Relaxation (NMR)

About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.

Resonant relaxation in stellar systems.

Abstract: We demonstrate the existence of an enhanced rate of angular momentum relaxation in nearly Keplerian star clusters, such as those found in the centers of galactic nuclei containing massive black holes. The enhanced relaxation arises because the radial and azimuthal orbital frequencies in a Keplerian potential are equal, and hence may be termed resonant relaxation. We explore the dynamics of resonant relaxation using both numerical simulations and order-of-magnitude analytic calculations. We find that the resonant angular momentum relaxation time is shorter than the non-resonant relaxation time by of order M★/M, where M★ is the mass in stars and M is the mass of the central object. Resonance does not enhance the energy relaxation rate. We examine the effect of resonant relaxation on the rate of tidal disruption of stars by the central mass; we find that the flux of stars into the loss cone is enhanced when the loss cone is empty, but that the disruption rate averaged over the entire cluster is not strongly affected. We show that relativistic precession can disable resonant relaxation near the main-sequence loss cone for black hole masses comparable to those in galactic nuclei. Resonant dynamical friction leads to growth or decay of the eccentricity of the orbit of a massive body, depending on whether the distribution function of the stars is predominantly radial or tangential. The accelerated relaxation implies that there are regions in nuclear star clusters that are relaxed in angular momentum but not in energy; unfortunately, these regions are not well-resolved in most nearby galaxies by the Hubble Space Telescope. K.C. Freeman

The effect of quadrupole relaxation on nuclear magnetic resonance multiplets

Abstract: A theory of the broadening of multiplet components in magnetic resonance spectra of coupled nuclei due to electric quadrupole spin-lattice relaxation is presented. It is shovm that the broadening of the components of the 1: 1: 1 triplet for nuclei of spin 1/2 coupled to a nucleus of spin 1, is 3/2 as great for the outer lines as for the central one, provided that the rate of quadrupole relaxation is not too large. This is in agreement with experimental observations on N14H3 A theory of the line shape of the partiy collapsed multiplet at higher rates of quadrupole relaxation is also given.

Spin precession and real-time dynamics in the Kondo model:Time-dependent numerical renormalization-group study

Abstract: A detailed derivation of the recently proposed time-dependent numerical renormalization-group (TD-NRG) approach to nonequilibrium dynamics in quantum-impurity systems is presented. We demonstrate that the method is suitable for fermionic as well as bosonic baths. Comparisons with exact analytical results for the charge relaxation in the resonant-level model and for dephasing in the spin-boson model establish the accuracy of the method. The real-time dynamics of a single spin coupled to each type of bath is investigated. We use the TD-NRG to calculate the spin relaxation and spin precession of a single Kondo impurity. The short- and long-time dynamics are studied as a function of temperature in the ferromagnetic and antiferromagnetic regimes. The short-time dynamics agrees very well with analytical results obtained at second order in the exchange coupling $J$. In the ferromagnetic regime, the transient spin decay is described by the scaling variable $x=2{\ensuremath{\rho}}_{F}\ensuremath{\mid}J(T)\ensuremath{\mid}Tt$. In the antiferromagnetic regime, the long-time decay is governed for $Tl{T}_{K}$ by the Kondo time scale $1∕{T}_{K}$. Here ${\ensuremath{\rho}}_{F}$ is the conduction-electron density of states, ${T}_{K}$ is the Kondo temperature, and $J(T)$ is the effective exchange coupling at temperature $T$. Results for spin precession are obtained by rotating the external magnetic field from the $x$ axis to the $z$ axis.