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Helicity is a pseudo-scalar quantity: it changes sign under change from a right-handed to a left-handed frame of reference; it can be considered as a measure of the handedness (or chirality) of the flow. Helicity is one of the four known integral invariants of the Euler equations; the other three are energy, momentum and angular momentum.
Helicity plays a central role in dynamo theory, the theory of spontaneous generation of magnetic fields in stars and planets (Moffatt 1978, Parker 1979, Krause & Rädler 1980). It is known that, with few exceptions, any statistically homogeneous turbulent flow having nonzero mean helicity in a sufficiently large expanse of conducting fluid will ...
Helicity may refer to: Helicity (fluid mechanics), the extent to which corkscrew-like motion occurs; Helicity (particle physics), the projection of the spin onto the ...
In 2016 he organised an IUTAM Symposium on helicity (hosted by the Istituto Veneto di Scienze, Lettere ed Arti in Venice) that gathered more than 100 scientists from 20 different countries, and in September 2019 he organised and directed at the Beijing University of Technology (BJUT) the first programme in China devoted to topological aspects ...
The above renormalization group calculation has been performed for both zero and nonzero cross helicity. The above phenomenologies assume isotropic turbulence that is not the case in the presence of a mean magnetic field. The mean magnetic field typically suppresses the energy cascade along the direction of the mean magnetic field. [9]
In fluid dynamics, d'Alembert's paradox (or the hydrodynamic paradox) is a paradox discovered in 1752 by French mathematician Jean le Rond d'Alembert. [1] D'Alembert proved that – for incompressible and inviscid potential flow – the drag force is zero on a body moving with constant velocity relative to the fluid . [ 2 ]
The helicity of a particle is positive (" right-handed") if the direction of its spin is the same as the direction of its motion and negative ("left-handed") if opposite. Helicity is conserved. [1] That is, the helicity commutes with the Hamiltonian, and thus, in the absence of external forces, is time-invariant. It is also rotationally ...
These amplitudes are called MHV amplitudes, because at tree level, they violate helicity conservation to the maximum extent possible. The tree amplitudes in which all gauge bosons have the same helicity or all but one have the same helicity vanish. MHV amplitudes may be calculated very efficiently by means of the Parke–Taylor formula.