Reversed size-dependent stabilization of ordered nanophases.

The size increase of a nanoscale material is commonly associated with the increased stability of its ordered phases. Here we give a counterexample to this trend by considering the formation of the defect-free L11 ordered phase in AgPt nanoparticles, and showing that it is better stabilized in small nanoparticles (up to 2.5 nm) than in larger ones, in which the ordered phase breaks in multiple domains or is interrupted by faults. The driving force for the L11 phase formation in small nanoparticles is the segregation of a monolayer silver shell (an Ag-skin) which prevents the element with higher surface energy (Pt) from occupying surface sites. With increasing particle size, the Ag-skin causes internal stress in the L11 domains which cannot thus exceed the critical size of ~2.5 nm. A multiscale modelling approach using full-DFT global optimization calculations and atomistic modelling is used to interpret the findings.

[Control of diabetes in the perioperative period]. / Le contrôle du diabète en période périopératoire.

Surgical procedure and anaesthesia commonly induce severe diabetes maladjustment. In these circumstances, optimal insulin administration is crucial and has been shown to prevent hyperglycaemia which is mostly due to insulin-counteracting hormones. We report the results obtained in 12 diabetic patients treated with a new method during various surgical procedures. The method consists of constant rate intravenous administration of a 5% glucose solution associated with intravenous insulin infusion delivered by an electric syringe at the rate of 1/2 U of insulin per hour for each glycaemic variation of 50 mg/dl. With this simple method, blood glucose concentrations remain close to physiological levels, and no hypoglycaemia occurs.

[Degenerative diabetic complications. Is persistent hyperglycemia more dangerous than wide glycemic fluctuations? (author's transl)]. / Complications dégénératives du diabète. Une hyperglycémie stable est-elle plus dangereuse que d'amples fluctuations glycémiques?

Consistant data drawn from animal experiments and from clinical statistics have shown the diabetic specific complications (neuropathy and microangiopathy) to be closely related to the hyperglycemic component of diabetes mellitus. Working directly or through more complicated biochemical disorders, high levels of blood glucose interfer with the metabolism of the lens, the retina and the peripheral axon (leading to cataracts, retinopahy, and neuropathy). High blood sugar also alters the metabolism of endothelial and blood cells as well as the composition of plasma proteins. Wall and content of the minute vessels are both affected resulting in disturbed local blood flows and hypoxic areas. Various intertricated mechanisms have been discovered. Some of them initiate vicious circles leading to self-supported functional and later on, morphological abnormalities of diabetic microangiopathy (retinopathy, glomerulosclerosis, etc., etc.). High blood sugar exerts its influence (directly or not) in terms of duration and intensity (hours per day, days per year). There are good reasons to believe that persistent hyperglycemia uninterrupted throughout the day is much more harmful than high peaks alternating with periods of normo- and even hypoglycemia. There is no experimental nor clinical data pointing to glycemic instability as a risk factor for the minute vessels and the nerves, and opinion still often hold in some quarters. Although undesirable, frequent bouts of hypoglycemia associated with insulin treatment are indices that a rather good glycemic control has been achieved. And this can greatly delay the development of specific complications.