliptical orbit of .
Mission
Three days after its launch, on 13 June 2007, IAI MBT Space Division received the first images taken by the satellite. The Ofeq-7 is a follow-on spacecraft to Ofeq-5 that was placed into orbit in 2002.
References
Reconnaissance satellites of Israel
Spacecraft launched in 2007
Spacecraft launched by Shavit rockets
2007 in Israel
Israel Aerospace Industries satellites | Ofeq-7 | Astronomy | 179 |
3,378,687 | https://en.wikipedia.org/wiki/Endoluminal%20capsule%20monitoring | Endoluminal capsule monitoring is a non-invasive medical diagnostic procedure which uses a miniaturized wireless radio transmitter embedded into an ingestible water-tight capsule. The patient ingests the capsule and while it transits through the gastrointestinal system, it sends signals to the outside, which are captured by a radio receiver, processed, displayed and stored in a computer.
According to the type or type(s) of biomedical sensors which are built into the capsule, several physiological parameters can be measured and transmitted by the capsule:
intraluminal pH in the esophagus, stomach, small intestine, and colon
temperature
intraluminal pressure
transit time
A wireless motility capsule (WMC) can measure gastric emptying time to diagnose gastroparesis or gastric dumping syndrome, and it can also measure transit time in the small intestine and colon. The WMC uses pH to detect passage through the pyloric sphincter and through the ileocecal valve, and it uses a temperature sensor to detect elimination from the body.
Modern capsules, called video pills or endoscopic capsules can also transmit endoscopic images from a miniature video camera.
The system is normally used for research purposes or for diagnosing long term changes in gastrointestinal physiological parameters. In some cases, the capsule is recovered in the feces, sterilized, and can be used again. In other cases, the capsule is discarded with the feces, serving as a disposable medical device.
References
Medical tests
Medical technology | Endoluminal capsule monitoring | Biology | 323 |
73,980,369 | https://en.wikipedia.org/wiki/Planet%20Lockdown | Planet Lockdown is a film containing misinformation about COVID-19 that was banned on YouTube and Facebook.
The film's producers describe it as a documentary.
Production
The 90-minute film was directed by James Patrick, and released online in December 2020. In addition to being shared on social media, the video was released on the Planet Lockdown website. The video's producers describe it as a documentary. A feature-length cut of the film premiered on November 20, 2021 at an event hosted by the Arlington Institute at Coolfont Resort in Berkeley Springs, West Virginia.
Synopsis
Planet Lockdown presents a wide range of falsehoods about COVID-19, including incorrect statements linking COVID-19 and human infertility, and misinformation alleging that vaccines contain microchips. The film also perpetuates myths about voter fraud during the 2020 United States presidential election.
The film includes an interview with Catherine Austin Fitts in which she shares her view that a global committee is engaged in mind control efforts, led by a character she identifies as Mr Global. Fitts also shares falsehoods that COVID-19 vaccines contain unknown ingredients. In addition to incorrectly stating that the COVID-19 is not real, Fitts also shares political conspiracy theories about electoral fraud during the 2020 U.S. presidential election. Other interviewees include QAnon supporting physician Carrie Madej, lawyer Markus Haintz, and COVID-19 herd-immunity supporting epidemiologist Knut Wittkowski.
Critical reception
In late 2020 and early 2021, the video was shared over 20 million times on Facebook and YouTube. Notable promoters of the video include Robert F. Kennedy Jr.
After a February analysis of the video by Media Matters for America, TikTok, Facebook and YouTube started removing the video from their platforms and GoFundMe removed a fundraising page to cover production costs.
Vice News described the video as "almost a carbon copy" of the 2020 conspiracy theory video Plandemic.
See also
COVID-19 misinformation
References
2020 films
2020 YouTube videos
American propaganda films about COVID-19
Anti-vaccination media
Censored films
Conspiracy theories in the United States
Fake news
Films about the COVID-19 pandemic
Health fraud media
Health-related conspiracy theories
COVID-19 vaccine misinformation and hesitancy
2020s English-language films
Pseudoscience documentary films
2020s American films
American propaganda films about vaccination | Planet Lockdown | Technology | 505 |
784,808 | https://en.wikipedia.org/wiki/Continuous%20functional%20calculus | In mathematics, particularly in operator theory and C*-algebra theory, the continuous functional calculus is a functional calculus which allows the application of a continuous function to normal elements of a C*-algebra.
In advanced theory, the applications of this functional calculus are so natural that they are often not even mentioned. It is no overstatement to say that the continuous functional calculus makes the difference between C*-algebras and general Banach algebras, in which only a holomorphic functional calculus exists.
Motivation
If one wants to extend the natural functional calculus for polynomials on the spectrum of an element of a Banach algebra to a functional calculus for continuous functions on the spectrum, it seems obvious to approximate a continuous function by polynomials according to the Stone-Weierstrass theorem, to insert the element into these polynomials and to show that this sequence of elements converges to
The continuous functions on are approximated by polynomials in and , i.e. by polynomials of the form Here, denotes the complex conjugation, which is an involution on the
To be able to insert in place of in this kind of polynomial, Banach *-algebras are considered, i.e. Banach algebras that also have an involution *, and is inserted in place of In order to obtain a homomorphism , a restriction to normal elements, i.e. elements with , is necessary, as the polynomial ring is commutative.
If is a sequence of polynomials that converges uniformly on to a continuous function , the convergence of the sequence in to an element must be ensured. A detailed analysis of this convergence problem shows that it is necessary to resort to C*-algebras. These considerations lead to the so-called continuous functional calculus.
Theorem
Due to the *-homomorphism property, the following calculation rules apply to all functions and scalars :
One can therefore imagine actually inserting the normal elements into continuous functions; the obvious algebraic operations behave as expected.
The requirement for a unit element is not a significant restriction. If necessary, a unit element can be adjoined, yielding the enlarged C*-algebra Then if and with , it follows that and
The existence and uniqueness of the continuous functional calculus are proven separately:
Existence: Since the spectrum of in the C*-subalgebra generated by and is the same as it is in , it suffices to show the statement for The actual construction is almost immediate from the Gelfand representation: it suffices to assume is the C*-algebra of continuous functions on some compact space and define
Uniqueness: Since and are fixed, is already uniquely defined for all polynomials , since is a *-homomorphism. These form a dense subalgebra of by the Stone-Weierstrass theorem. Thus is
In functional analysis, the continuous functional calculus for a normal operator is often of interest, i.e. the case where is the C*-algebra of bounded operators on a Hilbert space In the literature, the continuous functional calculus is often only proved for self-adjoint operators in this setting. In this case, the proof does not need the Gelfand
Further properties of the continuous functional calculus
The continuous functional calculus is an isometric isomorphism into the C*-subalgebra generated by and , that is:
for all ; is therefore continuous.
Since is a normal element of , the C*-subalgebra generated by and is commutative. In particular, is normal and all elements of a functional calculus
The holomorphic functional calculus is extended by the continuous functional calculus in an unambiguous Therefore, for polynomials the continuous functional calculus corresponds to the natural functional calculus for polynomials: for all
For a sequence of functions that converges uniformly on to a function , converges to For a power series , which converges absolutely uniformly on , therefore
If and , then holds for their If are two normal elements with and is the inverse function of on both and , then , since
The spectral mapping theorem applies: for all
If holds for , then also holds for all , i.e. if commutates with , then also with the corresponding elements of the continuous functional calculus
Let be an unital *-homomorphism between C*-algebras and Then commutates with the continuous functional calculus. The following holds: for all In particular, the continuous functional calculus commutates with the Gelfand
With the spectral mapping theorem, functions with certain properties can be directly related to certain properties of elements of C*-algebras:
is invertible if and only if has no zero on Then
is self-adjoint if and only if is real-valued, i.e.
is positive () if and only if , i.e.
is unitary if all values of lie in the circle group, i.e.
is a projection if only takes on the values and , i.e.
These are based on statements about the spectrum of certain elements, which are shown in the Applications section.
In the special case that is the C*-algebra of bounded operators for a Hilbert space , eigenvectors for the eigenvalue of a normal operator are also eigenvectors for the eigenvalue of the operator If , then also holds for all
Applications
The following applications are typical and very simple examples of the numerous applications of the continuous functional calculus:
Spectrum
Let be a C*-algebra and a normal element. Then the following applies to the spectrum
is self-adjoint if and only if
is unitary if and only if
is a projection if and only if
Proof. The continuous functional calculus for the normal element is a *-homomorphism with and thus is self-adjoint/unitary/a projection if is also self-adjoint/unitary/a projection. Exactly then is self-adjoint if holds for all , i.e. if is real. Exactly then is unitary if holds for all , therefore Exactly then is a projection if and only if , that is for all , i.e.
Roots
Let be a positive element of a C*-algebra Then for every there exists a uniquely determined positive element with , i.e. a unique -th
Proof. For each , the root function is a continuous function on If is defined using the continuous functional calculus, then follows from the properties of the calculus. From the spectral mapping theorem follows , i.e. is If is another positive element with , then holds, as the root function on the positive real numbers is an inverse function to the function
If is a self-adjoint element, then at least for every odd there is a uniquely determined self-adjoint element with
Similarly, for a positive element of a C*-algebra , each defines a uniquely determined positive element of , such that holds for all If is invertible, this can also be extended to negative values of
Absolute value
If , then the element is positive, so that the absolute value can be defined by the continuous functional calculus , since it is continuous on the positive real
Let be a self-adjoint element of a C*-algebra , then there exist positive elements , such that with holds. The elements and are also referred to as the In addition,
Proof. The functions and are continuous functions on with and Put and . According to the spectral mapping theorem, and are positive elements for which and Furthermore, , such that
Unitary elements
If is a self-adjoint element of a C*-algebra with unit element , then is unitary, where denotes the imaginary unit. Conversely, if is an unitary element, with the restriction that the spectrum is a proper subset of the unit circle, i.e. , there exists a self-adjoint element with
Proof. It is with , since is self-adjoint, it follows that , i.e. is a function on the spectrum of Since , using the functional calculus follows, i.e. is unitary. Since for the other statement there is a , such that the function is a real-valued continuous function on the spectrum for , such that is a self-adjoint element that satisfies
Spectral decomposition theorem
Let be an unital C*-algebra and a normal element. Let the spectrum consist of pairwise disjoint closed subsets for all , i.e. Then there exist projections that have the following properties for all
For the spectrum, holds.
The projections commutate with , i.e.
The projections are orthogonal, i.e.
The sum of the projections is the unit element, i.e.
In particular, there is a decomposition for which holds for all
Proof. Since all are closed, the characteristic functions are continuous on Now let be defined using the continuous functional. As the are pairwise disjoint, and holds and thus the satisfy the claimed properties, as can be seen from the properties of the continuous functional equation. For the last statement, let
Notes
References
English translation of
External links
Continuous functional calculus on PlanetMath
Theorems in functional analysis
C*-algebras
Functional calculus | Continuous functional calculus | Mathematics | 1,848 |
57,805,865 | https://en.wikipedia.org/wiki/Floc%20%28biofilm%29 | A floc is a type of microbial aggregate that may be contrasted with biofilms and granules, or else considered a specialized type of biofilm. Flocs appear as cloudy suspensions of cells floating in water, rather than attached to and growing on a surface like most biofilms. The floc typically is held together by a matrix of extracellular polymeric substance (EPS), which may contain variable amounts of polysaccharide, protein, and other biopolymers. The formation and the properties of flocs may affect the performance of industrial water treatment bioreactors such as activated sludge systems where the flocs form a sludge blanket.
Floc formation may benefit the constituent microorganisms in a number of ways, including protection from pH stress, resistance to predation, manipulation of microenvironments, and facilitation of mutualistic relationships in mixed microbial communities.
In general, the mechanisms by which flocculating microbial aggregates hold together are poorly understood. However, work on the activated sludge bacterium Zoogloea resiniphila has shown that PEP-CTERM proteins must be expressed for flocs to form; in their absence, growth is planktonic, even though exopolysaccharide is produced.
See also
Yeast flocculation#Process
References
Bacteriology
Biological matter
Environmental microbiology
Microbiology terms | Floc (biofilm) | Biology,Environmental_science | 290 |
74,477,694 | https://en.wikipedia.org/wiki/Consortium%20for%20Execution%20of%20Rendezvous%20and%20Servicing%20Operations | The Consortium for Execution of Rendezvous and Servicing Operations (CONFERS) is a program started by the Defense Advanced Research Projects Agency (DARPA) in 2017. The goal was to address the lack of widely accepted technical and safety standards for on-orbit servicing activities involving commercial satellites. In partnership with NASA, the CONFERS program was to establish a permanent, self-sustaining, and independent forum where industry could engage with the U.S. Government to collaborate and create standards for on-orbit servicing.
In 2017, DARPA provided funding to Advanced Technology International to form the consortium as an industry-led initiative. Since 2018, CONFERS holds annual Global Satellite Servicing Forum conferences.
In 2022, International Standards Organization (ISO) adopted CONFERS’ standard as ISO 24330, Space systems — Rendezvous and Proximity Operations (RPO) and On Orbit Servicing (OOS).
DARPA has transitioned the leadership and funding to CONFERS, Inc., a nonprofit 501(c)(6) organization.
References
DARPA projects
NASA programs
2017 establishments in the United States
501(c)(6) nonprofit organizations
Standards of the United States
Satellites | Consortium for Execution of Rendezvous and Servicing Operations | Astronomy | 229 |
360,725 | https://en.wikipedia.org/wiki/Acetylcysteine | N-acetylcysteine, also known as Acetylcysteine and NAC, is a medication that is used to treat paracetamol (acetaminophen) overdose and to loosen thick mucus in individuals with chronic bronchopulmonary disorders, such as pneumonia and bronchitis. It has been used to treat lactobezoar in infants. It can be taken intravenously, orally (swallowed by mouth), or inhaled as a mist. It is also sometimes used as a dietary supplement.
Common side effects include nausea and vomiting when taken orally. The skin may occasionally become red and itchy with any route of administration. A non-immune type of anaphylaxis may also occur. It appears to be safe in pregnancy. For paracetamol overdose, it works by increasing the level of glutathione, an antioxidant that can neutralize the toxic breakdown products of paracetamol. When inhaled, it acts as a mucolytic by decreasing the thickness of mucus.
Acetylcysteine was initially patented in 1960 and came into medical use in 1968. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication.
The sulfur-containing amino acids cysteine and methionine are more easily oxidized than the other amino acids.
Uses
Medical uses
Paracetamol overdose antidote
Intravenous and oral formulations of acetylcysteine are available for the treatment of paracetamol (acetaminophen) overdose. When paracetamol is taken in large quantities, a minor metabolite called N-acetyl-p-benzoquinone imine (NAPQI) accumulates within the body. It is normally conjugated by glutathione, but when taken in excess, the body's glutathione reserves are not sufficient to deactivate the toxic NAPQI. This metabolite is then free to react with key hepatic enzymes, thereby damaging liver cells. This may lead to severe liver damage and even death by acute liver failure.
In the treatment of paracetamol (acetaminophen) overdose, acetylcysteine acts to maintain or replenish depleted glutathione reserves in the liver and enhance non-toxic metabolism of acetaminophen. These actions serve to protect liver cells from NAPQI toxicity. It is most effective in preventing or lessening hepatic injury when administered within 8–10 hours after overdose. Research suggests that the rate of liver toxicity is approximately 3% when acetylcysteine is administered within 10 hours of overdose.
Although IV and oral acetylcysteine are equally effective for this indication, oral administration is generally poorly tolerated due to the higher dosing required to overcome its low oral bioavailability, its foul taste and odor, and a higher incidence of adverse effects when taken orally, particularly nausea and vomiting. Prior pharmacokinetic studies of acetylcysteine did not consider acetylation as a reason for the low bioavailability of acetylcysteine. Oral acetylcysteine is identical in bioavailability to cysteine precursors. However, 3% to 6% of people given intravenous acetylcysteine show a severe, anaphylaxis-like allergic reaction, which may include extreme breathing difficulty (due to bronchospasm), a decrease in blood pressure, rash, angioedema, and sometimes also nausea and vomiting. Repeated doses of intravenous acetylcysteine will cause these allergic reactions to progressively worsen in these people.
Several studies have found this anaphylaxis-like reaction to occur more often in people given intravenous acetylcysteine despite serum levels of paracetamol not high enough to be considered toxic.
Mucolytic agent
Acetylcysteine exhibits mucolytic properties, meaning it reduces the viscosity and adhesiveness of mucus. This therapeutic effect is achieved through the cleavage of disulfide bonds within mucoproteins (strongly cross-linked mucins), thereby decreasing the mucus viscosity and facilitating its clearance from the respiratory tract. This mechanism is particularly beneficial in conditions characterized by excessive or thickened mucus, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis, rhinitis or sinusitis. Acetylcysteine can be administered as a part of a complex molecule, Thiamphenicol glycinate acetylcysteine, which also contains thiamphenicol, an antibiotic.
Lungs
Inhaled acetylcysteine has been used for mucolytic therapy in addition to other therapies in respiratory conditions with excessive and/or thick mucus production. It is also used post-operatively, as a diagnostic aid, and in tracheotomy care. It may be considered ineffective in cystic fibrosis. A 2013 Cochrane review in cystic fibrosis found no evidence of benefit.
Acetylcysteine is used in the treatment of obstructive lung disease as an adjuvant treatment.
Other uses
Acetylcysteine has been used to complex palladium, to help it dissolve in water. This helps to remove palladium from drugs or precursors synthesized by palladium-catalyzed coupling reactions. N-acetylcysteine can be used to protect the liver.
Microbiological use
Acetylcysteine can be used in Petroff's method of liquefaction and decontamination of sputum, in preparation for recovery of mycobacterium. It also displays significant antiviral activity against influenza A viruses.
Acetylcysteine has bactericidal properties and breaks down bacterial biofilms of clinically relevant pathogens including Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Enterobacter cloacae, Staphylococcus epidermidis, and Klebsiella pneumoniae.
Side effects
The most commonly reported adverse effects for IV formulations of acetylcysteine are rash, urticaria, and itchiness.
Adverse effects for inhalational formulations of acetylcysteine include nausea, vomiting, stomatitis, fever, rhinorrhea, drowsiness, clamminess, chest tightness, and bronchoconstriction. Although infrequent, bronchospasm has been reported to occur unpredictably in some patients.
Adverse effects for oral formulations of acetylcysteine have been reported to include nausea, vomiting, rash, and fever.
Large doses in a mouse model showed that acetylcysteine could potentially cause damage to the heart and lungs. They found that acetylcysteine was metabolized to S-nitroso-N-acetylcysteine (), which increased blood pressure in the lungs and right ventricle of the heart (pulmonary artery hypertension) in mice treated with acetylcysteine. The effect was similar to that observed following a 3-week exposure to an oxygen-deprived environment (chronic hypoxia). The authors also found that SNOAC induced a hypoxia-like response in the expression of several important genes both in vitro and in vivo. The implications of these findings for long-term treatment with acetylcysteine have not yet been investigated. The dose used by Palmer and colleagues was dramatically higher than that used in humans, the equivalent of about 20 grams per day. In humans, a much lower dosages (600 mg per day) have been observed to counteract some age-related decline in the hypoxic ventilatory response as tested by inducing prolonged hypoxia.
Although N-acetylcysteine prevented liver damage in mice when taken before alcohol, when taken four hours after alcohol it made liver damage worse in a dose-dependent fashion.
Pharmacology
Pharmacodynamics
Acetylcysteine serves as a prodrug to L-cysteine, a precursor to the biologic antioxidant glutathione. Hence administration of acetylcysteine replenishes glutathione stores.
Glutathione, along with oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO), have been found to bind to the glutamate recognition site of the NMDA and AMPA receptors (via their γ-glutamyl moieties), and may be endogenous neuromodulators. At millimolar concentrations, they may also modulate the redox state of the NMDA receptor complex. In addition, glutathione has been found to bind to and activate ionotropic receptors that are different from any other excitatory amino acid receptor, and which may constitute glutathione receptors, potentially making it a neurotransmitter. As such, since N-acetylcysteine is a prodrug of glutathione, it may modulate all of the aforementioned receptors as well.
Glutathione also modulates the NMDA receptor by acting at the redox site.
L-cysteine also serves as a precursor to cystine, which in turn serves as a substrate for the cystine-glutamate antiporter on astrocytes; hence there is increasing glutamate release into the extracellular space. This glutamate in turn acts on mGluR2/3 receptors, and at higher doses of acetylcysteine, mGluR5. Acetylcysteine may have other biological functions in the brain, such as the modulation of dopamine release and the reduction in inflammatory cytokine formation possibly via inhibiting NF-κB and modulating cytokine synthesis. These properties, along with the reduction of oxidative stress and the re-establishment of glutamatergic balance, would lead to an increase in growth factors, such as brain-derived neurotrophic factor (BDNF), and the regulation of neuronal cell death through B-cell lymphoma 2 expression (BLC-2).
Pharmacokinetics
The oral bioavailability of acetylcysteine is relatively low due to extensive first-pass metabolism in the gut wall and liver. It ranges between 6% and 10%.
Intravenous administration of acetylcysteine bypasses the first-pass metabolism, resulting in higher bioavailability compared to oral administration. Intravenous administration of acetylcysteine ensures nearly 100% bioavailability as it directly enters the bloodstream.
Acetylcysteine is extensively liver metabolized, CYP450 minimal, urine excretion is 22–30% with a half-life of 5.6 hours in adults and 11 hours in newborns.
Acetylcysteine is the N-acetyl derivative of the amino acid L-cysteine, and is a precursor in the formation of the antioxidant glutathione in the body. The thiol (sulfhydryl) group confers antioxidant effects and is able to reduce free radicals.
Chemistry
Pure acetylcysteine is in a solid state at room temperature, appearing as a white crystalline powder or granules. The solid form of acetylcysteine is stable under normal conditions, but it can undergo oxidation if exposed to air or moisture over time, leading to the formation of its dimeric form, diacetylcysteine, which can have different properties. Acetylcysteine is highly hygroscopic, i.e., it absorbs moisture if exposed to open air.
Acetylcysteine can sometimes appear as a light yellow cast powder instead of pure white due to oxidation. The sulfur-containing amino acids, like cysteine, are more easily oxidized than other amino acids. When exposed to air or moisture, acetylcysteine can oxidize, leading to a slight yellowish tint.
Acetylcysteine in a form of a white or white with light yellow cast powder has a pKa of 9.5 at 30 °C.
N-acetyl-L-cysteine is soluble in water and alcohol, and practically insoluble in chloroform and ether.
Acetylcysteine is highly soluble in water: it dissolves readily in water, forming a clear solution. The pH of a maximum-saturated acetylcysteine solution typically ranges between 6.0 and 7.5, depending on temperature, purity of the compount, presense of other ions (thet can affect the pH by interacting with acetylcysteine or altering the overall ionic strength of the solution), thus on the concentraton of acetylcysteine itself: higher concentrations of acetylcysteine can lead to a lower pH due to the increased presence of the acetylcysteine molecule itself. This range of pH between 6.0 and 7.5 ensures that the solution is neither too acidic nor too alkaline, making it suitable for various medical applications. Aqueous solutions of acetylcysteine are compatible with 0.9% sodium chloride solution; compatibility with 5% and 10% glucose solutions is also good.
As for the sunlight stability, acetylcysteine in dry powder form is relatively stable and does not degrade quickly when exposed to sunlight, but when dissolved in aqueous solution, acetylcysteine can degrade when exposed to sunlight, especially if the solution is not stored in a dark, cool place. Besides that, acetylcysteine in aqueous solution can undergo hydrolysis, leading to the breakdown of the amide bond in the molecule. Still, aqueous solutions of acetylcysteine are generally stable when stored properly: the solutions should be kept in tightly sealed containers and stored at controlled room temperature to prolong the stability.
Society and culture
Acetylcysteine was first studied as a drug in 1963. Amazon removed acetylcysteine for sale in the US in 2021, due to claims by the FDA of it being classified as a drug rather than a supplement. In April 2022, the FDA released draft guidance on FDA's policy regarding products labeled as dietary supplements that contain N-acetyl-L-cysteine. Amazon subsequently re-listed NAC products as of August 2022.
Research
While many antioxidants have been researched to treat a large number of diseases by reducing the negative effect of oxidative stress, acetylcysteine is one of the few that has yielded promising results, and is currently already approved for the treatment of paracetamol overdose.
In mouse mdx models of Duchenne's muscular dystrophy, treatment with 1–2% acetylcysteine in drinking water significantly reduces muscle damage and improves strength.
It is being studied in conditions such as autism, where cysteine and related sulfur amino acids may be depleted due to multifactorial dysfunction of methylation pathways involved in methionine catabolism.
Animal studies have also demonstrated its efficacy in reducing the damage associated with moderate traumatic brain or spinal injury, and also ischaemia-induced brain injury. In particular, it has been demonstrated to reduce neuronal losses and to improve cognitive and neurological outcomes associated with these traumatic events.
Research on acetylcysteine usage seems to show a positive efficiency in treating androgenetic alopecia (male baldness), with or without adjacent treatments such as the use of topical minoxidil solution.
Research on mouse models also shows that acetylcysteine could be "used as an efficient and safe therapeutic option for hair loss induced by chemotherapy".
It has been suggested that acetylcysteine may help people with aspirin-exacerbated respiratory disease by increasing levels of glutathione allowing faster breakdown of salicylates, although there is no evidence that it is of benefit.
Small studies have shown acetylcysteine to be of benefit to people with blepharitis. It has been shown to reduce ocular soreness caused by Sjögren's syndrome.
Research has found that acetylcysteine may have otoprotective properties and could potentially be useful for preventing hearing loss and tinnitus in some cases. A 2011 study showed that N-acetylcysteine may protect the human cochlea from subclinical hearing loss caused by loud noises such as impulse noise. In animal models, it reduced age-related hearing loss.
It has been shown effective in the treatment of Unverricht-Lundborg disease in an open trial in four patients. A marked decrease in myoclonus and some normalization of somatosensory evoked potentials with acetylcysteine treatment has been documented.
Addiction to certain addictive drugs (including cocaine, heroin, alcohol, and nicotine) is correlated with a persistent reduction in the expression of excitatory amino acid transporter 2 (EAAT2) in the nucleus accumbens (NAcc); the reduced expression of EAAT2 in this region is implicated in addictive drug-seeking behavior. In particular, the long-term dysregulation of glutamate neurotransmission in the NAcc of long-term, drug-dependent users is associated with an increase in vulnerability to relapse after re-exposure to the addictive drug or its associated drug cues. Drugs that help to normalize the expression of EAAT2 in this region, such as N-acetylcysteine, have been proposed as an adjunct therapy for the treatment of addiction to cocaine, nicotine, alcohol, and other drugs.
It has been tested for the reduction of hangover symptoms, though the overall results indicate very limited efficacy.
A double-blind placebo controlled trial of 262 patients has shown NAC treatment was well-tolerated and resulted in a significant decrease in the frequency of influenza-like episodes, severity, and length of time confined to bed.
Kidney and bladder
N-acetylcysteine has been widely believed to prevent adverse effects of long term Ketamine use on the bladder and kidneys, and there is growing body of evidence to support this.
Evidence for the benefit of acetylcysteine to prevent radiocontrast induced kidney disease is mixed.
Acetylcysteine has been used for cyclophosphamide-induced haemorrhagic cystitis, although mesna is generally preferred due to the ability of acetylcysteine to diminish the effectiveness of cyclophosphamide.
Psychiatry
Acetylcysteine has been studied for major psychiatric disorders, including bipolar disorder, major depressive disorder, and schizophrenia.
Tentative evidence exists for N-acetylcysteine also in the treatment of Alzheimer's disease, autism, obsessive-compulsive disorder, specific drug addictions (cocaine), drug-induced neuropathy, trichotillomania, excoriation disorder, and a certain form of epilepsy (progressive myoclonic). Preliminary evidence showed efficacy in anxiety disorder, attention deficit hyperactivity disorder and mild traumatic brain injury although confirmatory studies are required. Tentative evidence also supports use in cannabis use disorder.
It is also being studied for use as a treatment of body-focused repetitive behavior.
Addiction
Evidence to date does not support the efficacy for N-acetylcysteine in treating addictions to gambling, methamphetamine, or nicotine. Based upon limited evidence, NAC appears to normalize glutamate neurotransmission in the nucleus accumbens and other brain structures, in part by upregulating the expression of excitatory amino acid transporter 2 (EAAT2), glutamate transporter 1 (GLT1), in individuals with addiction. While NAC has been demonstrated to modulate glutamate neurotransmission in adult humans who are addicted to cocaine, NAC does not appear to modulate glutamate neurotransmission in healthy adult humans. NAC has been hypothesized to exert beneficial effects through its modulation of glutamate and dopamine neurotransmission as well as its antioxidant properties.
Bipolar disorder
In bipolar disorder, N-acetylcysteine has been repurposed as an augmentation strategy for depressive episodes in light of the possible role of inflammation in the pathogenesis of mood disorders. Nonetheless, meta-analytic evidence shows that add-on N-acetylcysteine was more effective than placebo only in reducing depression scales scores (low quality evidence), without positive effects on response and remission outcomes, limiting its possible role in clinical practice to date.
COVID-19
Acetylcysteine has been studied as a possible treatment for COVID-19.
A combination of guanfacine and N-acetylcysteine has been found to lift the "brain fog" of eight patients with long COVID, according to researchers, but the results are inconclusive and have not been confirmed by other studies.
A combination of glycine and N-acetylcysteine is suspected to have potential to safely replenish depleted glutathione levels in COVID-19 patients.
External links
References
Acetamides
Alpha-Amino acids
Amino acid derivatives
Antidotes
Antioxidants
Excipients
Excitatory amino acid receptor ligands
Ophthalmology drugs
Sulfur compounds
Thiols
Treatment of bipolar disorder
Treatment of obsessive–compulsive disorder
Wikipedia medicine articles ready to translate
World Health Organization essential medicines | Acetylcysteine | Chemistry | 4,663 |
27,319,186 | https://en.wikipedia.org/wiki/MK%20II%20FPA | The MK II Method is one of the software sizing methods in functional point group of measurements. This is a method for analysis and measurement of information processing applications based on end user functional view of the system. The MK II Method (ISO/IEC 20968 Software engineering—Mk II Function Point Analysis—Counting Practices Manual) is one of five currently recognized ISO standards for Functionally sizing software.
Introduction
The MK II Method was defined by Charles Symons in book published in 1991. UK Software Metrics Association is now responsible for the method and its continuing development. The functional user requirements of the software are identified and each one is categorized into one of there types: inputs, exits and objects. In order to determine functional size of system these functional requirements are counted.
MkII FPA counting rules
MkII counting procedure contains several steps described below.
Determine the ViewPoint, Purpose and Type of the Count
Define the Boundary of the Count
Boundary of system represents logical line that separates users from a system. It is used to determine logical transactions such as inputs and exits that crosses boundary during the interaction between user and system.
Identify the Logical Transactions
Each transaction is counted once even though it may be executed from more than one point in the application.
Identify and Categorise Data Entity Types
Data entity types are logical data structures that contains information meaningful to the user. In MarkII method there is only one type of data entity types - Objects. Objects must be correctly identified so they can be counted.
Count the Input Data Element Types, the Data entity Types Referenced, and the Output Data Element Types
This can be done by a simple spreadsheet and needs to be added up and applied a formula to find the exact MKII FPA value
Count the Functional Size
Once the transactions and objects in the system are identified, they can be counted in order to find functional size of the system. Functional size of the system is represented as weighted counts of input/exit transactions and objects within the boundary of the system. Size can be expressed as following:
Size = Wi*ΣNi+ We*ΣNe + Wo*ΣNo
In the equation ΣNi, ΣNe and ΣNo are total numbers of unique inputs, exits and objects within the system. Currently recommended values for weighting coefficients are Wi = 0.58, We = 1.66, and Wo = 0.26.
See also
Function point
Software development effort estimation
Software Sizing
References
External links
Mk2 method explained
ISO/IEC Standard
Software metrics
Software engineering costs | MK II FPA | Mathematics,Engineering | 501 |
74,063,421 | https://en.wikipedia.org/wiki/Glaucocystis%20nostochinearum | Glaucocystis nostochinearum is a species of glaucophyte in the family Glaucocystaceae. The species is the type species of its genus, Glaucocystis. The species can be found in the waters of Northern Europe, North America and Oceania.
The species has one form and one variety:
Glaucocystis nostochinearum f. immanis Schmidle, 1902
Glaucocystis nostochinearum var. moebii Gutwinski, 1901
A second variety, Glaucocystis nostochinearum var. incrassata is now accepted as its own species, Glaucocystis incrassata.
References
Archaeplastida
Plants described in 1866 | Glaucocystis nostochinearum | Biology | 161 |
16,687,792 | https://en.wikipedia.org/wiki/Heliotropium%20curassavicum | Heliotropium curassavicum, commonly called salt heliotrope (among other names), a species of flowering plant in the borage family (Boraginaceae). It is native to much of the Americas, from Canada to Argentina, including the West Indies and Hawaii. It can be found as an introduced, and sometimes invasive, species in Africa, Asia, Australia, and Europe. It thrives in salty soils, such as beach sand, alkali flats, and salt marshes. It is often found in disturbed coastal sites.
Description
This is a perennial herb which can take the form of a prostrate creeper along the ground to a somewhat erect shrub approaching in height. The stem and foliage are fleshy, with the leaves thick and oval or spade-shaped. The plentiful inflorescences are curled, coiling double rows of small bell-shaped flowers. Each flower is white with five rounded lobes and a purple or yellow throat. The fruit is a smooth nutlet.
Names
Due to its wide geographical range that spans many nations and languages, Heliotropium curassavicum has been given an assortment of common names. In English, these include seaside heliotrope, salt heliotrope, monkey tail, quail plant and Chinese parsley. In Latin American Spanish, it is known as cola de mico, cola de gama or rabo alacrán. It is called kīpūkai in Hawaii.
Taxonomy
There are five currently recognized varieties. These are:
H. curassavicum var. argentinum - Native to the tropics of South America, including Argentina, Brazil, Paraguay, and Uruguay.
H. curassavicum var. curassavicum - Globally widespread, native from the eastern U.S. to Argentina, and naturalized on seashores elsewhere.
H. curassavicum var. fruticulosum - Endemic to the San Juan and Mendoza provinces of Argentina.
H. curassavicum var. obovatum - Widespread in western North America and Chihuahua, Mexico.
H. curassavicum var. oculatum - Native from southwestern Utah to Baja California.
References
External links
Jepson Manual Treatment
Calflora photo gallery
curassavicum
Plants described in 1753
Taxa named by Carl Linnaeus
Halophytes
Flora of Hawaii
Flora of Northern America
Flora of Southern America | Heliotropium curassavicum | Chemistry | 497 |
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