Critical behavior of a fluid in a disordered porous matrix: An Ornstein-Zernike approach

Using a liquid-state approach based on Ornstein-Zernike equations, we study the behavior of a fluid inside a porous disordered matrix near the liquid-gas critical point.The results obtained within various standard approximation schemes such as lowest-order $\gamma$-ordering and the mean-spherical approximation suggest that the critical behavior is closely related to that of the random-field Ising model (RFIM).Comment: 10 pages, revtex, to appear in Physical Review Letter

Why can pulmonary vein stenoses created by radiofrequency catheter ablation worsen during and after follow-up ? A potential explanation

<p>Abstract</p> <p>Background</p> <p>Radiofrequency catheter ablation of excitation foci inside pulmonary veins (PV) generates stenoses that can become quite severe during or after the follow-up period. Since severe PV stenoses have most often disastrous consequences, it would be important to know the underlying mechanism of this temporal evolution. The present study proposes a potential explanation based on mechanical considerations.</p> <p>Methods</p> <p>we have used a mathematical-physical model to examine the cyclic increase in axial wall stress induced in the proximal (= upstream), non-stenosed segment of a stenosed pulmonary vein during the forward flow phases. In a representative example, the value of this increase at peak flow was calculated for diameter stenoses (DS) ranging from 1 to 99%.</p> <p>Results</p> <p>The increase becomes appreciable at a DS of roughly 30% and rise then strongly with further increasing DS value. At high DS values (e.g. > 90%) the increase is approximately twice the value of the axial stress present in the PV during the zero-flow phase.</p> <p>Conclusion</p> <p>Since abnormal wall stresses are known to induce damages and abnormal biological processes (e.g., endothelium tears, elastic membrane fragmentations, matrix secretion, myofibroblast generation, etc) in the vessel wall, it seems plausible that the supplementary axial stress experienced cyclically by the stenotic and the proximal segments of the PV is responsible for the often observed progressive reduction of the vessel lumen after healing of the ablation injury. In the light of this model, the only potentially effective therapy in these cases would be to reduce the DS as strongly as possible. This implies most probably stenting or surgery.</p

Propriétés magnétiques des nitrures mixtes de vanadium et de chrome VxCr1-x N

For the FCC nitrides of the first transition series, a discontinuity exists between vanadium nitride which is a paramagnetic metal, and chromium nitride which is an antiferromagnet, and most probably an insulator when pure. The study of the magnetic properties of mixed VN-CrN alloys reveals on one side, for chromium rich alloys, a magnetic phase which is identical to the magnetic phase for CrN, on the other side, for vanadium rich alloys (between 30 and 50 % chromium) another phase which might be a magnetic glass, in which chromium atoms do not show long range magnetic ordering. Complex phenomena show up in between, around the V0,25Cr0,75N composition, which could be interpreted in terms of an ordering of metallic atoms.Pour les nitrures CFC de la première série de transition, une discontinuité apparaît entre le nitrure de vanadium, qui est un métal paramagnétique et le nitrure de chrome, qui est antiferromagnétique et sans doute isolant à l'état pur. L'étude du magnétisme des nitrures mixtes VN-CrN montre, d'une part pour les alliages riches en chrome une phase magnétique identique à celle qui apparaît en dessous de la température ambiante pour CrN, d'autre part pour les alliages riches en vanadium (30 à 50 % de chrome) une autre phase qui pourrait être un verre magnétique, dans lequel les atomes de chrome ne s'organisent pas à grande distance. Des phénomènes complexes apparaissent entre ces deux domaines au voisinage de la composition V 0,75Cr0,25N qui pourraient s'interpréter à partir d'un ordre des atomes métalliques