As part of the development of a methodology for investigating flow and transport in fractured rocks, a large‐scale experiment was recently performed at Fanay‐Augères, France. In a companion paper (Cacas et al., this issue) (paper 1) the results of the flow measurements were analyzed. In this paper, the results of the tracer experiments are interpreted. A particle following is coupled to the flow model, described in paper 1. Microscopic dispersion in the fractures and retardation effects due to unevenness of the flow paths are taken into account. The transport model is calibrated on in situ tracer tests, whereas the parameters of the hydraulic model were initially fitted on structural and hydraulic measurements (paper 1). The dispersive properties of the model are reasonably comparable to those of the real site. It tends to confirm the validity of the preliminary hydraulic calibration of the model and thus to validate further the approach used to simulate hydraulic and transport phenomena.
The electron spin-lattice relaxation time T1 of V 4+ in amorphous V2O5 has been measured in the X-band between 1.4 K and 100 K : [FORMULA]. We explain this behaviour using a process requiring one two-level system (T.L.S.) modulating the crystal field, and one phonon. The characteristic temperature 56 K must be associated not with the maximum energy of the T.L.S. but with the cut-off in the distribution of the asymmetry parameter Δ. Spin-lattice relaxation is thus able to give informations about the asymmetry
Résumé. 2014 ( 1 / T 1 0 3 B 1 T 7 I 6 ( 1 6 8 / T ) ) . Abstract. 2014 The relaxation behaviour of Mn2+ in cubic ZnS has been studied between 1.3 and 135 K, at 9.3 GHz, with a pulse saturation method. At low temperatures, the variation of the recovery signal with the saturating pulse duration indicates that the system acquires a spin-temperature before relaxing. The diffusion process maintaining the spin-temperature is temperature independent and has a time constant TD = 0.5 ms. Complementary studies using a fast field sweep technique confirm that the whole system of 30 EPR lines acquires a spin temperature. When T 10 K, relaxation takes place via a direct process, and T1 T = 1.18 Ks. When T1 > 10 K, we observe a Raman process ( 1 / T 1 ~ T I 6 ( 1 6 8 / T ) ) .In the case of the direct process, relaxation is well described by a dynamic hamiltonian deduced from uniaxial stress measurements. A determination of the Raman contribution to relaxation made with Van Vleck's normal mode formalism leads to a T1 value which is an order of magnitude greater than the experimental value. In both cases tranverse phonons are the most efficient.
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