The physics of dynamical atomic charges: the case of ABO3 compounds

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader...) or dynamical (Callen, Szigeti...). It is shown that static and dynamical charges are not driven by the same underlying parameters. A unified treatment of dynamical charges in periodic solids and large clusters is proposed. The origin of the difference between static and dynamical charges is discussed in terms of local polarizability and delocalized transfers of charge: local models succeed in reproducing anomalous effective charges thanks to large atomic polarizabilities but, in ABO3 compounds, ab initio calculations favor the physical picture based upon transfer of charges. Various results concerning barium and strontium titanates are presented. The origin of anomalous Born effective charges is discussed thanks to a band-by-band decomposition which allows to identify the displacement of the Wannier center of separated bands induced by an atomic displacement. The sensitivity of the Born effective charges to microscopic and macroscopic strains is examined. Finally, we estimate the spontaneous polarization in the four phases of barium titanate.Comment: 25 pages, 6 Figures, 10 Tables, LaTe

Micromechanical Properties of Injection-Molded Starch–Wood Particle Composites

The micromechanical properties of injection molded starch–wood particle composites were investigated as a function of particle content and humidity conditions. The composite materials were characterized by scanning electron microscopy and X-ray diffraction methods. The microhardness of the composites was shown to increase notably with the concentration of the wood particles. In addition,creep behavior under the indenter and temperature dependence were evaluated in terms of the independent contribution of the starch matrix and the wood microparticles to the hardness value. The influence of drying time on the density and weight uptake of the injection-molded composites was highlighted. The results revealed the role of the mechanism of water evaporation, showing that the dependence of water uptake and temperature was greater for the starch–wood composites than for the pure starch sample. Experiments performed during the drying process at 70°C indicated that the wood in the starch composites did not prevent water loss from the samples.Peer reviewe

Acute kidney injury in high-risk cardiac surgery patients: Roles of inflammation and coagulation

Aims Acute kidney injury (AKI) is a common complication following cardiac surgery. Cardiopulmonary bypass elicits coagulation and inflammation activation and oxidative stress, all involved in AKI but never simultaneously assessed. We aimed to evaluate relations between oxidative stress, inflammatory and coagulation systems activation and postoperative renal function in patients with normal preoperative renal function. Methods Forty-one high-risk patients (EuroSCORE >6 and preoperative haemoglobin <12 g/dl in women and <13g/dl in men) were prospectively enrolled. Prothrombin fragment 1.2 (coagulation marker), interleukin-6 and interleukin-10 (pro/anti-inflammatory markers) and 8-oxo-20-deoxyguanosine (oxidative stress marker) were evaluated until postoperative day 5. Results Patients were divided into two groups according to estimated glomerular filtration rate reduction observed postoperatively (reduction <25% in 26 patients: NO-AKI group; reduction >25% in 15 patients: AKI group). No differences were found for inflammatory markers. Oxidative stress slightly increased in the AKI group. Twenty-four hours after the operation prothrombin fragment 1.2 levels were significantly higher in the AKI group (506.6 W548 vs. 999 W 704.1 pmol/l; P =0.018), and they were independently associated with estimated glomerular filtration rate reduction, with an area under the receiving operating characteristic of 0.744. Conclusion Thrombin generation is higher in patients with renal function worsening, and it is an independent risk factor for AKI in patients with anaemia, possibly leading to microcirculation impairment and tubular cells damage