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Cluster Chemistry
In chemistry, a cluster is an ensemble of bound atoms or molecules that is intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group elements form especially robust clusters. Clusters can also consist solely of a certain kind of molecules, such as water clusters. The phrase cluster was coined by F.A. Cotton in the early 1960s to refer to compounds containing metal–metal bonds. In another definition a cluster compound contains a group of two or more metal atoms where direct and substantial metal bonding is present. The prefixed terms "nuclear" and "metallic" are used and imply different meanings. For example, polynuclear refers to a cluster with more than one metal atom, regardless of the elemental identities. Heteronuclear refers to a cluster with at least two different metal elements. The main cluster types are "naked" clusters (without stabilizing ligands) and those with ligands. For transition metal clusters, typical stabilizing ligands include carbon monoxide, halides, isocyanides, alkenes, and hydrides. For main group elements, typical clusters are stabilized by hydride ligands. Transition metal clusters are frequently composed of refractory metal atoms. In general metal centers with extended d-orbitals form stable clusters because of favorable overlap of valence orbitals. Thus, metals with a low oxidation state for the later metals and mid-oxidation states for the early metals tend to form stable clusters. Polynuclear metal carbonyls are generally found in late transition metals with low formal oxidation states. The polyhedral skeletal electron pair theory or Wade's electron counting rules predict trends in the stability and structures of many metal clusters. Jemmis mno rules have provided additional insight into the relative stability of metal clusters.
  • 8.3K
  • 08 Nov 2022
Topic Review
GEO600
GEO600 is a gravitational wave detector located near Sarstedt in the South of Hanover, Germany. It is designed and operated by scientists from the Max Planck Institute for Gravitational Physics, Max Planck Institute of Quantum Optics and the Leibniz Universität Hannover, along with University of Glasgow, University of Birmingham and Cardiff University in the United Kingdom, and is funded by the Max Planck Society and the Science and Technology Facilities Council (STFC). GEO600 is part of a worldwide network of gravitational wave detectors. This instrument, and its sister interferometric detectors, when operational, are some of the most sensitive gravitational wave detectors ever designed. They are designed to detect relative changes in distance of the order of 10−21, about the size of a single atom compared to the distance from the Sun to the Earth. GEO600 is capable of detecting gravitational waves in the frequency range 50 Hz to 1.5 kHz. Construction on the project began in 1995.
  • 998
  • 03 Nov 2022
Topic Review
Team-Based Learning
Team-based learning (TBL) is a collaborative learning and teaching strategy that enables people to follow a structured process to enhance student engagement and the quality of student or trainee learning. The term and concept was first popularized by Larry Michaelsen, the central figure in the development of the TBL method while at University of Oklahoma in the 1970s, as an educational strategy that he developed for use in academic settings, as in medical education. Team-based learning methodology can be used in any classroom or training sessions at school or in the workplace.
  • 1.6K
  • 03 Nov 2022
Topic Review
Working Bikes
Working Bikes is a not-for-profit tax-exempt 501(c)3 volunteer-driven organization based in Chicago, IL that aims to divert bicycles from the waste stream and put them to use in Chicago and abroad. It operates a warehouse, shipping center, repair shop and retail outlet from its location in the Pilsen neighborhood. Working Bikes mission is to provide bicycles to charity organizations in the Chicago area to benefit youth, transitioning homeless and refugees as well as to ship bicycles to the Gulf Coast and around the world. Each year Working Bikes aims to sell 2,000 refurbished bikes through its storefront and runs a repair shop to keep bikes in operation. It uses the proceeds from these activities to give away approximately 6,000 bikes per year. Since its inception, as cited within the Working Bikes 2018 Annual Report, "More than 70,000 bikes have been given new life across our region and the world".
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  • 03 Nov 2022
Topic Review
News Feed
News Feed is a feature of the social network Facebook. The web feed is the primary system through which users are exposed to content posted on the network. News Feed highlights information that includes profile changes, upcoming events, and birthdays, among other updates. Using a proprietary method, Facebook selects a handful of updates to show users every time they visit their feed, out of an average of 2,000 updates they can potentially receive. Over two billion people use Facebook every month, making the network's News Feed the most viewed and most influential aspect of the news industry.
  • 1.8K
  • 03 Nov 2022
Topic Review
Cell Wall Associated Kinase
Cell wall associated kinases (WAKs) are receptor-like protein kinases, found in plant cell walls, that have the capability to transmit signals directly by their cytoplasmic kinase domains. They usually link the plasma membrane to the protein and carbohydrate that composed the cell wall. The receptor-like proteins contain a cytoplasmic serine threonine kinase and a less conserved region; bound to the cell wall and contains a series of epidermal growth factor repeats. WAKs are found in various plants and crops like rice, and maize. In plants genome like Arabidopsis, WAKs, are encoded by five highly similar genes clustered in a 30-kb locus, among them WAK1 & WAK2 are highly distributed. They are primarily involved in regulating plant cell wall functions including cell expansion, bind as well as response to pectins, pathogen response and also protects plants from detrimental effects.
  • 1.2K
  • 03 Nov 2022
Topic Review
Vaccination and Religion
Vaccination and religion have interrelations of varying kinds. Almost no religions object to vaccination, and some parents either fake religious adherence or invent fake religions to provide exemption.
  • 1.0K
  • 03 Nov 2022
Topic Review
Apostolic Vicariate
An apostolic vicariate is a form of territorial jurisdiction of the Catholic Church centered in missionary regions and countries where a diocese has not yet been established. It is essentially provisional, though it may last for a century or more. The hope is that the region will generate sufficient numbers of Catholics for the Church to create a diocese. In turn, the status of Apostolic vicariate is often a promotion for a former apostolic prefecture, while either may have started out as a mission sui iuris.
  • 1.4K
  • 03 Nov 2022
Topic Review
Math 55
Math 55 is a two-semester long first-year undergraduate mathematics course at Harvard University, founded by Lynn Loomis and Shlomo Sternberg. The official titles of the course are Honors Abstract Algebra (Math 55a) and Honors Real and Complex Analysis (Math 55b). Previously, the official title was Honors Advanced Calculus and Linear Algebra.
  • 7.7K
  • 03 Nov 2022
Topic Review
105×617mm
The 105×617mm (4.1 inch) also known as 105 × 617 R is a common, NATO-standard, tank gun cartridge used in 105mm guns such as those derived from the Royal Ordnance L7. The 105 × 617 R cartridge was originally developed from the 84 mm (3.3 in) calibre Ordnance QF 20-pounder 84 × 618R cartridge as part of the development of the L7 105 mm rifled gun.
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  • 03 Nov 2022
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