Relaxation (NMR)

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

Dynamics of braided coronal loops - II. Cascade to multiple small-scale reconnection events

Abstract: Aims. Our aim is to investigate the resistive relaxation of a magnetic loop that contains braided magnetic flux but no net current or helicity. The loop is subject to line-tied boundary conditions. We investigate the dynamical processes that occur during this relaxation, in particular the magnetic reconnection that occurs, and discuss the nature of the final equilibrium. Methods. The three-dimensional evolution of a braided magnetic field is followed in a series of resistive MHD simulations. Results. It is found that, following an instability within the loop, a myriad of thin current layers forms, via a cascade-like process. This cascade becomes more developed and continues for a longer period of time for higher magnetic Reynolds number. During the cascade, magnetic flux is reconnected multiple times, with the level of this "multiple reconnection" positively correlated with the magnetic Reynolds number. Eventually the system evolves into a state with no more small-scale current layers. This final state is found to approximate a non-linear force-free field consisting of two flux tubes of oppositely-signed twist embedded in a uniform background field.

Nmr relaxation in solution of paramagnetic complexes: recent theoretical progress for s ≥ 1

Abstract: Publisher Summary This chapter focuses on the first place on the phenomenon of paramagnetic relaxation enhancement and mentions recent theoretical developments in the neighboring fields. The first issue that needs to be clarified is the relation between macroscopic, observable properties of nuclear spins, and their microscopic counterparts. In solutions of transition metal ions or complexes, one can commonly consider a situation where the ligands carrying nuclear spins can reside in two types of environment: in the coordination sphere of the paramagnetic metal ion or in the bulk. If the ligand contains only one type of magnetic nuclei or if interactions between nuclear spins can be disregarded, each of the two sites can be characterized by nuclear spin–lattice and spin–spin relaxation times, T 1 and T 2 , respectively.

Nuclear transfer and anisotropic motional spin phenomena: relaxation time temperature dependence studies of water adsorbed on silica gel. iv

Abstract: An experimental investigation of the temperature dependence of the nuclear magnetic resonance relaxation phenomena of water vapor adsorbed on silica gel is described. Two-component relaxation data are observed. With temperature increase, the longer T/sub 2/ value decreases while its fractional population increases. These data are shown to be consistent with nuclear transfers between two state environments possessing distinct relaxation characteristics. and a comparison with theory is made. Evidence of a change of surface characteristics is presented; for early experiments, two-component longitudinal relaxation occurs below a transition temperature; in later experiments, only one-component T/sub 1/ behavior is found. A theory for an anisotropic motional model for nuclear magnetic dipole-dipole relaxation on surfaces is presented. The motional model is random reorientation of the interproton vector about an axis normal to the surface that occurs much faster than the time dependence of the angle between the vector and this axis. The relaxation processes are thus related to multiple nuclear correlation times. Consequences of an anisotropic model agree with experimental observations. (auth)

Viscosity effect on the ultrafast bond twisting dynamics in an amyloid fibril sensor: thioflavin-T.

Abstract: The femtosecond fluorescence upconversion technique is used to study the effect of viscosity on the excited state relaxation dynamics of an amyloid fibril sensor, thioflavin-T, in different solvent media. The excited state decay in all of the solvents is seen to be dependent on the emission wavelength. From the constructed time-resolved emission spectra, it is seen that the present system shows dynamic Stokes’ shift as well as an appreciable increase in the spectral width with time. These temporal spectral characteristics of time-resolved emission spectra have been assigned to the formation of a new emissive species from the locally excited state of the thioflavin-T molecule. The formation of the new emissive state from the locally excited state is also supported by the fact that an iso-emissive point appears in the time-resolved area normalized emission spectra. From the detailed study on the excited state dynamics of thioflavin-T as a function of solvent viscosity, it is concluded that the new emissive ...

Long Polaron Lifetime in InAs/GaAs Self-Assembled Quantum Dots

Abstract: We have investigated the polaron dynamics in n-doped InAs/GaAs self-assembled quantum dots by pump-probe midinfrared spectroscopy. A long T1 polaron decay time is measured at both low temperature and room temperature, with values around 70 and 37 ps, respectively. The decay time decreases for energies closer to the optical phonon energy. The relaxation is explained by the strong coupling for the electron-phonon interaction and by the finite lifetime of the optical phonons. We show that, even for a large detuning of 19 meV from the LO photon energy in GaAs, the carrier relaxation remains phonon assisted.