Biomedical subjects

Ioan Ardelean

Publications and source records attributed to Ioan Ardelean.

3 recordsLinked to original sources

PubMed2005

NMR study of the vapor phase contribution to diffusion in partially filled silica glasses with nanometer and micrometer pores.

The contribution of the vapor phase to molecular diffusion in porous silica glasses with nanometer (Vycor) and micrometer (VitraPor#5) pores partially filled with water (polar) or cyclohexane (nonpolar) was investigated with the aid of field-gradient NMR diffusometry. Due to the vapor phase, the effective diffusion coefficient of cyclohexane filling micrometer pores (VitraPor#5) increased up to 10 times relative to the value in bulk liquid upon reduction of the pore space filling factor. On the other hand, the effective diffusion coefficient of water first decreases and then increases when the liquid content is reduced. The dependence of the effective diffusion coefficient on the pore filling factor is strongly related to the pore dimension. A general two-phase exchange model is presented that is well accounting for all experimental diffusion features.

Cyclohexanes↗

PubMed2004

Nuclear magnetic resonance study of the vapor contribution to diffusion in silica glasses with micrometer pores partially filled with liquid cyclohexane or water.

The contribution of the vapor phase to molecular diffusion in porous silica glass (Vitrapor#5; mean pore diameter 1 micrometer) partially filled with cyclohexane (nonpolar) or water (polar) was investigated with the aid of field-gradient NMR diffusometry. Due to the vapor phase, the effective diffusion coefficient of cyclohexane increased up to ten times relative to the value in bulk liquid upon reduction of the pore space filling factor. On the other hand, the effective diffusion coefficient of water first decreases and then increases when the liquid content is reduced. A two-phase exchange theory is presented accounting well for all experimental diffusion features. The diffusion behavior in the samples with micrometer pores under investigation here is in contrast to previous findings for the same solvents in a material with nanometer pores (Vycor; mean pore diameter 4 nm) where the fast-exchange limit had to be assumed [Ardelean et al., J. Chem. Phys. 119, 10358 (2003)]. It is concluded that the pore size plays a crucial role for the relevance of molecular exchange limits relative to the experimental diffusion/exchange time.

Journal Article↗

PubMed2004

NMR acceleration mapping in percolation model objects.

An NMR microscopy technique is described that permits direct mapping of local accelerations. The method is tested with water flow through a random site percolation model object and compared with computational fluid dynamics simulations. A general formalism, the "polygon rule," is reported for the design of gradient pulse sequences for phase encoding of higher order motions, or, in other words, for compensation of phase shifts by lower motional orders.

Journal Article↗