نتایج جستجو برای: helicity
تعداد نتایج: 4632 فیلتر نتایج به سال:
For the processes ee → μμ, ττ, bb̄ and cc̄ at a future ee collider with √s = 0.5 TeV, we examine the sensitivity of the helicity cross sections to four-fermion contact interactions. If longitudinal polarization of the electron beam were available, two polarized integrated cross sections would offer the opportunity to separate the helicity cross sections and, in this way, to derive model-independe...
Helicity, a measure of the linkage of flux lines, has subtle and largely unknown effects upon dynamics. Both magnetic and hydrodynamic helicity are conserved for ideal systems and could suppress nonlinear dynamics. What actually happens is not clear because in a fully three-dimensional system there are additional channels whereby intense, small-scale dynamics can occur. This contribution shows ...
Abstract. The explicit procedures are described for reconstruction of the full set of helicity amplitudes in proton-proton and proton-antiproton elastic scattering. The procedures are based on the derivative relations for the helicity amplitudes in s-channel, on the explicit parametrization of the leading spin non flip amplitudes and crossing symmetry relations. Asymptotic theorems are used for...
Inducing α-helicity through side-chain cross-linking is a strategy that has been pursued to improve peptide conformational rigidity and bio-availability. Here we describe the preparation of small peptides tethered to chiral sulfoxide-containing macrocyclic rings. Furthermore, a study of structure-activity relationships (SARs) disclosed properties with respect to ring size, sulfur position, oxid...
A simple explicit example of a Roberts-type dynamo is given in which the alpha effect of mean-field electrodynamics exists in spite of pointwise vanishing kinetic helicity of the fluid flow. In this way, it is shown that alpha-effect dynamos do not necessarily require nonzero kinetic helicity. A mean-field theory of Roberts-type dynamos is established within the framework of the second-order co...
The mean value of the normalized current helicity αp = B · (∇×B)/B 2 in solar active regions is on the order of 10 m, negative in the northern hemisphere, positive in the southern hemisphere. Observations indicate that this helicity has a subsurface origin. Possible mechanisms leading to a twist of this amplitude in magnetic flux tubes include the solar dynamo, convective buffeting of rising fl...
Key words galaxies: magnetic fields – magnetohydrodynamics (MHD) – turbulence We summarize the current state of the long term discussion about the saturation mechanisms associated with rapid growth of small-scale magnetic field, that operate in large-scale galactic dynamos, and related problems with magnetic helicity conservation. Our general conclusion is that, taking into account magnetic hel...
We present a photonic wave packet construction which is immune against the decoherence effects induced by the action of the Lorentz group. The amplitudes of a pure quantum state representing the wave packet remain invariant irrespective of the reference frame into which the wave packet has been transformed. Transmitted information is encoded in the helicity degrees of freedom of two correlated ...
Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polariz...
Three closely related stumbling blocks of solar mean field dynamo theory are discussed: how dominant are the small scale fields, how is the alpha effect quenched, and whether magnetic and current helicity fluxes alleviate the quenching? It is shown that even at the largest currently available resolution there is no clear evidence of power law scaling of the magnetic and kinetic energy spectra i...
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