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Quaternary ammonium cation. The R groups may be the same or different alkyl or aryl groups. Also, the R groups may be connected. In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure [NR 4] +, where R is an alkyl group, an aryl group [1] or organyl group.
Chemical Society Reviews publishes "Tutorial reviews" and "Critical reviews". The former are written to be of relevance both to the general research chemist who is new to the field, as well as the expert, whereas the latter aim to provide a deeper understanding of the topic in hand, but retain their accessibility through an introduction written for the general reader.
This quarter system was adopted by the oldest universities in the English-speaking world (Oxford, founded circa 1096, [1] and Cambridge, founded circa 1209 [2]). Over time, Cambridge dropped Trinity Term and renamed Hilary Term to Lent Term, and Oxford also dropped the original Trinity Term and renamed Easter Term as Trinity Term, thus establishing the three-term academic "quarter" year widely ...
Temperature vs. heat load diagram of hot stream (H 2 O entering at 20 bar, 473.15 K, and 4 kg/s) and cold stream (R-11 entering at 18 bar, 303.15 K, and 5 kg/s) in a counter-flow heat exchanger. "Pinch" is the point of closest approach between the hot and cold streams in the T vs. H diagram.
The components that allows us to go far beyond 30 includes very sophisticated new type of chemistry that on certain hyper serotypes can give several fold improvement in titer.
This test was implemented with the idea of creating standardized admissions for the United States in northeastern elite universities. Originally, the test was also meant for top boarding schools, in order to align the curriculum between schools. [11] Originally the standardized test was made of essays and was not intended for widespread testing ...
ISO 4 (Information and documentation — Rules for the abbreviation of title words and titles of publications) is an international standard which defines a uniform system for the abbreviation of serial publication titles, i.e., titles of publications such as scientific journals that are published in regular installments.
Wikipedia is the largest and most-read reference work in history, [3] [4] and is consistently ranked among the ten most visited websites; as of December 2024, it was ranked fifth by Semrush, [5] and seventh by Similarweb. [6]