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}^{\mathrm {eff} }\equiv (1-f_{\mathbf {k} }^{\mathrm {e} }-f_{\mathbf {k} }^{\mathrm {h} })V_{\mathbf {k} -\mathbf {k'} }\,,} where ( 1 − f k e − f k h ) {\displaystyle (1-f_{\mathbf {k} }^{\mathrm {e} }-f_{\mathbf {k} }^{\mathrm {h} })} weakens the Coulomb interaction via the so-called phase-space filling factor that stems from the Pauli exclusion principle preventing multiple excitations of fermions. Due to the phase-space filling factor, the Coulomb attraction becomes repulsive for excitations levels f k e + f k h > 1 {\displaystyle f_{\mathbf {k} }^{\mathrm {e} }+f_{\mathbf {k} }^{\mathrm {h} }>1} . At this regime, the generalized Wannier equation produces only unbound solutions which follow from the excitonic Mott transition from bound to ionized electron–hole pairs. Once electron–hole densities exist, the generalized Wannier equation is not Hermitian anymore. As a result, the eigenvalue problem has both left- and right-handed eigenstates ϕ λ L ( k ) {\displaystyle \phi _{\lambda }^{\mathrm {L} }(\mathbf {k} )} and ϕ λ R ( k ) {\displaystyle \phi _{\lambda }^{\mathrm {R} }(\mathbf {k} )} , respectively. They are connected via the phase-space filling factor, i.e. ϕ λ L ( k ) = ϕ λ R ( k ) / ( 1 − f k e − f k h ) {\displaystyle \phi _{\lambda }^{\mathrm {L} }(\mathbf {k} )=\phi _{\lambda }^{\mathrm {R} }(\mathbf {k} )/(1-f_{\mathbf {k} }^{\mathrm {e} }-f_{\mathbf {k} }^{\mathrm {h} })} . The left- and right-handed eigenstates have the same eigen value E λ {\displaystyle E_{\lambda }} (that is real valued for the form shown) and they form a complete set of orthogonal solutions since ∑ k [ ϕ λ L ( k ) ] ⋆ ϕ ν R ( k ) = ∑ k [ ϕ λ R ( k ) ] ⋆ ϕ ν L ( k ) = δ
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λ , ν {\displaystyle \sum _{\mathbf {k} }\left[\phi _{\lambda }^{L}(\mathbf {k} )\right]^{\star }\,\phi _{\nu }^{R}(\mathbf {k} )=\sum _{\mathbf {k} }\left[\phi _{\lambda }^{R}(\mathbf {k} )\right]^{\star }\,\phi _{\nu }^{L}(\mathbf {k} )=\delta _{\lambda ,\nu }} . The Wannier equations can also be generalized to include scattering and screening effects that appear due to two-particle correlations within the SBE. This extension also produces left- and right-handed eigenstate, but their connection is more complicated than presented above. Additionally, E λ {\displaystyle E_{\lambda }} becomes complex valued and the imaginary part of E λ {\displaystyle E_{\lambda }} defines the lifetime of the resonance λ {\displaystyle \lambda } . Physically, the generalized Wannier equation describes how the presence of other electron–hole pairs modifies the binding of one effective pair. As main consequences, an excitation tends to weaken the Coulomb interaction and renormalize the single-particle energies in the simplest form. Once also correlation effects are included, one additionally observes the screening of the Coulomb interaction, excitation-induced dephasing, and excitation-induced energy shifts. All these aspects are important when semiconductor experiments are explained in detail. == Applications == Due to the analogy with the hydrogen problem, the zero-density eigenstates are known analytically for any bulk semiconductor when excitations close to the bottom of the electronic bands are studied. In nanostructured materials, such as quantum wells, quantum wires, and quantum dots, the Coulomb-matrix element V k {\displaystyle V_{\mathbf {k} }} strongly deviates from the ideal two- and three-dimensional systems due to finite quantum confinement of electronic states. Hence, one cannot solve the zero-density Wannier equation analytically for those situations, but needs to resort to numerical eigenvalue solvers. In general, only numerical solutions are possible for all semiconductor cases when exciton states are solved within an excited matter. Further examples are shown in the context of the Elliott formula. == See also
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== Excitons Semiconductor Bloch equations Semiconductor luminescence equations Elliott formula Eigenvalues and eigenvectors Quantum well Quantum wire Quantum dot == References ==
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Neumann's law states that the molecular heat in compounds of analogous constitution is always the same. It is named after German mineralogist and physicist Franz Ernst Neumann, who extended the law of the heat of elements by stating that the molecular heat is equal to the sum of the heat of each constituent atom. == References ==
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This is a list of space probes that have left Earth orbit (or were launched with that intention but failed), organized by their planned destination. It includes planetary probes, solar probes, and probes to asteroids and comets. Flybys (such as gravity assists) that were incidental to the main purpose of the mission are also included. Excluded are lunar missions, which are listed separately at List of lunar probes and List of Apollo missions. Flybys of Earth are listed separately at List of Earth flybys. Planned and proposed missions are in the List of proposed Solar System probes. == Key == Colour key: † means "tentatively identified", as classified by NASA. These are Cold War-era Soviet missions, mostly failures, about which few or no details have been officially released. The information given may be speculative. Date is the date of: closest encounter (flybys) impact (impactors) orbital insertion to end of mission, whether planned or premature (orbiters) landing to end of mission, whether planned or premature (landers) launch (missions that never got underway due to failure at or soon after launch) In cases which do not fit any of the above, the event to which the date refers is stated. As a result of this scheme missions are not always listed in order of launch. Some of the terms used under Type: Flyby: The probe flies by an astronomical body, but does not orbit it Orbiter: Part of a probe that orbits an astronomical body Lander: Part of a probe that descend to the surface of an astronomical body Rover: Part of a probe that acts as a vehicle to move on the solid-surface of an astronomical body Penetrator: Part of a probe that impacts an astronomical body Atmospheric probe or balloon: Part of a probe that descend through or floats in
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"title": "List of Solar System probes"
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the atmosphere of an astronomical body; not restricted to weather balloons and other atmospheric sounders, as it can also be used for surface and subsurface imaging and remote sensing. Sample return: Parts of the probe return to Earth with physical samples Under Status, in the case of flybys (such as gravity assists) that are incidental to the main mission, "success" indicates the successful completion of the flyby, not necessarily that of the main mission. == Solar probes == While the Sun is not physically explorable with current technology, the following solar observation probes have been designed and launched to operate in heliocentric orbit or at one of the Earth–Sun Lagrangian points – additional solar observatories were placed in Earth orbit and are not included in this list: === 1960–1969 === === 1974–1997 === === Since 2000 === == Mercury probes == == Venus probes == Early programs encompassing multiple spacecraft include: Venera program — USSR Venus orbiter and lander (1961–1984) Pioneer Venus project — US Venus orbiter and entry probes (1978) Vega program — USSR mission to Venus and Comet Halley (1984) === 1961–1969 === === 1970–1978 === === 1982–1999 === === Since 2006 === == Earth flybys == See List of Earth flybys In addition, several planetary probes have sent back observations of the Earth-Moon system shortly after launch, most notably Mariner 10, Pioneers 10 and 11 and both Voyager probes (Voyager 1 and Voyager 2). == Lunar probes == See List of lunar probes == Mars probes == Major early programs encompassing multiple probes include: Zond program — failed USSR flyby probe Mars probe program — USSR orbiters and landers Viking program — two NASA orbiters and landers (1974) Phobos program — failed USSR orbiters and Phobos landers === 1960–1969 === === 1971–1976 === === 1988–1999 === ===
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"page_id": 788460,
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2001–2009 === === 2011–2018 === === Since 2020 === === Phobos probes === == Ceres probes == == Asteroid probes == == Jupiter probes == === Ganymede probes === == Saturn probes == === Titan probes === == Uranus probes == == Neptune probes == == Pluto probes == == Comet probes == == Kuiper belt probes == == Probes leaving the Solar System == == Other probes to leave Earth orbit == For completeness, this section lists probes that have left (or will leave) Earth orbit, but are not primarily targeted at any of the above bodies. == See also == Lists of spacecraft List of uncrewed spacecraft by program Discovery and exploration of the Solar System List of space telescopes Sample return mission Timeline of Solar System exploration List of interplanetary voyages List of missions to the outer planets == References == == External links == Planetary Society: Cassini's Tour of the Saturn System
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"page_id": 788460,
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"title": "List of Solar System probes"
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Bullseye! is a 1990 British–American action comedy film starring Michael Caine and Roger Moore. It was directed by Michael Winner. It was released on 2 November 1990, to mixed reviews, and was a box office disappointment. It has since developed a small cult following. == Plot == Moore and Caine play dual roles—a pair of small-time con-men and a pair of inept nuclear physicists who believe they have invented a limitless supply of energy. The con men use their resemblance to the scientists to con their way into the scientists' safe deposit boxes and steal the formula, but in so doing, they become entangled in a shady world of spies and international intrigue. The film includes a number of cameo appearances, including Jenny Seagrove (Winner's partner at the time) playing two different roles, John Cleese, Patsy Kensit, Alexandra Pigg and Nicholas Courtney. The film also features Roger Moore's daughter, Deborah Moore, in a supporting role. == Cast == == Reception == The Radio Times Guide to Films' review of Bullseye! states: "this appallingly unfunny comedy is a career low for all concerned". == Release and home video == This film has been released on several countries theatrically and later on VHS by RCA/Columbia Pictures Home Video. The film is available on the made-on-demand DVD-R service from MGM Home Entertainment through 20th Century Fox.Also released on Fabulous DvD in 2016 with special interview with RogerMoore and booklet. == References == == External links == Bullseye! at IMDb Bullseye! at Rotten Tomatoes
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Promoter activity is a term that encompasses several meanings around the process of gene expression from regulatory sequences —promoters and enhancers. Gene expression has been commonly characterized as a measure of how much, how fast, when and where this process happens. Promoters and enhancers are required for controlling where and when a specific gene is transcribed. Traditionally the measure of gene products (i.e. mRNA, proteins, etc.) has been the major approach of measure promoter activity. However, this method confront with two issues: the stochastic nature of the gene expression and the lack of mechanistic interpretation of the thermodynamical process involved in the promoter activation. The actual developments in metabolomics product of developments of next-generation sequencing technologies and molecular structural analysis have enabled the development of more accurate models of the process of promoter activation (e.g. the sigma structure of the polymerase holoenzyme domains) and a better understanding of the complexities of the regulatory factors involved. == Promoter binding == The process of binding is central in determining the "strength" of promoters, that is the relative estimation of how "well" a promoter perform the expression of a gene under specific circumstances. Brewster et al., using a simple thermodynamical model based on the postulate that transcriptional activity is proportional to the probability of finding the RNA polymerase bound at the promoter, obtained predictions of the scaling of the RNA polymerase binding energy. This models support the relationship between the probability of binding and the output of gene expression === Mathematical representation of promoter binding === The problem of gene regulation could be represented mathematically as the probability of n molecules — RNAP, activators, repressors and inducers — are bound to a target regions. To compute the probability of bound, it is needed to sum the Boltzmann weights over all possible states of
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P {\displaystyle P} polymerase molecules on DNA. Here in this deduction P {\displaystyle P} is the effective number of RNAP molecules available for binding to the promoter. This approach is based in statistical thermodynamics of two possible microscopic outcomes: one state where all P polymerases molecules are distributed among all the non-specific sites (sites not participating in gene expression) a promoter occupied and the remaining P-1 polymerases distributed among the non-specific sites. The statistical weight of promoter unoccupied Z(P) is defined: Z ( P ) = N N S ! P ! ∗ ( N N S − P ) ! ∗ e − E N S K b T {\displaystyle Z(P)=~{\frac {N_{NS}!}{P!*(N_{NS}-P)!}}*{e}^{-~{\frac {E_{NS}}{KbT}}}} Where the first term is the combinatorial result of taken P {\displaystyle P} polymerase of N N S {\displaystyle N_{NS}} non-specific sites available, and the second term are the Boltzmann weights, where E N S {\displaystyle E_{NS}} is the energy that represents the average binding energy of RNA polymerase to the genomic background (non-specific sites). Then, the total statistical weight Z ( P t o t a l ) {\displaystyle Z(Ptotal)} , can be written as the sum of the Z ( P ) {\displaystyle Z(P)} state and the RNA polymerase on promoter state: Z ( P t o t a l ) = Z ( P ) + Z ( P − 1 ) ∗ e − E S K b T {\displaystyle Z(Ptotal)=Z(P)+Z(P-1)*{e}^{-~{\frac {E_{S}}{KbT}}}} Where E S {\displaystyle E_{S}} in the Z ( P − 1 ) {\displaystyle Z(P-1)} state is the binding energy for RNA polymerase on the promoter (where the s stands for specific site). Finally, to find the probability of a RNA polymerase to binding ( P r o b b o u n d {\displaystyle Prob_{bound}} ) to a specific
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promoter, we divide Z ( P ) {\displaystyle Z(P)} by Z ( P t o t a l ) {\displaystyle Z(Ptotal)} which produces: P r o b b o u n d = 1 1 + N N S P ∗ e − Δ E K b T {\displaystyle Prob_{bound}={\frac {1}{1+{\frac {N_{N}S}{P}}*{e}^{-{\frac {\Delta E}{KbT}}}}}} Where, Δ E = E S − E N S {\displaystyle \Delta E=E_{S}-E_{NS}} An important result of this model is that any transcription factor, regulator or perturbation could be introduced as a term multiplying P {\displaystyle P} in the probability of binding equation. This term for any transcriptional factor (here called factor regulators) modify the probability of binding to: P r o b b o u n d = 1 1 + N N S P ∗ F R ∗ e − Δ E K b T {\displaystyle Prob_{bound}={\frac {1}{1+{\frac {N_{N}S}{P*F_{R}}}*{e}^{-{\frac {\Delta E}{KbT}}}}}} Where F R {\displaystyle F_{R}} is the term for transcriptional factors, and it has the value of F R > 1 {\displaystyle F_{R}>1} for increase of F R < 1 {\displaystyle F_{R}<1} for decrease of the number of RNA polymerase available to bind. This result has an important significance to represent mathematically all the possible configurations of transcriptional factor by derive different models to estimate F R {\displaystyle F_{R}} (for further developments, see also ). === Eukaryotes promoter structure === The process of activation and binding in eukaryotes is different from bacteria in the way that specific DNA elements bind the factors for a functional pre-initiation complex. In bacteria there is a single polymerase, that contain catalytic subunits and a single regulatory subunits known as sigma, which transcribe for different type of genes. In eukaryotes, the transcription is performed by three different RNA polymerase, RNA pol I for ribosomal RNAs (rRNAs), RNA polymerase
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II for messenger RNAs (mRNAs) and some small regulatory RNAs, and the RNA polymerase III for small RNAs such as transfer RNAs (tRNAs). The process of positioning of the RNA polymerase II and the transcriptional machinery require the recognition of a region known as "core promoter". The elements that could be found in the core promoter include the TATA element, the TFIIB recognition element (BRE), the initiator (Inr), and the downstream core promoter element (DPE). Promoters in eukaryotes contain one or more of these core promotes elements (but any of them are absolutely essential for promoter function), these elements are binding sites for subunits of the transcriptional machinery and are involve in the initiation of the transcription, but also they have some specific enhancer functions. In addition, the promoter activity in eukaryotes include some complexities in the way of how they integrate signals from distal factors with the core promoter. == Evolutionary processes == Unlike in protein coding regions, where the assumption of sequence conservation of functionally homologous genes have been frequently proved, there is not a clear relationship of conservation between sequences and their functions for regulatory regions. The transcriptional promoters regions are under less stringent selection, then have a higher substitutions rates, allowing transcription factor binding sites to be replaced easily be new ones arising from random mutations. Notwithstanding the sequence changes, mainly the functions of regulatory sequences remain conserved. In recents years with the increase of availability of genome sequences, phylogenetic footprinting open the possibility to identify cis-elements, and then study their evolution processes. In this sense, Raijman et al., Dermitzakis et al. have developed techniques for analyzing evolutionary processes in transcription factor regions in Saccharomyces species promoters and mammalian regulatory networks respectively. The basis for many of these evolutionary changes in nature are probably related with
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events within the cis-regulatory regions involve in gene expression. The impact of variation in regulatory regions is important for disease risk due their impact in the gene expression level. Furthermore, perturbations in the binding properties of proteins encoded by regulatory genes have been linked with phenotypes effects such as, duplicated structures, homeotic transformations and novel morphologies. == Measure of promoter activity == The measure of the promoter activity has a broad meaning. The promoter activity could be measured for different situations or research questions, such as: estimation of the level of expression in comparison (relative) to some known value how fast a gene is expressed after induction the timing of expression relative to others genes the specific spatial location of expression Methods to study promoter activity commonly are based in the expression of a reporter gene from the promoter of the gene of interest. Mutations and deletions are made in a promoter region, and their changes on couple expression of the reporter gene are measured. The most important reporter genes are the fluorescence proteins as GFP. These reporters allow to measure promoter activation by increasing fluorescent signals, and deactivation by decrease in the rate of fluorescence. == Promoter recognition in the RNA world == The RNA world hypothesis assumes that very early in evolution, prior to the emergence of DNA as a genetic material and prior to the emergence of protein enzymes, RNA was the key player in the emergence of life. A central idea in this hypothesis is an RNA replicase (ribozyme) that is capable of copying its own genome. A holopolymerase ribozyme has been engineered that uses a sigma factor-like specificity primer to recognize an RNA promoter sequence. This ribozyme can then, in a second step rearrange to a processive form that can polymerize from certain RNA promoters
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and not others. == See also == == References ==
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== See also == {{psychiatry-journal-stub}}
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"title": "Template:Neuroscience-journal-stub"
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The Kiln Site in Jinseo-ri, Buan (Korean: 부안 진서리 요지; Hanja: 扶安鎭西里窯址) refers to a Goryeo-era archaeological site in Jinseo-ri, Buan County, North Jeolla Province, South Korea. In the site are around 40 kilns used to produce Goryeo ware. On January 21, 1963, the site was made a Historic Site of South Korea. The kilns date to around the 11th to 13th centuries. The kilns were made by digging a long hole on a slope of a hill, with smoke holes on the upper side. == See also == Kiln Site in Yucheon-ri, Buan == References ==
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"title": "Kiln Site in Jinseo-ri, Buan"
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The Encyclopedia of Life (EOL) is a free, online encyclopedia intended to document all of the 1.9 million living species known to science. It aggregates content to form "pages" for every known species. Content is compiled from existing trusted databases which are curated by experts and it calls on the assistance of non-experts throughout the world. It includes video, sound, images, graphics, information on characteristics, as well as text. In addition, the Encyclopedia incorporates species-related content from the Biodiversity Heritage Library, which digitizes millions of pages of printed literature from the world's major natural history libraries. The BHL digital content is indexed with the names of organisms using taxonomic indexing software developed by the Global Names project. The EOL project was initially backed by a US$50 million funding commitment, led by the MacArthur Foundation and the Sloan Foundation, who provided US$20 million and US$5 million, respectively. The additional US$25 million came from five cornerstone institutions—the Field Museum, Harvard University, the Marine Biological Laboratory, the Missouri Botanical Garden, and the Smithsonian Institution. The project was initially led by Jim Edwards and the development team by David Patterson. Today, participating institutions and individual donors continue to support EOL through financial contributions. == Overview == EOL went live on 26 February 2008 with 30,000 entries. The site immediately proved to be extremely popular, and temporarily had to revert to demonstration pages for two days when over 11 million views of it were requested. The site relaunched on 5 September 2011 with a redesigned interface and tools. The new version – referred to as EOLv2 – was developed in response to requests from the general public, citizen scientists, educators and professional biologists for a site that was more engaging, accessible and personal. EOLv2 is redesigned to enhance usability and encourage contributions and interactions among
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users. It is also internationalized with interfaces provided for English, German, Spanish, French, Galician, Serbian, Macedonian, Arabic, Chinese, Korean and Ukrainian language speakers. On 16 January 2014, EOL launched TraitBank, a searchable, open digital repository for organism traits, measurements, interactions and other facts for all taxa. The initiative's executive committee includes senior officers from the Atlas of Living Australia, the Biodiversity Heritage Library consortium, the Chinese Academy of Sciences, CONABIO, Field Museum, Harvard University, the Bibliotheca Alexandrina (Library of Alexandria), MacArthur Foundation, Marine Biological Laboratory, Missouri Botanical Garden, Sloan Foundation, and the Smithsonian Institution. == Intention == Information about many species is already available from a variety of sources, in particular about the megafauna. Gathering currently available data on all 1.9 million species will take about 10 years. As of September 2011, EOL had information on more than 700,000 species available, along with more than 600,000 photos and millions of pages of scanned literature. The initiative relies on indexing information compiled by other efforts, including the Species 2000 and ITIS, Catalogue of Life, Fishbase and the Assembling Tree of Life project of NSF, AmphibiaWeb, Mushroom explorer, micro*scope, etc. The initial focus has been on living species but will later include extinct species. As the discovery of new species is expected to continue (currently at about 20,000 per year), the encyclopedia will continue to grow. As taxonomy finds new ways to include species discovered by molecular techniques, the rate of new additions will increase, particularly in respect to the microbial work of (eu)bacteria, archaebacteria and viruses. EOL's goal is to serve as a resource for the general public, enthusiastic amateurs, educators, students and professional scientists from around the world. == Resources and collaborations == The Encyclopedia of Life is an aggregative environment, that collects data from other on-line data sources. It
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provides full provenance for information through citations from its trusted databases. Professional researchers publishing academic research should cite directly to the underlying data. Users may not currently edit EOL's entries directly but may register for the site to join specialist expert communities to discuss relevant information, questions, possible corrections, sources, and potential updates, contribute images and sound, or volunteer for technical support services. Its interface is translated at translatewiki.net. EOL was made distinctive by its incorporation of 'taxonomic intelligence', a growing array of algorithms that sought to emulate the practices of taxonomists. These tools included names resolution so that data entered into different databases using different names for organisms could be combined. Components of hierarchical classifications systems could be used to drill-down or to expand data searches. Common components of different classification schemes were used to allow users to navigate using multiple classifications and to meander among schemes. This initiative overcame a major problem of many biological data bases, that of having rigid and singular classification structures that were unable to reflect the diversity of views, or evolving concepts of how names of species and other taxa should be interpreted. The names management systems continue to be developed by the Global Names project. == See also == All Species Foundation Biodiversity Heritage Library List of online encyclopedias Encyclopedia of Earth Wikispecies == References == == External links == Official website The Encyclopedia of Life – Introductory video on YouTube from May 2007. Encyclopedia of Life at the National Museum of Natural History
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List of desiccants: Activated alumina Aerogel Benzophenone (as anion) Bentonite clay Calcium chloride Calcium hydride Calcium oxide Calcium sulfate (Drierite) Cobalt(II) chloride Copper(II) sulfate Lithium chloride Lithium bromide Magnesium chloride hexahydrate Magnesium sulfate Magnesium perchlorate Molecular sieve Phosphorus pentoxide Potassium carbonate Potassium hydroxide Rice Silica gel Sodium Sodium chlorate Sodium chloride Sodium hydroxide Sodium sulfate Sucrose Sulfuric acid Triethylene glycol Zeolite (molecular sieves) == External links == Education Center == References ==
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Picollator is an Internet search engine that performs searches for web sites and multimedia by visual query (image) or text, or a combination of visual query and text. Picollator recognizes objects in the image, obtains their relevance to the text and vice versa, and searches in accordance with all information provided. == Description == Picollator identifies human faces in the images and creates a database of people's faces. This allows the user to search for other images of the submitted person, lookalikes and/or similar images in images found on websites. Picollator can be used in any language. == History == 2006 – Recogmission LLC developed a desktop application for photo collections management. The system automatically classifies, manages and retrieves photographs stored locally or in corporate databases. 2007 – Recogmission started Picollator multimedia search engine project, now in Beta stage. 2008 – Picollator.mobi is launched—a new universal search engine for mobile phones. 2009 – Recogmission opens the web based content filter service piFilter.com, which inherited some pattern recognition technologies from Picollator. == Features == Most image search engines match user textual query and picture tags. Picollator is based on a different approach. Patterns and objects found in the image are stored in its database, therefore it is able to recognise the contents of the image and compare it to other images to find similarities. To search for multimedia information, the user may submit Sample image to find images with relevant people Image to find web resources Text to find images Text to find web resources Text and Image to find images and/or web resources. == Company == ru:Recogmission LLC has developed an indexing engine for multimedia information search based on the visual query. Recogmission develops solutions for multimedia information (image, text and video) indexing and searching on the web and in
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corporate environments. == References == Picollator Loves My Girlish Smile, Inside the Marketers Studio - David Berkowitz's Marketing Blog Archived 2008-06-12 at the Wayback Machine. March 20, 2008 Picollator - Image search engine, Phil Bradley's weblog. March 31, 2008 Image-Based Queries, Techpin. March 16, 2008 Picollator: Buscador de rostros, Neoteo Archived 2008-08-20 at the Wayback Machine Picollator Online Search, buscador de caras dentro de las imágenes online, Genbeta Archived 2008-07-09 at the Wayback Machine. March 26, 2008 Picollator:基于脸部特征的图片搜索引擎, 天涯海阁 Archived 2008-08-05 at the Wayback Machine Picollator - Gesichter suchen mit Bildvorlagen, @-web Suchmaschinen Weblog. July 21, 2008 Picollator Launches New Web Search System, TMCnet.com Archived 2008-08-08 at the Wayback Machine. July 15, 2008 Picollator sucht Menschen mithilfe von Gesichtserkennung, Internet World Business Archived 2008-10-04 at the Wayback Machine. July 22, 2008 Sketch based query for image retrieval, Kmvirtual Archived 2009-03-01 at the Wayback Machine. May 30, 2008 Picollator - текстовый или визуальный поиск?, Стартаперы.ru Picollator ищет похожих людей, Новости Медиа Атлас Archived 2011-10-02 at the Wayback Machine. March 3, 2008 Picollator - Οπτική αναζήτηση… περίπου :), Internetakias.gr Archived 2008-10-02 at the Wayback Machine. April 7, 2008 Доступны мультимедийные запросы в новой поисковой системе Picollator, ITua.info. March 14, 2008 Как найти человека по рисунку лица?, Newsland Всевидящее око онлайна, Игромания. July, 2008 Microsoft поднимет долю программ в ВВП, OSP.ru July 1, 2008 Система поиска по мультимедийным запросам, Мониторинг Интернета. April 7, 2008 В Рунете запущена система мультимедийного поиска Picollator.ru, Elvisti.com. April 13, 2008 Мультимедийный поиск становится интеллектуальным, Rocit.ru Archived 2016-03-06 at the Wayback Machine. July 2, 2008 В Рунете появилась система поиска похожих картинок, Eplus.com.ua Archived 2008-07-25 at the Wayback Machine. March 11, 2008 Ресурсы в сети можно искать с помощью изображений, Commcenter.ru. March 29, 2008
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Thomsen–Friedenreich antigen (Galβ1-3GalNAcα1-Ser/Thr) is a disaccharide that serves as a core 1 structure in O-linked glycosylation. First described by Thomsen as a red blood cell's antigen, later research have determined it to be an oncofetal antigen. it is present in the body as a part of membrane transport proteins where it is normally masked from the immune system. It is commonly demasked in cancer cells, with it being expressed in up to 90% of carcinomas, making it a potential target for immunotherapy. == References == == External links == Dippold, W.; Steinborn, A.; Büschenfelde, K. H. M. z. (1990). "The Role of the Thomsen-Friedenreich Antigen As a Tumor-Associated Molecule". Environmental Health Perspectives. 88: 255–7. doi:10.2307/3431086. JSTOR 3431086. PMC 1568008. PMID 2272320. King, MJ; Holburn, AM (1979). "Radioassays of blood group M, N and T (Thomsen-Friedenreich) antigens". Immunology. 38 (1): 129–36. PMC 1457886. PMID 511213. Singh, R.; Campbell, BJ; Yu, LG; Fernig, DG; Milton, JD; Goodlad, RA; Fitzgerald, AJ; Rhodes, JM (2001). "Cell surface-expressed Thomsen-Friedenreich antigen in colon cancer is predominantly carried on high molecular weight splice variants of CD44". Glycobiology. 11 (7): 587–92. doi:10.1093/glycob/11.7.587. PMID 11447138. Wolf, Michael F.; Koerner, Ulrike; Schumacher, Kurt (1986). "Specificity of reagents directed to the Thomsen-Friedenreich antigen and their capacity to bind to the surface of human carcinoma cell lines". Cancer Research. 46 (4 Pt 1): 1779–82. PMID 2418954. Uhlenbruck, G. (1981). "The Thomsen-Friedenreich (TF) Receptor: An Old History with New Mystery". Immunological Investigations. 10 (3): 251–64. doi:10.3109/08820138109093459. PMID 7037612. Dippold, W; Steinborn, A; Meyer; Büschenfelde, KH (August 1990). "The role of the Thomsen-Friedenreich antigen as a tumor-associated molecule". Environ. Health Perspect. 88: 255–7. doi:10.2307/3431086. JSTOR 3431086. PMC 1568008. PMID 2272320.
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{
"page_id": 31131659,
"source": null,
"title": "Thomsen–Friedenreich antigen"
}
|
The Benary reaction is an organic reaction. In 1931 Erich Bénary discovered that β-(N,N-dialkylamino)-vinyl ketones reacted with Grignard reagents in a 1,4-addition to give α,β-unsaturated ketones, α,β-unsaturated aldehydes and α,β-unsaturated esters as well as poly-unsaturated ketones and aldehydes after hydrolysis of the reaction intermediate and elimination of a dialkylated amine. == References ==
|
{
"page_id": 10422282,
"source": null,
"title": "Benary reaction"
}
|
Inna Sekirov is a Moldovan-born, Canadian medical microbiologist and physician-scientist at the University of British Columbia. == Biography == Sekirov was born in Moldova and moved to Vancouver, British Columbia, Canada in 1995. She attended the University of British Columbia (UBC) and graduated with a BS in Microbiology and Immunology in 2003. Sekirov carried out her PhD work at the Brett Finlay lab as a Michael Smith Foundation for Health Research Senior Graduate Trainee. She then went on to complete her medical microbiology residency graduating with her PhD, MD, and FRCPC at UBC in 2011. She remained at UBC after graduation and became the Program Head for Tuberculosis (TB)/Mycobacteriology at the British Columbia Centre for Disease Control, and a Clinical Assistant Professor of Pathology and Laboratory Medicine at UBC. Her research focused on the public health-related aspects of medical microbiology, clinical applications of microbial genomics and TB/mycobacteriology diagnostic methods. She has also led COVID-19 research projects on ACEII, antibody responses, and seroprevalence using dried blood spots. == Selected works == Coburn, Bryan, Inna Sekirov, and B. Brett Finlay. "Type III secretion systems and disease." Clinical microbiology reviews 20, no. 4 (2007): 535-549. Sekirov, Inna, Nicola M. Tam, Maria Jogova, Marilyn L. Robertson, Yuling Li, Claudia Lupp, and B. Brett Finlay. "Antibiotic-induced perturbations of the intestinal microbiota alter host susceptibility to enteric infection." Infection and immunity 76, no. 10 (2008): 4726-4736. Sekirov, Inna, Shannon L. Russell, L. Caetano M. Antunes, and B. Brett Finlay. "Gut microbiota in health and disease." Physiological reviews (2010). Skowronski, Danuta M., Inna Sekirov, Suzana Sabaiduc, Macy Zou, Muhammad Morshed, David Lawrence, Kate Smolina et al. "Low SARS-CoV-2 sero-prevalence based on anonymized residual sero-survey before and after first wave measures in British Columbia, Canada, March-May 2020." MedRxiv (2020): 2020-07. == References ==
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{
"page_id": 68749327,
"source": null,
"title": "Inna Sekirov"
}
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Deep inspiration breath-hold (DIBH) is a method of delivering radiotherapy while limiting radiation exposure to the heart and lungs. It is used primarily for treating left-sided breast cancer. The technique involves a patient holding their breath during treatment. In DIBH techniques, treatment is only delivered at certain points in the breathing cycle, where the patient holds their breath. Since the relative positions of organs in the chest naturally changes during breathing, this allows treatment to be delivered to the target (tumour) while other organs are in the optimal position to receive least dose. == Treatment Methods == In the DIBH technique, the patient is initially maintained at quiet tidal breathing (i.e. normal, relaxed breathing), followed by a deep inspiration, a deep expiration, a second deep inspiration, and breath-hold. At this point the patient is at approximately 100% vital capacity, and simulation, verification, and treatment take place during this phase of breath-holding. DIBH is performed with several tangential fields for left-sided breast cancer. A patient is instructed to hold the breath while viewing the breathing pattern and the breath-hold position through a head-mounted mirror, thereby ensuring reproducibility of the breath-hold position in each delivery. A pair of video goggles may also be used for monitoring the breathing cycle. Patients who cannot maintain DIBH can still benefit from lung tracking techniques, for example 4DCT. There are two basic methods of performing DIBH: free-breathing breath-hold, and spirometry-monitored deep inspiration breath hold. === Free-breathing breath-hold === Free-breathing breath-hold, also known as real-time position management (RPM) DIBH utilises an infra-red camera and markers placed on the patient to track movement of their chest, and their breathing. Another device for DIBH is known as Abches that monitors the breathing pattern. With the Abches, a patient is instructed to hold the breath at a specified breathing position
|
{
"page_id": 49088528,
"source": null,
"title": "Deep inspiration breath-hold"
}
|
by viewing a breathing level indicator, thereby reproducing an identical breath-hold position. === Spirometry-monitored breath-hold === Spirometry based designs are known as active breathing coordinator (ABC) DIBH systems. ABC utilises a mouth piece for the patient which can be used to control the flow of air to provide more reproducible results. == Effectiveness == The DIBH technique provides an advantage to conventional free-breathing treatment by decreasing lung density, reducing normal safety margins, and enabling more accurate treatment. These improvements contribute to the effective exclusion of normal lung tissue from the high-dose region and permit the use of higher treatment doses without increased risks of toxicity. Treatment of patients with the DIBH technique is feasible in a clinical setting. With this technique, consistent lung inflation levels are achieved in patients, as judged by both spirometry and verification films. Breathing-induced tumor motion is significantly reduced using DIBH compared to free breathing, enabling better target coverage. == Future research == There is currently no clear selection criteria to predict which patients will benefit most from the DIBH technique, other than left breast laterality. There is evidence to suggest parasagittal cardiac contact distance is a promising metric for selection and should be assessed in all future DIBH planning studies. == References ==
|
{
"page_id": 49088528,
"source": null,
"title": "Deep inspiration breath-hold"
}
|
TB6Cs1H3 is a member of the H/ACA-like class of non-coding RNA (ncRNA) molecule that guide the sites of modification of uridines to pseudouridines of substrate RNAs. It is known as a small nucleolar RNA (snoRNA) thus named because of its cellular localization in the nucleolus of the eukaryotic cell. TB6Cs1H3 is predicted to guide the pseudouridylation of SSU ribosomal RNA (rRNA) at residue Ψ662. == References ==
|
{
"page_id": 21104657,
"source": null,
"title": "TB6Cs1H3 snoRNA"
}
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This is a partial list of molecules that contain 12 carbon atoms. == C12H0 – C12H8 == == C12H9 – C12H11 == == C12H12 – C12H14 == == C12H15 – C12H17 == == C12H18 – C12H19 == == C12H20 – C12H21 == == C12H22 == == C12H23 – C12H27 == == C12H28 – C12Hmany == == See also == Carbon number List of compounds with carbon number 11 List of compounds with carbon number 13
|
{
"page_id": 30935057,
"source": null,
"title": "List of compounds with carbon number 12"
}
|
Scientists against Nuclear Arms (SANA) was formed in 1981 by the physicist and peace activist Mike Pentz together with Steven Rose, both academics at the Open University, to oppose nuclear arms. SANA was one of the forerunner organisations of Scientists for Global Responsibility (SGR). == See also == Campaign for Nuclear Disarmament Anti-nuclear movement Anti-war European Nuclear Disarmament Independent Nuclear Disarmament Election Committee International Coalition to Ban Uranium Weapons Nuclear disarmament Nuclear-Free Future Award Nuclear Information Service Nuclear proliferation Peace movement == References ==
|
{
"page_id": 42338324,
"source": null,
"title": "Scientists against Nuclear Arms"
}
|
An ecological network is a representation of the biotic interactions in an ecosystem, in which species (nodes) are connected by pairwise interactions (links). These interactions can be trophic or symbiotic. Ecological networks are used to describe and compare the structures of real ecosystems, while network models are used to investigate the effects of network structure on properties such as ecosystem stability. == Properties == Historically, research into ecological networks developed from descriptions of trophic relationships in aquatic food webs; however, recent work has expanded to look at other food webs as well as webs of mutualists. Results of this work have identified several important properties of ecological networks. Complexity (linkage density): the average number of links per species. Explaining the observed high levels of complexity in ecosystems has been one of the main challenges and motivations for ecological network analysis, since early theory predicted that complexity should lead to instability. Connectance: the proportion of possible links between species that are realized (links/species2). In food webs, the level of connectance is related to the statistical distribution of the links per species. The distribution of links changes from (partial) power-law to exponential to uniform as the level of connectance increases. The observed values of connectance in empirical food webs appear to be constrained by the variability of the physical environment, by habitat type, which will reflect on an organism's diet breadth driven by optimal foraging behaviour. This ultimately links the structure of these ecological networks to the behaviour of individual organisms. Degree distribution: the degree distribution of an ecological network is the cumulative distribution for the number of links each species has. The degree distributions of food webs have been found to display the same universal functional form. The degree distribution can be split into its two component parts, links to a
|
{
"page_id": 17303574,
"source": null,
"title": "Ecological network"
}
|
species' prey (aka. in degree) and links to a species' predators (aka- out degree). Both the in degree and out degree distributions display their own universal functional forms. As there is a faster decay of the out-degree distribution than the in degree distribution we can expect that on average in a food web a species will have more in links than out links. Clustering: the proportion of species that are directly linked to a focal species. A focal species in the middle of a cluster may be a keystone species, and its loss could have large effects on the network. Compartmentalization: the division of the network into relatively independent sub-networks. Some ecological networks have been observed to be compartmentalized by body size and by spatial location. Evidence also exists which suggests that compartmentalization in food webs appears to result from patterns of species' diet contiguity and adaptive foraging Nestedness: the degree to which species with few links have a sub-set of the links of other species, rather than a different set of links. In highly nested networks, guilds of species that share an ecological niche contain both generalists (species with many links) and specialists (species with few links, all shared with the generalists). In mutualistic networks, nestedness is often asymmetrical, with specialists of one guild linked to the generalists of the partner guild. The level of nestedness is determined not by species features but overall network depictors (e.g. network size and connectance) and can be predicted by a dynamic adaptive model with species rewiring to maximize individual fitness or the fitness of the whole community. In-block nestedness: Also called compound structures, some ecological networks combine compartmentalization at large network scales with nestedness within compartments. Network motif: Motifs are unique sub-graphs composed of n-nodes found embedded in a network. For instance
|
{
"page_id": 17303574,
"source": null,
"title": "Ecological network"
}
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there exist thirteen unique motif structures containing three species, some of these correspond to familiar interaction modules studied by population ecologists such as food chains, apparent competition, or intraguild predation. Studies investigating motif structures of ecological networks, by examining patterns of under/over representation of certain motifs compared to a random graph, have found that food webs have particular motif structures Trophic coherence: The tendency of species to specialise on particular trophic levels leads to food webs displaying a significant degree of order in their trophic structure, known as trophic coherence, which in turn has important effects on properties such as stability and prevalence of cycles. == Stability and Optimisation == The relationship between ecosystem complexity and stability is a major topic of interest in ecology. Use of ecological networks makes it possible to analyze the effects of the network properties described above on the stability of an ecosystem. Ecosystem complexity was once thought to reduce stability by enabling the effects of disturbances, such as species loss or species invasion, to spread and amplify through the network. However, other characteristics of network structure have been identified that reduce the spread of indirect effects and thus enhance ecosystem stability. The relationship between complexity and stability can even be inverted in food webs with sufficient trophic coherence, so that increases in biodiversity would make a community more stable rather than less. Once ecological networks are described as transportation networks where the food flows along the predation links, one can extend the concept of allometric scaling to them. In doing so one could find that spanning trees are characterized by universal scaling relations, thereby suggesting that ecological network could be the product of an optimisation procedure. Interaction strength may decrease with the number of links between species, damping the effects of any disturbance and
|
{
"page_id": 17303574,
"source": null,
"title": "Ecological network"
}
|
cascading extinctions are less likely in compartmentalized networks, as effects of species losses are limited to the original compartment. Furthermore, as long as the most connected species are unlikely to go extinct, network persistence increases with connectance and nestedness. No consensus on the links between network nestedness and community stability in mutualistic species has however been reached among several investigations in recent years. Recent findings suggest that a trade-off between different types of stability may exist. The nested structure of mutual networks was shown to promote the capacity of species to persist under increasingly harsh circumstances. Most likely, because the nested structure of mutualistic networks helps species to indirectly support each other when circumstances are harsh. This indirect facilitation helps species to survive, but it also means that under harsh circumstances one species cannot survive without the support of the other. As circumstances become increasingly harsh, a tipping point may therefore be passed at which the populations of a large number of species may collapse simultaneously. == Other applications == Additional applications of ecological networks include exploration of how the community context affects pairwise interactions. The community of species in an ecosystem is expected to affect both the ecological interaction and coevolution of pairs of species. Related, spatial applications are being developed for studying metapopulations, epidemiology, and the evolution of cooperation. In these cases, networks of habitat patches (metapopulations) or individuals (epidemiology, social behavior), make it possible to explore the effects of spatial heterogeneity. == See also == Biological network Consumer-resource systems Food web Pollination network Recycling (ecological) == Notes == == References == === Specific === === General ===
|
{
"page_id": 17303574,
"source": null,
"title": "Ecological network"
}
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Journal of Photonics for Energy is a quarterly, online peer-reviewed scientific journal covering fundamental and applied research on the applications of photonics for renewable energy harvesting, conversion, storage, distribution, monitoring, consumption, and efficient usage, published by SPIE. The editor-in-chief is Sean Shaheen. == Abstracting and indexing == The journal is abstracted and indexed in: Science Citation Index Expanded Current Contents - Physical, Chemical & Earth Sciences Current Contents - Engineering, Computing & Technology Inspec Scopus Ei/Compendex According to the Journal Citation Reports, the journal has a 2020 impact factor of 1.836. == References == == External links == Official website
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{
"page_id": 54265881,
"source": null,
"title": "Journal of Photonics for Energy"
}
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Tennessine is a synthetic chemical element; it has symbol Ts and atomic number 117. It has the second-highest atomic number and joint-highest atomic mass of all known elements and is the penultimate element of the 7th period of the periodic table. It is named after the U.S. state of Tennessee, where key research institutions involved in its discovery are located (however, the IUPAC says that the element is named after the "region of Tennessee"). The discovery of tennessine was officially announced in Dubna, Russia, by a Russian–American collaboration in April 2010, which makes it the most recently discovered element. One of its daughter isotopes was created directly in 2011, partially confirming the experiment's results. The experiment was successfully repeated by the same collaboration in 2012 and by a joint German–American team in May 2014. In December 2015, the Joint Working Party of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), which evaluates claims of discovery of new elements, recognized the element and assigned the priority to the Russian–American team. In June 2016, the IUPAC published a declaration stating that the discoverers had suggested the name tennessine, a name which was officially adopted in November 2016. Tennessine may be located in the "island of stability", a concept that explains why some superheavy elements are more stable despite an overall trend of decreasing stability for elements beyond bismuth on the periodic table. The synthesized tennessine atoms have lasted tens and hundreds of milliseconds. In the periodic table, tennessine is expected to be a member of group 17, the halogens. Some of its properties may differ significantly from those of the lighter halogens due to relativistic effects. As a result, tennessine is expected to be a volatile metal that neither forms anions
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
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nor achieves high oxidation states. A few key properties, such as its melting and boiling points and its first ionization energy, are nevertheless expected to follow the periodic trends of the halogens. == Introduction == == History == === Pre-discovery === In December 2004, the Joint Institute for Nuclear Research (JINR) team in Dubna, Moscow Oblast, Russia, proposed a joint experiment with the Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, United States, to synthesize element 117 — so called for the 117 protons in its nucleus. Their proposal involved fusing a berkelium (element 97) target and a calcium (element 20) beam, conducted via bombardment of the berkelium target with calcium nuclei: this would complete a set of experiments done at the JINR on the fusion of actinide targets with a calcium-48 beam, which had thus far produced the new elements 113–116 and 118. ORNL—then the world's only producer of berkelium—could not then provide the element, as they had temporarily ceased production, and re-initiating it would be too costly. Plans to synthesize element 117 were suspended in favor of the confirmation of element 118, which had been produced earlier in 2002 by bombarding a californium target with calcium. The required berkelium-249 is a by-product in californium-252 production, and obtaining the required amount of berkelium was an even more difficult task than obtaining that of californium, as well as costly: It would cost around 3.5 million dollars, and the parties agreed to wait for a commercial order of californium production, from which berkelium could be extracted. The JINR team sought to use berkelium because calcium-48, the isotope of calcium used in the beam, has 20 protons and 28 neutrons, making a neutron–proton ratio of 1.4; and it is the lightest stable or near-stable nucleus with such a large neutron excess.
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
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Thanks to the neutron excess, the resulting nuclei were expected to be heavier and closer to the sought-after island of stability. Of the aimed for 117 protons, calcium has 20, and thus they needed to use berkelium, which has 97 protons in its nucleus. In February 2005, the leader of the JINR team — Yuri Oganessian — presented a colloquium at ORNL. Also in attendance were representatives of Lawrence Livermore National Laboratory, who had previously worked with JINR on the discovery of elements 113–116 and 118, and Joseph Hamilton of Vanderbilt University, a collaborator of Oganessian. Hamilton checked if the ORNL high-flux reactor produced californium for a commercial order: The required berkelium could be obtained as a by-product. He learned that it did not and there was no expectation for such an order in the immediate future. Hamilton kept monitoring the situation, making the checks once in a while. (Later, Oganessian referred to Hamilton as "the father of 117" for doing this work.) === Discovery === ORNL resumed californium production in spring 2008. Hamilton noted the restart during the summer and made a deal on subsequent extraction of berkelium (the price was about $600,000). During a September 2008 symposium at Vanderbilt University in Nashville, Tennessee, celebrating his 50th year on the Physics faculty, Hamilton introduced Oganessian to James Roberto (then the deputy director for science and technology at ORNL). They established a collaboration among JINR, ORNL, and Vanderbilt. Clarice Phelps was part of ORNL's team that collaborated with JINR; this is particularly notable as because of it the IUPAC recognizes her as the first African-American woman to be involved with the discovery of a chemical element. The eventual collaborating institutions also included The University of Tennessee (Knoxville), Lawrence Livermore National Laboratory, The Research Institute for Advanced Reactors (Russia), and The
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
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University of Nevada (Las Vegas). In November 2008, the U.S. Department of Energy, which had oversight over the reactor in Oak Ridge, allowed the scientific use of the extracted berkelium. The production lasted 250 days and ended in late December 2008, resulting in 22 milligrams of berkelium, enough to perform the experiment. In January 2009, the berkelium was removed from ORNL's High Flux Isotope Reactor; it was subsequently cooled for 90 days and then processed at ORNL's Radiochemical Engineering and Development Center to separate and purify the berkelium material, which took another 90 days. Its half-life is only 330 days: this means, after that time, half the berkelium produced would have decayed. Because of this, the berkelium target had to be quickly transported to Russia; for the experiment to be viable, it had to be completed within six months of its departure from the United States. The target was packed into five lead containers to be flown from New York to Moscow. Russian customs officials twice refused to let the target enter the country because of missing or incomplete paperwork. Over the span of a few days, the target traveled over the Atlantic Ocean five times. On its arrival in Russia in June 2009, the berkelium was immediately transferred to Research Institute of Atomic Reactors (RIAR) in Dimitrovgrad, Ulyanovsk Oblast, where it was deposited as a 300-nanometer-thin layer on a titanium film. In July 2009, it was transported to Dubna, where it was installed in the particle accelerator at the JINR. The calcium-48 beam was generated by chemically extracting the small quantities of calcium-48 present in naturally occurring calcium, enriching it 500 times. This work was done in the closed town of Lesnoy, Sverdlovsk Oblast, Russia. The experiment began in late July 2009. In January 2010, scientists at the Flerov
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
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Laboratory of Nuclear Reactions announced internally that they had detected the decay of a new element with atomic number 117 via two decay chains: one of an odd–odd isotope undergoing 6 alpha decays before spontaneous fission, and one of an odd–even isotope undergoing 3 alpha decays before fission. The obtained data from the experiment was sent to the LLNL for further analysis. On 9 April 2010, an official report was released in the journal Physical Review Letters identifying the isotopes as 294117 and 293117, which were shown to have half-lives on the order of tens or hundreds of milliseconds. The work was signed by all parties involved in the experiment to some extent: JINR, ORNL, LLNL, RIAR, Vanderbilt, the University of Tennessee (Knoxville, Tennessee, U.S.), and the University of Nevada (Las Vegas, Nevada, U.S.), which provided data analysis support. The isotopes were formed as follows: 24997Bk + 4820Ca → 297117* → 294117 + 3 10n (1 event) 24997Bk + 4820Ca → 297117* → 293117 + 4 10n (5 events) === Confirmation === All daughter isotopes (decay products) of element 117 were previously unknown; therefore, their properties could not be used to confirm the claim of discovery. In 2011, when one of the decay products (289115) was synthesized directly, its properties matched those measured in the claimed indirect synthesis from the decay of element 117. The discoverers did not submit a claim for their findings in 2007–2011 when the Joint Working Party was reviewing claims of discoveries of new elements. The Dubna team repeated the experiment in 2012, creating seven atoms of element 117 and confirming their earlier synthesis of element 118 (produced after some time when a significant quantity of the berkelium-249 target had beta decayed to californium-249). The results of the experiment matched the previous outcome; the scientists then
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
filed an application to register the element. In May 2014, a joint German–American collaboration of scientists from the ORNL and the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Hessen, Germany, claimed to have confirmed discovery of the element. The team repeated the Dubna experiment using the Darmstadt accelerator, creating two atoms of element 117. In December 2015, the JWP officially recognized the discovery of 293117 on account of the confirmation of the properties of its daughter 289115, and thus the listed discoverers — JINR, LLNL, and ORNL — were given the right to suggest an official name for the element. (Vanderbilt was left off the initial list of discoverers in an error that was later corrected.) In May 2016, Lund University (Lund, Scania, Sweden) and GSI cast some doubt on the syntheses of elements 115 and 117. The decay chains assigned to 289115, the isotope instrumental in the confirmation of the syntheses of elements 115 and 117, were found based on a new statistical method to be too different to belong to the same nuclide with a reasonably high probability. The reported 293117 decay chains approved as such by the JWP were found to require splitting into individual data sets assigned to different isotopes of element 117. It was also found that the claimed link between the decay chains reported as from 293117 and 289115 probably did not exist. (On the other hand, the chains from the non-approved isotope 294117 were found to be congruent.) The multiplicity of states found when nuclides that are not even–even undergo alpha decay is not unexpected and contributes to the lack of clarity in the cross-reactions. This study criticized the JWP report for overlooking subtleties associated with this issue, and considered it "problematic" that the only argument for the acceptance of the
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
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discoveries of elements 115 and 117 was a link they considered to be doubtful. On 8 June 2017, two members of the Dubna team published a journal article answering these criticisms, analysing their data on the nuclides 293117 and 289115 with widely accepted statistical methods, noted that the 2016 studies indicating non-congruence produced problematic results when applied to radioactive decay: they excluded from the 90% confidence interval both average and extreme decay times, and the decay chains that would be excluded from the 90% confidence interval they chose were more probable to be observed than those that would be included. The 2017 reanalysis concluded that the observed decay chains of 293117 and 289115 were consistent with the assumption that only one nuclide was present at each step of the chain, although it would be desirable to be able to directly measure the mass number of the originating nucleus of each chain as well as the excitation function of the 243Am + 48Ca reaction. === Naming === Using Mendeleev's nomenclature for unnamed and undiscovered elements, element 117 should be known as eka-astatine. Using the 1979 recommendations by the International Union of Pure and Applied Chemistry (IUPAC), the element was temporarily called ununseptium (symbol Uus), formed from Latin roots "one", "one", and "seven", a reference to the element's atomic number 117. Many scientists in the field called it "element 117", with the symbol E117, (117), or 117. According to guidelines of IUPAC valid at the moment of the discovery approval, the permanent names of new elements should have ended in "-ium"; this included element 117, even if the element was a halogen, which traditionally have names ending in "-ine"; however, the new recommendations published in 2016 recommended using the "-ine" ending for all new group 17 elements. After the original synthesis in
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
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|
2010, Dawn Shaughnessy of LLNL and Oganessian declared that naming was a sensitive question, and it was avoided as far as possible. However, Hamilton, who teaches at Vanderbilt University in Nashville, Tennessee, declared that year, "I was crucial in getting the group together and in getting the 249Bk target essential for the discovery. As a result of that, I'm going to get to name the element. I can't tell you the name, but it will bring distinction to the region." In a 2015 interview, Oganessian, after telling the story of the experiment, said, "and the Americans named this a tour de force, they had demonstrated they could do [this] with no margin for error. Well, soon they will name the 117th element." In March 2016, the discovery team agreed on a conference call involving representatives from the parties involved on the name "tennessine" for element 117. In June 2016, IUPAC published a declaration stating the discoverers had submitted their suggestions for naming the new elements 115, 117, and 118 to the IUPAC; the suggestion for the element 117 was tennessine, with a symbol of Ts, after "the region of Tennessee". The suggested names were recommended for acceptance by the IUPAC Inorganic Chemistry Division; formal acceptance was set to occur after a five-month term following publishing of the declaration expires. In November 2016, the names, including tennessine, were formally accepted. Concerns that the proposed symbol Ts may clash with a notation for the tosyl group used in organic chemistry were rejected, following existing symbols bearing such dual meanings: Ac (actinium and acetyl) and Pr (praseodymium and propyl). The naming ceremony for moscovium, tennessine, and oganesson was held on 2 March 2017 at the Russian Academy of Sciences in Moscow; a separate ceremony for tennessine alone had been held at ORNL in
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
January 2017. == Predicted properties == Other than nuclear properties, no properties of tennessine or its compounds have been measured; this is due to its extremely limited and expensive production and the fact that it decays very quickly. Properties of tennessine remain unknown and only predictions are available. === Nuclear stability and isotopes === The stability of nuclei quickly decreases with the increase in atomic number after curium, element 96, whose half-life is four orders of magnitude longer than that of any subsequent element. All isotopes with an atomic number above 101 undergo radioactive decay with half-lives of less than 30 hours. No elements with atomic numbers above 82 (after lead) have stable isotopes. This is because of the ever-increasing Coulomb repulsion of protons, so that the strong nuclear force cannot hold the nucleus together against spontaneous fission for long. Calculations suggest that in the absence of other stabilizing factors, elements with more than 104 protons should not exist. However, researchers in the 1960s suggested that the closed nuclear shells around 114 protons and 184 neutrons should counteract this instability, creating an "island of stability" where nuclides could have half-lives reaching thousands or millions of years. While scientists have still not reached the island, the mere existence of the superheavy elements (including tennessine) confirms that this stabilizing effect is real, and in general the known superheavy nuclides become exponentially longer-lived as they approach the predicted location of the island. Tennessine is the second-heaviest element created so far, and all its known isotopes have half-lives of less than one second. Nevertheless, this is longer than the values predicted prior to their discovery: the predicted lifetimes for 293Ts and 294Ts used in the discovery paper were 10 ms and 45 ms respectively, while the observed lifetimes were 21 ms and 112 ms
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
respectively. The Dubna team believes that the synthesis of the element is direct experimental proof of the existence of the island of stability. It has been calculated that the isotope 295Ts would have a half-life of about 18 milliseconds, and it may be possible to produce this isotope via the same berkelium–calcium reaction used in the discoveries of the known isotopes, 293Ts and 294Ts. The chance of this reaction producing 295Ts is estimated to be, at most, one-seventh the chance of producing 294Ts. This isotope could also be produced in a pxn channel of the 249Cf+48Ca reaction that successfully produced oganesson, evaporating a proton alongside some neutrons; the heavier tennessine isotopes 296Ts and 297Ts could similarly be produced in the 251Cf+48Ca reaction. Calculations using a quantum tunneling model predict the existence of several isotopes of tennessine up to 303Ts. The most stable of these is expected to be 296Ts with an alpha-decay half-life of 40 milliseconds. A liquid drop model study on the element's isotopes shows similar results; it suggests a general trend of increasing stability for isotopes heavier than 301Ts, with partial half-lives exceeding the age of the universe for the heaviest isotopes like 335Ts when beta decay is not considered. Lighter isotopes of tennessine may be produced in the 243Am+50Ti reaction, which was considered as a contingency plan by the Dubna team in 2008 if 249Bk proved unavailable; the isotopes 289Ts through 292Ts could also be produced as daughters of element 119 isotopes that can be produced in the 243Am+54Cr and 249Bk+50Ti reactions. === Atomic and physical === Tennessine is expected to be a member of group 17 in the periodic table, below the five halogens; fluorine, chlorine, bromine, iodine, and astatine, each of which has seven valence electrons with a configuration of ns2np5. For tennessine, being in
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
the seventh period (row) of the periodic table, continuing the trend would predict a valence electron configuration of 7s27p5, and it would therefore be expected to behave similarly to the halogens in many respects that relate to this electronic state. However, going down group 17, the metallicity of the elements increases; for example, iodine already exhibits a metallic luster in the solid state, and astatine is expected to be a metal. As such, an extrapolation based on periodic trends would predict tennessine to be a rather volatile metal. Calculations have confirmed the accuracy of this simple extrapolation, although experimental verification of this is currently impossible as the half-lives of the known tennessine isotopes are too short. Significant differences between tennessine and the previous halogens are likely to arise, largely due to spin–orbit interaction—the mutual interaction between the motion and spin of electrons. The spin–orbit interaction is especially strong for the superheavy elements because their electrons move faster—at velocities comparable to the speed of light—than those in lighter atoms. In tennessine atoms, this lowers the 7s and the 7p electron energy levels, stabilizing the corresponding electrons, although two of the 7p electron energy levels are more stabilized than the other four. The stabilization of the 7s electrons is called the inert pair effect; the effect that separates the 7p subshell into the more-stabilized and the less-stabilized parts is called subshell splitting. Computational chemists understand the split as a change of the second (azimuthal) quantum number l from 1 to 1/2 and 3/2 for the more-stabilized and less-stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s27p21/27p33/2. Differences for other electron levels also exist. For example, the 6d electron levels (also split in two, with four
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
being 6d3/2 and six being 6d5/2) are both raised, so they are close in energy to the 7s ones, although no 6d electron chemistry has ever been predicted for tennessine. The difference between the 7p1/2 and 7p3/2 levels is abnormally high; 9.8 eV. Astatine's 6p subshell split is only 3.8 eV, and its 6p1/2 chemistry has already been called "limited". These effects cause tennessine's chemistry to differ from those of its upper neighbors (see below). Tennessine's first ionization energy—the energy required to remove an electron from a neutral atom—is predicted to be 7.7 eV, lower than those of the halogens, again following the trend. Like its neighbors in the periodic table, tennessine is expected to have the lowest electron affinity—energy released when an electron is added to the atom—in its group; 2.6 or 1.8 eV. The electron of the hypothetical hydrogen-like tennessine atom—oxidized so it has only one electron, Ts116+—is predicted to move so quickly that its mass is 1.90 times that of a non-moving electron, a feature attributable to relativistic effects. For comparison, the figure for hydrogen-like astatine is 1.27 and the figure for hydrogen-like iodine is 1.08. Simple extrapolations of relativity laws indicate a contraction of atomic radius. Advanced calculations show that the radius of a tennessine atom that has formed one covalent bond would be 165 pm, while that of astatine would be 147 pm. With the seven outermost electrons removed, tennessine is finally smaller; 57 pm for tennessine and 61 pm for astatine. The melting and boiling points of tennessine are not known; earlier papers predicted about 350–500 °C and 550 °C, respectively, or 350–550 °C and 610 °C, respectively. These values exceed those of astatine and the lighter halogens, following periodic trends. A later paper predicts the boiling point of tennessine to be 345 °C
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
(that of astatine is estimated as 309 °C, 337 °C, or 370 °C, although experimental values of 230 °C and 411 °C have been reported). The density of tennessine is expected to be between 7.1 and 7.3 g/cm3. === Chemical === The known isotopes of tennessine, 293Ts and 294Ts, are too short-lived to allow for chemical experimentation at present. Nevertheless, many chemical properties of tennessine have been calculated. Unlike the lighter group 17 elements, tennessine may not exhibit the chemical behavior common to the halogens. For example, fluorine, chlorine, bromine, and iodine routinely accept an electron to achieve the more stable electronic configuration of a noble gas, obtaining eight electrons (octet) in their valence shells instead of seven. This ability weakens as atomic weight increases going down the group; tennessine would be the least willing group 17 element to accept an electron. Of the oxidation states it is predicted to form, −1 is expected to be the least common. The standard reduction potential of the Ts/Ts− couple is predicted to be −0.25 V; this value is negative, unlike for all the lighter halogens. There is another opportunity for tennessine to complete its octet—by forming a covalent bond. Like the halogens, when two tennessine atoms meet they are expected to form a Ts–Ts bond to give a diatomic molecule. Such molecules are commonly bound via single sigma bonds between the atoms; these are different from pi bonds, which are divided into two parts, each shifted in a direction perpendicular to the line between the atoms, and opposite one another rather than being located directly between the atoms they bind. Sigma bonding has been calculated to show a great antibonding character in the At2 molecule and is not as favorable energetically. Tennessine is predicted to continue the trend; a strong pi character
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
should be seen in the bonding of Ts2. The molecule tennessine chloride (TsCl) is predicted to go further, being bonded with a single pi bond. Aside from the unstable −1 state, three more oxidation states are predicted; +5, +3, and +1. The +1 state should be especially stable because of the destabilization of the three outermost 7p3/2 electrons, forming a stable, half-filled subshell configuration; astatine shows similar effects. The +3 state should be important, again due to the destabilized 7p3/2 electrons. The +5 state is predicted to be uncommon because the 7p1/2 electrons are oppositely stabilized. The +7 state has not been shown—even computationally—to be achievable. Because the 7s electrons are greatly stabilized, it has been hypothesized that tennessine effectively has only five valence electrons. The simplest possible tennessine compound would be the monohydride, TsH. The bonding is expected to be provided by a 7p3/2 electron of tennessine and the 1s electron of hydrogen. The non-bonding nature of the 7p1/2 spinor is because tennessine is expected not to form purely sigma or pi bonds. Therefore, the destabilized (thus expanded) 7p3/2 spinor is responsible for bonding. This effect lengthens the TsH molecule by 17 picometers compared with the overall length of 195 pm. Since the tennessine p electron bonds are two-thirds sigma, the bond is only two-thirds as strong as it would be if tennessine featured no spin–orbit interactions. The molecule thus follows the trend for halogen hydrides, showing an increase in bond length and a decrease in dissociation energy compared to AtH. The molecules TlTs and NhTs may be viewed analogously, taking into account an opposite effect shown by the fact that the element's p1/2 electrons are stabilized. These two characteristics result in a relatively small dipole moment (product of difference between electric charges of atoms and displacement of the
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
atoms) for TlTs; only 1.67 D, the positive value implying that the negative charge is on the tennessine atom. For NhTs, the strength of the effects are predicted to cause a transfer of the electron from the tennessine atom to the nihonium atom, with the dipole moment value being −1.80 D. The spin–orbit interaction increases the dissociation energy of the TsF molecule because it lowers the electronegativity of tennessine, causing the bond with the extremely electronegative fluorine atom to have a more ionic character. Tennessine monofluoride should feature the strongest bonding of all group 17 monofluorides. VSEPR theory predicts a bent-T-shaped molecular geometry for the group 17 trifluorides. All known halogen trifluorides have this molecular geometry and have a structure of AX3E2—a central atom, denoted A, surrounded by three ligands, X, and two unshared electron pairs, E. If relativistic effects are ignored, TsF3 should follow its lighter congeners in having a bent-T-shaped molecular geometry. More sophisticated predictions show that this molecular geometry would not be energetically favored for TsF3, predicting instead a trigonal planar molecular geometry (AX3E0). This shows that VSEPR theory may not be consistent for the superheavy elements. The TsF3 molecule is predicted to be significantly stabilized by spin–orbit interactions; a possible rationale may be the large difference in electronegativity between tennessine and fluorine, giving the bond a partially ionic character. == Notes == == References == == Bibliography ==
|
{
"page_id": 67611,
"source": null,
"title": "Tennessine"
}
|
The Tipson–Cohen reaction is a name reaction first discovered by Stuart Tipson and Alex Cohen at the National Bureau of Standards in Washington D.C. The Tipson–Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust (Zn) and sodium iodide (NaI) in a refluxing solvent such as N,N-dimethylformamide (DMF) to give an unsaturated carbohydrate. == Background == Unsaturated carbohydrates are desired as they are versatile building blocks that can be used in a variety of reactions. For example, they can be used as intermediates in the synthesis of natural products, or as dienophiles in the Diels-Alder reaction, or as precursors in the synthesis of oligosaccharides. The Tipson–Cohen reaction goes through a syn or anti elimination mechanism to produce an alkene in high to moderate yields. The reaction depends on the neighboring substituents. A mechanism for glucopyranosides and mannooyranosides is shown below. Scheme 1: Syn elimination occurs with the glucopyranosides. Galactopyranosides follows a similar syn mechanism. Whereas, anti elimination occurs with mannopyranosides. Note that R could be a methanesulfonyl CH2O2S (Ms), or a toluenesulfonyl CH3C6H4O2S (Ts). == Reaction mechanism == Scheme 3: The scheme illustrates the first displacement, the rate determining step and slowest step, where the starting material is converted to the iodo-intermediate. The intermediate is not detectable as it is rapidly converted to the unsaturated sugar. Experiments with azide instead of the iodide confirmed attack occurs at the C-3 as nitrogen-intermediates were isolated. The order of reactivity from most reactive to least reactive is: β-glucopyranosides > β-mannopyranosides > α-glucopyranosides> α-mannopyranosides. The reaction of β–mannopyranosides gives low yields and required longer reaction times than with β-glucopyranosides due to the presence of a neighboring axial substituent (sulfonyloxy) relative to C-3 sulfonyloxy group in the starting material. The axial substituent increases the steric interactions in
|
{
"page_id": 22480924,
"source": null,
"title": "Tipson–Cohen reaction"
}
|
the transition state, causing unfavorable eclipsing of the two sulfonyloxy groups. α-Glucopyranosides possess a β-trans-axial substituent relative to C-3 sulfonyloxy (anomeric OCH3 group) in the starting material. The β-trans-axial substituent influences the transition state by also causing an unfavorable steric interaction between the two groups. In the case of α-mannopyranosides, both a neighboring axial substituent (2-sulfonyloxy group) and a β-trans-axial substituent (anomeric OCH3 group) are present, therefore significantly increasing the reaction time and decreasing the yield. == Reaction conditions == Table 1: Reaction times and yield vary on the substrate. The β-glucopyranoside was found to be the best substrate for the Tipson–Cohen reaction as the reaction time and yield were much superior that any other substrate proposed in the study. aSubstrates possess benzylidene protecting groups at C-4 and C-6, OMe groups at anomeric position and OTs groups at C-2 and C-3. Reaction temperature 95–100 ˚C == Reaction scope == The reaction has been attempted in the microwave, improving yields with the α-glucopyranoside to 88% and reducing the reaction time significantly to 14 minutes. The original paper by Tipson and Cohen also used acyclic sugars to illustrate the utility of the reaction. Thus the reaction is not limited to cyclic carbohydrate derivatives. Sulphonoxy groups such as methanesulfonyl and toluenesulfonyl were both used, however it was found that substrates with toluenesulfonyl groups gave higher yields and lower reaction times. == References ==
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{
"page_id": 22480924,
"source": null,
"title": "Tipson–Cohen reaction"
}
|
Staurostoma falklandica is a species of jellyfish first discovered in 1907 by the Scottish Antarctic Expedition aboard the S.S. Scotia in Stanley Harbour, Falkland Islands. == Description == Staurostoma falklandica is very similar to the related White cross jellyfish, with the distinguishing feature being the much more diminutive second set of tentacles.: 236 It has a thin umbrella, measuring 90mm in diameter, with a stomach in four radiating arms across it. The mouth is the same length as the stomach, and its edges are a complicated series of folds. The gonads are along the edge of the stomach in deeper folds.: 235 There are several hundred principle tentacles closely packed round the edge of the bell. In between each pair of tentacles is a much smaller tentacle, similar in shape. Between the smaller and larger tentacles is a cordylus (sensory club).: 236 == Range == Staurostoma falklandica is a marine species which inhabits the southern hemisphere near Antarctica. Observations have been made in Chile, Argentina, Australia and New Zealand. == References ==
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{
"page_id": 79235105,
"source": null,
"title": "Staurostoma falklandica"
}
|
Red plague is an accelerated corrosion of copper when plated with silver. After storage, damage or use in high-humidity environment, cuprous oxide forms on the surface of the parts. The corrosion is identifiable by presence of patches of brown-red powder deposit on the exposed copper. Red plague is caused by normally occurring electrode potential difference between the copper and silver, leading to galvanic corrosion occurring in pits or breaks in the silver plating. It develops in the presence of moisture and oxygen when the porosity of the silver layer allows them to come in contact with the copper-silver interface. It is an electrochemical corrosion—a copper-silver galvanic cell forms and the copper acts as sacrificial anode. In suitable conditions, the corrosion can proceed rather quickly and lead to total circuit failure. More details can be seen in ESA document PSS-01-720, with details on determining the susceptibility of silver-plated copper wire to red plague corrosion found in ECSS-Q-ST-70-20C. It is not to be confused with purple plague, a type of galvanic corrosion that occurs between gold and aluminum. == References ==
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{
"page_id": 2820131,
"source": null,
"title": "Red plague (corrosion)"
}
|
Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a single mycelium. It can be contrasted to heterothallic. It is often used to categorize fungi. In yeast, heterothallic cells have mating types a and α. An experienced mother cell (one that has divided at least once) will switch mating type every cell division cycle because of the HO allele. Sexual reproduction commonly occurs in two fundamentally different ways in fungi. These are outcrossing (in heterothallic fungi) in which two different individuals contribute nuclei to form a zygote, and self-fertilization or selfing (in homothallic fungi) in which both nuclei are derived from the same individual. Homothallism in fungi can be defined as the capability of an individual spore to produce a sexually reproducing colony when propagated in isolation. Homothallism occurs in fungi by a wide variety of genetically distinct mechanisms that all result in sexually reproducing cultures from a single cell. Among the 250 known species of aspergilli, about 36% have an identified sexual state. Among those Aspergillus species for which a sexual cycle has been observed, the majority in nature are homothallic (self-fertilizing). Selfing in the homothallic fungus Aspergillus nidulans involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self-fertilization does not bypass required pathways for outcrossing sex but instead requires activation of these pathways within a single individual. Fusion of haploid nuclei occurs within reproductive structures termed cleistothecia, in which the diploid zygote undergoes meiotic divisions to yield haploid ascospores. Several ascomycete fungal species of the genus Cochliobolus (C. luttrellii, C. cymbopogonis, C. kusanoi and C. homomorphus) are homothallic. The ascomycete fungus Pneumocystis jirovecii is considered to
|
{
"page_id": 19925030,
"source": null,
"title": "Homothallism"
}
|
be primarily homothallic. The ascomycete fungus Neosartorya fischeri is also homothallic. Cryptococcus depauperatus, a homothallic basidiomycete fungus, grows as long, branching filaments (hyphae). C. depauperatus can undergo meiosis and reproduce sexually with itself throughout its life cycle. A lichen is a composite organism consisting of a fungus and a photosynthetic partner that are growing together in a symbiotic relationship. The photosynthetic partner is usually either a green alga or a cyanobacterium. Lichens occur in some of the most extreme environments on Earth—arctic tundra, hot deserts, rocky coasts, and toxic slag heaps. Most lichenized fungi produce abundant sexual structures and in many species sexual spores appear to be the only means of dispersal (Murtagh et al., 2000). The lichens Graphis scripta and Ochrolechia parella do not produce symbiotic vegetative propagules. Rather the lichen-forming fungi of these species reproduce sexually by self-fertilization (i.e. they are homothallic), and it was proposed that this breeding system allows successful reproduction in harsh environments (Murtagh et al., 2000). Homothallism appears to be common in natural populations of fungi. Although self-fertilization employs meiosis, it produces minimal genetic variability. Homothallism is thus a form of sex that is unlikely to be adaptively maintained by a benefit related to producing variability. However, homothallic meiosis may be maintained in fungi as an adaptation for surviving stressful conditions; a proposed benefit of meiosis is the promoted homologous meiotic recombinational repair of DNA damages that are ordinarily caused by a stressful environment. == Evolution == Homothallism evolved repeatedly from heterothallism. == See also == Mating of yeast Hermaphroditism == References == == External links == 4 Growth and Life Cycles (of Yeast)
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{
"page_id": 19925030,
"source": null,
"title": "Homothallism"
}
|
The Miscarriage & Infant Loss Memorial Book was a prayer request facility, open for new entries from 1995 to 2011, for those who suffered the loss of a baby from conception to three years old. It is kept at the Church of St Paul the Apostle in Tintagel, Cornwall, United Kingdom, where this book is placed on the altar at all Masses. == History == The Miscarriage & Infant Loss Memorial Book was founded by Myke and Dr Miriam Rosenthal-English of Füssen in Bavaria after the loss of their first baby "Ruth" aged 14 weeks due to miscarriage in 1995. Since then the Memorial Book project grew from one which served the Roman Catholic Diocese of Plymouth into one which served people of all beliefs, worldwide. On February 27, 2011, after 16 years the Memorial Book was finally closed; the related website now refers those in need of prayer for their lost babies to Poor Clare Sisters in Wales. == Further reading == Morning Light Ministry - A Catholic Ministry based in Canada which helps bereaved mothers & fathers in Canada and the United States which follows a similar mission and cooperated closely with Miscarriage & Infant Loss Memorial Book == External links == "Miscarriage and Infant Loss Memorial Book". Archived from the original on 2 March 2009. Retrieved 15 September 2008. "Catholic Diocese of Plymouth, UK". Retrieved 21 March 2009. Plymouth is the Diocese where the Miscarriage & Infant Loss Memorial Book is based
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{
"page_id": 7473196,
"source": null,
"title": "Miscarriage & Infant Loss Memorial Book"
}
|
Colour retention agents are food additives that are added to food to prevent the colour from changing. Many of them work by absorbing or binding to oxygen before it can damage food (antioxidants). For example, ascorbic acid (vitamin C) is often added to brightly coloured fruits such as peaches during canning. == List of colour retention agent == == See also == Artificial sweetener Acidity regulator Codex Alimentarius E number Food colouring Food safety List of antioxidants in food List of food additives List of food additives, Codex Alimentarius List of fruits List of vegetables == References ==
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{
"page_id": 15665197,
"source": null,
"title": "Colour retention agent"
}
|
In cell biology, chromosome territories are regions of the nucleus preferentially occupied by particular chromosomes. Interphase chromosomes are long DNA strands that are extensively folded, and are often described as appearing like a bowl of spaghetti. The chromosome territory concept holds that despite this apparent disorder, chromosomes largely occupy defined regions of the nucleus. Most eukaryotes are thought to have chromosome territories, although the budding yeast S. cerevisiae is an exception to this. == Characteristics == Chromosome territories are spheroid with diameters on the order of one to few micrometers. Nuclear compartments devoid of DNA called interchromatin compartments have been reported to tunnel into chromosome territories to facilitate molecular diffusion into the otherwise tightly packed chromosome-occupied regions. == History and experimental support == The concept of chromosome territories was proposed by Carl Rabl in 1885 based on studies of Salamandra maculata. Chromosome territories have gained recognition using fluorescence labeling techniques (fluorescence in situ hybridization). Studies of genomic proximity using techniques like chromosome conformation capture have supported the chromosome territory concept by showing that DNA-DNA contacts predominantly happen within particular chromosomes. == See also == Transcription factories – Sites in the cell nucleus where DNA transcription occursPages displaying short descriptions of redirect targets Nuclear bodies – Structures found in the cell nuclei Epigenetics – Study of DNA modifications that do not change its sequence == References ==
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{
"page_id": 47515694,
"source": null,
"title": "Chromosome territories"
}
|
Pyrococcus yayanosii is a strictly anaerobic, hyperthermophilic archaeon, first identified through samples from the Mid-Atlantic Ridge. Isolated from a deep-sea hydrothermal vent, it is characterized as a motile Gram-negative marine bacteria that is roughly cocci shaped and 1-1.5 μm in diameter, with lophotrichous flagellation. As the current most thermophilic species within the order of Thermococcales, P. yayanosii exhibit various selective conditions for growth, including high pressures and temperatures, with an average doubling time of 50 minutes. Genome analysis reveal a 49 percent guanine-cytosine DNA content with Pyrococcus furiosus being its closest species relative. Pyrococcus yayanosii are unicellular organisms that are salt-dependent, residing in environments that exhibit moderate concentrations of NaCl. Through utilizing an anaerobic growth method, P. yayanosii is capable of using various simple and complex substrates for fermentation. While this pathway results in slower growth rates compared to aerobic metabolism, elemental sulfur has been found to promote growth for this species. Similar to some hydrothermal vent microbes, P. yayanosii employs sulfur assimilation in facilitating biological processes, thereby producing byproducts such as 3'-Phosphoadenosine 5'-monophosphate (pAp). == History == === Initial isolation === Pyrococcus yayanosii was originally isolated by Birrien et al. (2011) on the Serpentine cruise of March 2007 in the Central Equatorial Atlantic. The research team collected black smoker samples at a depth of 4100m on the Mid-Atlantic Ridge, specifically at the Ashadze site, an active hydrothermal vent field. Due to the strict conditions of P. yayanosii for growth, special care was taken to incubate the samples anaerobically at an optimal pressure of 52 MPa and temperature of 98 °C. Growth of an isolated colony designated as strain CH1T was observed after two days under these conditions. The cloning and sequencing of the 16S rRNA gene, as well as microscopic observation, verified the purity of the CH1T isolate. After
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
purity confirmation, a light microscope was used to observe the isolated strain CH1T. Certain traits were being screened for, as Pyrococcus species are known for their characteristic spherical (cocci) shape as well as their flagellar motility. The cells of CH1T appeared to resemble irregular cocci shapes and were observed frequently as single cells or in pairs, or infrequently in a line formation. The researchers also noticed that individual cells were especially motile. This finding prompted the use of a Spot Test Flagella kit, which confirmed the presence of a polar spot of flagella. Other tests performed included the Gram stain, varied substrate utilization assays, and direct cell counting. These tests characterized Pyrococccus yayanosii as a gram-negative bacterium with the ability to metabolize proteinaceous substrates and carbohydrates for energy and release hydrogen sulfide. === Classification === Cells of strain CH1T were harvested in their peak growth phase, followed by DNA being isolated by chemical extraction. Through amplification, sequencing and analysis of the 16S rRNA gene, strain CH1T was classified to belong within the genus Pyrococcus, sharing a gene sequence most similar to Pyrococcus furiosus. Birrien et al. (2011) compared the DNA sequences of three Pyrococcus reference species (P. furiosus, P. abyssi, P. horikoshii) to the DNA isolated from strain CH1T and found that the DNA similarity values between them were significantly lower than the similarity values between the two distinct species P. abyssi and P. horikoshii. This provided evidence that strain CH1T itself was a distinct species, and thus was named Pyrococcus yayanosii, in honour of a pioneer in microbiological research, Aristides Yayanos, who specialized in the study of piezophilic bacteria. === Advancements === The discovery of P. yayanosii opened many doors for broader future research. As P. yayanosii is both an obligate piezophile and hyperthermophile, the organism is an attractive
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
model for studying early life evolution and the biochemical strategies underlying piezophilic adaptation. In 2014, Li et al. generated a derivative strain, P. yayanosii A1, which is facultatively (originally obligately) piezophilic. This strain can grow under both atmospheric pressure and high-pressure conditions while maintaining similar physiology (optimal temperature, pH, and salt concentration) to wild type P. yayanosii. The ability to cultivate A1 under normal atmospheric conditions simplifies genetic manipulations. The researchers subsequently constructed several plasmids that were able to genetically manipulate the A1 strain. The transformation efficiency reached significant levels, indicating an effective system for gene disruption. This system can be applied in future studies on the functional genomics of P. yayanosii. Consequently, it would further allow researchers to investigate the molecular mechanisms that underpin piezophilic and hyperthermophilic adaptation, potentially providing insights into early life evolution and the adaptation of microorganisms to extreme environments. == Optimal conditions and adaptation to high pressures == === Environment and general conditions === Isolated from the deepest hydrothermal vent field explored to date, P. yayanosii is a strictly anaerobic organism adapted to a deep ocean, seawater environment lacking oxygen. It is considered an extremophile as it grows under high temperatures and high pressures. === Optimal conditions === Incubation experiments of P. yayanosii allowed identification of its optimal conditions. The specific strain CH1T was found to have an optimal temperature of 98 °C despite being capable of growing at temperatures between 80 and 108 °C. Similarly, while this strain exhibits optimal growth at a pH of around 7.5 to 8, it is capable of growth when exposed to a pH range between 6.0 and 9.5. It has a salinity optimum nearing 3.5% in weight by volume, with a range where growth is possible from 2.5 to 5.5%. An optimal pressure of 52 MPa was identified
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
for P. yayanosii. While some studies identified stressful pressures at 20 and 80 MPa, with growth rates half as great as the rate at the optimum, others observed no growth was observed for the strain CH1T below 20 MPa and above 120 MPa. Other substrates were also tested as potential carbon and energy sources; P. yayanosii was able to use casein, cellobiose, sucrose, glucose, starch, chitin, pyruvate, glycerol, and acetate for fermentation. The addition of elemental sulfur also promoted its growth. === Adaptations to high pressure === Multiple mechanisms are thought allow P. yayanosii to adapt to changes in hydrostatic pressures. First, a gene expression analysis revealed an overrepresentation of genes involved in energy production and conversion, with genes coding for ATP- and ADP-synthase, as well as hydrogenases and ferredoxin oxidoreductases. More specifically, transcriptome and proteome analyses showed that while the genes associated with hydrogenases are downregulated under stressful conditions, the proteins associated with these energy pathways are upregulated. The hydrogenase energy pathway involves the production of protons, and it has been hypothesized that other upregulated genes associated with ATPase could contribute to maintaining pH homeostasis. Several CRISPR-cas clusters, which are usually associated with immunity and pathogen resistance, are also regulated (either upregulated or downregulated) under stressuful pressures. Additionally, chemotaxis genes upregulated at stressful pressure could increase the motility of the organism, which in turn is thought to help the organism seek nutrients. Similarly, proteins associated with ribosome recycling and subunits synthesis are upregulated in stressfully high and low pressures, enhancing the synthesis and activity of proteins. Evolutionarily, Genomic Islands (GIs) contribute to gene modification and plasticity and thereby promote the genetic diversity and adaptation of species to their environment. In P. yayanosii, 15 GIs were identified from DNA fragments. The transcription levels of the largest of these GIs, PYG1,
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
revealed variations in gene expression under different temperature and pressure conditions. It was found to be generally nonessential but to facilitate adaptation in stressful conditions. Experiments involving removing PYG1 also highlighted a tradeoff in the adaptation to high pressure versus high temperature. This GI bears a resemblance to GIs and similar structures in other extremophilic archea such as Thermococcus barophilus and Pyrococcus abyssi. In this GI, a potential toxin-antitoxin system was identified, with toxin gene pygT and antitoxin gene pygA. Experiments conducted using mutant strains and different pressure conditions suggested that this system might play a role in both plasmid stability and adaptation to high hydrostatic pressure. == Proteins and enzymes == The genome of P. yayanosii CH1T was completey sequenced, and analyses found a proteome of 1,926 proteins, 21% of which are still only hypothetical. === PYCH_01220 === PYCH_01220 is one of the hypothetical proteins with a crystal structure composed of two domains. Previous research found similarity between this protein and Escherichia coli's ribonuclease colicin D, suggesting that its potential function could be to bind the nucleic acids of DNA. === Pullulanase === A complete genome mapping of P. Yayanosii led to the discovery of a gene hypothesized to produce an amylopullulanase, referred henceforth as Pul PY. Pullulanase is responsible for debranching α-1, 6 glycosidic linkages in oligosaccharides. Subsequent NCBI Protein Blast analysis allowed researchers to deduce active site structure and homology testing showed substantial similarities to other Pyrococcus and Thermococcus species. Tests reveals that Pul PY has optimal temperature of 95 °C and is able to maintain a minimum 80% functionality around 100 °C. Pul PY functions optimally at pH 6.6 and showed significant functionality within a pH range of 5.8-8.0. Additional comparative testing for thermal stability against other thermostable enzymes found similarity with Pyrococcus woesei, proving significant
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
thermostability. Due to its ability to survive in extreme conditions over a long period of time, Pul PY is ideal for use in starch liquefaction. When used in conjunction with amylase, it can improve the efficiency of hydrolysis. === Papase === pApase is a type of enzyme responsible for breaking down 3′-phosphoadenosine 5′-monophosphate (pAp) into AMP and phosphate. Prior to testing P. yayanosii pApase, not much was known about the archaeal methods of pAp turnover. Inspection of the gene cluster involved in assimilatory sulfate reduction yielded PYCH_17540, which codes for pApase. Homologic testing shows that this pApase is derived from a common ancestor with NmA nucleases, which are bacterial in nature. Testing shows that pApase functions optimally at pH 6.5, while maintaining significant performance within a pH range of 5.5-8.0. pApase shows positive linear correlation between temperature and performance within 25-90 °C, showing approximately 4 times more turnover at 90 °C compared to 25 °C. Additionally, pApase requires co-factors for optimal functionality. Cobalt is the best cofactor, being closely followed by Nickel and Manganese. Archael pApase also has a high specificity for substrates. It is only capable of attaching to and hydrolysing cyclic nucelotides, nanoRNAs and small ssDNA. The structure of pApase includes a DHH domain attached to a DHHA1 domain via a long α-helix, where the cleft between its domains is the active site. In comparison to bacterial pApase, the α-helix is much longer, which makes the active site smaller and thus, more substrate specific. == Clinical dignificance == Pyrococcus yayanosii naturally possess a thermostable ferritin, PcFn, capable of withstanding high temperature exposures up to 110 °C. Understanding this protein can provide future directions clinically in developing drugs with well-maintained efficiency despite storage under higher temperatures. The synthesis of PcFn into thermostable magnetoferritins (M-PcFn) by monodispered iron oxide nanoparticles
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
form crystalline core structures with negligible change in hydrodynamic diameters. This finding in regards to resistance to change reinforce that PcFn plays a critical role in thermostability, thereby influencing the overall properties observed in P. yayanosii. These noticeable characteristics found in M-PcFn, such as PcFn5000, offer insight on approaches that can increase thermostability of molecules and substances. In addition to the species' resistance to molecular changes in structure, the 51st and 298th residues found in L-asparaginase II of P. yayanosii interplay in thermostability. These residues allow for molecular maintenance and increased thermostability through supporting a tightly bound C terminal, reducing surface charges at reaction regions, and retaining loop rigidity. Recognition on the influence of amino acids on heat tolerance introduce alternative perspectives into industrial applications and new findings. == Industrial significance == While only the cold shock-inducible and sugar-inducible promoters were previously identified within the order Thermococcales, a recent study found a high hydrostatic pressure (HHP) inducible promoter in P. yayanosii. Given promoters are known to be regions where gene transcription occurs, identification of the HHP promoter can provide biological knowledge on the interactive dynamics between the components that allow for transcription. Hence, the proteins produced as a product of translation can introduce analysis into mechanisms that allow for tolerance to high pressure, thereby providing insight useful to improve industrial equipment. Pyrococcus yayanosii was found to exhibit low variability with respect to the core lipids, which are essential components that determine bacterial structure and function. Given that lipids are abundant in various systems, such as biologically within cells and chemically within organic compounds, and are key determinants to heat adaptability, knowledge may be borrowed from this organism in constructing pharmaceutical products that incorporate heat resistance properties. Therefore, this finding offers new avenues of exploration that may be key to industrial
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
development. == References ==
|
{
"page_id": 78907439,
"source": null,
"title": "Pyrococcus yayanosii"
}
|
A stabilized liquid membrane device or SLMD is a type of passive sampling device which allows for the in situ, integrative collection of waterborne, labile ionic metal contaminants. By capturing and sequestering metal ions onto its surface continuously over a period of days to weeks, an SLMD can provide an integrative measurement of bioavailable toxic metal ions present in the aqueous environment. As such, they have been used in conjunction with other passive samplers in ecological field studies. The simple device is composed of nonporous low-density plastic lay-flat tubing, which is filled with a chemical mixture containing a chelating agent (metal-binding agent) and a long chain organic acid. The water-insoluble chelating agent-organic acid mixture diffuses in a controlled manner to the exterior surface of the sampler membrane and binds to environmental metals. In practice, the SLMD provides for continuous sequestration of bioavailable forms of trace metals, such as, cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). The SLMD can also be utilized for in-laboratory preconcentration and speciation of bioavailable trace metals from grab water samples. == Background == Passive samplers were first developed in the early 1970s to monitor concentrations of airborne contaminants industrial workers might be exposed to, but by the 1990s researchers had developed and utilized passive samplers to monitor contaminants in the aqueous environment. The first type of passive sampler made for use in the aqueous environment was the semipermeable membrane device (SPMD). SPMDs could be used to determine time-weighted average concentrations of hydrophobic organic contaminants, but until the early 2000s passive sampling devices for metal contaminants had not yet emerged. Metals in the environment can speciate into different forms. Most metals dissolved in the aqueous environment are present as any of several ionic, complex-ion, and organically bound states. For most toxic
|
{
"page_id": 54200367,
"source": null,
"title": "Stabilized liquid membrane device"
}
|
metals, bioavailability is greatest for labile metals in their free ionic state. Recognizing the potential usefulness of a passive sampling device that could be used to measure trace amounts of bioavailable toxic metals, researchers at the United States Geological Survey (USGS) and University of Missouri began development on a counterpart to SPMDs that could be used to sample for labile metals. == Structure and function == The outer portion of a SLMD consists of a section of sealed, flat, semi-permeable polyethylene tubing. Sealed inside this tubing is a 1:1 mixture of a hydrophobic metal complexing agent and a long chain organic acid. The organic acid diffuses through the tubing to the outer surface, where the carboxylic acid portion can form stable complexes with calcium and magnesium ions in the water. This allows a waxy layer to slowly accumulate on the outside of the tube. the metal complexing agent continuously mobilizes into this waxy layer, where it can sequester metal ions from the water. The hydrophobic metal complexing agent most commonly used in SLMDs is an alkylated 8-hydroxyquinoline. Oleic acid is commonly used as the other half of the 1:1 hydrophobic reagent mixture, as it readily forms calcium oleates in the aqueous sampling media. In addition to the base device, hydrophobic plastic sheaths are sometimes used to house SLMDs in the field. Variable water flow can alter the sampling rates of metals by SLMDs, making a time-averaged concentration difficult to determine. By allowing liable metal analytes to diffuse to the SLMD's surface while limiting the diffusion of particulate, colloidal, or humic substances, these hydrophobic sheaths help reduce variability of SLMD uptake in faster moving waters. After being deployed for a known time interval, SLMDs can be recovered from the field for analysis. Washing with 20% nitric acid allows for the extraction
|
{
"page_id": 54200367,
"source": null,
"title": "Stabilized liquid membrane device"
}
|
of accumulated metals, and by using analytical techniques like inductively coupled plasma mass spectroscopy (ICP-MS) or atomic absorption spectroscopy (flame AAS) to measure the concentration of metal in the extract, the amount of metal accumulated by the SLMD can be determined. The simple device can be created in the laboratory using a nonporous polymeric tube, such as low-density polyethylene (LDPE) plastic. A sequestration medium within the tube slowly defuses through the membrane, binding to ionic metals creating non-mobile metals species that can later be extracted from the other membrane. The sequestration medium generally consists of a metal binding agent, or chelating agent, and a long chain organic acid, commonly oleic acid. The SLMD tube is flat with a membrane thickness that can vary between 2 and 500 μm depending on the application. The approximate width of the SLMD is 2.5 cm and approximate length is 15 cm (these dimensions may vary based on application). The sequestration medium reagent is typically composed of an equal mixture of oleic acid (cis-9-octadecenoic acid) and Kelex-100 (ethyl-methyl-octyl, 8-quinolinol), however other chemicals may be used to perform similar functions. After deployment, the immobilized metal species can then be extracted from the outer membrane. The metal species can be identified and analyzed using widely recognized standard techniques (e.g., digestion, atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, etc.). In this regard, any procedure or analytical technique applicable to measuring ionic or complexed metal species is suitable for determining metal concentrations sequestered by the SLMD. == Applications == SLMDs are known to accumulate cadmium, cobalt, copper, nickel, lead, and zinc, and have been deployed in freshwater monitoring studies by The Washington State Department of Ecology (Ecology) and the USGS. Ecology deployed SLMDs in upper and lower Indian Creek for 28 and 27 days respectively. Metal concentrations on
|
{
"page_id": 54200367,
"source": null,
"title": "Stabilized liquid membrane device"
}
|
the SLMDs were used to estimate the true concentration of metals in the creek. The estimated concentration was expressed as a range based on sampling rate of SLMDs as well as the length of exposure. The purpose of the sampling was to investigate potential causes of sublethal effects of young trout and loss of benthic biodiversity in the creek. === Environmental metal toxicology === Exposure to ionic metals has been shown to result in deleterious effects for aquatic organisms and may induce oxidative stress, cause DNA damage, and decrease enzyme activity. In contrast, some metals under certain environmental conditions have potential moderating effects on other more toxic metals; one example being zinc (Zn), which has been shown to reduce copper (Cu) toxicity when both metals are present. Given that the presence of particular aqueous metals may have a wide array of effects on organisms, aquatic toxicologists have developed various methods for sampling them. Passive, or in situ, environmental sampling is an important tool used by toxicologists for evaluating toxicants that may exist in very small concentrations—not easily detectable via grab samples. One passive sampler, the semipermeable membrane device, or SPMD, is commonly used to measure organic contaminants in aquatic ecosystems. The SLMD was developed as a counterpart device for sampling metals. Passive sampling for trace metals is more complex than for organic toxicants as most dissolved metals can simultaneously exist in any of several ionic, complex-ion, and organically bound states. Metals can also bind with suspended or dissolved organic matter and exist as ultra-fine colloids, or lipophilic complexes. First developed by Petty, Brumbaugh, Huckins, May, and Wiedmeyer, the SLMD is used to monitor ionic metals in aquatic environments. Due to anthropogenic factors such as mining, metal refining, and industrial activity, global emissions of metals has significantly increased within the last
|
{
"page_id": 54200367,
"source": null,
"title": "Stabilized liquid membrane device"
}
|
100 years, and will likely continue to increase during the foreseeable future. == Advantages and limitations == Toxic metals can be present in the aqueous environment at trace or ultra-trace concentrations, yet still be toxicologically significant and thus cause harm to humans or the environment. Because these concentrations are so low, they would fall beyond the detection limits of most analytical instruments if the media had been sampled using traditional grab samples. Using SLMDs to passively collect metals over an extended period of time allows for trace metals to accumulate to detectable levels, which can give more accurate estimate of aquatic chemistry and contamination. SLMDs also have the advantage of being able to capture pulses of metal contamination that might otherwise go undetected when using grab samples. SLMDs are limited to the assessment of labile metals, and cannot be used to monitor for organic contaminants. Further, while the ability of SLMDs to sample copper, zinc, nickel, lead, and cadmium has been repeatedly demonstrated, there has been little laboratory research on their ability to reliably uptake other toxic metals. Still, while laboratory studies on the effectiveness of SLMDs have only investigated copper, zinc, nickel, lead, and cadmium, SLMDs have been used with success in field studies to assess a wider range of metals. == See also == Semipermeable membrane devices Polar organic chemical integrative sampler Diffusive gradients in thin films Chemcatcher == References ==
|
{
"page_id": 54200367,
"source": null,
"title": "Stabilized liquid membrane device"
}
|
Zoidogamy is a type of plant reproduction in which male gametes (antherozoids) swim in a path of water to the female gametes (archegonium). Zoidogamy is found in algae, bryophytes, pteridophytes, and some gymnosperms (others use siphonogamy). Zoidogamy relates to evolution, as it provides a pathway from wind-borne abiotic pollination and similar mechanisms to fluid-based mechanisms used in most animals. == References ==
|
{
"page_id": 10094642,
"source": null,
"title": "Zoidogamy"
}
|
Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids. When these processes occur in food, undesirable odors and flavors can result. In processed meats, these flavors are collectively known as warmed-over flavor. In certain cases, however, the flavors can be desirable (as in aged cheeses). Rancidification can also detract from the nutritional value of food, as some vitamins are sensitive to oxidation. Similar to rancidification, oxidative degradation also occurs in other hydrocarbons, such as lubricating oils, fuels, and mechanical cutting fluids. == Pathways == Five pathways for rancidification are recognized: === Hydrolytic === Hydrolytic rancidity refers to the odor that develops when triglycerides are hydrolyzed and free fatty acids are released. This reaction of lipid with water may require a catalyst (such as a lipase, or acidic or alkaline conditions) leading to the formation of free fatty acids and glycerol. In particular, short-chain fatty acids, such as butyric acid, are malodorous. When short-chain fatty acids are produced, they serve as catalysts themselves, further accelerating the reaction, a form of autocatalysis. === Oxidative === Oxidative rancidity is associated with the degradation by oxygen in the air. ==== Free-radical oxidation ==== The double bonds of an unsaturated fatty acid can be cleaved by free-radical reactions involving molecular oxygen. This reaction causes the release of malodorous and highly volatile aldehydes and ketones. Because of the nature of free-radical reactions, the reaction is catalyzed by sunlight. Oxidation primarily occurs with unsaturated fats. For example, even though meat is held under refrigeration or in a frozen state, the poly-unsaturated fat will continue to oxidize and slowly become rancid. The fat oxidation process, potentially resulting in rancidity, begins immediately after the animal is
|
{
"page_id": 198711,
"source": null,
"title": "Rancidification"
}
|
slaughtered and the muscle, intra-muscular, inter-muscular and surface fat becomes exposed to oxygen of the air. This chemical process continues during frozen storage, though more slowly at lower temperature. Oxidative rancidity can be prevented by light-proof packaging, oxygen-free atmosphere (air-tight containers) and by the addition of antioxidants. ==== Enzyme-catalysed oxidation ==== A double bond of an unsaturated fatty acid can be oxidised by oxygen from the air in reactions catalysed by plant or animal lipoxygenase enzymes, producing a hydroperoxide as a reactive intermediate, as in free-radical peroxidation. The final products depend on conditions: the lipoxygenase article shows that if a hydroperoxide lyase enzyme is present, it can cleave the hydroperoxide to yield short-chain fatty acids and dicarboxylic acids (several of which were first discovered in rancid fats). === Microbial === Microbial rancidity refers to a water-dependent process in which microorganisms, such as bacteria or molds, use their enzymes such as lipases to break down fat. Pasteurization and/or addition of antioxidant ingredients such as vitamin E, can reduce this process by destroying or inhibiting microorganisms. == Food safety == Despite concerns among the scientific community, there is little data on the health effects of rancidity or lipid oxidation in humans. Animal studies show evidence of organ damage, inflammation, carcinogenesis, and advanced atherosclerosis, although typically the dose of oxidized lipids is larger than what would be consumed by humans. Antioxidants are often used as preservatives in fat-containing foods to delay the onset or slow the development of rancidity due to oxidation. Natural antioxidants include ascorbic acid (vitamin C) and tocopherols (vitamin E). Synthetic antioxidants include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), TBHQ, propyl gallate and ethoxyquin. The natural antioxidants tend to be short-lived, so synthetic antioxidants are used when a longer shelf-life is preferred. The effectiveness of water-soluble antioxidants is limited in
|
{
"page_id": 198711,
"source": null,
"title": "Rancidification"
}
|
preventing direct oxidation within fats, but is valuable in intercepting free radicals that travel through the aqueous parts of foods. A combination of water-soluble and fat-soluble antioxidants is ideal, usually in the ratio of fat to water. In addition, rancidification can be decreased by storing fats and oils in a cool, dark place with little exposure to oxygen or free radicals, since heat and light accelerate the rate of reaction of fats with oxygen. Antimicrobial agents can also delay or prevent rancidification by inhibiting the growth of bacteria or other micro-organisms that affect the process. Oxygen scavenging technology can be used to remove oxygen from food packaging and therefore prevent oxidative rancidification. == Oxidative stability measurement == Oxidative stability is a measure of oil or fat resistance to oxidation. Because the process takes place through a chain reaction, the oxidation reaction has a period when it is relatively slow, before it suddenly speeds up. The time for this to happen is called the "induction time", and it is repeatable under identical conditions (temperature, air flow, etc.). There are a number of ways to measure the progress of the oxidation reaction. One of the most popular methods currently in use is the Rancimat method. The Rancimat method is carried out using an air current at temperatures between 50 and 220 °C. The volatile oxidation products (largely formic acid) are carried by the air current into the measuring vessel, where they are absorbed (dissolve) in the measuring fluid (distilled water). By continuous measurement of the conductivity of this solution, oxidation curves can be generated. The cusp point of the oxidation curve (the point where a rapid rise in the conductivity starts) gives the induction time of the rancidification reaction, and can be taken as an indication of the oxidative stability of the
|
{
"page_id": 198711,
"source": null,
"title": "Rancidification"
}
|
sample. The Rancimat method, the oxidative stability instrument (OSI) and the oxidograph were all developed as automatic versions of the more complicated AOM (active oxygen method), which is based on measuring peroxide values for determining the induction time of fats and oils. Over time, the Rancimat method has become established, and it has been accepted into a number of national and international standards, for example AOCS Cd 12b-92 and ISO 6886. == See also == Deep frying § Oil deterioration and chemical changes Fermentation Food preservation Lipid peroxidation Preservative Putrefaction == References == == Further reading == Imark, Christian; Kneubühl, Markus; Bodmer, Stefan (December 2000). "Occurrence and activity of natural antioxidants in herbal spirits". Innovative Food Science & Emerging Technologies. 1 (4): 239–243. doi:10.1016/S1466-8564(00)00018-7.
|
{
"page_id": 198711,
"source": null,
"title": "Rancidification"
}
|
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word surfactant is a blend of "surface-active agent", coined in 1950. As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt. Surfactants are among the most widespread and commercially important chemicals. Private households as well as many industries use them in large quantities as detergents and cleaning agents, but also for example as emulsifiers, wetting agents, foaming agents, antistatic additives, or dispersants. Surfactants occur naturally in traditional plant-based detergents, e.g. horse chestnuts or soap nuts; they can also be found in the secretions of some caterpillars. Today one of the most commonly used anionic surfactants, linear alkylbenzene sulfates (LAS), are produced from petroleum products. However, surfactants are increasingly produced in whole or in part from renewable biomass, like sugar, fatty alcohol from vegetable oils, by-products of biofuel production, or other biogenic material. == Classification == Most surfactants are organic compounds with hydrophilic "heads" and hydrophobic "tails." The "heads" of surfactants are polar and may or may not carry an electrical charge. The "tails" of most surfactants are fairly similar, consisting of a hydrocarbon chain, which can be branched, linear, or aromatic. Fluorosurfactants have fluorocarbon chains. Siloxane surfactants have siloxane chains. Many important surfactants include a polyether chain terminating in a highly polar anionic group. The polyether groups often comprise ethoxylated (polyethylene oxide-like) sequences inserted to increase the hydrophilic character of a surfactant. Polypropylene oxides conversely, may be inserted to increase the lipophilic character of a surfactant. Surfactant molecules have either one tail or two; those with two tails are said to be double-chained. Most commonly, surfactants
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
are classified according to polar head group. A non-ionic surfactant has no charged groups in its head. The head of an ionic surfactant carries a net positive, or negative, charge. If the charge is negative, the surfactant is more specifically called anionic; if the charge is positive, it is called cationic. If a surfactant contains a head with two oppositely charged groups, it is termed zwitterionic, or amphoteric. Commonly encountered surfactants of each type include: === Anionic: sulfate, sulfonate, and phosphate, carboxylate derivatives === Anionic surfactants contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates. Prominent alkyl sulfates include ammonium lauryl sulfate, sodium lauryl sulfate (sodium dodecyl sulfate, SLS, or SDS), and the related alkyl-ether sulfates sodium laureth sulfate (sodium lauryl ether sulfate or SLES), and sodium myreth sulfate. Others include: Alkylbenzene sulfonates Docusate (dioctyl sodium sulfosuccinate) Perfluorooctanesulfonate (PFOS) Perfluorobutanesulfonate Alkyl-aryl ether phosphates Alkyl ether phosphates Carboxylates are the most common surfactants and comprise the carboxylate salts (soaps), such as sodium stearate. More specialized species include sodium lauroyl sarcosinate and carboxylate-based fluorosurfactants such as perfluorononanoate, perfluorooctanoate (PFOA or PFO). === Cationic head groups === pH-dependent primary, secondary, or tertiary amines; primary and secondary amines become positively charged at pH < 10: octenidine dihydrochloride. Permanently charged quaternary ammonium salts: cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, and dioctadecyldimethylammonium bromide (DODAB). === Zwitterionic surfactants === Zwitterionic (ampholytic) surfactants have both cationic and anionic centers attached to the same molecule. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. The anionic part can be more variable and include sulfonates, as in the sultaines CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) and cocamidopropyl hydroxysultaine. Betaines such as cocamidopropyl betaine have a carboxylate with the ammonium. The most common biological zwitterionic surfactants
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
have a phosphate anion with an amine or ammonium, such as the phospholipids phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelins. Lauryldimethylamine oxide and myristamine oxide are two commonly used zwitterionic surfactants of the tertiary amine oxides structural type. === Non-ionic === Non-ionic surfactants have covalently bonded oxygen-containing hydrophilic groups, which are bonded to hydrophobic parent structures. The water-solubility of the oxygen groups is the result of hydrogen bonding. Hydrogen bonding decreases with increasing temperature, and the water solubility of non-ionic surfactants therefore decreases with increasing temperature. Non-ionic surfactants are less sensitive to water hardness than anionic surfactants, and they foam less strongly. The differences between the individual types of non-ionic surfactants are slight, and the choice is primarily governed having regard to the costs of special properties (e.g., effectiveness and efficiency, toxicity, dermatological compatibility, biodegradability) or permission for use in food. ==== Ethoxylates ==== ===== Fatty alcohol ethoxylates ===== Narrow-range ethoxylate Octaethylene glycol monododecyl ether Pentaethylene glycol monododecyl ether ===== Alkylphenol ethoxylates (APEs or APEOs) ===== Nonoxynols Triton X-100 ===== Fatty acid ethoxylates ===== Fatty acid ethoxylates are a class of very versatile surfactants, which combine in a single molecule the characteristic of a weakly anionic, pH-responsive head group with the presence of stabilizing and temperature responsive ethyleneoxide units. ===== Special ethoxylated fatty esters and oils ===== ===== Ethoxylated amines and/or fatty acid amides ===== Polyethoxylated tallow amine Cocamide monoethanolamine Cocamide diethanolamine ===== Terminally blocked ethoxylates ===== Poloxamers ==== Fatty acid esters of polyhydroxy compounds ==== ===== Fatty acid esters of glycerol ===== Glycerol monostearate Glycerol monolaurate ===== Fatty acid esters of sorbitol ===== Spans: Sorbitan monolaurate Sorbitan monostearate Sorbitan tristearate Tweens: Tween 20 Tween 40 Tween 60 Tween 80 ===== Fatty acid esters of sucrose ===== ===== Alkyl polyglucosides ===== Decyl glucoside Lauryl glucoside Octyl glucoside === Other classifications === Amino
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
acid-based surfactants are surfactants derived from an amino acid. Their properties vary and can be either anionic, cationic, or zwitterionic, depending on the amino acid used and which part of the amino acid is condensed with the alkyl/aryl chain. Gemini surfactants consist of two surfactant molecules linked together at or near their head groups. Compared to monomeric surfactants, they have much lower critical micelle concentrations. == Composition and structure == Surfactants are usually organic compounds that are akin to amphiphilic, which means that this molecule, being as double-agent, each contains a hydrophilic "water-seeking" group (the head), and a hydrophobic "water-avoiding" group (the tail). As a result, a surfactant contains both a water-soluble component and a water-insoluble component. Surfactants diffuse in water and get adsorbed at interfaces between air and water, or at the interface between oil and water in the case where water is mixed with oil. The water-insoluble hydrophobic group may extend out of the bulk water phase into a non-water phase such as air or oil phase, while the water-soluble head group remains bound in the water phase. The hydrophobic tail may be either lipophilic ("oil-seeking") or lipophobic ("oil-avoiding") depending on its chemistry. Hydrocarbon groups are usually lipophilic, for use in soaps and detergents, while fluorocarbon groups are lipophobic, for use in repelling stains or reducing surface tension. World production of surfactants is estimated at 15 million tons per year, of which about half are soaps. Other surfactants produced on a particularly large scale are linear alkylbenzene sulfonates (1.7 million tons/y), lignin sulfonates (600,000 tons/y), fatty alcohol ethoxylates (700,000 tons/y), and alkylphenol ethoxylates (500,000 tons/y). === Structure of surfactant phases in water === In the bulk aqueous phase, surfactants form aggregates, such as micelles, where the hydrophobic tails form the core of the aggregate and the hydrophilic heads
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
are in contact with the surrounding liquid. Other types of aggregates can also be formed, such as spherical or cylindrical micelles or lipid bilayers. The shape of the aggregates depends on the chemical structure of the surfactants, namely the balance in size between the hydrophilic head and hydrophobic tail. A measure of this is the hydrophilic-lipophilic balance (HLB). Surfactants reduce the surface tension of water by adsorbing at the liquid-air interface. The relation that links the surface tension and the surface excess is known as the Gibbs isotherm. === Dynamics of surfactants at interfaces === The dynamics of surfactant adsorption is of great importance for practical applications such as in foaming, emulsifying or coating processes, where bubbles or drops are rapidly generated and need to be stabilized. The dynamics of absorption depend on the diffusion coefficient of the surfactant. As the interface is created, the adsorption is limited by the diffusion of the surfactant to the interface. In some cases, there can exist an energetic barrier to adsorption or desorption of the surfactant. If such a barrier limits the adsorption rate, the dynamics are said to be ‘kinetically limited'. Such energy barriers can be due to steric or electrostatic repulsions. The surface rheology of surfactant layers, including the elasticity and viscosity of the layer, play an important role in the stability of foams and emulsions. === Characterization of interfaces and surfactant layers === Interfacial and surface tension can be characterized by classical methods such as the -pendant or spinning drop method. Dynamic surface tensions, i.e. surface tension as a function of time, can be obtained by the maximum bubble pressure apparatus The structure of surfactant layers can be studied by ellipsometry or X-ray reflectivity. Surface rheology can be characterized by the oscillating drop method or shear surface rheometers such as
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
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double-cone, double-ring or magnetic rod shear surface rheometer. == Applications == Surfactants play an important role as cleaning, wetting, dispersing, emulsifying, foaming and anti-foaming agents in many practical applications and products, including detergents, fabric softeners, motor oils, emulsions, soaps, paints, adhesives, inks, anti-fogs, ski waxes, snowboard wax, deinking of recycled papers, in flotation, washing and enzymatic processes, and laxatives. Also agrochemical formulations such as herbicides (some), insecticides, biocides (sanitizers), and spermicides (nonoxynol-9). Personal care products such as cosmetics, shampoos, shower gel, hair conditioners, and toothpastes. Surfactants are used in firefighting (to make "wet water" that more quickly soaks into flammable materials) and pipelines (liquid drag reducing agents). Alkali surfactant polymers are used to mobilize oil in oil wells. Surfactants act to cause the displacement of air from the matrix of cotton pads and bandages so that medicinal solutions can be absorbed for application to various body areas. They also act to displace dirt and debris by the use of detergents in the washing of wounds and via the application of medicinal lotions and sprays to surface of skin and mucous membranes. Surfactants enhance remediation via soil washing, bioremediation, and phytoremediation. === Detergents in biochemistry and biotechnology === In solution, detergents help solubilize a variety of chemical species by dissociating aggregates and unfolding proteins. Popular surfactants in the biochemistry laboratory are sodium lauryl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB). Detergents are key reagents to extract protein by lysis of the cells and tissues: they disorganize the membrane's lipid bilayer (SDS, Triton X-100, X-114, CHAPS, DOC, and NP-40), and solubilize proteins. Milder detergents such as octyl thioglucoside, octyl glucoside or dodecyl maltoside are used to solubilize membrane proteins such as enzymes and receptors without denaturing them. Non-solubilized material is harvested by centrifugation or other means. For electrophoresis, for example, proteins are
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
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classically treated with SDS to denature the native tertiary and quaternary structures, allowing the separation of proteins according to their molecular weight. Detergents have also been used to decellularise organs. This process maintains a matrix of proteins that preserves the structure of the organ and often the microvascular network. The process has been successfully used to prepare organs such as the liver and heart for transplant in rats. Pulmonary surfactants are also naturally secreted by type II cells of the lung alveoli in mammals. === Quantum dot preparation === Surfactants are used with quantum dots in order to manipulate their growth, assembly, and electrical properties, in addition to mediating reactions on their surfaces. Research is ongoing in how surfactants arrange themselves on the surface of the quantum dots. === Surfactants in droplet-based microfluidics === Surfactants play an important role in droplet-based microfluidics in the stabilization of the droplets, and the prevention of the fusion of droplets during incubation. === Heterogeneous catalysis === Janus-type material is used as a surfactant-like heterogeneous catalyst for the synthesis of adipic acid. == In biology == The human body produces diverse surfactants. Pulmonary surfactant is produced in the lungs in order to facilitate breathing by increasing total lung capacity, and lung compliance. In respiratory distress syndrome or RDS, surfactant replacement therapy helps patients have normal respiration by using pharmaceutical forms of the surfactants. One example of a pharmaceutical pulmonary surfactant is Survanta (beractant) or its generic form Beraksurf, produced by Abbvie and Tekzima respectively. Bile salts, a surfactant produced in the liver, play an important role in digestion. == Safety and environmental risks == Most anionic and non-ionic surfactants are non-toxic, having LD50 comparable to table salt. The toxicity of quaternary ammonium compounds, which are antibacterial and antifungal, varies. Dialkyldimethylammonium chlorides (DDAC, DSDMAC) used as
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
fabric softeners have high LD50 (5 g/kg) and are essentially non-toxic, while the disinfectant alkylbenzyldimethylammonium chloride has an LD50 of 0.35 g/kg. Prolonged exposure to surfactants can irritate and damage the skin because surfactants disrupt the lipid membrane that protects skin and other cells. Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants. Surfactants are routinely deposited in numerous ways on land and into water systems, whether as part of an intended process or as industrial and household waste. Anionic surfactants can be found in soils as the result of sewage sludge application, wastewater irrigation, and remediation processes. Relatively high concentrations of surfactants together with multimetals can represent an environmental risk. At low concentrations, surfactant application is unlikely to have a significant effect on trace metal mobility. In the case of the Deepwater Horizon oil spill, unprecedented amounts of Corexit were sprayed directly into the ocean at the leak and on the sea-water's surface. The apparent theory was that the surfactants isolate droplets of oil, making it easier for petroleum-consuming microbes to digest the oil. The active ingredient in Corexit is dioctyl sodium sulfosuccinate (DOSS), sorbitan monooleate (Span 80), and polyoxyethylenated sorbitan monooleate (Tween-80). === Biodegradation === Because of the volume of surfactants released into the environment, for example laundry detergents in waters, their biodegradation is of great interest. Attracting much attention is the non-biodegradability and extreme persistence of fluorosurfactant, e.g. perfluorooctanoic acid (PFOA). Strategies to enhance degradation include ozone treatment and biodegradation. Two major surfactants, linear alkylbenzene sulfonates (LAS) and the alkyl phenol ethoxylates (APE) break down under aerobic conditions found in sewage treatment plants and in soil to nonylphenol, which is thought to be an endocrine disruptor. Interest in biodegradable surfactants has led to much interest in "biosurfactants" such as those derived from amino acids.
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
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|
Biobased surfactants can offer improved biodegradation. However, whether surfactants damage the cells of fish or cause foam mountains on bodies of water depends primarily on their chemical structure and not on whether the carbon originally used came from fossil sources, carbon dioxide or biomass. == See also == Anti-fog – Chemicals that prevent the condensation of water as small droplets on a surface Cleavable detergent – class of chemical compoundsPages displaying wikidata descriptions as a fallback Disodium cocoamphodiacetate – mixture of chemicals used as a surfactantPages displaying wikidata descriptions as a fallback Emulsion – Mixture of two or more immiscible liquids Hydrotrope – chemical substancePages displaying wikidata descriptions as a fallback MBAS assay – Scientific testing method, an assay that indicates anionic surfactants in water with a bluing reaction. Niosome – Non-ionic surfactant-based vesicle Oil dispersants – Mixture of emulsifiers and solvents used to treat oil spillsPages displaying short descriptions of redirect targets Surfactants in paint Surfactant leaching == References == == External links == Media related to Surfactants at Wikimedia Commons
|
{
"page_id": 133176,
"source": null,
"title": "Surfactant"
}
|
Paula R. L. Heron is a Canadian-American physics educator who works as a professor of physics at the University of Washington. == Education == Heron has bachelor's and master's degrees in physics from the University of Ottawa in 1990 and 1991. She completed her Ph.D. at the University of Western Ontario in 1995. == Service == Heron is one of the founders and leaders of "Foundations and Frontiers in Physics Education Research", a biennial conference in physics education. In 2014 she became co-chair of the Joint Task Force on Undergraduate Physics Programs of the American Association of Physics Teachers and American Physical Society (APS). She was chair for the 2020 term of the APS Topical Group on Physics Education Research. == Recognition == In 2007, Heron was named a Fellow of the American Physical Society, after a nomination from the APS Forum on Education, "for her leadership in the physics education research community and development and active dissemination of research-based curricula that significantly impact physics instruction throughout the world". She was part of the University of Washington Physics Education Group that was honored in 2008 with the APS Excellence in Physics Education Award, "for leadership in advancing research methods in physics education, promoting the importance of physics education research as a subdiscipline of physics, and developing research-based curricula that have improved students' learning of physics from kindergarten to graduate school". == References == == External links == Home page Paula Heron publications indexed by Google Scholar
|
{
"page_id": 66062396,
"source": null,
"title": "Paula Heron"
}
|
The Swedish ethyl acetate method (SweEt) is a method for chemical analysis of pesticide residues in food using ethyl acetate as an extraction medium followed by analysis with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS). It was developed by the Swedish National Food Agency (National Reference Laboratory for pesticide analysis) for quantitative analysis of over 500 pesticides in fruits, vegetables, cereals and products of animal origin. == References ==
|
{
"page_id": 35457085,
"source": null,
"title": "Swedish ethyl acetate method"
}
|
Cephalonyx is a genus of filamentous acritarchs known from the Precambrian and early Cambrian (and possibly other times). == References ==
|
{
"page_id": 45025342,
"source": null,
"title": "Cephalonyx"
}
|
The Crabbé reaction (or Crabbé allene synthesis, Crabbé–Ma allene synthesis) is an organic reaction that converts a terminal alkyne and aldehyde (or, sometimes, a ketone) into an allene in the presence of a soft Lewis acid catalyst (or stoichiometric promoter) and secondary amine. Given continued developments in scope and generality, it is a convenient and increasingly important method for the preparation of allenes, a class of compounds often viewed as exotic and synthetically challenging to access. == Overview and scope == The transformation was discovered in 1979 by Pierre Crabbé and coworkers at the Université Scientifique et Médicale (currently merged into Université Grenoble Alpes) in Grenoble, France. As initially discovered, the reaction was a one-carbon homologation reaction (the Crabbé homologation) of a terminal alkyne into a terminal allene using formaldehyde as the carbon source, with diisopropylamine as base and copper(I) bromide as catalyst. Despite the excellent result for the substrate shown, yields were highly dependent on substrate structure and the scope of the process was narrow. The author noted that iron salts were completely ineffective, while cupric and cuprous chloride and bromide, as well as silver nitrate provided the desired product, but in lower yield under the standard conditions. Shengming Ma (麻生明) and coworkers at the Shanghai Institute of Organic Chemistry (SIOC, Chinese Academy of Sciences) investigated the reaction in detail, including clarifying the critical role of the base, and developed conditions that exhibited superior functional-group compatibility and generally resulted in higher yields of the allene. One of the key changes was the use of dicyclohexylamine as the base. In another important advance, the Ma group found that the combination of zinc iodide and morpholine allowed aldehydes besides formaldehyde, including benzaldehyde derivatives and a more limited range of aliphatic aldehydes, to be used as coupling partners, furnishing 1,3-disubstituted allenes via
|
{
"page_id": 60819517,
"source": null,
"title": "Crabbé reaction"
}
|
an alkyne-aldehyde coupling method of substantial generality and utility. A separate protocol utilizing copper catalysis and a fine-tuned amine base was later developed to obtain better yields for aliphatic aldehydes. The Crabbé reaction is applicable to a limited range of ketone substrates for the synthesis of trisubstituted allenes; however, a near stoichiometric quantity (0.8 equiv) of cadmium iodide (CdI2) is needed to promote the reaction. Alternatively, the use of cuprous bromide and zinc iodide sequentially as catalysts is also effective, provided the copper catalyst is filtered before zinc iodide is added. == Prevailing mechanism == The reaction mechanism was first investigated by Scott Searles and coworkers at the University of Missouri. Overall, the reaction can be thought of as a reductive coupling of the carbonyl compound and the terminal alkyne. In the Crabbé reaction, the secondary amine serves as the hydride donor, which results in the formation of the corresponding imine as the byproduct. Thus, remarkably, the secondary amine serves as Brønsted base, ligand for the metal ion, iminium-forming carbonyl activator, and the aforementioned two-electron reductant in the same reaction. In broad strokes, the mechanism of the reaction is believed to first involve a Mannich-like addition of the alkynylmetal species into the iminium ion formed by condensation of the aldehyde and the secondary amine. This first part of the process is a so-called A3 coupling reaction (A3 stands for aldehyde-alkyne-amine). In the second part, the α-amino alkyne then undergoes a formal retro-imino-ene reaction, an internal redox process, to deliver the desired allene and an imine as the oxidized byproduct of the secondary amine. These overall steps are supported by deuterium labeling and kinetic isotope effect studies. Density functional theory computations were performed to better understand the second part of the reaction. These computations indicate that the uncatalyzed process (either a
|
{
"page_id": 60819517,
"source": null,
"title": "Crabbé reaction"
}
|
concerted but highly asynchronous process or a stepwise process with a fleeting intermediate) involves a prohibitively high-energy barrier. The metal-catalyzed reaction, on the other hand, is energetically reasonable and probably occurs via a stepwise hydride transfer to the alkyne followed by C–N bond scission in a process similar to those proposed for formal [3,3]-sigmatropic rearrangements and hydride transfer reactions catalyzed by gold(I) complexes. A generic mechanism showing the main features of the reaction (under Crabbé's original conditions) is given below:(The copper catalyst is shown simply as "CuBr" or "Cu+", omitting any additional amine or halide ligands or the possibility of dinuclear interactions with other copper atoms. Condensation of formaldehyde and diisopropylamine to form the iminium ion and steps involving complexation and decomplexation of Cu+ are also omitted here for brevity.) Since 2012, Ma has reported several catalytic enantioselective versions of the Crabbé reaction in which chiral PINAP (aza-BINAP) based ligands for copper are employed. The stepwise application of copper and zinc catalysis was required: the copper promotes the Mannich-type condensation, while subsequent one-step addition of zinc iodide catalyzes the imino-retro-ene reaction. == See also == Mannich reaction Ene reaction Coupling reaction Alkynylation == References ==
|
{
"page_id": 60819517,
"source": null,
"title": "Crabbé reaction"
}
|
Barton Zwiebach (born Barton Zwiebach Cantor, October 4, 1954) is a Peruvian string theorist and professor at the Massachusetts Institute of Technology. == Work == Zwiebach's undergraduate work was in Electrical Engineering at the Universidad Nacional de Ingeniería in Peru, from which he graduated in 1977. His graduate work was in physics at the California Institute of Technology. Zwiebach obtained his Ph.D. in 1983, working under the supervision of Murray Gell-Mann. He has held postdoctoral positions at the University of California, Berkeley, and at the Massachusetts Institute of Technology, where he became an assistant professor of physics in 1987, and a permanent member of the faculty in 1994. He is one of the world's leading experts in string field theory. He wrote the textbook A First Course in String Theory (2004, ISBN 0-521-83143-1), meant for undergraduates. == Selected publications == Professor Zwiebach's publications are available on the SPIRES HEP Literature Database. == References == https://dspace.mit.edu/handle/1721.1/42752 == External links == Barton Zwiebach at the Mathematics Genealogy Project
|
{
"page_id": 1247296,
"source": null,
"title": "Barton Zwiebach"
}
|
Regeneration in biology is the process of renewal, restoration, and tissue growth that makes genomes, cells, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. Regeneration can either be complete where the new tissue is the same as the lost tissue, or incomplete after which the necrotic tissue becomes fibrotic. At its most elementary level, regeneration is mediated by the molecular processes of gene regulation and involves the cellular processes of cell proliferation, morphogenesis and cell differentiation. Regeneration in biology, however, mainly refers to the morphogenic processes that characterize the phenotypic plasticity of traits allowing multi-cellular organisms to repair and maintain the integrity of their physiological and morphological states. Above the genetic level, regeneration is fundamentally regulated by asexual cellular processes. Regeneration is different from reproduction. For example, hydra perform regeneration but reproduce by the method of budding. The regenerative process occurs in two multi-step phases: the preparation phase and the redevelopment phase. Regeneration begins with an amputation which triggers the first phase. Right after the amputation, migrating epidermal cells form a wound epithelium which thickens, through cell division, throughout the first phase to form a cap around the site of the wound. The cells underneath this cap then begin to rapidly divide and form a cone shaped end to the amputation known as a blastema. Included in the blastema are skin, muscle, and cartilage cells that de-differentiate and become similar to stem cells in that they can become multiple types of cells. Cells differentiate to the same purpose they originally filled meaning skin cells again become skin cells and muscle cells become muscles. These de-differentiated cells divide until enough cells are available at which point they differentiate again and the shape of the blastema
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
begins to flatten out. It is at this point that the second phase begins, the redevelopment of the limb. In this stage, genes signal to the cells to differentiate themselves and the various parts of the limb are developed. The end result is a limb that looks and operates identically to the one that was lost, usually without any visual indication that the limb is newly generated. The hydra and the planarian flatworm have long served as model organisms for their highly adaptive regenerative capabilities. Once wounded, their cells become activated and restore the organs back to their pre-existing state. The Caudata ("urodeles"; salamanders and newts), an order of tailed amphibians, is possibly the most adept vertebrate group at regeneration, given their capability of regenerating limbs, tails, jaws, eyes and a variety of internal structures. The regeneration of organs is a common and widespread adaptive capability among metazoan creatures. In a related context, some animals are able to reproduce asexually through fragmentation, budding, or fission. A planarian parent, for example, will constrict, split in the middle, and each half generates a new end to form two clones of the original. Echinoderms (such as the sea star), crayfish, many reptiles, and amphibians exhibit remarkable examples of tissue regeneration. The case of autotomy, for example, serves as a defensive function as the animal detaches a limb or tail to avoid capture. After the limb or tail has been autotomized, cells move into action and the tissues will regenerate. In some cases a shed limb can itself regenerate a new individual. Limited regeneration of limbs occurs in most fishes and salamanders, and tail regeneration takes place in larval frogs and toads (but not adults). The whole limb of a salamander or a triton will grow repeatedly after amputation. In reptiles, chelonians, crocodilians and
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
snakes are unable to regenerate lost parts, but many (not all) kinds of lizards, geckos and iguanas possess regeneration capacity in a high degree. Usually, it involves dropping a section of their tail and regenerating it as part of a defense mechanism. While escaping a predator, if the predator catches the tail, it will disconnect. == Ecosystems == Ecosystems can be regenerative. Following a disturbance, such as a fire or pest outbreak in a forest, pioneering species will occupy, compete for space, and establish themselves in the newly opened habitat. The new growth of seedlings and community assembly process is known as regeneration in ecology. == Cellular molecular fundamentals == Pattern formation in the morphogenesis of an animal is regulated by genetic induction factors that put cells to work after damage has occurred. Neural cells, for example, express growth-associated proteins, such as GAP-43, tubulin, actin, an array of novel neuropeptides, and cytokines that induce a cellular physiological response to regenerate from the damage. Many of the genes that are involved in the original development of tissues are reinitialized during the regenerative process. Cells in the primordia of zebrafish fins, for example, express four genes from the homeobox msx family during development and regeneration. == Tissues == "Strategies include the rearrangement of pre-existing tissue, the use of adult somatic stem cells and the dedifferentiation and/or transdifferentiation of cells, and more than one mode can operate in different tissues of the same animal. All these strategies result in the re-establishment of appropriate tissue polarity, structure and form.": 873 During the developmental process, genes are activated that serve to modify the properties of cell as they differentiate into different tissues. Development and regeneration involves the coordination and organization of populations cells into a blastema, which is "a mound of stem cells from which
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
regeneration begins". Dedifferentiation of cells means that they lose their tissue-specific characteristics as tissues remodel during the regeneration process. This should not be confused with the transdifferentiation of cells which is when they lose their tissue-specific characteristics during the regeneration process, and then re-differentiate to a different kind of cell. == In animals == === Arthropods === ==== Limb regeneration ==== Many arthropods can regenerate limbs and other appendages following either injury or autotomy. Regeneration capacity is constrained by the developmental stage and ability to molt. Crustaceans, which continually molt, can regenerate throughout their lifetimes. While molting cycles are generally hormonally regulated, limb amputation induces premature molting. Hemimetabolous insects such as crickets can regenerate limbs as nymphs, before their final molt. Holometabolous insects can regenerate appendages as larvae prior to the final molt and metamorphosis. Beetle larvae, for example, can regenerate amputated limbs. Fruit fly larvae do not have limbs but can regenerate their appendage primordia, imaginal discs. In both systems, the regrowth of the new tissue delays pupation. Mechanisms underlying appendage limb regeneration in insects and crustaceans are highly conserved. During limb regeneration species in both taxa form a blastema that proliferates and grows to repattern the missing tissue. ==== Venom regeneration ==== Arachnids, including scorpions, are known to regenerate their venom, although the content of the regenerated venom is different from the original venom during its regeneration, as the venom volume is replaced before the active proteins are all replenished. ==== Fruit fly model ==== The fruit fly Drosophila melanogaster is a useful model organism to understand the molecular mechanisms that control regeneration, especially gut and germline regeneration. In these tissues, resident stem cells continually renew lost cells. The Hippo signaling pathway was discovered in flies and was found to be required for midgut regeneration. Later, this conserved
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
signaling pathway was also found to be essential for regeneration of many mammalian tissues, including heart, liver, skin, and lung, and intestine. === Annelids === Many annelids (segmented worms) are capable of regeneration. For example, Chaetopterus variopedatus and Branchiomma nigromaculata can regenerate both anterior and posterior body parts after latitudinal bisection. The relationship between somatic and germline stem cell regeneration has been studied at the molecular level in the annelid Capitella teleta. Leeches, however, appear incapable of segmental regeneration. Furthermore, their close relatives, the branchiobdellids, are also incapable of segmental regeneration. However, certain individuals, like the lumbriculids, can regenerate from only a few segments. Segmental regeneration in these animals is epimorphic and occurs through blastema formation. Segmental regeneration has been gained and lost during annelid evolution, as seen in oligochaetes, where head regeneration has been lost three separate times. Along with epimorphosis, some polychaetes like Sabella pavonina experience morphallactic regeneration. Morphallaxis involves the de-differentiation, transformation, and re-differentation of cells to regenerate tissues. How prominent morphallactic regeneration is in oligochaetes is currently not well understood. Although relatively under-reported, it is possible that morphallaxis is a common mode of inter-segment regeneration in annelids. Following regeneration in L. variegatus, past posterior segments sometimes become anterior in the new body orientation, consistent with morphallaxis. Following amputation, most annelids are capable of sealing their body via rapid muscular contraction. Constriction of body muscle can lead to infection prevention. In certain species, such as Limnodrilus, autolysis can be seen within hours after amputation in the ectoderm and mesoderm. Amputation is also thought to cause a large migration of cells to the injury site, and these form a wound plug. === Echinoderms === Tissue regeneration is widespread among echinoderms and has been well documented in starfish (Asteroidea), sea cucumbers (Holothuroidea), and sea urchins (Echinoidea). Appendage regeneration in
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
echinoderms has been studied since at least the 19th century. In addition to appendages, some species can regenerate internal organs and parts of their central nervous system. In response to injury starfish can autotomize damaged appendages. Autotomy is the self-amputation of a body part, usually an appendage. Depending on severity, starfish will then go through a four-week process where the appendage will be regenerated. Some species must retain mouth cells to regenerate an appendage, due to the need for energy. The first organs to regenerate, in all species documented to date, are associated with the digestive tract. Thus, most knowledge about visceral regeneration in holothurians concerns this system. === Planaria (Platyhelminthes) === Regeneration research using Planarians began in the late 1800s and was popularized by T.H. Morgan at the beginning of the 20th century. Alejandro Sanchez-Alvarado and Philip Newmark transformed planarians into a model genetic organism in the beginning of the 20th century to study the molecular mechanisms underlying regeneration in these animals. Planarians exhibit an extraordinary ability to regenerate lost body parts. For example, a planarian split lengthwise or crosswise will regenerate into two separate individuals. In one experiment, T.H. Morgan found that a piece corresponding to 1/279th of a planarian or a fragment with as few as 10,000 cells can successfully regenerate into a new worm within one to two weeks. After amputation, stump cells form a blastema formed from neoblasts, pluripotent cells found throughout the planarian body. New tissue grows from neoblasts with neoblasts comprising between 20 and 30% of all planarian cells. Recent work has confirmed that neoblasts are totipotent since one single neoblast can regenerate an entire irradiated animal that has been rendered incapable of regeneration. In order to prevent starvation a planarian will use their own cells for energy, this phenomenon is known as
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
de-growth. === Amphibians === Limb regeneration in the axolotl and newt has been extensively studied and researched. Although researchers have developed genetically altered axolotls, live cell imaging remains difficult due to the large size of adult axolotls. To fix this issue, they use small juvenile axolotls, focus on smaller amputations like digits, and reduce light distortion caused by refraction in water by using iodixanol, a substance that is safe for living cells and tissues. The nineteenth century studies of this subject are reviewed in Holland (2021). Urodele amphibians, such as salamanders and newts, display the highest regenerative ability among tetrapods. As such, they can fully regenerate their limbs, tail, jaws, and retina via epimorphic regeneration leading to functional replacement with new tissue. Salamander limb regeneration occurs in two main steps. First, the local cells dedifferentiate at the wound site into progenitor to form a blastema. Second, the blastemal cells will undergo cell proliferation, patterning, cell differentiation and tissue growth using similar genetic mechanisms that deployed during embryonic development. Ultimately, blastemal cells will generate all the cells for the new structure. After amputation, the epidermis migrates to cover the stump in 1–2 hours, forming a structure called the wound epithelium (WE). Epidermal cells continue to migrate over the WE, resulting in a thickened, specialized signaling center called the apical epithelial cap (AEC). Over the next several days there are changes in the underlying stump tissues that result in the formation of a blastema (a mass of dedifferentiated proliferating cells). As the blastema forms, pattern formation genes – such as HoxA and HoxD – are activated as they were when the limb was formed in the embryo. The positional identity of the distal tip of the limb (i.e. the autopod, which is the hand or foot) is formed first in the blastema.
|
{
"page_id": 854081,
"source": null,
"title": "Regeneration (biology)"
}
|
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