Influence of ageing heat treatment on microstructure of aluminum silicon alloy

RESUMEN: Aleaciones de aluminio silicio (Al-Si) fundidas con contenido de otros aleantes como Cu y Mg se vuelven susceptibles al tratamiento térmico de solubilización y envejecimiento con el cual pueden mejorar las propiedades mecánicas y se amplía su gama de aplicaciones. Se presentan los resultados del efecto del tratamiento térmico de solubilización y envejecimiento de una aleación de aluminiosilicio (Al-Si), sobre la microestructura. Para la obtención de las muestras se utilizó un horno eléctrico de crisol para la fundición. El vaciado se hizo en moldes de arena en verde para obtener bloques en Y. En la parte inferior de los moldes se insertó un enfriador para direccionar la solidificación y para generar una variación en el tamaño de grano. Se analizaron muestras tanto de la zona cercana como alejada del enfriador, las cuales poseían tamaños de grano diferentes. Las muestras se solubilizaron a 510°C por un tiempo de 8 horas y posteriormente se envejecieron artificialmente a 160°C por 4, 8, 12 y 16 horas. Se realizó una caracterización microestructural utilizando microscopía óptica (OM) y microscopia electrónica de barrido (MEB) además de la medición de dureza Vickers. Los resultados permitieron determinar el efecto de las condiciones de solubilización y envejecimiento, sobre la microestructura final obtenida y la dureza de la aleación.ABSTRACT: Aluminum-silicon (Al-Si) cast alloys with Mg and Cu has susceptibility to solution and ageing heat treatments that improve the mechanical properties and its application is expands. This paper presents the results of the study of the effect of solution and ageing heat treatments of an aluminumsilicon (Al-Si) alloy on microstructure. The alloy was produced using an electric crucible furnace and poured into green sand molds to obtain Y blocks. A chiller was placed in the bottom of the mold to get directional solidification, which generates a variation in grain size. Samples taken close and far from the chiller with different grain sizes were solubilized at 510°C for 8 hours and then artificially aged at 160°C for 4, 8, 12 and 16 hours. Microstructural characterization was performed using optical microscopy (MO) and scanning electron microscopy (SEM) techniques, and hardness measurement were performed. The results showed the effects of solution and ageing conditions, on the microstructure and hardness of the alloy

Antimicrobial Lessons From a Large Observational Cohort on Intra-abdominal Infections in Intensive Care Units

evere intra-abdominal infection commonly requires intensive care. Mortality is high and is mainly determined by disease-specific characteristics, i.e. setting of infection onset, anatomical barrier disruption, and severity of disease expression. Recent observations revealed that antimicrobial resistance appears equally common in community-acquired and late-onset hospital-acquired infection. This challenges basic principles in anti-infective therapy guidelines, including the paradigm that pathogens involved in community-acquired infection are covered by standard empiric antimicrobial regimens, and second, the concept of nosocomial acquisition as the main driver for resistance involvement. In this study, we report on resistance profiles of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis and Enterococcus faecium in distinct European geographic regions based on an observational cohort study on intra-abdominal infections in intensive care unit (ICU) patients. Resistance against aminopenicillins, fluoroquinolones, and third-generation cephalosporins in E. coli, K. pneumoniae and P. aeruginosa is problematic, as is carbapenem-resistance in the latter pathogen. For E. coli and K. pneumoniae, resistance is mainly an issue in Central Europe, Eastern and South-East Europe, and Southern Europe, while resistance in P. aeruginosa is additionally problematic in Western Europe. Vancomycin-resistance in E. faecalis is of lesser concern but requires vigilance in E. faecium in Central and Eastern and South-East Europe. In the subcohort of patients with secondary peritonitis presenting with either sepsis or septic shock, the appropriateness of empiric antimicrobial therapy was not associated with mortality. In contrast, failure of source control was strongly associated with mortality. The relevance of these new insights for future recommendations regarding empiric antimicrobial therapy in intra-abdominal infections is discussed.Severe intra-abdominal infection commonly requires intensive care. Mortality is high and is mainly determined by diseasespecific characteristics, i.e. setting of infection onset, anatomical barrier disruption, and severity of disease expression. Recent observations revealed that antimicrobial resistance appears equally common in community-acquired and late-onset hospital-acquired infection. This challenges basic principles in anti-infective therapy guidelines, including the paradigm that pathogens involved in community-acquired infection are covered by standard empiric antimicrobial regimens, and second, the concept of nosocomial acquisition as the main driver for resistance involvement. In this study, we report on resistance profiles of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis and Enterococcus faecium in distinct European geographic regions based on an observational cohort study on intra-abdominal infections in intensive care unit (ICU) patients. Resistance against aminopenicillins, fluoroquinolones, and third-generation cephalosporins in E. coli, K. pneumoniae and P. aeruginosa is problematic, as is carbapenem-resistance in the latter pathogen. For E. coli and K. pneumoniae, resistance is mainly an issue in Central Europe, Eastern and South-East Europe, and Southern Europe, while resistance in P. aeruginosa is additionally problematic in Western Europe. Vancomycin-resistance in E. faecalis is of lesser concern but requires vigilance in E. faecium in Central and Eastern and South-East Europe. In the subcohort of patients with secondary peritonitis presenting with either sepsis or septic shock, the appropriateness of empiric antimicrobial therapy was not associated with mortality. In contrast, failure of source control was strongly associated with mortality. The relevance of these new insights for future recommendations regarding empiric antimicrobial therapy in intra-abdominal infections is discussed

Poor timing and failure of source control are risk factors for mortality in critically ill patients with secondary peritonitis

Purpose: To describe data on epidemiology, microbiology, clinical characteristics and outcome of adult patients admitted in the intensive care unit (ICU) with secondary peritonitis, with special emphasis on antimicrobial therapy and source control. Methods: Post hoc analysis of a multicenter observational study (Abdominal Sepsis Study, AbSeS) including 2621 adult ICU patients with intra-abdominal infection in 306 ICUs from 42 countries. Time-till-source control intervention was calculated as from time of diagnosis and classified into 'emergency' (< 2 h), 'urgent' (2-6 h), and 'delayed' (> 6 h). Relationships were assessed by logistic regression analysis and reported as odds ratios (OR) and 95% confidence interval (CI). Results: The cohort included 1077 cases of microbiologically confirmed secondary peritonitis. Mortality was 29.7%. The rate of appropriate empiric therapy showed no difference between survivors and non-survivors (66.4% vs. 61.3%, p = 0.1). A stepwise increase in mortality was observed with increasing Sequential Organ Failure Assessment (SOFA) scores (19.6% for a value ≤ 4-55.4% for a value > 12, p < 0.001). The highest odds of death were associated with septic shock (OR 3.08 [1.42-7.00]), late-onset hospital-acquired peritonitis (OR 1.71 [1.16-2.52]) and failed source control evidenced by persistent inflammation at day 7 (OR 5.71 [3.99-8.18]). Compared with 'emergency' source control intervention (< 2 h of diagnosis), 'urgent' source control was the only modifiable covariate associated with lower odds of mortality (OR 0.50 [0.34-0.73]). Conclusion: 'Urgent' and successful source control was associated with improved odds of survival. Appropriateness of empirical antimicrobial treatment did not significantly affect survival suggesting that source control is more determinative for outcome