Biomedical subjects

Ph Germain

Publications and source records attributed to Ph Germain.

4 recordsLinked to original sources

PubMed2004

When mixtures of hard-sphere-like colloids do not behave as mixtures of hard spheres.

The validity of the concept of "hard-sphere-like" particles for mixtures of colloids is questioned from a theoretical point of view. This concerns the class of pseudobinary mixtures in which the nonsteric interactions between the colloids are "residual" (with very small range and moderate strength). It is shown that contrary to common expectation, such interactions may have unexpected consequences on the theoretical phase diagram. The distinction between this situation and true solute-solvent mixtures is emphasized.

Journal Article↗

PubMed2003

Is the binary hard-sphere mixture a good reference system for sterically stabilized colloids?

The relevance of the hard-sphere mixture model as a starting point for the study of sterically stabilized colloids is discussed. Two physical situations are distinguished: true molecular solvent-colloid mixtures, and pseudobinary mixtures of two supramolecular objects. For the former, the limitation of the hard-sphere mixture model are recalled. Its potential use as a reference system for perturbation treatments is then analyzed. The accuracy of the latter is tested numerically. This study shows that the hard-sphere mixture is, in general, not a good reference system for sterically stabilized colloids in molecular solvents. For pseudobinary mixtures, the potential of mean force between the bigger solutes induced by the smaller ones is considered. The influence of a very short-range heteroattraction is discussed.

Journal Article↗

PubMed2002

Validity of the perturbation theory for hard particle systems with very-short-range attraction.

Motivated by recent studies of colloidal systems at the effective one-component level, the validity of the first-order perturbation theory of classical systems of hard particles interacting via short-range potentials is investigated. The influence of the physical parameters on the accuracy of the perturbation theory is examined. It is shown that this simple method is intrinsically appropriate to describe the fluid-solid transition. Concerning the fluid-fluid one, the first-order perturbation theory provides acceptable results when the interaction range is not too small. For very-short-range potentials it systematically leads to an unphysical fluid-fluid transition. In the case of the depletion interaction between hard sphere solutes such a transition is found even at moderate size asymmetry. It is finally shown that the perturbation theory is not more appropriate for an extended solid than for a liquid with the same density, thus making difficult a quantitative description of the isostructural solid-solid transition.

Journal Article↗

PubMed2002

[Value and limitations of coronary artery imaging with the MRI navigator technique. Comparison with coronary angiography results in 37 patients].

The introduction of a non-invasive method of imaging the coronary arteries would be a great advance in daily cardiological practice. The authors report their experience of imaging the coronary arteries with 1 Tesla MRI using the "navigator technique". Twenty-five sections 1.2 mm thick, focused on the proximal left coronary artery, were acquired with a 512 matrix, without injecting contrast during normal respiration with a tolerance on the portion of the right diaphragmatic cupola of 5 mm. Analysis of the coronary segments included in the field of view was performed on native sections after curve reconstruction and on targetedMIP series. A comparison of the results with respect to conventional coronary angiography showed a relatively limited visualisation of the proximal coronary segments because, in addition to the impossibility of carrying out the investigation in 24% of cases (faulty cardiac or respiratory synchronisation, poor signal/noise ratio), only 93% of the left main coronary and 75% of the proximal left anterior descending arteries could be visualised. In the analyzable segments, the diagnostic performances were modest with a global sensitivity of 60.8% and specificity of 91%. With the exception of the left main coronary artery, the sensitivities observed did not make MRI of the coronary arteries a rival to conventional coronary angiography. These limited performances may be explained by the lack of rapidity of the sequences of acquisition compared to the rapid motion of the structures under investigation whose dimensions are 5 to 10 times smaller than their amplitude of excursion. Technical developments are regularly accomplished in this domain, especially 3rd generation sequences in apnoea with injection of contrast media. At present, despite some results reported in the literature, angio-MRI of the coronary arteries cannot be used reliably to guide clinical decisions in coronary artery disease with the exception of some situations like congenital abnormalities of the coronary arteries, non-invasive follow-up of coronary aneurysms or analysis of the left main coronary artery.

Coronary Aneurysm↗