Rheological properties of fresh and cryopreserved human arteries tested in vitro

Cryopreservation is widely used to preserve blood vessels for a while but is controversially suspected to affect the mechanical behavior of these allografts. The aim of this study was to determine whether differences in the three-dimensional mechanical behavior exist or not between fresh and cryopreserved arteries. Using a previously developed experimental system, in vitro inflation tests were performed on twenty segments of human fresh and cryopreserved arteries, in static conditions. Opening angles were also measured from images of rings in zero-stress state. The initial reference state was chosen as the unloaded state and tests were performed on specimens stretched at natural “in vivo” length. Mechanical measures calculated are “natural” (Hencky) strains (finite deformations), “true” (Cauchy) stresses in radial, circumferential, and longitudinal directions as well as strain energy per unit volume. Tangent moduli are derived from radial and circumferential stress-strain characteristics using non-linear curve fitting. Values of incremental and pressure-strain elastic parameters, wall stiffness, and compliance per unit length are also calculated. Results are presented in terms of characteristics of stresses and strains in the three directions, axial force, tangent moduli vs strains or stresses, and energy per unit volume, for both types of artery, with reference to transmural pressure. Detailed numerical results are given at mean transmural pressure or in the physiological range. Significant differences are indicated by statistic Student T-tests. Results obtained show that significant differences exist between rheological properties of fresh and cryopreserved segments of human artery. Strains, stresses, axial force, strain energy, and wall stiffness values highlight those differences whereas elastic parameters, compliance, and opening angle do not. The usefulness of some parameters to compare the mechanical behavior existing between fresh and cryopreserved arteries is therefore underlined. Received: 3 January 2000 Revision received: 12 April 2000 Accepted: 8 May 2000     

Energy levels of paramagnetic ions: Algebra. IV. The case of fN ions in cubical symmetry

The symmetry-adapted formalism and the weak-field model described in the first three papers of this series are applied to the case of a configuration nf^N in octahedral symmetry. In this case, the latter weakfield model is restricted to a 30-parameter model which accounts for isotropic and anisotropic Coulomb (repulsion) interactions, isotropic and anisotropic spin-orbit interactions, and crystal-field interactions. A comparison between this 30-parameter weak-field model and a 33-parameter strong-field model is established. Equivalence between these two models requires three constraint relations to be satisfied for some strong-field parameters. The three relations are examined on various viewpoints.     

White-light toxicity, resulting from systemically administered 5-aminolevulinic acid, under normal operating conditions

This study has investigated damage to the intraperitoneal organs of the rat after systemic (intraperitoneal and intravenous) administration of low doses of 5-aminolevulinic acid (ALA) and illumination with a standard white-light operating-room (o.r.) lamp. The study has been done within the framework of a larger study in which the possibility of using ALA for localization of small-volume macroscopically nonvisible peritoneal metastasis of ovarian tumors is being investigated. Fluorescence diagnostics are done in addition to the standard staging and localization procedures, either through a laparoscope or during laparotomy. In these circumstances, fluorescence diagnostics involve some risk of photosensitization of critical organs since a broad-band (o.r.) light source is used during the surgical procedures for illumination of the operating area. The drug dose and the time interval between administration of ALA and illumination are varied and normal tissues are examined both macroscopically and microscopically for damage. A relationship is demonstrated between the maximum tolerable dose (MTD) of ALA (defined as the dose that does not cause any tissue damage) and the time interval between administration and illumination. The white light that is used for illumination of the operating area is sufficient to induce damage to the peritoneal organs at relatively low ALA doses. The MDTs for 2, 6 and 16 h intervals are found to be respectively 1, 10 and 100 mg kg⁻¹. The results are similar for both intraperitoneal and intravenous administration.     

Batch processing with interval graph compatibilities between tasks

We analyze batch-scheduling problems that arise in connection with certain industrial applications. The models concern processing on a single max-batch machine with the additional feature that the tasks of the same batch have to be compatible. Compatibility is a symmetric binary relation—the compatible pairs are described with an undirected “compatibility graph”, which is often an interval graph according to some natural practical conditions that we present. We consider several models with varying batch capacities, processing times or compatibility graphs. We summarize known results, and present a min-max formula and polynomial time algorithms.     

Die gleichzeitige Bestimmung von Methylalkohol und Formaldehyd in sehr kleinen Mengen in ein und derselben L?sung

Ohne Zusammenfassung     

Untersuchung von Seifen

Ohne Zusammenfassung     

Les dimensions d'un ensemble abstrait

Sans résumé     

Unusual reactivity of bicyclo[2.2.1]heptene derivatives during the ozonolysis. Part 2

The ozonation of four bornene derivatives, prepared from (R)-(+)-pulegone, which possess a particularly hindered double bond, led to the formation of unexpected products depending on the nature of the solvent. The formation of the corresponding epoxides, ketones with the same skeleton, various lactones and even an allyl alcohol and an allyl chloride (allylic functionalisation) was observed. In two cases, products presenting a pulegone modified skeleton resulting from a Wagner-Meerwein rearrangement were obtained. The structure of three products was confirmed by crystallographic X-ray analysis. Mechanisms taking into account the rigid and congested structure of the reactants explain these results. The most striking steps were backed up by theoretical calculations.