Structural Investigations of the α12\alpha_{12} Si-Ge Superstructure

This article reports the X-ray diffraction-based structural characterization of the [alpha]12 multilayer structure SiGe2Si2Ge2SiGe12 [d'Avezac, Luo, Chanier & Zunger (2012). Phys. Rev. Lett. 108, 027401], which is predicted to form a direct bandgap material. In particular, structural parameters of the superlattice such as thickness and composition as well as interface properties, are obtained. Moreover, it is found that Ge subsequently segregates into layers. These findings are used as input parameters for band structure calculations. It is shown that the direct bandgap properties depend very sensitively on deviations from the nominal structure, and only almost perfect structures can actually yield a direct bandgap. Photoluminescence emission possibly stemming from the superlattice structure is observed

New insights on the kinetic analysis of isothermal data: The independence of the activation energy from the assumed kinetic model

© 2014 American Chemical Society. Isothermal experiments are widely employed to study the kinetics of solid-state reactions or processes to extract essential kinetic information needed for modeling the processes at an industrial scale. The kinetic analysis of isothermal data requires finding or assuming a kinetic function that can properly fit the evolution of the reaction rate with time, so that the resulting parameters, i.e., the activation energy and pre-exponential factor, can be considered reliable. In the present work, we demonstrate using both simulated and experimental data that the kinetic analysis of a set of isothermal plots obtained at different temperatures, considering a single-step solid-state reaction, necessarily leads to the real activation energy, regardless the mathematical function selected for performing the kinetic analysis. This makes irrelevant the election of the kinetic function used to fit the experimental data and greatly facilitates the estimation of the activation energy for any single process.Peer Reviewe

The prevalence of antibiotic resistance to polymyxins in clinical isolates of acinetobacter baumannii in Iran and the world: A systematic review and meta-analysis

Background: Acinetobacter baumannii is one of the most important opportunistic pathogens responsible for several nosocomial infections. A major problem in treatment is antibiotic resistance. Methods: By searching international and national databases, including PubMed, Google Scholar, Web of Science, SID, Magiran, IranDoc and IranMedex, 38 articles between years 2002 to 2016 published world-wide were extracted and analyzed using the meta-analysis method and random effects model. The heterogeneity of studies was assessed using the I2 index. Data were analyzed with the R and STATA (Ver 11/2) software. Results: Forty-three articles were selected for this study. Drug-resistance of Acinetobacter baumannii towards Polymyxin was reported as 5, yet for Colistin 4 was estimated. Resistance rates to Polymyxin and Colistin in the continent of America and Asia was 6 and Sensitivity rate to Polymyxin and Colistin was 96 and 80, respectively. Conclusions: Given that drug resistance rate of Acinetobacter baumannii to Polymyxin and Colistin in this study was 5 and 4, respectively, thus indicating high sensitivity of Acinetobacter baumannii to these antibiotics, this group can be administered as appropriate therapeutic agents against these bacteria. © 2017, Shiraz E-Medical Journal