Contact interactions

Indirect spin u / 1-1Q3 Spin-spin interaction mediated via the bonding electrons through the contact interaction... 

Knight shift K s 10 -10 Interaction with conduction electrons via the contact interaction... 

The simplest system exliibiting a nuclear hyperfme interaction is the hydrogen atom with a coupling constant of 1420 MHz. If different isotopes of the same element exhibit hyperfme couplings, their ratio is detemiined by the ratio of the nuclear g-values. Small deviations from this ratio may occur for the Femii contact interaction, since the electron spin probes the inner stmcture of the nucleus if it is in an s orbital. However, this so-called hyperfme anomaly is usually smaller than 1 %. 

Figure C2.5.8. Plot of the folding times Tp as a fimction of cr nfor tlie 22 sequences. This figure shows tlrat under tire external conditions when tire NBA is tire most populated tlrere is a remarkable correlation between ip and The correlation coefficient is 0.94. It is clear tlrat over a four orders of magnitude of folding times Xp = expf-a, / Oq) where CTq is a constant. The filled and open circles correspond to different contact interactions used in C2.5.1. The open squares are for A = 36.

From the isotropic coupling constant one may calculate C12, the fractional occupancy of the nitrogen s orbital, which is equal to AUo/Ao. The term Ao is the Fermi contact interaction for an unpaired electron in a pure nitrogen 2s orbital. For NO2 the value of ci2 = 56.5/550 = 0.103. The fraction of the unpaired electron associated with the N nucleus is then... 

Before formally developing the tensor it is perhaps worthwhile to discuss the various types of interactions which contribute to it. The coupling between nuclear and electron magnetic moments are conveniently divided into those which are isotropic and those which depend on orientation. The former is the result of the impaired electron having a finite probability of being at the nucleus. This type of interaction is termed the contact interaction, and is described by the constant,... 

It should now be evident that the experimental tensor may be expressed as the sum of an isotropic term resulting from the contact interaction, and a tensor resulting from dipolar interactions and any indirect coupling via the orbital angular momentum. This may be written in the form of an equation ... 

Fermi contact interaction. The coupling constant of the Fermi contact term for the nucleus N has the form127 ... 

The color superconducting DFS-phase, which is treated in a four-fermion contact interaction model, is preferred to the homogeneous 2SC state for asymmetries that are typical to matter under /1-equilibrium. 

Here we demonstrate some numerical results we replaced the original OGE by the contact interaction with the cutoff around the Fermi surface in the momentum space,... 

The mean values (A ) begin to split with each other at a density where U a becomes finite. We d like to make a comment here. One may be surprised to see their value of O(GeV), coming from our parameter choice. However, what we d like to reveal here is not their realistic values but a possibility of color magnetic superconductivity and its qualitative features. More realistic study, of course, is needed by carefully checking our approximations, especially the contact interaction and the sharp cutoff at the Fermi surface. 

The nuclear spins can interact with the time-averaged magnetic moments via either through-space (dipolar) or through-bond (Fermi-contact) interactions. The Li MAS NMR spectrum of LiMn204 is... 

This is a measure of the unpaired electron spin density that is transferred from the paramagnet to the nucleus of the spin under observation. In the regime defined by eq 2, the NMR shift (d = (Acolcoo)) induced by the Fermi-contact interaction is directly proportional to... 

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