University of Bordeaux

About: University of Bordeaux is a education organization based out in Bordeaux, France. It is known for research contribution in the topics: Population & Laser. The organization has 28811 authors who have published 55536 publications receiving 1619635 citations. The organization is also known as: UB.

Towards a Fundamental Understanding of the Improved Electrochemical Performance of Silicon–Carbon Composites†

Abstract: Silicon–carbon composites consisting of Si particles embedded in a dense and non-porous carbon matrix are prepared by the pyrolysis of intimate mixtures of poly(vinyl chloride) (PVC) and Si powder at 900 °C under a flow of N2. In contrast to bare micrometer-sized (1–10 μm) and nanometer-sized (10–100 nm) Si powders, which show poor cycling behavior with almost no capacity remaining after 15 cycles, the texture of the composite is seen to greatly enhance the reversibility of the alloying reaction of Si with Li. For instance, a capacity of ca. 1000 mA h g–1 is achieved for 20 cycles (0–2.0 V vs. Li+/Li) for a silicon–carbon composite containing nanometer-sized Si particles. We also demonstrate that a mild manual grinding treatment degrades the cycling performance of the composites to levels as low as the parent Si, even though free Si is not released. The electrochemical measurements in conjunction with Raman spectroscopy data indicate that a huge stress is exerted on the Si domains by the in situ formed carbon. This carbon-induced stress is found to disappear during the milling of the composites, indicating that the carbon-induced pressure, along with the accompanying improvement in electrical connectivity, are the key parameters for the improved cycling behavior of Si versus Li.

Postoperative atrial fibrillation: mechanisms, manifestations and management.

Abstract: Postoperative atrial fibrillation (POAF) complicates 20-40% of cardiac surgical procedures and 10-20% of non-cardiac thoracic operations. Typical features include onset at 2-4 days postoperatively, episodes that are often fleeting and a self-limited time course. Associated adverse consequences of POAF include haemodynamic instability, increased risk of stroke, lengthened hospital and intensive care unit stays and greater costs. Underlying mechanisms are incompletely defined but include intraoperative and postoperative phenomena, such as inflammation, sympathetic activation and cardiac ischaemia, that combine to trigger atrial fibrillation, often in the presence of pre-existing factors, making the atria vulnerable to atrial fibrillation induction and maintenance. A better understanding of the underlying mechanisms might enable the identification of new therapeutic targets. POAF can be prevented by targeting autonomic alterations and inflammation. β-Blocker prophylaxis is the best-established preventive therapy and should be started or continued before cardiac surgery, unless contraindicated. When POAF occurs, rate control usually suffices, and routine rhythm control is unnecessary; rhythm control should be reserved for patients who develop haemodynamic instability or show other indications that rate control alone will be insufficient. In this Review, we summarize the epidemiological and clinical features of POAF, the available pathophysiological evidence from clinical and experimental investigations, the results of prophylactic and therapeutic approaches and the consensus recommendations of various national and international societies.