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MLKL, ferroptosis via GPX4 suppression, system Xc suppression, and NAPDH loss, as well as apoptosis via RIPK1 and caspase 8. These distressed cells then excrete alarmins, proteases, and damage-associated molecular patterns including HMGB1, histones, mitochondrial DNA, demethylated DNA and RNA, ATP, uric acid, and double-stranded DNA, which further activates Toll-like receptors and inflammasomes. Finally, this activates the inflammatory response including the release of pro-inflammatory interleukin 1 alpha, interleukin 1 beta, cytokines, kinins, lipid inflammatory mediators, complement system activation, vasodilation, an increase in endothelial permeability and leukocyte influx, and pain. Macrophages are key cells that try to remove crystals from tissues by phagocytosis. As part of the inflammatory response, they undergo polarization into a pro-inflammatory state called M1. Macrophages can ingest particles at most a few microns in diameter. If digestion of the crystalline material fails in the lysosomes however, macrophages undergo autophagy, form foam cells and giant cells, and try to do extracellular digestion in a process called frustrated phagocytosis. Crystals do not always cause acute inflammation but instead lead to chronic tissue remodelling. This process is possible because crystals get shielded from pro-inflammatory processes by compartmentalization (e.g. granuloma formation, fibrosis, and wound-healing) or molecular coating, or because inflammatory responses are suppressed with direct anti-inflammatory signalling (e.g. CLEC12A and NETosis). Crystals can attach to membranes via annexin II, CD44, and osteopontin. == Interventions == The most straightforward treatment of crystallopathies would be dissolving the crystals. Crystal dissolvents have been under research, for example with cyclodextrin in atherosclerosis. Another approach would be to modify the inflammatory pathways common for crystallopathies with treatments such as IL-1a and IL-1b antagonists, NLRP3-antagonists, or blockers of ferroptosis and necroptosis. For protein-based crystallopathy, pharmacologic chaperones, protein stabilizing small molecules, and protein refolding agents have been under consideration. == References ==
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"page_id": 63834727,
"source": null,
"title": "Crystallopathy"
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Biological agents, also known as biological weapons or bioweapons, are pathogens used as weapons. In addition to these living or replicating pathogens, toxins and biotoxins are also included among the bio-agents. More than 1,200 different kinds of potentially weaponizable bio-agents have been described and studied to date. Some biological agents have the ability to adversely affect human health in a variety of ways, ranging from relatively mild allergic reactions to serious medical conditions, including serious injury, as well as serious or permanent disability or death. Many of these organisms are ubiquitous in the natural environment where they are found in water, soil, plants, or animals. Bio-agents may be amenable to "weaponization" to render them easier to deploy or disseminate. Genetic modification may enhance their incapacitating or lethal properties, or render them impervious to conventional treatments or preventives. Since many bio-agents reproduce rapidly and require minimal resources for propagation, they are also a potential danger in a wide variety of occupational settings. The 1972 Biological Weapons Convention is an international treaty banning the development, use or stockpiling of biological weapons; as of March 2021, there were 183 states parties to the treaty. Bio-agents are, however, widely studied for both defensive and medical research purposes under various biosafety levels and within biocontainment facilities throughout the world. == Classifications == === Operational === The former United States biological weapons program (1943–1969) categorized its weaponized anti-personnel bio-agents as either "lethal agents" (Bacillus anthracis, Francisella tularensis, Botulinum toxin) or "incapacitating agents" (Brucella suis, Coxiella burnetii, Venezuelan equine encephalitis virus, staphylococcal enterotoxin B). === Legal === Since 1997, United States law has declared a list of bio-agents designated by the U.S. Department of Health and Human Services or the U.S. Department of Agriculture that have the "potential to pose a severe threat to public health and
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safety" to be officially defined as "select agents" and possession or transportation of them are tightly controlled as such. Select agents are divided into "HHS select agents and toxins", "USDA select agents and toxins" and "Overlap select agents and toxins". === Regulatory === The US Centers for Disease Control and Prevention (CDC) breaks biological agents into three categories: Category A, Category B, and Category C. Category A agents pose the greatest threat to the US. Criteria for being a Category "A" agent include high rates of morbidity and mortality, ease of dissemination and communicability, ability to cause a public panic, and special action required by public health officials to respond. Category A agents include anthrax, botulism, plague, smallpox, and viral hemorrhagic fevers. == List of bio-agents of military importance == The following pathogens and toxins were weaponized by one nation or another at some time. NATO abbreviations are included where applicable. === Bacterial bio-agents === === Chlamydial bio-agents === === Rickettsial bio-agents === === Viral bio-agents === === Mycotic bio-agents === === Biological toxins === === Biological vectors === === Simulants === Simulants are organisms or substances which mimic physical or biological properties of real biological agents, without being pathogenic. They are used to study the efficiency of various dissemination techniques or the risks caused by the use of biological agents in bioterrorism. To simulate dispersal, attachment or the penetration depth in human or animal lungs, simulants must have particle sizes, specific weight and surface properties, similar to the simulated biological agent. The typical size of simulants (1–5 μm) enables it to enter buildings with closed windows and doors and penetrate deep into the lungs. This bears a significant health risk, even if the biological agent is normally not pathogenic. Bacillus globigii (historically named Bacillus subtilis in the context of
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"title": "Biological agent"
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bio-agent simulants) (BG, BS, or U) Serratia marcescens (SM or P) Aspergillus fumigatus mutant C-2 (AF) Escherichia coli (EC) Bacillus thuringiensis (BT) Erwinia herbicola (current accepted name: Pantoea agglomerans) (EH) Fluorescent particles such as zinc cadmium sulfide, ZnCdS (FP) == International law == While the history of biological weapons use goes back more than six centuries to the siege of Caffa in 1346, international restrictions on biological weapons began only with the 1925 Geneva Protocol, which prohibits the use but not the possession or development of chemical and biological weapons in international armed conflicts. Upon ratification of the Geneva Protocol, several countries made reservations regarding its applicability and use in retaliation. Due to these reservations, it was in practice a "no-first-use" agreement only. The 1972 Biological Weapons Convention supplements the Geneva Protocol by prohibiting the development, production, acquisition, transfer, stockpiling and use of biological weapons. Having entered into force on 26 March 1975, this agreement was the first multilateral disarmament treaty to ban the production of an entire category of weapons of mass destruction. As of March 2021, 183 states have become party to the treaty. The treaty is considered to have established a strong global norm against biological weapons, which is reflected in the treaty's preamble, stating that the use of biological weapons would be "repugnant to the conscience of mankind". However, its effectiveness has been limited due to insufficient institutional support and the absence of any formal verification regime to monitor compliance. In 1985, the Australia Group was established, a multilateral export control regime of 43 countries aiming to prevent the proliferation of chemical and biological weapons. In 2004, the United Nations Security Council passed Resolution 1540, which obligates all UN Member States to develop and enforce appropriate legal and regulatory measures against the proliferation of chemical, biological,
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"page_id": 723561,
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"title": "Biological agent"
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radiological, and nuclear weapons and their means of delivery, in particular, to prevent the spread of weapons of mass destruction to non-state actors. == In popular culture == == See also == Biological hazard Biological contamination Laboratory Response Network Pulsed ultraviolet light == References == == External links == Rafał L. Górny, Biological agents, OSHwiki (Archived 2023-01-30 at the Wayback Machine) Biological Agents, OSHA Select Agents and Toxins, Centers for Disease Control and Prevention Biological weapons e-learning module in the EU's non-proliferation and disarmament course (taught by Filippa Lentzos)
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{
"page_id": 723561,
"source": null,
"title": "Biological agent"
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The Census of Diversity of Abyssal Marine Life (CeDAMar) is a field project of the Census of Marine Life that studies the species diversity of one of the largest and most inaccessible environments on the planet, the abyssal plain. CeDAMar uses data to create an estimation of global species diversity and provide a better understanding of the history of deep-sea fauna, including its present diversity and dependence on environmental parameters. CeDAMar initiatives aim to identify centers of high biodiversity useful for planning both commercial and conservation efforts, and are able to be used in future studies on the effects of climate change on the deep sea. As of May 2009, participation by upwards of 56 institutions in 17 countries has resulted in the publication of nearly 300 papers. Results of CeDAMar-related research were also published in a 2010 textbook on deep-sea biodiversity by Michael Rex and Ron Etter, members of CeDAMar's Scientific Steering Committee.(ISBN 978-0674036079) CeDAMar is led by Dr. Pedro Martinez Arbizu of Germany and Dr. Craig Smith, USA. == External links == Census of Diversity of Abyssal Marine Life Census of Antarctic Marine Life official web site == References ==
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{
"page_id": 21957226,
"source": null,
"title": "Census of Diversity of Abyssal Marine Life"
}
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The Quest for Consciousness: A Neurobiological Approach is a 2004 book on consciousness written by Christof Koch. == References ==
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{
"page_id": 47778410,
"source": null,
"title": "The Quest for Consciousness"
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A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as Candida, Basidiomycota such as Panus, and various Mortierellales species. It is the life-stage which survives in unfavourable conditions, such as dry or hot seasons. Fusarium oxysporum which causes the plant disease Fusarium wilt is one which forms chlamydospores in response to stresses like nutrient depletion. Mycelia of the pathogen can survive in this manner and germinate in favorable conditions. Chlamydospores are usually dark-coloured, spherical, and have a smooth (non-ornamented) surface. They are multicellular, with cells connected by pores in the septae between cells. Chlamydospores are a result of asexual reproduction (in which case they are conidia called chlamydoconidia) or sexual reproduction (rare). Teliospores are special kind of chlamydospores formed by rusts and smuts. == See also == Conidium Resting spore Zygospore == References == == External links == The chlamydospores of Candida albicans[1], Chlamydospore Production and Germ-Tube Formation by Auxotrophs of Can… Chlamydospore development Allenpress.com
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{
"page_id": 5311084,
"source": null,
"title": "Chlamydospore"
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The central dogma of molecular biology deals with the flow of genetic information within a biological system. It is often stated as "DNA makes RNA, and RNA makes protein", although this is not its original meaning. It was first stated by Francis Crick in 1957, then published in 1958: The Central Dogma. This states that once "information" has passed into protein it cannot get out again. In more detail, the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible. Information here means the precise determination of sequence, either of bases in the nucleic acid or of amino acid residues in the protein. He re-stated it in a Nature paper published in 1970: "The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid." A second version of the central dogma is popular but incorrect. This is the simplistic DNA → RNA → protein pathway published by James Watson in the first edition of The Molecular Biology of the Gene (1965). Watson's version differs from Crick's because Watson describes a two-step (DNA → RNA and RNA → protein) process as the central dogma. While the dogma as originally stated by Crick remains valid today, Watson's version does not. == Biological sequence information == The biopolymers that comprise DNA, RNA and (poly)peptides are linear heteropolymers (i.e.: each monomer is connected to at most two other monomers). The sequence of their monomers effectively encodes information. The transfers of information from one molecule to another are faithful, deterministic transfers, wherein one biopolymer's sequence is used as a template for the
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construction of another biopolymer with a sequence that is entirely dependent on the original biopolymer's sequence. When DNA is transcribed to RNA, its complement is paired to it. DNA codes are transferred to RNA codes in a complementary fashion. The encoding of proteins is done in groups of three, known as codons. The standard codon table applies for humans and mammals, but some other lifeforms (including human mitochondria) use different translations. == General transfers of biological sequential information == === DNA replications === In the sense that DNA replication must occur if genetic material is to be provided for the progeny of any cell, whether somatic or reproductive, the copying from DNA to DNA arguably is the fundamental step in information transfer. A complex group of proteins called the replisome performs the replication of the information from the parent strand to the complementary daughter strand. === Transcription === Transcription is the process by which the information contained in a section of DNA is replicated in the form of a newly assembled piece of messenger RNA (mRNA). Enzymes facilitating the process include RNA polymerase and transcription factors. In eukaryotic cells the primary transcript is pre-mRNA. Pre-mRNA must be processed for translation to proceed. Processing includes the addition of a 5' cap and a poly-A tail to the pre-mRNA chain, followed by splicing. Alternative splicing occurs when appropriate, increasing the diversity of the proteins that any single mRNA can produce. The product of the entire transcription process (that began with the production of the pre-mRNA chain) is a mature mRNA chain. === Translation === The mature mRNA finds its way to a ribosome, where it gets translated. In prokaryotic cells, which have no nuclear compartment, the processes of transcription and translation may be linked together without clear separation. In eukaryotic cells, the
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site of transcription (the cell nucleus) is usually separated from the site of translation (the cytoplasm), so the mRNA must be transported out of the nucleus into the cytoplasm, where it can be bound by ribosomes. The ribosome reads the mRNA triplet codons, usually beginning with an AUG (adenine−uracil−guanine), or initiator methionine codon downstream of the ribosome binding site. Complexes of initiation factors and elongation factors bring aminoacylated transfer RNAs (tRNAs) into the ribosome-mRNA complex, matching the codon in the mRNA to the anti-codon on the tRNA. Each tRNA bears the appropriate amino acid residue to add to the polypeptide chain being synthesised. As the amino acids get linked into the growing peptide chain, the chain begins folding into the correct conformation. Translation ends with a stop codon which may be a UAA, UGA, or UAG triplet. The mRNA does not contain all the information for specifying the nature of the mature protein. The nascent polypeptide chain released from the ribosome commonly requires additional processing before the final product emerges. For one thing, the correct folding process is complex and vitally important. For most proteins it requires other chaperone proteins to control the form of the product. Some proteins then excise internal segments from their own peptide chains, splicing the free ends that border the gap; in such processes the inside "discarded" sections are called inteins. Other proteins must be split into multiple sections without splicing. Some polypeptide chains need to be cross-linked, and others must be attached to cofactors such as haem (heme) before they become functional. == Additional transfers of biological sequential information == === Reverse transcription === Reverse transcription is the transfer of information from RNA to DNA (the reverse of normal transcription). This is known to occur in the case of retroviruses, such as HIV, as
|
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well as in eukaryotes, in the case of retrotransposons and telomere synthesis. It is the process by which genetic information from RNA gets transcribed into new DNA. The family of enzymes involved in this process is called Reverse Transcriptase. === RNA replication === RNA replication is the copying of one RNA to another. Many viruses replicate this way. The enzymes that copy RNA to new RNA, called RNA-dependent RNA polymerases, are also found in many eukaryotes where they are involved in RNA silencing. RNA editing, in which an RNA sequence is altered by a complex of proteins and a "guide RNA", could also be seen as an RNA-to-RNA transfer. == Activities unrelated to the central dogma == The central dogma of molecular biology states that once sequential information has passed from nucleic acid to protein it cannot flow back from protein to nucleic acid. Some people believe that the following activities conflict with the central dogma. === Post-translational modification === After protein amino acid sequences have been translated from nucleic acid chains, they can be edited by appropriate enzymes. This is a form of protein affecting protein sequence not protein transferring information to nucleic acid. === Nonribosomal peptide synthesis === Some proteins are synthesized by nonribosomal peptide synthetases, which can be big protein complexes, each specializing in synthesizing only one type of peptide. Nonribosomal peptides often have cyclic and/or branched structures and can contain non-proteinogenic amino acids - both of these factors differentiate them from ribosome synthesized proteins. An example of nonribosomal peptides are some of the antibiotics. === Inteins === An intein is a "parasitic" segment of a protein that is able to excise itself from the chain of amino acids as they emerge from the ribosome and rejoin the remaining portions with a peptide bond in such a
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manner that the main protein "backbone" does not fall apart. This is a case of a protein changing its own primary sequence from the sequence originally encoded by the DNA of a gene. Additionally, most inteins contain a homing endonuclease or HEG domain which is capable of finding a copy of the parent gene that does not include the intein nucleotide sequence. On contact with the intein-free copy, the HEG domain initiates the DNA double-stranded break repair mechanism. This process causes the intein sequence to be copied from the original source gene to the intein-free gene. This is an example of protein directly editing DNA sequence, as well as increasing the sequence's heritable propagation. === Prions === Prions are proteins of particular amino acid sequences in particular conformations. They propagate themselves in host cells by making conformational changes in other molecules of protein with the same amino acid sequence, but with a different conformation that is functionally important or detrimental to the organism. Once the protein has been transconformed to the prion folding it changes function. In turn it can convey information into new cells and reconfigure more functional molecules of that sequence into the alternate prion form. In some types of prion in fungi this change is continuous and direct; the information flow is Protein → Protein. Some scientists such as Alain E. Bussard and Eugene Koonin have argued that prion-mediated inheritance violates the central dogma of molecular biology. However, Rosalind Ridley in Molecular Pathology of the Prions (2001) has written that "The prion hypothesis is not heretical to the central dogma of molecular biology—that the information necessary to manufacture proteins is encoded in the nucleotide sequence of nucleic acid—because it does not claim that proteins replicate. Rather, it claims that there is a source of information within protein
|
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molecules that contributes to their biological function, and that this information can be passed on to other molecules." == Use of the term dogma == In his autobiography, What Mad Pursuit, Crick wrote about his choice of the word dogma and some of the problems it caused him: "I called this idea the central dogma, for two reasons, I suspect. I had already used the obvious word hypothesis in the sequence hypothesis, and in addition I wanted to suggest that this new assumption was more central and more powerful. ... As it turned out, the use of the word dogma caused almost more trouble than it was worth. Many years later Jacques Monod pointed out to me that I did not appear to understand the correct use of the word dogma, which is a belief that cannot be doubted. I did apprehend this in a vague sort of way but since I thought that all religious beliefs were without foundation, I used the word the way I myself thought about it, not as most of the world does, and simply applied it to a grand hypothesis that, however plausible, had little direct experimental support." Similarly, Horace Freeland Judson records in The Eighth Day of Creation: "My mind was, that a dogma was an idea for which there was no reasonable evidence. You see?!" And Crick gave a roar of delight. "I just didn't know what dogma meant. And I could just as well have called it the 'Central Hypothesis,' or — you know. Which is what I meant to say. Dogma was just a catch phrase." == Comparison with the Weismann barrier == The Weismann barrier, proposed by August Weismann in 1892, distinguishes between the "immortal" germ cell lineages (the germ plasm) which produce gametes and the "disposable" somatic cells.
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"page_id": 68206,
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Hereditary information moves only from germline cells to somatic cells (that is, somatic mutations are not inherited). This, before the discovery of the role or structure of DNA, does not predict the central dogma, but does anticipate its gene-centric view of life, albeit in non-molecular terms. == See also == Life Cell (biology) Cell division Gene Gene expression Epigenetics Genome Alternative splicing Genetic code Riboswitch == References == == Further reading == == External links == The Elaboration of the Central Dogma – Scitable: By Nature education Animation of Central Dogma from RIKEN - NatureDocumentaries.org Discussion on challenges to the "Central Dogma of Molecular Biology" Explanation of the central dogma using a musical analogy "Francis Harry Compton Crick (1916–2004)" by A. Andrei at the Embryo Project Encyclopedia
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"page_id": 68206,
"source": null,
"title": "Central dogma of molecular biology"
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The World Cell Race is a competition among labs to see which biological cell type can travel 600 microns the fastest. The idea is to promote research into how to make cells move faster to aid immune system response or slow metastatic cancers. A fork with a dead end was added to the course in 2013 to assess responses to growth-factor protein. The race was broadcast live online. A Dicty World Race "to find the fastest and smartest Dicty cells" took take place on May 16, 2014 in Boston. == References == == External links == World Cell Race 2014 website World Cell Race 2013 website World Cell Race 2012 website
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{
"page_id": 42535535,
"source": null,
"title": "World Cell Race"
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3-Arylpropiolonitriles (APN) belong to a class of electron-deficient alkyne derivatives substituted by two electron-withdrawing groups – a nitrile and an aryl moieties. Such activation results in improved selectivity towards highly reactive thiol-containing molecules, namely cysteine residues in proteins. APN-based modification of proteins was reported to surpass several important drawbacks of existing strategies in bioconjugation, notably the presence of side reactions with other nucleophilic amino acid residues and the relative instability of the resulting bioconjugates in the blood stream. The latter drawback is especially important for the preparation of targeted therapies, such as antibody-drug conjugates. == Synthesis == The synthesis of 3-arylpropiolonitriles has been the subject of several studies. The most elaborated and often used approach is based on MnO2-mediated free radical oxidation of the corresponding propargylic alcohols obtained using Sonogashira coupling of the corresponding iodo-derivative in the presence of ammonia (Figure 1). == Applications in biotechnology == In bioconjugation (forming a stable covalent link between a biomolecule and a functional payloads, such as fluorescent dyes, cytotoxic agents, or tracers), linking of the payload was classically achieved using maleimide heterobifunctional reagents (for example, see SMCC). However, when administered into living organisms, maleimide-containing bioconjugates were found to be relatively unstable and lose the payload in the blood circulation due to reversibility of the addition reaction between maleimide moiety and cysteine residue of a protein (retro Michael addition). Due to increased stability of bioconjugates obtained with analogous APN-based payloads (a schematic reaction is shown in the Figure 2 below), their use is often preferable when high selectivity and biostability are especially important: namely for the preparation of antibody−drug conjugates and other biologics. Standard procedure for APN protein labeling consists in incubation of a protein containing free cysteine residues with an APN-functionalized probe in PBS buffer at pH 7.5-9.0 at room temperature for 2–12
|
{
"page_id": 54069873,
"source": null,
"title": "3-Arylpropiolonitriles"
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hours, followed by an optional step of purification of the resulting bioconjugate using size exclusion chromatography or ultrafiltration. == References ==
|
{
"page_id": 54069873,
"source": null,
"title": "3-Arylpropiolonitriles"
}
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PM Sayeed Marine Birds Conservation Reserve is the first protected area for marine birds in India. It is located in the Indian Union Territory of Lakshadweep. It was formed in 2020. It covers an area of 62 km2. The PM Sayeed Marine Birds Conservation Reserve will be home to four species of pelagic seabirds – the Greater crested tern, Lesser crested tern, Sooty tern, and the Brown noddy. == See also == Dr. K.K. Mohammed Koya Sea Cucumber Conservation Reserve Pichavaram Karimpuzha Wildlife Sanctuary == References ==
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"page_id": 64621169,
"source": null,
"title": "PM Sayeed Marine Birds Conservation Reserve"
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Electrochromatography is a chemical separation technique in analytical chemistry, biochemistry and molecular biology used to resolve and separate mostly large biomolecules such as proteins. It is a combination of size exclusion chromatography (gel filtration chromatography) and gel electrophoresis. These separation mechanisms operate essentially in superposition along the length of a gel filtration column to which an axial electric field gradient has been added. The molecules are separated by size due to the gel filtration mechanism and by electrophoretic mobility due to the gel electrophoresis mechanism. Additionally there are secondary chromatographic solute retention mechanisms. == Capillary electrochromatography == Capillary electrochromatography (CEC) is an electrochromatography technique in which the liquid mobile phase is driven through a capillary containing the chromatographic stationary phase by electroosmosis. It is a combination of high-performance liquid chromatography and capillary electrophoresis. The capillaries is packed with HPLC stationary phase and a high voltage is applied to achieve separation is achieved by electrophoretic migration of the analyte and differential partitioning in the stationary phase. == See also == Chromatography Protein electrophoresis Electrofocusing Two-dimensional gel electrophoresis Temperature gradient gel electrophoresis == References ==
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{
"page_id": 9505399,
"source": null,
"title": "Electrochromatography"
}
|
The International Census of Marine Microbes is a field project of the Census of Marine Life that inventories microbial diversity by cataloging all known diversity of single-cell organisms including bacteria, Archaea, Protista, and associated viruses, exploring and discovering unknown microbial diversity, and placing that knowledge into ecological and evolutionary contexts. The ICoMM program, led by Mitchell Sogin, has discovered that marine microbial diversity is some 10 to 100 times more than expected, and the vast majority are previously unknown, low abundance organisms thought to play an important role in the oceans. == References == == External links == ICoMM Website Archived 2015-03-17 at the Wayback Machine
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{
"page_id": 22022775,
"source": null,
"title": "International Census of Marine Microbes"
}
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Sea air has traditionally been thought to offer health benefits associated with its unique odor, which is caused by dimethyl sulfide, released by microbes. Salts generally do not dissolve in air, but can be carried by sea spray in the form of particulate matter. In the early 19th century, a lower prevalence of disease in coastal regions or islands was attributed to the sea air. Such medical beliefs were translated into the literature of Jane Austen and other authors. Victorians mistakenly attributed the odor of sea air to ozone. Later that century, such beliefs led to the establishment of seaside resorts for the treatment of tuberculosis, with medical beliefs of its efficacy continuing into the 20th century. However, the quality of sea air was often degraded by pollution from wood- and coal-burning ships. Today those fuels are gone, replaced by high sulphur oil in diesel engines, which generate sulphate aerosols. == See also == Sea spray == References == == Further reading == Hassan, John. The Seaside, Health and Environment in England and Wales Since 1800. Ashgate Publishing.
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{
"page_id": 23202425,
"source": null,
"title": "Sea air"
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The deep transverse fascia or transverse intermuscular septum of leg is a transversely placed, intermuscular septum, from the deep fascia, between the superficial and deep muscles of the back of the leg. At the sides it is connected to the margins of the tibia and fibula. Above, where it covers the popliteus, it is thick and dense, and receives an expansion from the tendon of the semimembranosus. It is thinner in the middle of the leg; but below, where it covers the tendons passing behind the malleoli, it is thickened and continuous with the laciniate ligament. == References == This article incorporates text in the public domain from page 483 of the 20th edition of Gray's Anatomy (1918) == External links == Horizontal section through the middle of the leg Archived 2020-01-12 at the Wayback Machine from www.dartmouth.edu Muscles of the Leg
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{
"page_id": 15338107,
"source": null,
"title": "Deep transverse fascia"
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Economizers (US and Oxford spelling), or economisers (UK), are mechanical devices intended to reduce energy consumption, or to perform useful function such as preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant, heating, refrigeration, ventilating, and air conditioning (HVAC) may all use economizers. In simple terms, an economizer is a heat exchanger. == Stirling engine == Robert Stirling's innovative contribution to the design of hot air engines of 1816 was what he called the 'Economiser'. Later known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of the Stirling engine enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine. == Boilers == In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water). Steam boilers use large amounts of energy raising feed water to the boiling temperature, converting the water to steam and sometimes superheating that steam above saturation temperature. Heat transfer efficiency is improved when the highest temperatures near the combustion sources are used for boiling and superheating, while using the residual heat
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"page_id": 4655742,
"source": null,
"title": "Economizer"
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of the cooled combustion gases exhausting from the boiler through an economizer to raise the temperature of feed water entering the steam drum. An indirect contact or direct contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from the boiling temperature of the fluid to little more than the incoming feed water temperature while preheating that feed water to the boiling temperature. High pressure boilers typically have larger economizer surfaces than low pressure boilers. Economizer tubes often have projections like fins to increase the heat transfer surface on the combustion gas side. On average over the years, boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency. The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam, and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38 °C and there is 15% excess air, then the efficiency will be 94%. The condensing economizer can thus recover the sensible and latent heat in the steam condensate contained in the
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{
"page_id": 4655742,
"source": null,
"title": "Economizer"
}
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flue gases for the process. The economizer is made of an aluminium and stainless steel alloy. The gases pass through the cylinder, and the water passes through the finned tubes. It condenses about 11% of the water contained in the gases. === History === The first successful economizer design was used to increase the steam-raising efficiency of the boilers of stationary steam engines. It was patented by Edward Green in 1845, and since then has been known as Green's economiser. It consisted of an array of vertical cast iron tubes connected to a tank of water above and below, between which the boiler's exhaust gases passed. This is the reverse arrangement to that usually but not always seen in the fire tubes of a boiler; there the hot gases usually pass through tubes immersed in water, whereas in an economizer the water passes through tubes surrounded by hot gases. While both are heat exchange devices, in a boiler the burning gases heat the water to produce steam to drive an engine, whether piston or turbine, whereas in an economizer, some of the heat energy that would otherwise all be lost to the atmosphere is instead used to heat the water and/or air that will go into the boiler, thus saving fuel. The most successful feature of Green's design of economizer was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of soot. Economizers were eventually fitted to virtually all stationary steam engines in the decades following Green's invention. Some preserved stationary steam engine sites still have their Green's economisers although usually they are not used. One such preserved site is the Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring one set of economisers and the associated steam engine which
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drove them. Another such example is the British Engineerium in Brighton & Hove, where the economiser associated with the boilers for Number 2 Engine is in use, complete with its associated small stationary engine. A third site is Coldharbour Mill Working Wool Museum, where the Green's economiser is in working order, complete with the drive shafts from the Pollit and Wigzell steam engine. == Power plants == Modern-day boilers, such as those in coal-fired power stations, are still fitted with economizers which are descendants of Green's original design. In this context they are often referred to as feedwater heaters and heat the condensate from turbines before it is pumped to the boilers. Economizers are commonly used as part of a heat recovery steam generator (HRSG) in a combined cycle power plant. In an HRSG, water passes through an economizer, then a boiler and then a superheater. The economizer also prevents flooding of the boiler with liquid water that is too cold to be boiled given the flow rates and design of the boiler. A common application of economizers in steam power plants is to capture the waste heat from boiler stack gases (flue gas) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater, lowering the needed energy input, in turn reducing the firing rates needed for the rated boiler output. Economizers lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection. == HVAC == A building's HVAC (heating, ventilating, and air conditioning) system can make use of an air-side economizer to save energy in buildings by using cool outside air as a means of cooling the indoor space. When the temperature of the outside air is less
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than the temperature of the recirculated air, conditioning with the outside air is more energy efficient than conditioning with recirculated air. When the outside air is both sufficiently cool and sufficiently dry (depending on the climate) the amount of enthalpy in the air is acceptable and no additional conditioning of it is needed; this portion of the air-side economizer control scheme is called free cooling. Air-side economizers can reduce HVAC energy costs in cold and temperate climates while also potentially improving indoor air quality, but are most often not appropriate in hot and humid climates. With the appropriate controls, economizers can be used in climates which experience various weather systems. When the outside air's dry- and wet-bulb temperatures are low enough, a water-side economizer can use water cooled by a wet cooling tower or a dry cooler (also called a fluid cooler) to cool buildings without operating a chiller. They are historically known as the strainer cycle, but the water-side economizer is not a true thermodynamic cycle. Also, instead of passing the cooling tower water through a strainer and then to the cooling coils, which causes fouling, more often a plate-and-frame heat exchanger is inserted between the cooling tower and chilled water loops. Good controls, and valves or dampers, as well as maintenance, are needed to ensure proper operation of the air- and water-side economizers. == Refrigeration == === Cooler economizer === A common form of refrigeration economizer is a "walk-in cooler economizer" or "outside air refrigeration system". In such a system outside air that is cooler than the air inside a refrigerated space is brought into that space and the same amount of warmer inside air is ducted outside. The resulting cooling supplements or replaces the operation of a compressor-based refrigeration system. If the air inside a cooled space
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is only about 5 °F warmer than the outside air that replaces it (that is, the ∆T>5 °F) this cooling effect is accomplished more efficiently than the same amount of cooling resulting from a compressor based system. If the outside air is not cold enough to overcome the refrigeration load of the space the compressor system will need to also operate, or the temperature inside the space will rise. === Vapor-compression refrigeration === Another use of the term occurs in industrial refrigeration, specifically vapor-compression refrigeration. Normally, the economizer concept is applied when a particular design or feature on the refrigeration cycle, allows a reduction either in the amount of energy used from the power grid, in the size of the components (basically the gas compressor's nominal capacity) used to produce refrigeration, or both. For example, for a walk-in freezer that is kept at −20 °F (−29 °C), the main refrigeration components would include: an evaporator coil (a dense arrangement of pipes containing refrigerant and thin metal fins used to remove heat from inside the freezer), fans to blow air over the coil and around the box, an air-cooled condensing unit sited outdoors, and valves and piping. The condensing unit would include a compressor and a coil and fans to exchange heat with the ambient air. An economizer display takes advantage of the fact that refrigeration systems have increasing efficiencies at increasing pressures and temperatures. The power the gas compressor needs is strongly correlated to both the ratio and the difference, between the discharge and the suction pressures (as well as to other features like the refrigerant's heat capacity and the type of compressor). Low temperature systems such as freezers move less fluid in same volumes. That means the compressor's pumping is less efficient on low temperature systems. This phenomenon is
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notorious when taking in account that the evaporation temperature for a walk-in freezer at −20 °F (−29 °C) may be around −35 °F (−37 °C). Systems with economizers aim to produce part of the refrigeration work on high pressures, condition in which gas compressors are normally more efficient. Depending on the application, this technology either allows smaller compression capacities to be able to supply enough pressure and flow for a system that normally would require bigger compressors, increases the capacity of a system that without economizer would produce less refrigeration, or allows the system to produce the same amount of refrigeration using less power. The economizer concept is linked to subcooling as the condensed liquid line temperature is usually higher than that on the evaporator, making it a good place to apply the notion of increasing efficiencies. Recalling the walk-in freezer example, the normal temperature of the liquid line in that system is around 60 °F (16 °C) or even higher (it varies depending on the condensing temperature). That condition is by far less hostile to produce refrigeration, than the evaporator at −35 °F (−37 °C). === Economizer setups in refrigeration === Several configurations of the refrigeration cycle incorporate an economizer, and benefit from this idea. The design of these systems requires expertise and extra components. Pressure drop, electronic valve control, and oil drag, must all be considered. ==== Two staged systems and boosters ==== A system is said to be a two staged set-up if two gas compressors work together in serial to produce the compression. A normal booster installation is a two staged system that receives fluid to cool down the discharge of the first compressor, before it is input to the second compressor. The fluid that arrives at the interstage of both compressors comes from the liquid
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line and is normally controlled by expansion, pressure and solenoid valves. A standard two staged cycle of this kind has an expansion valve that expands and modulates the amount of refrigerant incoming at the interstage. As the fluid arriving at the interstage expands, it will tend to evaporate, producing a temperature drop and cooling the second compressor's suction when mixed with the fluid discharged by the first compressor. This kind of set-up may have a heat exchanger between the expansion and the interstage, which may be a second evaporator to produce an additional refrigeration effect, though not as cool as the main evaporator (for example to produce air conditioning or for keeping fresh products). A two staged system is said to be set-up as a booster with subcooling, if the refrigerant arriving at the interstage passes through a subcooling heat exchanger that subcools the main liquid line arriving at the main evaporator of the same system. ==== Economizer gas compressors ==== The need to use two compressors in a booster set-up tends to increase the cost of a refrigeration system. A two staged system also needs synchronization, pressure control and lubrication. To reduce these costs, specialized equipment has been developed. Economizer screw compressors are built by several manufacturers like Refcomp, Mycom, Bitzer and York. These machines merge both compressors of a two staged system into one screw compressor with two inputs: the main suction and an interstage side entrance for higher pressure gas. This means there is no need to install two compressors and still benefit from the booster concept. There are two types of economizer setups for these compressors, flash and subcooling. The latter works like a two staged booster with subcooling. The flash economizer is different because it doesn't use a heat exchanger to produce the subcooling. Instead,
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it has a flash chamber or tank, in which flash gas is produced to lower the temperature of the liquid before the expansion. The flash gas that is produced in this tank leaves the liquid line and goes to the economizer entrance of the screw compressor. ==== Subcooling and refrigeration cycle optimizers ==== The above systems produce an economizer effect by using compressors, meters, valves and heat exchangers within the refrigeration cycle. In some refrigeration systems the economizer can be an independent refrigeration mechanism. Such is the case of subcooling the liquid line by any other means that draws the heat out of the main system. For example, a heat exchanger that preheats cold water needed for another process or human use, may take heat from the liquid line, effectively subcooling it and increasing the system's capacity. Recently, machines exclusively designed for this purpose have been developed. In Chile, the manufacturer EcoPac Systems developed a cycle optimizer able to stabilize the temperature of the liquid line and allow either an increase in the refrigeration capacity of the system, or a reduction of the power consumption. Such systems have the advantage of not interfering with the original design of the refrigeration system and are a way to expand a single staged system that does not possess an economizer compressor. ==== Internal heat exchangers ==== Subcooling may also be produced by superheating the gas leaving the evaporator and heading to the gas compressor. These systems withdraw heat from the liquid line and heat up the gas compressor's suction line. This is a very common solution to insure that gas reaches the compressor and liquid reaches the valve. It also allows maximum heat exchanger use as minimizes the portion of the heat exchangers used to change the temperature of the fluid, and maximizes
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the volume in which the refrigerant changes its phase (phenomena involving much more heat flow, the base principle of vapor-compression refrigeration). An internal heat exchanger is simply a heat exchanger that uses the cold gas leaving the evaporator coil to cool the high-pressure liquid that is headed into the beginning of the evaporator coil via an expansion device. The gas is used to chill a chamber that normally has a series of pipes for the liquid running through it. The superheated gas then proceeds on to the compressor. The subcooling term refers to cooling the liquid below its boiling point. 10 °F (5.6 °C) of subcooling means it is 10 °F colder than boiling at a given pressure. As it represents a difference of temperatures, the subcooling value is not measured on an absolute temperature scale, only on a relative scale as a temperature difference. == See also == Countercurrent exchange Regenerative heat exchanger Feedwater heater Thermal efficiency == References == Hills, Richard L. (1989). Power from Steam. Cambridge University Press. ISBN 0-521-45834-X.
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In electrochemistry, polarization is a collective term for certain mechanical side-effects (of an electrochemical process) by which isolating barriers develop at the interface between electrode and electrolyte. These side-effects influence the reaction mechanisms, as well as the chemical kinetics of corrosion and metal deposition.: 56 In a reaction, the attacking reagents can displace the bonding electrons. This electronic displacement in turn may be due to certain effects, some of which are permanent (inductive and mesomeric effects), and the others are temporary (electromeric effect). Those effects which are permanently operating in the molecule are known as polarization effects, and those effects which are brought into play by attacking reagent (and as the attacking reagent is removed, the electronic displacement disappears) are known as polarisability effects. The term 'polarization' derives from the early 19th-century discovery that electrolysis causes the elements in an electrolyte to be attracted towards one or the other pole— i.e. the gasses were polarized towards the electrodes. Thus, initially polarization was essentially a description of electrolysis itself, and in the context of electrochemical cells used to describe the effects on the electrolyte (which was then called "polarization liquid"). In time, as more electrochemical processes were invented, the term polarization evolved to denote any (potentially undesirable) mechanical side-effects that occur at the interface between electrolyte and electrodes. These mechanical side-effects are: activation polarization: the accumulation of gasses (or other non-reagent products) at the interface between electrode and electrolyte. concentration polarization: uneven depletion of reagents in the electrolyte cause concentration gradients in boundary layers. Both effects isolate the electrode from the electrolyte, impeding reaction and charge transfer between the two. The immediate consequences of these barriers are: the reduction potential decreases, the reaction rate slows and eventually halts. electric current is increasingly converted into heat rather than into desired electrochemical work.
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"page_id": 25037439,
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as predicted by Ohm's law, either electromotive force decreases and current increases, or vice versa. the self-discharge rate increases in electrochemical cells. Each of these immediate consequences has multiple secondary effects. For instance, heat affects the crystalline structure of the electrode material. This in turn can influence reaction rate, and/or accelerate dendrite formation, and/or deform the plates, and/or precipitate thermal runaway. The mechanical side-effects can be desirable in some electrochemical processes, for example, certain types of electropolishing and electroplating take advantage of the fact that evolved gasses will first accumulate in the depressions of the plate. This feature can be used to reduce current in the depressions, and exposes ridges and edges to higher currents. Undesirable polarization can be suppressed by vigorous agitation of the electrolyte, or – when agitation is impractical (such as in a stationary battery) – with a depolarizer. == See also == Depolarizer Nernst equation == References ==
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This article discusses women who have made an important contribution to the field of physics. == International physics awards == === Nobel laureates === Five women have won the Nobel Prize in Physics, awarded annually since 1901 by the Royal Swedish Academy of Sciences. These are: 1903 Marie Curie: "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel" 1963 Maria Goeppert Mayer: "for their discoveries concerning nuclear shell structure" 2018 Donna Strickland: "for their method high-intensity, ultra-short optical pulses" 2020 Andrea Ghez: "for the discovery of a supermassive compact object at the centre of our galaxy." 2023 Anne L'Huillier "for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter." Marie Curie was the first woman to be nominated in 1902 and to receive the prize in 1903 and shared 1/2 of the prize with her husband Pierre Curie for their joint work on radioactivity, discovered by Henri Becquerel who got the other half of the prize. Marie Curie was the first woman to also receive the Nobel Prize in Chemistry in 1911, making her the first person to win two Nobel prizes and, as of 2023, the only person to be awarded two Nobel prizes in two different scientific categories. Maria Goeppert Mayer became the second woman to win the prize in 1963, for the theoretical development of the nuclear shell model, a half of the prize shared with J. Hans D. Jensen (the other half given to Eugene Wigner). Donna Strickland shared half of the prize in 2018 with Gérard Mourou, for their work in chirped pulse amplification beginning in the 1980s (the other half given to Arthur Ashkin). Andrea Ghez was the fourth female Nobel laureate in 2020,
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she shared one half of the prize with Reinhard Genzel for the discovery of the supermassive compact object Sagittarius A* at the center of our galaxy (the other half given to Roger Penrose). In 2023, Anne L'Huillier shared the prize in equal parts with Pierre Agostini and Ferenc Krausz for their experimental contribution and development of attosecond physics. L'Huillier is the first female laureate to receive 1/3 of monetary award of the Nobel Prize in Physics (Curie, Goeppert–Mayer, Strickland and Ghez received 1/4). Physicists and physicochemists that won a Nobel Prize in Chemistry include Marie Curie, Irène Joliot-Curie, daughter of Marie Curie, in 1935, and Dorothy Hodgkin in 1964. Nuclear physicist Rosalyn Sussman Yalow was the second female scientist to win the Nobel Prize in Physiology or Medicine in 1977 for the development of radioimmunoassays. Human right activist and 2023 Nobel Peace Prize, Narges Mohammadi, was trained in nuclear physics. ==== Nobel nominees and nominators ==== According to the Nobel archives (updated up to 1970), other physicists that were nominated to the Nobel Prize in Physics but did not receive it, include: Lise Meitner, nominated 21 times; Chien-Shiung Wu, nominated 5 times; Marietta Blau, nominated 3 times; and Hertha Wambacher, Margaret Burbidge and Janine Connes, nominated once. Irène Joliot-Curie and Dorothy Hodgkin were also nominated for the Nobel Prize in Physics, but received a Nobel Prize in Chemistry in 1935 and 1964, respectively. Lise Meitner is the female physicist the most nominated, 16 times for Physics and 14 times for Chemistry. About 1.7% of the Nobel nominations in Physics up to 1970 were women. Aside from the named above, other physicists and physicochemists that were nominated to the Nobel Prize in Chemistry but dit not receive it, include Ida Noddack, Marguerite Perey, Alberte Pullman, and Erika Cremer. Up to 1970,
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eight female scientists have participated as nominators for the Nobel Prize in Physics. These are Marie Curie, Hertha Sponer, Marie-Antoinette Tonnelat, Anne Barbara Underhill, Katharina Boll-Dornberger, Maria Goeppert Mayer, Dorothy Hodgkin, and Margaret Burbidge. ==== Clarivate Citation ==== Several women have been selected as Clarivate Citation laureates in Physics, which makes an annual list of possible candidates for the Nobel Prize in Physics based on citation statistics, these include: 2008 Vera Rubin † "for her pioneering research indicating the existence of dark matter in the universe." 2012 Lene Hau "for the experimental demonstration of electromagnetically induced transparency 'slow light' (with Stephen E. Harris)." 2015 Deborah S. Jin † "for pioneering research on atomic gases at ultra-cold temperatures and the creation of the first fermionic condensate." 2018 Sandra Faber "for pioneering methods to determine the age, size and distance of galaxies and for other contributions to cosmology." 2023 Sharon Glotzer "for demonstrating the role of entropy in the self-assembly of matter and for introducing strategies to control the assembly process to engineer new materials." †: deceased, no longer eligible. === Wolf Prize === Two women have been awarded the Wolf Prize in Physics, awarded by the Wolf Foundation in Israel since 1978. They are: 1978 Chien-Shiung Wu, "for her explorations of the weak interaction, helping establish the precise form and the non-conservation of parity for this natural force." 2022 Anne L'Huillier, "for pioneering contributions to ultrafast laser science and attosecond physics". === Breakthrough Prize === Women who have been awarded the Breakthrough Prize in Fundamental Physics since 2012, include: 2018 WMAP Probe team, 27 listed members, including Hiranya Peiris, Licia Verde, Janet L. Weiland and Joanna Dunkley for "For detailed maps of the early universe that greatly improved our knowledge of the evolution of the cosmos and the fluctuations that seeded
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the formation of galaxies." 2018 Special recognition to Jocelyn Bell Burnell for "For fundamental contributions to the discovery of pulsars, and a lifetime of inspiring leadership in the scientific community." === Prizes only for female physicists === L'Oréal-UNESCO For Women in Science Awards, awarded bi-annually to one laureate per continent for outstanding contributions to the physical sciences. Maria Goeppert-Mayer Award of the American Physical Society awarded annually in recognition of an outstanding contribution to physics research. Jocelyn Bell Burnell Medal and Prize by the Institute of Physics in UK, for contributions to physics by a very early career physicist. Annie Jump Cannon Award in Astronomy awarded annually for outstanding contributions to astronomy within five years of earning a doctorate degree. == Topics named after female scientists == Female scientist have sometimes not been recognized in the naming of topics they discovered due to Matilda effect. Some physics phenomena that are named after female scientists include: === Physical models and theories === Birge–Sponer method, in molecular physics, partially named after Hertha Sponer. Fermi–Pasta–Ulam–Tsingou problem in chaos theory, partially named after Mary Tsingou. Frenkel–Kontorova model, in non-linear physics, partially named after Tatiana Kontorova. Kovalevskaya top in rotational dynamics, named after Sofya Kovalevskaya. Pasterski–Strominger–Zhiboedov triangle in quantum gravity, is partially named after Sabrina Gonzalez Pasterski. Peccei–Quinn theory in particle physics, partially named after Helen Quinn. Pöschl–Teller potential in quantum mechanics, partially named after Herta Pöschl. Randall–Sundrum model in theoretical physics, partially named after Lisa Randall. Falkner–Skan boundary layer in fluid mechanics, partially named after Sylvia Skan === Physical phenomena and empirical laws === Faber–Jackson relation, in astronomomy, partially named after Sandra Faber. Goos–Hänchen effect in optics, partially named after Hilda Hänchen. Leavitt's law in astronomy, named after Henrietta Swan Leavitt. Pockels point in surface physics, named after Agnes Pockels. Rubin–Ford effect in cosmology,
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partially named after Vera Rubin. === Physical theorems === Bohr–Van Leeuwen theorem in thermodynamics, partially named after Hendrika Johanna van Leeuwen Coffman–Kundu–Wootters inequality, in quantum information, partially named after Valerie Coffman Noether's theorem in modern physics, named after Emmy Noether === Experiments and equipment === Langmuir–Blodgett film, partially named after Katharine Burr Blodgett Curie (unit), Ci, partially named after Marie Curie Morton number (dimensionless number), Mo, used to characterize bubbles is named after Rose Morton Goeppert Mayer (unit), GM, unit of absorption cross section named after Maria Goeppert Mayer Wu experiment named after Chien-Shiung Wu == Timeline == === Antiquity === c. 150 BCE: Aglaonice became the first female astronomer to be recorded in Ancient Greece. c. 355–415 CE: Greek astronomer, mathematician and philosopher, Hypatia became renowned as a respected academic teacher, editor of Ptolemy's Almagest astronomical data, and head of her own science academy. === 16th century === 1572: astronomer Sophia Brahe assists her older brother Tycho Brahe finding a new bright object in the night sky, now known as called SN 1572 (a supernova). Sophia would help her brother in astronomy throughout his life. === 17th century === 1650: astronomer Maria Cunitz publishes Urania Propitia. 1668: After separating from her husband, French polymath Marguerite de la Sablière established a popular salon in Paris. Scientists and scholars from different countries visited the salon regularly to discuss ideas and share knowledge, and Sablière studied physics, astronomy and natural history with her guests. 1680: Astronomer Jeanne Dumée published a summary of arguments supporting the Copernican theory of heliocentrism. She wrote "between the brain of a woman and that of a man there is no difference". 1690: astronomer Elisabeth Hevelius published Prodromus Astronomiae, compiling the star catalog of 1560 stars by her and her husband Johannes Hevelius. 1693–1698: German astronomer and illustrator
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Maria Clara Eimmart created more than 350 detailed drawings of the moon phases. === 18th century === 1702: Maria Margaretha Kirch becomes the first woman to discover a comet. 17010: Due to her various contribution Maria Margaretha Kirch ask to enter the Royal Berlin Academy of Sciences. The request was denied. 1715: Eustachio Manfredi and his sisters Maddalena and Teresa Manfredi publish Ephemerides of Celestial Motion. The learning of the Manfredi sisters was acknowledged by Pope Benedict XIV. 1732: At the age of 20, Italian physicist Laura Bassi became the first female member of the Bologna Academy of Sciences. One month later, she publicly defended her academic theses and received a PhD. Bassi was awarded an honorary position as professor of physics at the University of Bologna. She was the first female physics professor in the world. 1738: French polymath Émilie du Châtelet became the first woman to have a paper published by the Paris Academy, following a contest on the nature of fire. 1740: Du Châtelet publishes Institutions de Physique, or Foundations of Physics, providing a metaphysical basis for Newtonian physics. 1751: 19-year-old Italian physicist Cristina Roccati received her PhD from the University of Bologna. 1755: Sculptor Jean-Jacques Caffieri makes a medallion of physicist Maria Angela Ardinghelli to be hung in French Academy of Sciences. The academy did not accept female members at the time. Ardinghelli worked as the main correspondent and translator between Paris and Naples in terms of physics discussions. 1757: Nicole-Reine Lepaute works out the return of Halley's Comet, in collaboration with Alexis Clairaut and Jérôme Lalande. 1776: At the University of Bologna, Italian physicist Laura Bassi became the first woman appointed as chair of physics at a university. 1789: astronomer Louise du Pierry becomes the first female professor at the Sorbonne. 1798: Marie-Jeanne de Lalande
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and Princess Charlotte of Saxe-Meiningen are the only female astronomers in the first European congress of astronomers. === 19th century === 1806: Carl Friedrich Gauss recognizes Marie-Jeanne de Lalande as the only woman he knows working in science. Unaware that his correspondent Sophie Germain was a woman. 1816: French mathematician and physicist Sophie Germain became the first women to win a prize from the Paris Academy of Sciences for her work on elasticity theory. 1828: Caroline Herschel, sister of William Herschel, becomes the first woman to publish in the Philosophical Transactions of the Royal Society and is awarded the Gold Medal of the Royal Astronomical Society. 1835: Caroline Herschel and Mary Somerville became the first female Honorary Members of the Royal Astronomical Society. 1856: Amateur scientist Eunice Newton Foote provides the first demonstration of the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide (greenhouse effect). 1890: Alice Everett becomes the first woman to be employed and payed at the Royal Observatory, Greenwich. 1891: Agnes Pockels, gets help from Rayleigh to publish her first paper on nature of surface tension. There she first introduces the concept of the Pockels point and pioneers the field of surface science. 1893: Alice Everett becomes the first woman to have a paper published by the Physical Society of London. 1895: Margaret Eliza Maltby becomes the first woman to earn a doctorate in the University of Göttingen. 1896: Elizabeth Stephansen becomes the first woman to complete the physics program of Zurich Polytechnic. 1897: American physicist Isabelle Stone became the first woman to receive a PhD in physics in the United States. She wrote her dissertation "On the Electrical Resistance of Thin Films" at the University of Chicago. 1898: Danish
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physicist Kirstine Meyer was awarded the gold medal of the Royal Danish Academy of Sciences and Letters. 1888: The Kovalevskaya top, one of a brief list of known examples of integrable rigid body motion, was discovered by Sofia Kovalevskaya. 1899: Irish physicist Edith Anne Stoney was appointed a physics lecturer at the London School of Medicine for Women, becoming the first woman medical physicist. She later became a pioneering figure in the use of x-ray machines on the front lines of World War I. 1899: American physicists Marcia Keith and Isabelle Stone became charter members of the American Physical Society. === 20th century === ==== 1900s ==== 1903: Marie Curie was the first woman to receive a Nobel Prize; she received the Nobel Prize in Physics along with her husband, Pierre Curie "for their joint researches on the radiation phenomena discovered by Professor Henri Becquerel", and Henri Becquerel, "for his discovery of spontaneous radioactivity". 1900: Physicists Marie Curie and Isabelle Stone attended the first International Congress of Physics in Paris, France. They were the only two women out of 836 participants. 1904: Annie S. D. Maunder and her husband Edward Walter Maunder publish the butterfly diagram to study sunspots. They also identify the Maunder Minimum. 1906: English physicist, mathematician and engineer Hertha Ayrton became the first female recipient of the Hughes Medal from the Royal Society of London. She received the award for her experimental research on electric arcs and sand ripples. The first woman to be nominated for the Royal Society and to give a lecture to the Society. 1907: Ayrton joins the Suffragettes and the Women's Social and Political Union (WSPU). 1909: Danish physicist Kristine Meyer became the first Danish woman to receive a doctorate degree in natural sciences. She wrote her dissertation on the topic of "the
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development of the temperature concept" within the history of physics. ==== 1910s ==== 1911: Marie Curie became the first woman to receive the Nobel Prize in Chemistry, which she received "[for] the discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element". This made her the only woman to win two Nobel Prizes. 1912: Astronomer Henrietta Swan Leavitt studied the bright-dim cycle periods of Cepheid stars, then found a way to calculate the distance from such stars to Earth. 1913: Geertruida de Haas-Lorentz is the first to study of thermal noise in electric circuits, predating the discovery of the Johnson–Nyquist noise. 1918: Emmy Noether created Noether's theorem explaining the connection between symmetry and conservation laws. 1919: Hendrika Johanna van Leeuwen proves the Bohr–Van Leeuwen theorem in her thesis explaining why magnetism is an essentially quantum mechanical effect. ==== 1920s ==== 1922: the International Astronomical Union adopts the stellar classification used by Annie Jump Cannon. She came up with the first serious attempt to organize and classify stars based on their temperatures and spectral types. 1925: Annie Jump Cannon became the first woman to receive an honorary doctorate of science from Oxford University. 1925: Astrophysicist Cecilia Payne-Gaposchkin established that hydrogen is the most common element in stars, and thus the most abundant element in the universe. 1926: Katharine Burr Blodgett was the first women to earn a Ph.D. in physics from the University of Cambridge. 1926: The first application of quantum mechanics to molecular systems was done by Lucy Mensing. She studied the rotational spectrum of diatomic molecules using the methods of matrix mechanics. ==== 1930s ==== 1931: Sylvia Skan and Victor Montague Falkner publish their work on the Falkner–Skan boundary layer. 1933: Herta Pöschl (abbreviated G.
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Pöschl) working with Edward Teller, find that the Pöschl–Teller potential is analytically solvable in quantum mechanics. 1934: Olga N. Trapeznikowa and his husband Lev Shubnikov finish an experiment showing one of the first evidences for the existence of antiferromagnetism. 1935: Katharine Burr Blodgett improves Irving Langmuir experimental set up leading to the development of the Langmuir–Blodgett trough and the discovery of the Langmuir–Blodgett films. 1935: Grete Hermann provides the earliest refutation to John von Neumann's attempt to prove that quantum mechanics is incompatible with hidden variables. 1936: Hertha Sponer becomes the first female professor in the physics faculty in Duke University. 1937: Marietta Blau and her student Hertha Wambacher, both Austrian physicists, received the Lieben Prize of the Austrian Academy of Sciences for their work on cosmic ray observations using the technique of nuclear emulsions. 1938: Tatiana Kontorova, in collaboration with Yakov Frenkel, develops the Frenkel-Kontorova model to describe the structure and nonlinear dynamics of a crystal lattice in the vicinity of the dislocation core. 1939 Lise Meitner helped lead a small group of scientists who first discovered the nuclear fission of uranium when it absorbed an extra neutron. Nuclear physicist Marguerite Perey discovers francium. Sameera Moussa became the first woman to earn a doctorate in atomic radiation and the first woman to hold a teaching post in Cairo University. ==== 1940s ==== c. 1940: Elizabeth Alexander and Ruby Payne-Scott become the first women to work in radio astronomy. Making important results on the study of radar signals coming from the sun. 1941: Ruby Payne-Scott joined the Radio Physics Laboratory of the Australia Government's CSIRO; she was the first woman radio astronomer. 1942: Chicago Pile-1 led by Enrico Fermi, the first nuclear reactor reaches criticality. Leona Woods was the only woman in the team and she was instrumental in the
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"page_id": 7932544,
"source": null,
"title": "Women in physics"
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construction and then use of geiger counters for analysis during experimentation. 1943: the Manhattan project hires the Calutron Girls, a large group of young girls to monitor dials and watch meters for calutrons, mass spectrometers adapted for separation of uranium isotopes, unaware of the purpose of the project. 1943: Berta Karlik discovers astatine as a product of two naturally occurring decay chains. She was awarded the Haitinger Prize of the Austrian Academy of Sciences for this discovery. 1944: Curium (atomic number 96, symbol Cm) gets discovered a gets named after Marie and Pierre Curie, the "m" in Cm as a reference to Marie. 1945: American physicists and mathematicians Frances Spence, Ruth Teitelbaum, Marlyn Meltzer, Betty Holberton, Jean Bartik and Kathleen Antonelli programmed the electronic general-purpose computer ENIAC, becoming some of the world's first computer programmers. 1947: Hilda Hänchen, in collaboration with Fritz Goos, demonstrates a new optical phenomena, now known as the Goos–Hänchen effect. 1949: Rosemary Brown (later Fowler), a student of C.F. Powell at the University of Bristol, discovers the k-meson in what Heisenberg calls "most beautiful" pictures of cosmic ray tracks from the Jungfraujoch (the 'k' track in Brown, R. et al. Nature, 163, 47 (1949). This discovery and the prior finding of a very similar particle in 1947 led to the "τ–θ puzzle", the discovery of parity violation in weak interactions, and hence the Standard Model. ==== 1950s ==== 1951: Cécile DeWitt-Morette founds the École de physique des Houches, one of the most prestigious scientific centers for international physics summer schools in Europe. 1952: Photograph 51, an X-ray diffraction image of crystallized DNA, was taken by Raymond Gosling in May 1952, working as a PhD student under the supervision of British chemist and biophysicist Rosalind Franklin; it was critical evidence in identifying the structure of DNA. 1952:
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
}
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Yvonne Choquet-Bruhat proves that Einstein field equations can be formulated as an initial value problem (local existence of solutions and uniqueness). 1953: Various authors, including Arianna W. Rosenbluth and Augusta H. Teller, led by Nicholas Metropolis, write the paper titled "Equation of State Calculations by Fast Computing Machines" that introduced the Metropolis–Hastings algorithm. 1953: Rose Morton and William L. Haberman identify a constant to characterize bubbles. The constant is now called the Morton number. 1954: Janine Connes pioneers the new field of Fourier transform infrared spectroscopy for astronomy. 1954: Sulamith Goldhaber, along with her husband Gerson Goldhaber, start a series of important experiments to measure the properties of the K meson. 1955: the results of the Fermi–Pasta–Ulam–Tsingou simulation is published in Los Alamos National Laboratory. It was coded by Mary Tsingou using the MANIAC I computer working with Enrico Fermi, John Pasta, and Stanislaw Ulam in the Manhattan Project. It represents one of the first computational experiments in mathematics and chaos theory. 1956: Chinese-American physicist Chien-Shiung Wu conducted a nuclear physics experiment in collaboration with the Low Temperature Group of the US National Bureau of Standards. The experiment, becoming known as the Wu experiment, showed that parity could be violated in weak interaction. 1957: Margaret Burbidge releases the landmark B2FH paper as first author along with Geoffrey Burbidge, William A. Fowler, and Fred Hoyle. The paper reviewed stellar nucleosynthesis theory and identified nucleosynthesis processes that are responsible for producing the elements heavier than iron and explained their relative abundances. 1958: Olga Ladyzhenskaya provides the first rigorous proofs of the convergence of a finite difference method for the Navier–Stokes equations. 1960: American medical physicist Rosalyn Yalow received the Nobel Prize in Physiology or Medicine "for the development of radioimmunoassays of peptide hormones" along with Roger Guillemin and Andrew V. Schally who
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
}
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received it "for their discoveries concerning the peptide hormone production of the brain". ==== 1960s ==== 1961: Ellen Fetter and Margaret Hamilton were collaborators with Edward Norton Lorenz in weather forecasting, establishing together modern chaos theory. 1962: French physicist Marguerite Perey became the first female Fellow elected to the Académie des Sciences. 1963: Maria Goeppert Mayer became the first American woman to receive a Nobel Prize in Physics; she shared the prize with J. Hans D. Jensen "for their discoveries concerning nuclear shell structure” and Eugene Paul Wigner "for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles". 1963: Experiments by Myriam Sarachik provided the first data that confirmed the Kondo effect. 1964: Chien-Shiung Wu spoke at MIT about gender discrimination. 1967: Astrophysicist Jocelyn Bell Burnell co-discovered the first radio pulsars.: minute 8:59 1970: Astronomer Vera Rubin published the first evidence for dark matter. 1970: Madeleine Veyssié, coins the term soft matter. ==== 1970s ==== 1971 Mina Rees became the first woman president of American Association for the Advancement of Science (AAAS) founded in 1848. 1972: Willie Hobbs Moore became the first African-American woman to receive a Ph.D. in physics. 1972: Sandra Faber became the first woman to join the Lick Observatory staff at the University of California, Santa Cruz. 1973: American physicist Anna Coble became the first African-American woman to receive a PhD in biophysics, completing her dissertation at University of Illinois. 1975: Mary K. Gaillard, working with Benjamin W. Lee and Jonathan L. Rosner, predicts the mass of the charm quark before it was measured. She will later also predict the mass of the bottom quark. 1975: María Teresa Ruiz, becomes the first woman to obtain a PhD in astrophysics at Princeton University. 1976:
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
}
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Sandra Faber publishes her Faber–Jackson relation, providing the first empirical power-law relation between the luminosity and the central stellar velocity dispersion of elliptical galaxy. 1977: Helen Quinn develops the Peccei–Quinn theory as one of the first possible solutions to the strong CP problem, in collaboration with Roberto Peccei. 1978: Chien-Shiung Wu becomes the inaugural laureate of the Wolf Prize in Physics for her help with the development of the Standard Model. 1980: Nigerian geophysicist Deborah Ajakaiye became the first woman in any West African country to be appointed a full professor of physics. Over the course of her scientific career, she became the first female Fellow elected to the Nigerian Academy of Science, and the first female dean of science in Nigeria. 1980: Mary K. Gaillard produces a report at CERN (European Organization for Nuclear Research) addressing the fact that just 3% of the staff were women. She called for the elimination of gender discrimination through equality in promotion, maternity leave and full-day child care. ==== 1980s ==== 1981: Mary K. Gaillard becomes the first woman with a tenured position in the physics faculty at the University of California, Berkeley. 1985: Mildred Dresselhaus was appointed the first women Institute Professor at MIT 1986: Maria Goeppert Mayer Award was awarded for the first time to honor young female physicists at the beginning of their careers 1986 Jean M. Bennett became the first woman president of The Optical Society founded in 1916. ==== 1990s ==== 1991: Ana María López, graduate student of Eduardo Fradkin, develops the first Chern–Simons theory for composite fermions to explain the fractional quantum Hall effect. 1992: Claudine Hermann first woman to be appointed professor at École Polytechnique. 1995: Reva Williams works out the Penrose process for rotating black holes. 1997: Chemical element with atomic number 278 is officially
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
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named meitnerium, after Lise Meitner. 1999: Lisa Randall published the Randall–Sundrum model, with Raman Sundrum. 2000 Mildred Dresselhaus became the director of the Office of Science at the United States Department of Energy. Helen Quinn becomes the first woman to receive the Dirac Medal of the International Centre for Theoretical Physics (ICTP) "pioneering contributions to the quest for a unified theory of quarks and leptons and the strong, weak and electromagnetic interactions." Valerie Coffman, working with Joydip Kundu and William Wootters establish the concept of monogamy of entanglement for tripartite systems, using their Coffman–Kundu–Wooters inequality. === 21st century === ==== 2000s ==== 2001: Lene Hau stopped a beam of light completely 2001: Wendy Freedman and her team published the measured Hubble constant from measurements of the Hubble Space Telescope. 2003: Geophysicist Claudia Alexander oversaw the final stages of Project Galileo, a space exploration mission that ended at the planet Jupiter. Deborah S. Jin and her team were the first to condense pairs of fermionic atoms Physicists Ayşe Erzan, Karimat El-Sayed, Li Fanghua, Mariana Weissmann and Anneke Levelt Sengers win the first L'Oréal-UNESCO For Women in Science Awards in Physical Sciences. 2005: Myriam Sarachik becomes the first woman to win the Oliver E. Buckley Condensed Matter Prize for her contributions to quantum spin dynamics and spin coherence in condensed matter systems, along with David Awschalom and Gabriel Aeppli. 2007: Physicist Ibtesam Badhrees was the first Saudi Arabian woman to become a member of the European Organization for Nuclear Research (CERN). 2009: Margaret Reid becomes the first woman to win the Moyal Medal fromm Macquarie University, for her In 2019, her work on how to demonstrate the Einstein-Podolsky-Rosen paradox using squeezing and parametric down conversion. ==== 2010s ==== 2011: Taiwanese-American astrophysicist Chung-Pei Ma led a team of scientists in discovering two of
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{
"page_id": 7932544,
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the largest black holes ever observed. 2012: Mildred Dresselhaus becomes the first female laureate of the Kavli Prize in Nanosciences "for her pioneering contributions to the study of phonons, electron-phonon interactions, and thermal transport in nanostructures". 2013: Nashwa Eassa founded the NGO Sudanese Women in Sciences. 2014: American theoretical physicist Shirley Anne Jackson was awarded the National Medal of Science. Jackson had been the first African-American woman to receive a PhD from the Massachusetts Institute of Technology (MIT) during the early 1970s, and the first woman to chair the U.S. Nuclear Regulatory Commission. 2014: Amanda Barnard becomes the first woman to win the Feynman Prize in Nanotechnology for her computational simulations on diamond nanoparticles. 2015: Sabrina Gonzalez Pasterski, working with Andrew Strominger and Alexander Zhiboedov, develops the Pasterski–Strominger–Zhiboedov triangle relating soft particle theorems of quantum field theory, symmetries of space-time and memory effects in gravitational waves. 2016: Fabiola Gianotti became the first woman Director-General of CERN (European Organization for Nuclear Research) 2018: Astrophysicists Hiranya Peiris and Joanna Dunkley and Italian cosmologist Licia Verde were among 27 scientists awarded the Breakthrough Prize in Fundamental Physics for their contributions to "detailed maps of the early universe that greatly improved our knowledge of the evolution of the cosmos and the fluctuations that seeded the formation of galaxies". Astrophysicist Jocelyn Bell Burnell received the special Breakthrough Prize in Fundamental Physics for her scientific achievements and “inspiring leadership”, worth $3 million. She donated the entirety of the prize money towards the creation of scholarships to assist women, underrepresented minorities and refugees who are pursuing the study of physics. Physicist Donna Strickland received the Nobel Prize in Physics "for groundbreaking inventions in the field of laser physics"; she shared it with Arthur Ashkin and Gérard Mourou. For the first time in history, women received the Nobel
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
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Prize in Chemistry and the Nobel Prize in Physics in the same year. Human right activist and physicist Narges Mohammadi wins the Andrei Sakharov prize by the American Physical Society, "for her leadership in campaigning for peace, justice, and the abolition of the death penalty and for her unwavering efforts to promote the human rights and freedoms of the Iranian people, despite persecution that has forced her to suspend her scientific pursuits and endure lengthy incarceration." Ewine van Dishoeck becomes the first female laureate of the Kavli Prize in Astrophysics for "for her combined contributions to observational, theoretical, and laboratory astrochemistry, elucidating the life cycle of interstellar clouds and the formation of stars and planets" 2019: Mathematician Karen Uhlenbeck became the first woman to win the Abel Prize for "her pioneering achievements in geometric partial differential equations, gauge theory, and integrable systems, and for the fundamental impact of her work on analysis, geometry and mathematical physics." 2020: Andrea M. Ghez received the Nobel Prize in Physics "for the discovery of a supermassive compact object at the centre of our galaxy." She shared half of the prize with Reinhard Genzel, while the other half was awarded to Roger Penrose. Geoscientist Ingeborg Levin was the first woman to receive the Alfred Wegener medal from the European Geosciences Union "for fundamental contributions to our present knowledge and understanding of greenhouse gases in the atmosphere, including the global carbon cycle." Françoise Combes becomes the first female astrophysicist to win the CNRS Gold Medal, highest degree in research by the French government. ==== 2020s ==== 2022: Anne L’Huillier becomes the second female scientist to receive the Wolf Prize in Physics “for pioneering contributions to ultrafast laser science and attosecond physics”. 2022: Astronomer Ewine van Dishoeck is awarded the UNESCO Niels Bohr Medal. 2023: Professor Polina
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{
"page_id": 7932544,
"source": null,
"title": "Women in physics"
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Bayvel becomes the first woman to win the Rumford Medal by the Royal Society. 2023: Anne l'Huillier receives the 2023 Nobel Prize in Physics for "for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter" shared with Pierre Agostini and Ferenc Krausz. == See also == Timeline of women in science Timeline of women in science in the United States Women in NASA Women in science Women in the workforce == References ==
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{
"page_id": 7932544,
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Superlubricity is a regime of relative motion in which friction vanishes or very nearly vanishes. However, the definition of "vanishing" friction level is not clear, which makes the term vague. As an ad hoc definition, a kinetic coefficient of friction less than 0.01 can be adopted. This definition also requires further discussion and clarification. Superlubricity may occur when two crystalline surfaces slide over each other in dry incommensurate contact. This was first described in the early 1980s for Frenkel–Kontorova models and is called the Aubry transition. It has been extensively studied as a mathematical model, in atomistic simulations and in a range of experimental systems. This effect, also called structural lubricity, was verified between two graphite surfaces in 2004. The atoms in graphite are oriented in a hexagonal manner and form an atomic hill-and-valley landscape, which looks like an egg-crate. When the two graphite surfaces are in registry (every 60 degrees), the friction force is high. When the two surfaces are rotated out of registry, the friction is greatly reduced. This is like two egg-crates which can slide over each other more easily when they are "twisted" with respect to each other. Observation of superlubricity in microscale graphite structures was reported in 2012, by shearing a square graphite mesa a few micrometers across, and observing the self-retraction of the sheared layer. Such effects were also theoretically described for a model of graphene and nickel layers. This observation, which is reproducible even under ambient conditions, shifts interest in superlubricity from a primarily academic topic, accessible only under highly idealized conditions, to one with practical implications for micro and nanomechanical devices. A state of ultralow friction can also be achieved when a sharp tip slides over a flat surface and the applied load is below a certain threshold. Such a "superlubric" threshold
|
{
"page_id": 592513,
"source": null,
"title": "Superlubricity"
}
|
depends on the tip-surface interaction and the stiffness of the materials in contact, as described by the Tomlinson model. The threshold can be significantly increased by exciting the sliding system at its resonance frequency, which suggests a practical way to limit wear in nanoelectromechanical systems. Superlubricity was also observed between a gold AFM tip and Teflon substrate due to repulsive Van der Waals forces and a hydrogen-bonded layer formed by glycerol on the steel surfaces. Formation of the hydrogen-bonded layer was also shown to lead to superlubricity between quartz glass surfaces lubricated by biological liquid obtained from mucilage of Brasenia schreberi. Other mechanisms of superlubricity may include: (a) thermodynamic repulsion due to a layer of free or grafted macromolecules between the bodies so that the entropy of the intermediate layer decreases at small distances due to stronger confinement; (b) electrical repulsion due to external electrical voltage; (c) repulsion due to electrical double layer; (d) repulsion due to thermal fluctuations. The similarity of the term superlubricity with terms such as superconductivity and superfluidity is misleading; other energy dissipation mechanisms can lead to a finite (normally small) friction force. Superlubricity is more analogous to phenomena such as superelasticity, in which substances such as Nitinol have very low, but nonzero, elastic moduli; supercooling, in which substances remain liquid until a lower-than-normal temperature; super black, which reflects very little light; giant magnetoresistance, in which very large but finite magnetoresistance effects are observed in alternating nonmagnetic and ferromagnetic layers; superhard materials, which are diamond or nearly as hard as diamond; and superlensing, which have a resolution which, while finer than the diffraction limit, is still finite. == Macroscale == In 2015, researchers first obtained evidence for superlubricity at microscales. The experiments were supported by computational studies. The Mira supercomputer simulated up to 1.2 million atoms
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{
"page_id": 592513,
"source": null,
"title": "Superlubricity"
}
|
for dry environments and up to 10 million atoms for humid environments. The researchers used LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) code to carry out reactive molecular dynamics simulations. The researchers optimized LAMMPS and its implementation of ReaxFF by adding OpenMP threading, replacing MPI point-to-point communication with MPI collectives in key algorithms, and leveraging MPI I/O. These enhancements doubled performance. == Applications == Friction is known to be a major consumer of energy; for instance in a detailed study it was found that it may lead to one third of the energy losses in new automobile engines. Superlubricious coatings could reduce this. Potential applications include computer hard drives, wind turbine gears, and mechanical rotating seals for microelectromechanical and nanoelectromechanical systems. == See also == Friction force microscopy Tomlinson model == References ==
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{
"page_id": 592513,
"source": null,
"title": "Superlubricity"
}
|
Voltage-gated proton channels are ion channels that have the unique property of opening with depolarization, but in a strongly pH-sensitive manner. The result is that these channels open only when the electrochemical gradient is outward, such that their opening will only allow protons to leave cells. Their function thus appears to be acid extrusion from cells. Another important function occurs in phagocytes (e.g. eosinophils, neutrophils, and macrophages) during the respiratory burst. When bacteria or other microbes are engulfed by phagocytes, the enzyme NADPH oxidase assembles in the membrane and begins to produce reactive oxygen species (ROS) that help kill bacteria. NADPH oxidase is electrogenic, moving electrons across the membrane, and proton channels open to allow proton flux to balance the electron movement electrically. The functional expression of Hv1 in phagocytes has been well characterized in mammals, and recently in zebrafish, suggesting its important roles in the immune cells of mammals and non-mammalian vertebrates. A group of small molecule inhibitors of the Hv1 channel are shown as chemotherapeutics and anti-inflammatory agents. When activated, the voltage-gated proton channel Hv1 can allow up to 100,000 hydrogen ions across the membrane each second. Whereas most voltage-gated ion channels contain a central pore that is surrounding by alpha helices and the voltage-sensing domain (VSD), voltage-gated hydrogen channels contain no central pore, so their voltage-sensing regions (VSD) carry out the job of bringing acidic protons across the membrane. Because the relative H+ concentrations on each side of the membrane result in a pH gradient, these voltage-gated hydrogen channels only carry outward current, meaning they are used to move acidic protons out of the membrane. As a result, the opening of voltage-gated hydrogen channels usually hyperpolarize the cell membrane, or makes the membrane potential more negative. A recent discovery has shown that the voltage-gated proton channel Hv1
|
{
"page_id": 13437576,
"source": null,
"title": "Voltage-gated proton channel"
}
|
is highly expressed in human breast tumor tissues that are metastatic, but not in non-metastatic breast cancer tissues. Because it has also been found to be highly expressed in other cancer tissues, the study of the voltage-gated proton channel has led many scientists to wonder what its importance is in cancer metastasis. However, much is still being discovered concerning the structure and function of the voltage-gated proton channel. == Known types == HVCN1 == References ==
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{
"page_id": 13437576,
"source": null,
"title": "Voltage-gated proton channel"
}
|
In classical electromagnetism, Ampère's circuital law (not to be confused with Ampère's force law) relates the circulation of a magnetic field around a closed loop to the electric current passing through the loop. James Clerk Maxwell derived it using hydrodynamics in his 1861 published paper "On Physical Lines of Force". In 1865, he generalized the equation to apply to time-varying currents by adding the displacement current term, resulting in the modern form of the law, sometimes called the Ampère–Maxwell law, which is one of Maxwell's equations that form the basis of classical electromagnetism. == Ampère's original circuital law == In 1820 Danish physicist Hans Christian Ørsted discovered that an electric current creates a magnetic field around it, when he noticed that the needle of a compass next to a wire carrying current turned so that the needle was perpendicular to the wire. He investigated and discovered the rules which govern the field around a straight current-carrying wire: The magnetic field lines encircle the current-carrying wire. The magnetic field lines lie in a plane perpendicular to the wire. If the direction of the current is reversed, the direction of the magnetic field reverses. The strength of the field is directly proportional to the magnitude of the current. The strength of the field at any point is inversely proportional to the distance of the point from the wire. This sparked a great deal of research into the relation between electricity and magnetism. André-Marie Ampère investigated the magnetic force between two current-carrying wires, discovering Ampère's force law. In the 1850s Scottish mathematical physicist James Clerk Maxwell generalized these results and others into a single mathematical law. The original form of Maxwell's circuital law, which he derived as early as 1855 in his paper "On Faraday's Lines of Force" based on an analogy to
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{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
hydrodynamics, relates magnetic fields to electric currents that produce them. It determines the magnetic field associated with a given current, or the current associated with a given magnetic field. The original circuital law only applies to a magnetostatic situation, to continuous steady currents flowing in a closed circuit. For systems with electric fields that change over time, the original law (as given in this section) must be modified to include a term known as Maxwell's correction (see below). === Equivalent forms === The original circuital law can be written in several different forms, which are all ultimately equivalent: An "integral form" and a "differential form". The forms are exactly equivalent, and related by the Kelvin–Stokes theorem (see the "proof" section below). Forms using SI units, and those using cgs units. Other units are possible, but rare. This section will use SI units, with cgs units discussed later. Forms using either B or H magnetic fields. These two forms use the total current density and free current density, respectively. The B and H fields are related by the constitutive equation: B = μ0H in non-magnetic materials where μ0 is the magnetic constant. === Explanation === The integral form of the original circuital law is a line integral of the magnetic field around some closed curve C (arbitrary but must be closed). The curve C in turn bounds both a surface S which the electric current passes through (again arbitrary but not closed—since no three-dimensional volume is enclosed by S), and encloses the current. The mathematical statement of the law is a relation between the circulation of the magnetic field around some path (line integral) due to the current which passes through that enclosed path (surface integral). In terms of total current, (which is the sum of both free current and bound
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{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
current) the line integral of the magnetic B-field (in teslas, T) around closed curve C is proportional to the total current Ienc passing through a surface S (enclosed by C). In terms of free current, the line integral of the magnetic H-field (in amperes per metre, A·m−1) around closed curve C equals the free current If,enc through a surface S. J is the total current density (in amperes per square metre, A·m−2), Jf is the free current density only, ∮C is the closed line integral around the closed curve C, ∬S denotes a surface integral over the surface S bounded by the curve C, · is the vector dot product, dl is an infinitesimal element (a differential) of the curve C (i.e. a vector with magnitude equal to the length of the infinitesimal line element, and direction given by the tangent to the curve C) dS is the vector area of an infinitesimal element of surface S (that is, a vector with magnitude equal to the area of the infinitesimal surface element, and direction normal to surface S. The direction of the normal must correspond with the orientation of C by the right hand rule), see below for further explanation of the curve C and surface S. ∇ × is the curl operator. === Ambiguities and sign conventions === There are a number of ambiguities in the above definitions that require clarification and a choice of convention. First, three of these terms are associated with sign ambiguities: the line integral ∮C could go around the loop in either direction (clockwise or counterclockwise); the vector area dS could point in either of the two directions normal to the surface; and Ienc is the net current passing through the surface S, meaning the current passing through in one direction, minus the current
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
in the other direction—but either direction could be chosen as positive. These ambiguities are resolved by the right-hand rule: With the palm of the right-hand toward the area of integration, and the index-finger pointing along the direction of line-integration, the outstretched thumb points in the direction that must be chosen for the vector area dS. Also the current passing in the same direction as dS must be counted as positive. The right hand grip rule can also be used to determine the signs. Second, there are infinitely many possible surfaces S that have the curve C as their border. (Imagine a soap film on a wire loop, which can be deformed by blowing on the film). Which of those surfaces is to be chosen? If the loop does not lie in a single plane, for example, there is no one obvious choice. The answer is that it does not matter: in the magnetostatic case, the current density is solenoidal (see next section), so the divergence theorem and continuity equation imply that the flux through any surface with boundary C, with the same sign convention, is the same. In practice, one usually chooses the most convenient surface (with the given boundary) to integrate over. == Free current versus bound current == The electric current that arises in the simplest textbook situations would be classified as "free current"—for example, the current that passes through a wire or battery. In contrast, "bound current" arises in the context of bulk materials that can be magnetized and/or polarized. (All materials can to some extent.) When a material is magnetized (for example, by placing it in an external magnetic field), the electrons remain bound to their respective atoms, but behave as if they were orbiting the nucleus in a particular direction, creating a microscopic current. When
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{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
the currents from all these atoms are put together, they create the same effect as a macroscopic current, circulating perpetually around the magnetized object. This magnetization current JM is one contribution to "bound current". The other source of bound current is bound charge. When an electric field is applied, the positive and negative bound charges can separate over atomic distances in polarizable materials, and when the bound charges move, the polarization changes, creating another contribution to the "bound current", the polarization current JP. The total current density J due to free and bound charges is then: J = J f + J M + J P , {\displaystyle \mathbf {J} =\mathbf {J} _{\mathrm {f} }+\mathbf {J} _{\mathrm {M} }+\mathbf {J} _{\mathrm {P} }\,,} with Jf the "free" or "conduction" current density. All current is fundamentally the same, microscopically. Nevertheless, there are often practical reasons for wanting to treat bound current differently from free current. For example, the bound current usually originates over atomic dimensions, and one may wish to take advantage of a simpler theory intended for larger dimensions. The result is that the more microscopic Ampère's circuital law, expressed in terms of B and the microscopic current (which includes free, magnetization and polarization currents), is sometimes put into the equivalent form below in terms of H and the free current only. For a detailed definition of free current and bound current, and the proof that the two formulations are equivalent, see the "proof" section below. == Shortcomings of the original formulation of the circuital law == There are two important issues regarding the circuital law that require closer scrutiny. First, there is an issue regarding the continuity equation for electrical charge. In vector calculus, the identity for the divergence of a curl states that the divergence of the curl
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{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
of a vector field must always be zero. Hence ∇ ⋅ ( ∇ × B ) = 0 , {\displaystyle \nabla \cdot (\nabla \times \mathbf {B} )=0\,,} and so the original Ampère's circuital law implies that ∇ ⋅ J = 0 , {\displaystyle \nabla \cdot \mathbf {J} =0\,,} i.e. that the current density is solenoidal. But in general, reality follows the continuity equation for electric charge: ∇ ⋅ J = − ∂ ρ ∂ t , {\displaystyle \nabla \cdot \mathbf {J} =-{\frac {\partial \rho }{\partial t}}\,,} which is nonzero for a time-varying charge density. An example occurs in a capacitor circuit where time-varying charge densities exist on the plates. Second, there is an issue regarding the propagation of electromagnetic waves. For example, in free space, where J = 0 , {\displaystyle \mathbf {J} =\mathbf {0} \,,} the circuital law implies that ∇ × B = 0 , {\displaystyle \nabla \times \mathbf {B} =\mathbf {0} \,,} i.e. that the magnetic field is irrotational, but to maintain consistency with the continuity equation for electric charge, we must have ∇ × B = 1 c 2 ∂ E ∂ t . {\displaystyle \nabla \times \mathbf {B} ={\frac {1}{c^{2}}}{\frac {\partial \mathbf {E} }{\partial t}}\,.} To 'resolve' these situations (w/ eqn. above), the contribution of displacement current must be added to the current term in the circuital law. James Clerk Maxwell conceived of displacement current as a polarization current in the dielectric vortex sea, which he used to model the magnetic field hydrodynamically and mechanically. He added this displacement current to Ampère's circuital law at equation 112 in his 1861 paper "On Physical Lines of Force". === Displacement current === In free space, the displacement current is related to the time rate of change of electric field. In a dielectric the above contribution to displacement
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
current is present too, but a major contribution to the displacement current is related to the polarization of the individual molecules of the dielectric material. Even though charges cannot flow freely in a dielectric, the charges in molecules can move a little under the influence of an electric field. The positive and negative charges in molecules separate under the applied field, causing an increase in the state of polarization, expressed as the polarization density P. A changing state of polarization is equivalent to a current. Both contributions to the displacement current are combined by defining the displacement current as: J D = ∂ ∂ t D ( r , t ) , {\displaystyle \mathbf {J} _{\mathrm {D} }={\frac {\partial }{\partial t}}\mathbf {D} (\mathbf {r} ,\,t)\,,} where the electric displacement field is defined as: D = ε 0 E + P = ε 0 ε r E , {\displaystyle \mathbf {D} =\varepsilon _{0}\mathbf {E} +\mathbf {P} =\varepsilon _{0}\varepsilon _{\mathrm {r} }\mathbf {E} \,,} where ε0 is the electric constant, εr the relative static permittivity, and P is the polarization density. Substituting this form for D in the expression for displacement current, it has two components: J D = ε 0 ∂ E ∂ t + ∂ P ∂ t . {\displaystyle \mathbf {J} _{\mathrm {D} }=\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}+{\frac {\partial \mathbf {P} }{\partial t}}\,.} The first term on the right hand side is present everywhere, even in a vacuum. It doesn't involve any actual movement of charge, but it nevertheless has an associated magnetic field, as if it were an actual current. Some authors apply the name displacement current to only this contribution. The second term on the right hand side is the displacement current as originally conceived by Maxwell, associated with the polarization of the individual molecules
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
of the dielectric material. Maxwell's original explanation for displacement current focused upon the situation that occurs in dielectric media. In the modern post-aether era, the concept has been extended to apply to situations with no material media present, for example, to the vacuum between the plates of a charging vacuum capacitor. The displacement current is justified today because it serves several requirements of an electromagnetic theory: correct prediction of magnetic fields in regions where no free current flows; prediction of wave propagation of electromagnetic fields; and conservation of electric charge in cases where charge density is time-varying. For greater discussion see Displacement current. == Extending the original law: the Ampère–Maxwell equation == Next, the circuital equation is extended by including the polarization current, thereby remedying the limited applicability of the original circuital law. Treating free charges separately from bound charges, the equation including Maxwell's correction in terms of the H-field is (the H-field is used because it includes the magnetization currents, so JM does not appear explicitly, see H-field and also Note): ∮ C H ⋅ d l = ∬ S ( J f + ∂ D ∂ t ) ⋅ d S {\displaystyle \oint _{C}\mathbf {H} \cdot \mathrm {d} {\boldsymbol {l}}=\iint _{S}\left(\mathbf {J} _{\mathrm {f} }+{\frac {\partial \mathbf {D} }{\partial t}}\right)\cdot \mathrm {d} \mathbf {S} } (integral form), where H is the magnetic H field (also called "auxiliary magnetic field", "magnetic field intensity", or just "magnetic field"), D is the electric displacement field, and Jf is the enclosed conduction current or free current density. In differential form, ∇ × H = J f + ∂ D ∂ t . {\displaystyle \mathbf {\nabla } \times \mathbf {H} =\mathbf {J} _{\mathrm {f} }+{\frac {\partial \mathbf {D} }{\partial t}}\,.} On the other hand, treating all charges on the same footing (disregarding whether
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
they are bound or free charges), the generalized Ampère's equation, also called the Maxwell–Ampère equation, is in integral form (see the "proof" section below): In differential form, In both forms J includes magnetization current density as well as conduction and polarization current densities. That is, the current density on the right side of the Ampère–Maxwell equation is: J f + J D + J M = J f + J P + J M + ε 0 ∂ E ∂ t = J + ε 0 ∂ E ∂ t , {\displaystyle \mathbf {J} _{\mathrm {f} }+\mathbf {J} _{\mathrm {D} }+\mathbf {J} _{\mathrm {M} }=\mathbf {J} _{\mathrm {f} }+\mathbf {J} _{\mathrm {P} }+\mathbf {J} _{\mathrm {M} }+\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}=\mathbf {J} +\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}\,,} where current density JD is the displacement current, and J is the current density contribution actually due to movement of charges, both free and bound. Because ∇ ⋅ D = ρ, the charge continuity issue with Ampère's original formulation is no longer a problem. Because of the term in ε0∂E/∂t, wave propagation in free space now is possible. With the addition of the displacement current, Maxwell was able to hypothesize (correctly) that light was a form of electromagnetic wave. See electromagnetic wave equation for a discussion of this important discovery. === Proof of equivalence === Proof that the formulations of the circuital law in terms of free current are equivalent to the formulations involving total current In this proof, we will show that the equation ∇ × H = J f + ∂ D ∂ t {\displaystyle \nabla \times \mathbf {H} =\mathbf {J} _{\mathrm {f} }+{\frac {\partial \mathbf {D} }{\partial t}}} is equivalent to the equation 1 μ 0 ( ∇ × B ) = J + ε 0
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
∂ E ∂ t . {\displaystyle {\frac {1}{\mu _{0}}}(\mathbf {\nabla } \times \mathbf {B} )=\mathbf {J} +\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}\,.} Note that we are only dealing with the differential forms, not the integral forms, but that is sufficient since the differential and integral forms are equivalent in each case, by the Kelvin–Stokes theorem. We introduce the polarization density P, which has the following relation to E and D: D = ε 0 E + P . {\displaystyle \mathbf {D} =\varepsilon _{0}\mathbf {E} +\mathbf {P} \,.} Next, we introduce the magnetization density M, which has the following relation to B and H: 1 μ 0 B = H + M {\displaystyle {\frac {1}{\mu _{0}}}\mathbf {B} =\mathbf {H} +\mathbf {M} } and the following relation to the bound current: J b o u n d = ∇ × M + ∂ P ∂ t = J M + J P , {\displaystyle {\begin{aligned}\mathbf {J} _{\mathrm {bound} }&=\nabla \times \mathbf {M} +{\frac {\partial \mathbf {P} }{\partial t}}\\&=\mathbf {J} _{\mathrm {M} }+\mathbf {J} _{\mathrm {P} },\end{aligned}}} where J M = ∇ × M , {\displaystyle \mathbf {J} _{\mathrm {M} }=\nabla \times \mathbf {M} ,} is called the magnetization current density, and J P = ∂ P ∂ t , {\displaystyle \mathbf {J} _{\mathrm {P} }={\frac {\partial \mathbf {P} }{\partial t}},} is the polarization current density. Taking the equation for B: 1 μ 0 ( ∇ × B ) = ∇ × ( H + M ) = ∇ × H + J M = J f + J P + ε 0 ∂ E ∂ t + J M . {\displaystyle {\begin{aligned}{\frac {1}{\mu _{0}}}(\mathbf {\nabla } \times \mathbf {B} )&=\mathbf {\nabla } \times \left(\mathbf {H} +\mathbf {M} \right)\\&=\mathbf {\nabla } \times \mathbf {H} +\mathbf {J} _{\mathrm {M} }\\&=\mathbf {J} _{\mathrm {f}
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
}+\mathbf {J} _{\mathrm {P} }+\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}+\mathbf {J} _{\mathrm {M} }.\end{aligned}}} Consequently, referring to the definition of the bound current: 1 μ 0 ( ∇ × B ) = J f + J b o u n d + ε 0 ∂ E ∂ t = J + ε 0 ∂ E ∂ t , {\displaystyle {\begin{aligned}{\frac {1}{\mu _{0}}}(\mathbf {\nabla } \times \mathbf {B} )&=\mathbf {J} _{\mathrm {f} }+\mathbf {J} _{\mathrm {bound} }+\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}\\&=\mathbf {J} +\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}},\end{aligned}}} as was to be shown. == Ampère's circuital law in cgs units == In cgs units, the integral form of the equation, including Maxwell's correction, reads ∮ C B ⋅ d l = 1 c ∬ S ( 4 π J + ∂ E ∂ t ) ⋅ d S , {\displaystyle \oint _{C}\mathbf {B} \cdot \mathrm {d} {\boldsymbol {l}}={\frac {1}{c}}\iint _{S}\left(4\pi \mathbf {J} +{\frac {\partial \mathbf {E} }{\partial t}}\right)\cdot \mathrm {d} \mathbf {S} ,} where c is the speed of light. The differential form of the equation (again, including Maxwell's correction) is ∇ × B = 1 c ( 4 π J + ∂ E ∂ t ) . {\displaystyle \mathbf {\nabla } \times \mathbf {B} ={\frac {1}{c}}\left(4\pi \mathbf {J} +{\frac {\partial \mathbf {E} }{\partial t}}\right).} == See also == == Notes == == Further reading == Griffiths, David J. (1998). Introduction to Electrodynamics (3rd ed.). Prentice Hall. ISBN 0-13-805326-X. Tipler, Paul (2004). Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics (5th ed.). W. H. Freeman. ISBN 0-7167-0810-8. == External links == Media related to Ampere's law at Wikimedia Commons MISN-0-138 Ampere's Law (PDF file) by Kirby Morgan for Project PHYSNET. MISN-0-145 The Ampere–Maxwell Equation; Displacement Current (PDF file) by J. S. Kovacs for
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{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
Project PHYSNET. A Dynamical Theory of the Electromagnetic Field Maxwell's paper of 1864
|
{
"page_id": 199304,
"source": null,
"title": "Ampère's circuital law"
}
|
The fusome is a membranous structure found in the developing germ cell cysts of many insect orders. Initial description of the fusome occurred in the 19th century and since then the fusome has been extensively studied in Drosophila melanogaster male and female germline development. This structure has roles in maintaining germline cysts, coordinating the number of mitotic divisions prior to meiosis, and oocyte determination by serving as a structure for intercellular communication. == Structure == In D. melanogaster, germline cysts form from four mitotic divisions with incomplete cytokinesis that originated from one germline stem cell. Incomplete cytokinesis results in intercellular bridges connecting every cell in the cyst, called ring canals3. The four mitotic divisions result in cysts of 16 cells connected by 15 ring canals. The fusome is composed of membrane vesicles and originates from endoplasmic reticulum. Fusome material is inside ring canals and can range in size from 1 to 10 um depending on the stage of development. 1.1 Fusome Development The spectrosome is a round structure in germline stem cells that develops into the fusome in cyst cells. Fusome divides asymmetrically into daughter cells in females by attaching to one spindle pole during meiosis, resulting in one cell receiving all fusome material. Fusome is generated de novo in the ring canal connecting the two cells. The two fusome parts then fuse together to connect the cells. Asymmetric fusome partitioning and new formation followed by fusion occurs at each mitotic division. In spermatogenesis, the fusome partitioning is symmetric and the fusome is still present during the meiotic divisions. 1.2 Fusome components Many proteins and organelles associate with the fusome throughout germ cell development. Cytoskeleton components, such as alpha and beta spectrins, hu-li tai shao (hts), and ankyrin were the first proteins identified in the fusome. Centrosomes travel along the
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{
"page_id": 53021322,
"source": null,
"title": "Fusome"
}
|
fusome and the fusome is involved in microtubule organization. The interactions between the fusome and microtubules result in cyst polarity in oogenesis. Associations between the fusome and microtubules change throughout the cell cycle. Mitochondria associates with the fusome and travel through ring canals to the oocyte. Microtubules travel through ring canals and form the tracks for transport of materials between cells. == Function == There are numerous functions of the fusome as a structure necessary for cell-cell communication in developing germ cell cysts. The fusome connects cells, allowing for transport of proteins and RNAs between cells and synchronous activities. Mutations in essential fusome components can result in infertility. 2.1 Role in cell cycle synchrony Developing cells in germline cysts undergo mitotic divisions synchronously and in males all cells in a cyst also undergo meiosis synchronously. The fusome is a track where an event can happen and then feedback mechanisms quickly communicate to each cell to ensure a specific outcome occurs simultaneously in every cell. Cells in a cyst fail to divide synchronously if the fusome is disrupted. The rosette formation of germline cyst cells allows cells to be in the closest configuration for communication. Throughout the cell cycle, different cyclins associate with the fusome to induce synchronous cell divisions. Cyclin A and Cyclin E localize to the fusome in female germline cysts and are required for the correct number of mitotic divisions to occur. Abnormal cyclin levels result in too few or too many divisions. Cyclin E at the fusome is phosphorylated for degradation by the SCF complex and if not degraded, an extra division occurs. The fusome may be the degradation site for other cell cycle proteins. Myt1 kinase inhibits CycA/Cdk1 in males during G2. Without Myt1 regulation, fusome and centrosome behavior is abnormal, resulting in cells with irregular
|
{
"page_id": 53021322,
"source": null,
"title": "Fusome"
}
|
spindles. 2.2 Differences in male vs female fusomes In females, the fusome plays a role in cell fate and differentiation. Asymmetric fusome distribution and centriole orientation determines which cell in the developing female germline cyst becomes the oocyte. One of the two cells from the first division within the cyst becomes the oocyte and contains the most fusome material. The fusome degrades after the 16-cell cyst forms. In females, the connections are the channels through which nurse cells send proteins and RNAs to the oocyte along polarized microtubules. In males, the fusome is necessary for ensuring quality control in individual cysts. DNA damage in one cell leads to all cells in a cyst dying by communication through the fusome, either by disseminating a death signal or additive DNA damage inducing apoptosis. This ensures mature sperm cells have intact genomes before fertilizing an egg. In addition, the fusome connections ensure haploid spermatids have proteins and RNA made by the other chromosome for “gamete equivalency”. == Similar structures in other animals == Fusomes were previously thought to be specific to insect gametogenesis. Fusome-like structures have been identified in Xenopus laevis oogenesis by electron microscopy and immunostaining for fusome components such as spectrin and hts. Intercellular bridges also connect developing germ cells in mammals, contributing to cell cycle synchrony and gamete quality control by sharing substances between cells. Future studies are required to elucidate all of the functions that arise from cell-cell communication through intercellular bridges. In addition, a future area of research is to determine why some organisms lack fusomes. Do these organisms have another structure that carries out the role of the fusome or are these roles not necessary in germline cyst development of these other organisms? == See also == Intercellular junctions Gametogenesis Spectrin Cyclin == References == ^PG Wilson
|
{
"page_id": 53021322,
"source": null,
"title": "Fusome"
}
|
Cell Biol Int. 2005 May;29(5):360-9. Centrosome inheritance in the male germ line of Drosophila requires hu-li tai-shao function. == External links == Huynh JR. (2006) Fusome as a Cell-Cell Communication Channel of Drosophila Ovarian Cyst. In: Cell-Cell Channels. Springer, New York, NYhttps://www.ncbi.nlm.nih.gov/books/NBK6300/ http://www.oxfordreference.com/view/10.1093/acref/9780195307610.001.0001/acref-9780195307610-e-2383?rskey=LqAWUj&result=2381 Lighthouse, D. V., M. Buszczak, and A. C. Spradling. (2008). New components of the Drosophila fusome suggest it plays novel roles in signaling and transport. Dev Biol 317: 59–71. doi:10.1016/j.ydbio.2008.02.009 de Cuevas, M., M. A. Lilly, and A. C. Spradling. (1997). Germline cyst formation in Drosophila. Annu. Rev. Genet. 31: 405–428. DOI: 10.1146/annurev.genet.31.1.405 Yamashita, Y. M., H. Yuan, J. Cheng, and A. J. Hunt. (2010). Polarity in stem cell division: asymmetric stem cell division in tissue homeostasis. Cold Spring Harb Perspect Biol 2:a001313 doi: 10.1101/cshperspect.a001313 Rieger R. Michaelis A., Green M. M. (1976). Glossary of genetics and cytogenetics: Classical and molecular. Heidelberg - New York: Springer-Verlag. ISBN 3-540-07668-9. King R. C., Stransfield W. D. (1998): Dictionary of genetics. Oxford University Press, New York, Oxford, ISBN 0-19-50944-1-7; ISBN 0-19-509442-5.
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{
"page_id": 53021322,
"source": null,
"title": "Fusome"
}
|
The sterile fungi, or mycelia sterilia, are a group of fungi that do not produce any known spores, either sexual or asexual. This is considered a form group, not a taxonomic division, and is used as a matter of convenience only, as various isolates within such morphotypes could include distantly related taxa or different morphotypes of the same species, leading to incorrect identifications. Because these fungi do not produce spores, it is impossible to use traditional methods of morphological comparison to classify them. However, molecular techniques can be applied to determine their evolutionary history, with ITS testing being the preferred method.According to one study, approximately 42% of fluids collected from broncho-alveolar lavage have had sterile mycelium observed in them. == References ==
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{
"page_id": 1247882,
"source": null,
"title": "Sterile fungi"
}
|
Thymidine triphosphate (TTP), also called deoxythymidine triphosphate (dTTP), is one of the four nucleoside triphosphates that are used in the in vivo synthesis of DNA. Unlike the other deoxyribonucleoside triphosphates, thymidine triphosphate does not always contain the "deoxy" prefix in its name. This is because dTTP does not have a corresponding ribonucleoside triphosphate, as the uridine triphosphate, which lacks thymidine's 5-methylation, is used instead. dTTP is synthesized via the methylation of dUMP via thymidylate synthase. It can be used by DNA ligase to create overlapping "sticky ends" so that protruding ends of opened microbial plasmids may be closed up. == References ==
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{
"page_id": 31001227,
"source": null,
"title": "Thymidine triphosphate"
}
|
Tantalum–tungsten alloys are in the refractory metals group that maintain useful physical and chemical properties even at high temperatures. The tantalum–tungsten alloys are characterized by their high melting point and the tension resistance. The properties of the final alloy are a combination of properties from the two elements: tungsten, the element with the highest melting point in the periodic table, and tantalum which has high corrosion resistance. The tantalum–tungsten alloys typically vary in their percentage of tungsten. Some common variants are: (Ta – 2.5% W) → also called 'tantaloy 63 metal.' The percentage of tungsten is about 2 to 3% and includes 0.5% of niobium. This alloy has a good resistance to corrosion and performs well at high temperatures. An example application is piping in chemical industries. (Ta - 7.5% W) → also called 'tantaloy 61 metal,' has between 7 and 8% tungsten. The difference from this alloy to the others is that this alloy represents a high resilience modulus while maintaining its refractory properties. (Ta - 10% W) → also called 'tantaloy 60 metal,' contains 9 to 11% tungsten. This alloy is less ductile than the other alloys and exhibits less plasticity. Applications include high-temperature, high-corrosion environments such as aerospace components, furnaces, and piping in nuclear plants. == Mechanical properties == The alloys of tantalum–tungsten have high corrosion resistance, and refractory properties. The crystalline structure of the material is body-centered cubic with a substitutional solid solution with atoms of tungsten. The alloy also has a high melting point and can reach high elastic modulus and high tensile strength. == Phase diagram == The equilibrium phase diagram of the alloy formed between the two components tantalum and tungsten is a binary diagram, where the two components are totally soluble on each other. In this diagram the melting temperature of the
|
{
"page_id": 44632714,
"source": null,
"title": "Tantalum–tungsten alloys"
}
|
two elements are shown. It can be seen that there are two lines, representing the solidus and liquidus. == References ==
|
{
"page_id": 44632714,
"source": null,
"title": "Tantalum–tungsten alloys"
}
|
Physics of Life Reviews is a quarterly peer-reviewed scientific journal covering research on living systems. It was established in 2004 and is published by Elsevier. The editor-in-chief is Leonid Perlovsky. The scope of the journal includes living systems, complex phenomena in biological systems, and related fields of artificial life, robotics, mathematical biosemiotics, and artificial intelligent systems. According to the Journal Citation Reports, the journal has impact factor of 13.7. == References == == External links == Official website
|
{
"page_id": 32246414,
"source": null,
"title": "Physics of Life Reviews"
}
|
The Krüppel associated box (KRAB) domain is a category of transcriptional repression domains present in approximately 400 human zinc finger protein-based transcription factors (KRAB zinc finger proteins). The KRAB domain typically consists of about 75 amino acid residues, while the minimal repression module is approximately 45 amino acid residues. It is predicted to function through protein-protein interactions via two amphipathic helices. The most prominent interacting protein is called TRIM28 initially visualized as SMP1, cloned as KAP1 and TIF1-beta. Substitutions for the conserved residues abolish repression. Over 10 independently encoded KRAB domains have been shown to be effective repressors of transcription, suggesting this activity to be a common property of the domain. KRAB domains can be fused with dCas9 CRISPR tools to form even stronger repressors. == Evolution == The KRAB domain had initially been identified in 1988 as a periodic array of leucine residues separated by six amino acids 5’ to the zinc finger region of KOX1/ZNF10 coined heptad repeat of leucines (also known as a leucine zipper). Later, this domain was named in association with the C2H2-Zinc finger proteins Krüppel associated box (KRAB). The KRAB domain is confined to genomes from tetrapod organisms. The KRAB containing C2H2-ZNF genes constitute the largest sub-family of zinc finger genes. More than half of the C2H2-ZNF genes are associated with a KRAB domain in the human genome. They are more prone to clustering and are found in large clusters on the human genome. The KRAB domain presents one of the strongest repressors in the human genome. Once the KRAB domain was fused to the tetracycline repressor (TetR), the TetR-KRAB fusion proteins were the first engineered drug-inducible repressor that worked in mammalian cells. Two distinct types of KRAB A domains can be structurally and functionally distinguished. Ancestral KRAB A domains present in human PDRM9
|
{
"page_id": 4000401,
"source": null,
"title": "Krüppel associated box"
}
|
proteins are even evolutionary conserved in mussel genomes. Modern KRAB A domain sequences are found in coelacanth latimeria chalumnae and in Lungfish genomes. == Examples == Human genes encoding KRAB-ZFPs include KOX1/ZNF10, KOX8/ZNF708, ZNF43, ZNF184, ZNF91, HPF4, HTF10 and HTF34. == References == == Further reading ==
|
{
"page_id": 4000401,
"source": null,
"title": "Krüppel associated box"
}
|
The molecular formula C18H14O8 (molar mass: 358.302 g/mol) may refer to: Psoromic acid MCPO
|
{
"page_id": 60099218,
"source": null,
"title": "C18H14O8"
}
|
DNA barcoding of algae is commonly used for species identification and phylogenetic studies. Algae form a phylogenetically heterogeneous group, meaning that the application of a single universal barcode/marker for species delimitation is unfeasible, thus different markers/barcodes are applied for this aim in different algal groups. == Diatoms == Diatom DNA barcoding is a method for taxonomical identification of diatoms even to species level. It is conducted using DNA or RNA followed by amplification and sequencing of specific, conserved regions in the diatom genome followed by taxonomic assignment. One of the main challenges of identifying diatoms is that it is often collected as a mixture of diatoms from several species. DNA metabarcoding is the process of identifying the individual species from a mixed sample of environmental DNA (also called eDNA) which is DNA extracted straight from the environment such as in soil or water samples. A newly applied method is diatom DNA metabarcoding which is used for ecological quality assessment of rivers and streams because of the specific response of diatoms to particular ecologic conditions. As species identification via morphology is relatively difficult and requires a lot of time and expertise, high-throughput sequencing (HTS) DNA metabarcoding enables taxonomic assignment and therefore identification for the complete sample regarding the group specific primers chosen for the previous DNA amplification. Until now, several DNA markers have already been developed, mainly targeting the 18S rRNA. Using the V4 hypervariable region of the ribosomal small subunit DNA (SSU rDNA), DNA-based identification was found to be more efficient than the classical morphology-based approach. Other conserved regions in the genomes which are frequently used as marker genes are ribulose-1-5-bisphosphate carboxylase (rbcL), cytochrome oxidase I (cox1, COI), ITS and 28S. It has been shown repeatedly that the molecular data gained by diatom eDNA metabarcoding quite faithfully reflect the morphology-based
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
biotic diatom indices and therefore provide a similar assessment of ecosystem status. In the meantime, diatoms are routinely used for the assessment of ecological quality in other freshwater ecosystems. Together with aquatic invertebrates they are considered as the best indicators of disturbance related to physical, chemical or biological conditions of watercourses. Numerous studies are using benthic diatoms for biomonitoring. Because no ideal diatom DNA barcode was found, it has been proposed that different markers are used for different purposes. Indeed, the highly variable cox1, ITS and 28S genes were considered more suitable for taxonomic studies, while more conserved 18S and rbcL genes seem more appropriate for biomonitoring. === Advantages === Applying the DNA barcoding concept to diatoms promises great potential to resolve the problem of inaccurate species identification and thus facilitate analyses of the biodiversity of environmental samples. Molecular methods based on the NGS technology almost always leads to a higher number of identified taxa whose presence could subsequently be verified by light microscopy. Results of this study provides evidence that eDNA barcoding of diatoms is suitable for water quality assessment and could complement or improve traditional methods. Stoeck et al. also showed that eDNA barcoding provides a more insight into diatom diversity or other protist communities and therefore could be used for ecological projection of global diversity. Other studies showed different results. For example, inventories obtained from the molecular-based method were closer to those obtained by the morphology-based method when abundant species are in focus. DNA metabarcoding can also increase the taxonomic resolution and comparability across geographic regions, which is often difficult using morphological characters only. Moreover, DNA-based identification allows extending the range of potential bioindicators, including the inconspicuous taxonomic groups that could be highly sensitive or tolerant to particular stressors. Indirectly, the molecular methods can also help filling
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
the gaps in knowledge of species ecology, by increasing the number of samples processed coupled with a decrease in processing time (cost-effectiveness), as well as by increasing the accuracy and precision of correlation between species/MOTUs occurrence and environmental factors. === Challenges === Currently there is no consensus concerning methods for DNA preservation and isolation, the choice of DNA barcodes and PCR primers, nor agreement concerning the parameters of MOTU clustering and their taxonomic assignment. Sampling and molecular steps need to be standardize through development studies. One of the major limitation is the availability of reference barcodes for diatoms species. The reference database of bioindicator taxa is far from complete despite the constant efforts of numerous national barcoding initiatives a lot of species are still lacking barcode information. Furthermore, most existing metabarcoding data are only locally available and geographically scattered, which is hindering the development of globally useful tools. Visco et al. estimated that no more than 30% of European diatoms species are currently represented in reference databases. For example, there is an important lack for a number of species from the Fennoscandian communities (especially acidophilic diatoms, such as Eunotia incisa). It has also been shown that taxonomic identification with DNA barcoding is not accurate above species level, to discriminate varieties for example (reference missing). Another well-known limitation of barcoding for taxonomic identification is the clustering method used before the taxonomic assignation: It often leads to massive loss of genetic information and the only reliable way to assess the effects of different clustering and different taxonomic assignation processes would be to compare the species list generated by different pipelines when using the same reference database. This has yet to be done for the variety of pipelines used in molecular assessment of diatom communities in Europe. Taxonomically validated databases, which includes accessible
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
vouchers are also crucial for reliable taxa identification via NGS. Additionally, primer bias is often found to be a major source of variation in barcoding and PCR primers efficiency can differ between diatoms species, i.e. some primers lead to a preferential amplification of one taxon over another. The inference of abundance from metabarcoding data is considered as one of the most difficult issues in environmental use. The number of generated sequences by HTS does not directly correspond to the number of specimen or biomass and that different species can produce different amount of reads, (for example, due to differences in the chloroplast size with the rbcL marker). Vasselon et al. recently created a biovolume correction factor when using the rbcL marker. For example, Achnanthidium minutissimum has a small biovolume, and thus will generate less copies of the rbcL fragment (located in the chloroplast) than larger species. This correction factor, however, requires extensive calibration with each species own biovolume and has been tested only on a few species that far. Fluctuations of gene copy number for other markers, such as the 18S marker, does not seem to be species specific, but have not been tested yet. === Diatom target regions === Barcoding marker usually combine hypervariable regions of the genome (to allow the distinction between species) with very conserved region (to insure a specificity to the target organism). Several DNA markers, belonging to the nuclear, mitochondrial, and chloroplast genomes (rbcL, COI, ITS+5.8S, SSU, 18S...), have been designed and successfully used for diatoms identification with NGS. ==== 18S and V4 subunit ==== The 18S gene region has been widely used as a marker in other protist groups and Jahn et al. were the first to test the 18S gene region for diatoms barcoding. Zimmerman et al. proposed a 390–410 bp long fragment
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
of the 1800 bp long 18S rRNA gene locus as a barcode marker for the analysis of environmental samples with HTS. and discusses its use and limitations for diatom identification. This fragment includes the V4 subunit which is the largest and most complex of the highly variable regions within the 18S locus. They highlighted that this hypervariable region of the 18S gene have great potential for studying protist diversity at large scale but has limited efficiency to identification below species level or cryptic species. ==== rbcL ==== The rbcl gene is used for taxonomy studies (Trobajo et al. 2009) which benefits include that rarely any intragenomic variation and they are very easily aligned and compared. An open-access reference library, called R-Syst::diatom includes data for two barcodes (18S and rbcL). It is freely accessible through a website. Kermmarec et al. also successfully used the rbcL gene for ecological assessment of diatoms. The rbcL marker is also easily aligned and compared. Moniz and Kaczmarska investigated the amplification success of the SSU, COI, and ITS2 markers and found that the 300 – 400 bp ITS-2 + 5.8S fragment provided the highest success rate of amplification and good species resolution. This marker was subsequently used to separate morphologically defined species with a success rate of 99.5%. Despite this amplification success, Zimmerman et al. criticised the use of ITS-2 due to intra-individual heterogeneity. It has been suggested that SSU or the rbcL (Mann et al., 2010) markers less heterogenous between individuals and therefore more beneficial when distinguishing between species. === Applications === ==== Genetic tool for biomonitoring and bioassessment ==== Diatoms are routinely used as part of a suite of biomonitoring tools which must be monitored as part of the European Water Framework Directive. Diatoms are used as an indicator of ecosystem health in freshwaters
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
because they are ubiquitous, directly affected by the changes in physico-chemical parameters and show a better relationship with environmental variables than other taxa e.g. invertebrates, giving a better overall picture of water quality. Over the recent years, researchers have developed and standardised the tools for the metabarcoding and sequencing of diatoms, to complement the traditional assessment using microscopy, opening up a new avenue of biomonitoring for aquatic systems. Using benthic diatoms through a method of next-generation sequencing approach to river biomonitoring revealed a good potential in it. Many studies have shown that metabarcoding and HTS (high-throughput sequencing) can be utilized to estimate the quality status and diversity in freshwaters. As part of the Environment Agency, Kelly et al. has developed a DNA-based metabarcoding approach to assess diatom communities in rivers for the UK. Vasselon et al. compared morphological and HTS approaches for diatoms and found that HTS gave a reliable indication of quality status for most rivers in terms of Specific Polluosensitivity Index (SPI). Vasselon et al. also applied DNA metabarcoding of diatoms communities to the monitoring network of rivers on the tropical Island Mayotte (French DOM-TOM). Rimet et al. also explored the possibility of using HTS for assessing diatom diversity and showed that diversity indices from both HTS and microscopic analysis were well correlated although not perfect. DNA barcoding and metabarcoding can be used to establish molecular metrics and indices, which potentially provide conclusions broadly similar to those of the traditional approaches about the ecological and environmental status of aquatic ecosystems. ==== Forensics ==== Diatoms are used to as a diagnosis tool for drowning in forensic practices. The diatom test is based on the principle of diatom inhalation from water into the lungs and distribution and deposition around the body. DNA methods can be used to confirm if the
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
cause of death was indeed drowning and locate the origin of drowning. Diatom DNA metabarcoding, provides the opportunity to quickly analyse the diatom community present within a body and locate the origin of drowning and investigate if a body may have been moved from one place to another. ==== Cryptic species and databasing ==== Diatom metabarcoding may help delimit cryptic species that are difficult to identify using microscopy and help complete reference databases by comparing morphological assemblages to metabarcoding data. == Other Microalgae == Chlorophytes possess an ancients and taxonomically very diverse lineage (Fang et al. 2014), including terrestrial plants too. Even though more than 14 000 species have been described based on structural and ultrastructural criteria (Hall et al. 2010) their morphological identification is often limited. Several barcodes for chlorophytes have been proposed for DNA-based identification in order to bypass the problematics of the morphological one. Although the cytochrome oxidase I (COI, COX) coding gene (link) is a standard barcode for animals it proved to be unsatisfactory for chlorophytes because the gene contains several introns in this algae group (Turmel et al. 2002). Nuclear marker genes have been used for chlorophytes are SSU rDNA, LSU rDNA, rDNA ITS (Leliaert et al. 2014). == Macroalgae == Macroalgae—a morphological rather than taxonomic grouping—can be very challenging to identify because of their simple morphology, phenotypic plasticity and alternate lifecycle stages. Thus, algal systematics and identification have come to rely heavily on genetic/molecular tools such as DNA barcoding. The SSU rDNA gene is a common used barcode for phylogenetic studies on macroalgae. However, the SSU rDNA is a highly conserved region and typically lack resolution for species identification. Over the past 2 decades certain standards for DNA barcoding with the aim of species identification have been developed for each of the main groups
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
of macroalgae. The cytochrome c oxidase subunit I (COI) gene is commonly used as a barcode for red and brown algae, while tufA (plastid elongation factor), rbcL (rubisco large subunit) and ITS (internal transcribe spacer) are commonly used for green algae. These barcodes are typically 600-700 bp long. The barcodes typically differ between the 3 main groups of macroalgae (red, green and brown) because their evolutionary heritage is very diverse. Macroalgae is a polyphyletic group, meaning that within the group they do not all share a recent common ancestor, making it challenging to find a gene that is conserved among all but variable enough for species identification. == Target regions == Adapted from == See also == Detailed information on DNA barcoding of different organisms can be found here: Microbial DNA barcoding DNA barcoding Fish DNA barcoding DNA barcoding in diet assessment == References ==
|
{
"page_id": 60361363,
"source": null,
"title": "Algae DNA barcoding"
}
|
Rearrangements, especially those that can participate in cascade reactions, such as the aza-Cope rearrangements, are of high practical as well as conceptual importance in organic chemistry, due to their ability to quickly build structural complexity out of simple starting materials. The aza-Cope rearrangements are examples of heteroatom versions of the Cope rearrangement, which is a [3,3]-sigmatropic rearrangement that shifts single and double bonds between two allylic components. In accordance with the Woodward-Hoffman rules, thermal aza-Cope rearrangements proceed suprafacially. Aza-Cope rearrangements are generally classified by the position of the nitrogen in the molecule (see figure): The first example of an aza-Cope rearrangement was the ubiquitous cationic 2-aza-Cope rearrangement, which takes place at temperatures 100-200 °C lower than the Cope rearrangement due to the facile nature of the rearrangement. The facile nature of this rearrangement is attributed both to the fact that the cationic 2-aza-Cope is inherently thermoneutral, meaning there's no bias for the starting material or product, as well as to the presence of the charged heteroatom in the molecule, which lowers the activation barrier. Less common are the 1-aza-Cope rearrangement and the 3-aza-Cope rearrangement, which are the microscopic reverse of each other. The 1- and 3-aza-Cope rearrangements have high activation barriers and limited synthetic applicability, accounting for their relative obscurity. To maximize its synthetic utility, the cationic 2-aza-Cope rearrangement is normally paired with a thermodynamic bias toward one side of the rearrangement. The most common and synthetically useful strategy couples the cationic 2-aza-Cope rearrangement with a Mannich cyclization, and is the subject of much of this article. This tandem aza-Cope/Mannich reaction is characterized by its mild reaction conditions, diastereoselectivity, and wide synthetic applicability. It provides easy access to acyl-substituted pyrrolidines, a structure commonly found in natural products such as alkaloids, and has been used in the synthesis of a number
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
of them, notably strychnine and crinine. Larry E. Overman and coworkers have done extensive research on this reaction. == The cationic 2-aza-Cope rearrangement == The cationic 2-aza-Cope rearrangement, most properly called the 2-azonia-[3,3]-sigmatropic rearrangement, has been thoroughly studied by Larry E. Overman and coworkers. It is the most extensively studied of the aza-Cope rearrangements due to the mild conditions required to carry the arrangement out, as well as for its many synthetic applications, notably in alkaloid synthesis. Thermodynamically, the general 2-aza-Cope rearrangement does not have a product bias, as the bonds broken and formed are equivalent in either direction of the reaction, similar to the Cope rearrangement. The presence of the ionic nitrogen heteroatom accounts for the more facile rearrangement of the cationic 2-aza-Cope rearrangement in comparison to the Cope rearrangement. Hence, it is often paired with a thermodynamic sink to bias a rearrangement product. In 1950, Horowitz and Geissman reported the first example of the 2-aza-Cope rearrangement, a surprising result in a failed attempt to synthesize an amino alcohol. This discovery identified the basic mechanism of the rearrangement, as the product was most likely produced through a nitrogen analog of the Cope rearrangement. Treatment of an allylbenzylamine (A) with formic acid and formaldehyde leads to an amino alcohol (B). The amino alcohol converts to an imine under addition of acid (C), which undergoes the cationic 2-aza-Cope rearrangement (D). Water hydrolyses the iminium ion to an amine (E). Treating this starting material with only formaldehyde showed that alkylation of the amine group occurred after the cationic 2-aza-Cope rearrangement, a testament to the quick facility of the rearrangement. Due to the mild heating conditions of the reaction carried out, unlike the more stringent ones for a purely hydrocarbon Cope rearrangement, this heteroatomic Cope rearrangement introduced the hypothesis that having a positive
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
charge on a nitrogen in the cope rearrangement significantly reduces the activation barrier for the rearrangement. === Reaction mechanism === ==== Rate acceleration due to positively charged nitrogen ==== The aza-Cope rearrangements are predicted by the Woodward-Hoffman rules to proceed suprafacially. However, while never explicitly studied, Overman and coworkers have hypothesized that, as with the base-catalyzed oxy-Cope rearrangement, the charged atom distorts the sigmatropic rearrangement from a purely concerted reaction mechanism (as expected in the Cope rearrangement), to one with partial diradical/dipolar character, due to delocalization of the positive charge onto the allylic fragment, which weakens the allylic bond. This results in a lowered activation barrier for bond breaking. Thus the cationic-aza-Cope rearrangement proceeds more quickly than more concerted processes such as the Cope rearrangement. ==== Transition state and stereochemistry ==== The cationic 2-aza-Cope rearrangement is characterized by its high stereospecificity, which arises from its high preference for a chair transition state. In their exploration of this rearrangement's stereospecificity, Overman and coworkers used logic similar to the classic Doering and Roth experiments, which showed that the Cope rearrangement prefers a chair conformation. By using the cationic 2-aza-Cope/Mannich reaction on pyrrolizidine precursors, they showed that pyrrolizidines with cis substituents from E-alkenes and trans substituents from Z-alkenes are heavily favored, results that are indicative of a chair transition state. If a boat transition state was operative, the opposite results would have been obtained (detailed in image below). As is the trend with many reactions, conversion of the Z-enolate affords lower selectivity due to 1,3 diaxial steric interactions between the enolate and the ring, as well as the fact that substituents prefer quasi-equatorial positioning. This helps explain the higher temperatures required for Z-enolate conversion. The boat transition state is even less favored by the cationic-2-aza-Cope rearrangement than it is for the Cope rearrangement:
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
in analogous situations to where the Cope rearrangement takes on a boat transition state, the aza-Cope rearrangement continues in the chair geometry. These results are in accord with computational chemistry results, which further assert that the transition state is under kinetic control. Significantly, these stereochemical experiments imply that the cationic 2-aza-Cope rearrangement (as well as Mannich cyclization) occur faster than enol or iminium tautomerization. If they were not, no meaningful stereochemistry would have been observed, highlighting the facility of this fast reaction. ==== Additional considerations for stereochemistry ==== The aza-Cope/Mannich reaction, when participating in ring-expanding annulations, follows the stereochemistry dictated by the most favorable chair conformation, which generally places bulky substituents quasi-equatorially. The vinyl and amine components can have either syn or anti relationships when installed on a ring. This relationship is typically dictated by the amine substituent: bulky substituents lead to syn aza-Cope precursors. While anti vinyl and amine substituents generally only have one favored transition state, leading to a cis fused ring system, the favored product of syn substituents can change, dictated by steric interactions with solvents or large N-substituents, which may take preference over bulky substituents and change the transition state. For simple aza-Cope/Mannich reactions that do not participate in ring-expanding annulation, namely condensations of amino alcohols and ethers, bond rotation occurs more quickly than the Mannich cyclization, and racemic products are observed. This can be avoided by using a chiral auxiliary substituent on the amine. Reactions tethered to rings cannot undergo these bond rotations. ==== Possible thermodynamic sinks for biasing a rearrangement product ==== Horowitz and Geissman's first example demonstrates a possible thermodynamic sink to couple with the cationic 2-aza-Cope rearrangement, where the product is biased by the phenyl substituent through aryl conjugation, then captured by hydrolysis of the iminium. Other methods of biasing a product
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
include using substituents which are more stable on substituted carbons, releasing ring strain (for instance, by pairing the rearrangement with cyclopropane opening), intramolecular trapping (pictured), and pairing the rearrangement with the Mannich cyclization. == The aza-Cope/Mannich reaction == The aza-Cope/Mannich reaction is a synthetically powerful reaction, as it is able to create complex cyclic molecules from simple starting materials. This tandem reaction provides a thermodynamic bias towards one rearrangement product, as the Mannich cyclization is irreversible and its product, an acyl substituted pyrrolidine ring, more stable than that of the rearrangement. === The first aza-Cope/Mannich reaction === Overman and coworkers recognized that the cationic 2-aza-Cope rearrangement could potentially be synthetically powerful if an appropriate thermodynamic sink could be introduced. Their logic was to incorporate a nucleophilic substituent into the starting material, namely an alcohol group, which acts only after rearrangement, converted into an enol primed to attack the iminium ion. This first report of the reaction was a reaction between aldehydes and 2-alkoxy-3-butenamines, which formed an amino alcohol whose aza-Cope/Mannich reaction product was an acyl-substituted pyrrolidine ring. This simple procedure only involved mild heating for several hours. Significantly, the aza-Cope/Mannich reaction occurs in a single step with excellent yield. This procedure is easily applied to condensation of amino ethers (shown below), where the alcohol has been methylated first. After the aza-Cope/Mannich reaction is carried out, the ketone is formed by addition of NaOH. The amine, in this simple case, cannot form the iminium ion from basic ketones; subsequent methods found ways of incorporating ketones into the reaction. The utility of this reaction is evident in the fact that even when a less stable isomer is formed, the reaction proceeds, demonstrating its high thermodynamic favorability. === Reaction mechanism === The general product of the reaction can potentially occur via two separate
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
pathways: the aza-Cope/Mannich reaction, or an aza-Prins cyclization/pinacol rearrangement. These mechanisms have different stereochemical properties, which elucidate the dominance of the aza-Cope/Mannich reaction. The aza-Cope/Mannich reaction forces each atom in the [1,5] diene analog to undergo sp2 hybridization, erasing the starting material's stereochemistry at the labelled R' position, while the aza-Prins/pinacol rearrangement retains stereochemistry at the labelled R' position, pointing to a simple test that reveals the active mechanism. An enantiomerically pure starting material at the "R'" position should lead to a racemic product if the dominant mechanism is the aza-Cope/Mannich reaction, while the stereochemistry should be retained if the dominant mechanism is an aza-Prins cyclization/pinacol rearrangement pathway. A simple experiment verified that the product was racemic, providing clear evidence of the aza-Cope Mannich reaction as the operative mechanism. Further experiments verified this, using the knowledge that the carbenium ion formed in an aza-Prins/pinacol pathway would be effected by its substituent's ability to stabilize its positive charge, thus changing the reactivity of the pathway. However, a variety of substituents were shown to have little effect on the outcome of the reaction, again pointing to the aza-Cope Mannich reaction as the operative mechanism. Recent literature from the Shanahan lab supports the rare aza-Prins/pinacol pathway only associated with significantly increased alkene nucleophilicity and iminium electrophilicity. The aza-Cope/Mannich reaction shows high diastereoselectivity, generally in accordance the results of the stereochemical experiments elucidating the transition state of the cationic 2-aza-Cope rearrangement, which follows as this tandem reaction pathway was an integral part of these experiments. The stereochemistry of the rearrangement is slightly more complicated when the allyl and amine substituents are installed on a ring, and thus cis or trans to one another. The aza-Cope/Mannich reaction starting material, the amino alcohol, can also be thought of as related to the oxy-Cope rearrangement (below), both
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
for its rate acceleration due to ionic involvement, as well as the analogous enol collapsing function of the Mannich cyclization and the keto-enol tautomerization in the oxy-Cope rearrangement. == Synthetic applications of the 2-aza-Cope/Mannich reaction == The aza-Cope/Mannich reaction is often the most efficient way to synthesize pyrrolidine rings, and thus has a number of applications in natural product total syntheses. Because of its diastereoselectivity this reaction has added to the catalog of asymmetric synthesis tools, as seen in the many examples of asymmetric alkaloids synthesized using the reaction. As we have seen in the first aza-Cope/Mannich reaction and in the elucidation of the reaction's stereochemistry, the aza-Cope/Mannich reaction can be used to form pyrrolidine rings and pyrrolizidine rings. It can be used to create many additional ring structures useful in synthesis, such as indolizidine cycles and indole rings. === (−)-Strychnine total synthesis === The classic example demonstrating the utility of this reaction is the Overman synthesis of strychnine. Strychnine is a naturally occurring highly poisonous alkaloid, found in the tree and climbing shrub genus Strychnos. Strychnine is commonly used as a small vertebrate pesticide. The first strychnine total synthesis, by R. B. Woodward, represented a major step in natural product synthesis: no molecule approaching its complexity had been synthesized before. The next total syntheses were not reported until the late 1980s, using similar methods, namely by using an intermediate available by degradated strychnine. All of these syntheses used harsh conditions. The Overman synthesis sidesteps these problems, and is the first asymmetric total synthesis of strychnine, taking advantage of the diastereoselectivity and mild reaction conditions of the aza-Cope/Mannich reaction. The aza-Cope/Mannich reaction step proceeded in near quantitative yield. The Overman synthesis is accordingly several orders of magnitude more efficient than its predecessors. Overman's synthesis of strychnine represents a useful example
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
of the preparation of precursors necessary for the aza-Cope/Mannich rearrangement, representing effective usage of an epoxide ring opening. The key steps of the synthesis of the rearrangement substrate leading to the starting materials necessary for the aza-Cope/Mannich reaction included a Stille reaction to piece together two precursors, an epoxidation of a double bond using tert-Butyl hydroperoxide, a Wittig reaction to convert the ketone to an alkene, and a cyclization step. Amine alkylation (not shown), transforms the molecule to the rearrangement substrate. Significantly, this molecule shows the enantiomeric precision of the aza-Cope/Mannich reaction, as a simple enantiomeric starting material dictates the final enantiomer: the enantiomer of strychnine was produced by using the enantiomer of the starting material. The Overman synthesis, with in-depth details of the synthesis of the rearrangement substrate, as well as the final steps of the reaction, is detailed here: Overman synthesis of (−)-strychnine. === Synthesis of (−)-crinine === Crinine is an alkaloid of the family Amaryllidaceae, and its asymmetric total synthesis was one of the first using the aza-Cope/Mannich reaction. This synthesis represents a significant step in the development of the aza-Cope/Mannich reaction, as it takes advantage of several of the most useful synthetic strategies characteristic of the reaction. This reaction takes advantage of the cationic-2-aza-Cope rearrangement's high diastereoselectivity, as well as usage of the cyanomethyl group to protect the amine during vinyllithium addition and as a leaving group to promote iminium formation, assisted by addition of silver nitrate. This synthesis is one example of many of the cyanomethyl group providing a synthetically useful route towards pyrrolidine and indolizidine formation. === Synthesis of bridged tricyclic alkaloids === Overman and coworkers developed methods to synthesize complicated bridged tricyclic structures using the aza-Cope/Mannich reaction. These aza-tricyclic structures are found in the complex Stemona alkaloid family, as well as in potential
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
drugs such as some immunosuppressants. The example shown is a facile reaction combining a 1-aza-bicyclo[2.2.1]heptane salt starting material with paraformaldehyde at 80 °C to form the pivotal aza-tricyclic structure of the Stemona alkaloid molecules. Saliently, despite unfavorable orbital overlap due to the sterics of this ring system, the reaction proceeds with 94% yield, highlighting the power of this reaction even under unfavorable conditions. === General ring opening and expansion === The aza-Cope/Mannich reaction, when coupled with existing ring cycles, is often used to create indolizidine cycles (a pyrrolidine connected to a cyclohexane ring). This typical ring annulation, where the cyclopentane moiety is opened with the rearrangement and closed with the Mannich cyclization to form a six membered ring attached to a pyrrolidine ring, while the most popular aza-Cope/Mannich annulation, is not the only one. Seven-membered ring cycles are also possible to synthesize, as the enol and iminium ions stay in close enough proximity to undergo Mannich cyclization. Macrocycle synthesis has not been reported using this reaction, due to the lack of proximity between the enol and iminium. Vinyl oxazolidines can also be used as rearrangement substrates. This rearrangement first creates the vinyl oxazolidine from attack on the cyclohexanone by the aminobutenol, which then undergoes the aza-Cope/Mannich reaction using heat and acid (Lewis or protic). This example breaks and then forms a five-membered ring. More complex examples attach the oxazolidine to another ring, presenting additional methods for the formation of indolizidine cycles. == Scope of the aza-Cope/Mannich reaction == The aza-Cope/Mannich reaction has numerous advantages in comparison to other methods. The gentle conditions of the reaction aren't matched: light heating, normally no higher than 80 °C, a wide range of solvents, and addition of 1 stoichiometric equivalent of acid, commonly camphorsulfonic acid (CSA) or a Lewis acid. Other routes toward pyrrolidine
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
synthesis cannot compete with the stereospecificity, widescale applications in structures containing pyrrolidine derivatives, and large scope of possible starting materials. The reaction exhibits high diastereoselectivity, and is robust, proceeding even when faced with poor orbital overlap in the transition state. The advantages of the aza-Cope/Mannich reaction have motivated research on the synthesis of the starting materials for the reaction, which split into two main categories: amine addition and iminium formation (red) and installation of the vinyl substituent (blue). A wide variety of N-substituents (R), alkyl and aryl, can be used in the reaction, some of which affect the stereochemical outcome of the reaction. Vinyl groups are generally limited to those which are either 1,1 or 1,2-Disubstituted (vinyl with substituents at R1, and R1,R2 respectively), with a wide range of electronic and steric variety tolerated. === Amine addition and iminium formation === ==== Epoxide ring opening ==== The ring strain of epoxides provide useful methodology for installation of an amine group two atoms away from an alcohol group. The epoxide may be first broken by bromide nucleophilic attack. Primary amines, aromatic amines, or lithium anilides can also be used as nucleophiles. Protective O-methylation often follows this step and proceeds easily. When sterics allow for attack on only the appropriate carbon (the terminal carbon as opposed to the second carbon), direct attack by an intramolecular nitrogen is effective, as is the case with strychnine synthesis. === Iminium ion formation === The most common way to generate the iminium ion from the installed amine is by adding formaldehyde or paraformaldehyde, which undergoes acid-catalyzed condensation to form the iminium. Overman's strychnine synthesis typifies this method. Occasionally, intramolecular carbonyls are used. Other methods for iminium ion formation include using cyanomethyl groups or using oxazolidines as carbonyl precursors. ==== Amine alkylation ==== Amine alkylation represents a
|
{
"page_id": 43256469,
"source": null,
"title": "Aza-Cope rearrangement"
}
|
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