Projects / Programmes
Nove merilne tehnike in metode magnetne resonance (Slovene)
January 1, 1999
- December 31, 2003
| Code |
Science |
Field |
Subfield |
| 1.02.00 |
Natural sciences and mathematics |
Physics |
|
| Code |
Science |
Field |
| P260 |
Natural sciences and mathematics |
Condensed matter: electronic structure, electrical, magnetic and optical properties, supraconductors, magnetic resonance, relaxation, spectroscopy |
| P180 |
Natural sciences and mathematics |
Metrology, physical instrumentation |
| P230 |
Natural sciences and mathematics |
Atomic and molecular physics |
Researchers (6)
Organisations (1)
Abstract
With the newly developed modulated gradient spin-echo method (MGSE), which uses a repetitive train of RF pulses with interspersed gradient pulses to periodically modulate the spin phase, the signal attenuation proportional to a value of the molecular velocity correlation spectrum at the modulation frequency. Covering the frequency range between Hz and MHz it is a complement to the quasi-elastic neutron scattering, and so a suitable technique for the investigation of low frequency molecular dynamics in fluids. We are using it to study liquids entrapped in a system of closely packed polystyrene beads and other porous mediums
It is also shown that the method can be used to measure the susceptibility magnetic field that appears at liquid-solid or liquid-tissue interfaces in porous medium or biological tissue. Due to a different dependence on the modulation period for the static and the pulsed magnetic field gradient, the spin echo attenuation provides the information about intrinsic magnetic field.
The question of a proper treatment of stochastic process with the self-diffusion spin-echo attenuation of confined particles is considered. Namely, the diffusion propagator approach with Einstein's approximation of the velocity correlation function (VCF) (delta function), is adequate only for particle displacements much smaller than the size of the confinement. It is shown that interplay of the motional correlation dynamics and the boundary conditions is taking place for large diffusion displacements. The results of calculation have been compared with simulation and experiments on the edge enhancement by magnetic resonance imaging (MRI) of a pore.
The parallel measurements of setting time during the early hydration on PC cements was performed by the standard Vicat apparatus and by the home-made pulsed ultrasonic shear wave reflection USWR-2 Hardening meter. The measurements were carried out on the same samples and under the same ambient conditions. In contrast with Vicat needle test, the USWR method gives a continuous information of the stiffening and hardening process with the time via reflection changes as the rigidity of the pastes grows on hydration. The magnitudes of change in selected cement pastes (CEM I 52.5R and PC 30dz 45s) at Vicat setting times are used to determine the correlation between the two methods. With such a calibration, the setting times of production samples can be satisfactorily measured with the USWR method.
