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According to the sigma bond rule, the number of sigma bonds in a molecule is equivalent to the number of atoms plus the number of rings minus one. N σ = N atoms + N rings − 1 This rule is a special-case application of the Euler characteristic of the graph which represents the molecule.
The basic idea is that for any two reactions with two aromatic reactants only differing in the type of substituent, the change in free energy of activation is proportional to the change in Gibbs free energy. [5] This notion does not follow from elemental thermochemistry or chemical kinetics and was introduced by Hammett intuitively. [a]
In the empirical sciences, the so-called three-sigma rule of thumb (or 3 σ rule) expresses a conventional heuristic that nearly all values are taken to lie within three standard deviations of the mean, and thus it is empirically useful to treat 99.7% probability as near certainty.
Sigma complexes are of great mechanistic significance, despite their frequent fragility. They represent an initial interaction between the metal center and a hydrocarbon substrate. As such, sigma complexes are generally assumed to be intermediates prior to full oxidative addition .
The sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation (up and / or down quarks), ...
The activation function of a node in an artificial neural network is a function that calculates the output of the node based on its individual inputs and their weights. Nontrivial problems can be solved using only a few nodes if the activation function is nonlinear .
The SDS Sigma series is a series of third generation computers [1] [2] [3] that were introduced by Scientific Data Systems of the United States in 1966. [4] The first machines in the series are the 16-bit Sigma 2 and the 32-bit Sigma 7; the Sigma 7 was the first 32-bit computer released by SDS.
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