Refinement of the Cast Microstructure of Hypereutectic Aluminum-Silicon Alloys with an Applied Electric Potential

Hypereutectic aluminum-silicon (Al-Si) alloys are widely used in the aerospace and automobile industries because of their low density, excellent wear and corrosion resistance, low coefficient of thermal expansion, good strength, and excellent castability. They are used in applications that typically require a combination of light weight and high wear resistance, such as liner-less engine blocks, pistons, and pumps. However, the performance of these alloys depends on the fineness of their cast microstructure, especially dendrite cell size, primary and eutectic silicon particles. In this study, the effects of applied electric current on the cast microstructure of Al-13 wt.% Si and Al-20 wt.% Si were investigated. This involved application of a steady electric current density of about 500 mA/cm2 during solidification of laboratory-size ingots in a metal mold. Microscopic examination of the cast ingots with a metallurgical microscope revealed that the applied electric refined the cast microstructure of the hypereutectic Al-Si alloys. Specifically, it appeared that the electric current changed the size distribution of the primary silicon particles by increasing the population of comparatively smaller size particles, although it did not affect the eutectic silicon particles. The applied electric current also decreased the average dendrite cell size. The extent of the observed cast microstructure refinement was less than the reported effects of applied electric current in the technical literature. It was also significantly less than the effects of traditional refinement obtained by addition of strontium and phosphorus to the molten hypereutectic Al-Si alloys prior to casting

Modeling fluid interactions with the rigid mush in alloy solidification

Macrosegregation is a casting defect characterized by long range composition differences on the length scale of the ingot. These variations in local composition can lead to the development of unwanted phases that are detrimental to mechanical properties. Unlike microsegregation, in which compositions vary over the length scale of the dendrite arms, macrosegregation cannot be removed by subsequent heat treatment, and so it is critical to understand its development during solidification processing. Due to the complex nature of the governing physical phenomena, many researchers have turned to numerical simulations for these predictions, but properly modeling alloy solidification presents a variety of challenges. Among these is the appropriate treatment of the interface between the bulk fluid and the rigid mushy zone. In this region, the non-linear and coupled behavior of heat transfer, fluid mechanics, solute transport, and alloy thermodynamics has a dramatic effect on macrosegregation predictions. This work investigates the impact of numerical approximations at this interface in the context of a mixture model for alloy solidification. First, the numerical prediction of freckles in columnar solidification is investigated, and the predictive ability of the model is evaluated. The model is then extended to equiaxed solidification, in which the analogous interface is the transition of free-floating solid particles to a rigid dendritic network. Various models for grain attachment are investigated, and found to produce significant artifacts caused by the discrete nature of their implementation on the numerical grid. To reduce the impact of these artifacts, a new continuum grain attachment model is proposed and evaluated. The differences between these models are compared using uncertainty quantification, and recommendations for future research are presented

Pintura acrílica: da crise da representação artística que favoreceu sua implantação no século XX às peculiaridades de sua conservação-restauração

A partir da primeira metade do século XX, a expressividade plástica de pintores de vanguarda do mundo ocidental foi enriquecida pela apropriação de tintas industriais em que resinas sintéticas foram utilizadas como aglutinante dos pigmentos. Essas novas tintas diferenciavam-se das tradicionais, à base de óleo, por características estéticas específicas e outras, de ordem prática, como maior resistência e estabilidade, reduzidos tempo de secagem, toxicidade e custo. A experimentação dessas novas tintas coincidiu com a mudança substancial no modo de entendimento das artes pictóricas: da reprodução figurativa da realidade para a arte abstrata, em que a figuração óbvia desapareceu e as tintas ganharam força própria. A partir de então, cores, formas e texturas deixaram de estar a serviço da imagem e tornaram-se a própria obra. Entre as novas tintas experimentadas, aquelas à base de dispersão acrílica obtiveram plena aceitação pelos artistas. Porém, sua presença em uma pintura, em substituição às tintas a óleo, repercute tanto na imprevisibilidade de como se dará o envelhecimento da obra quanto no planejamento de sua conservação. As tintas acrílicas têm mantido propriedades ópticas e mecânicas satisfatórias ao longo dos cerca de 60 anos decorridos desde seu lançamento, mas apresentam algumas características indesejadas, que podem comprometer sua conservação, como a tendência a absorver sujidades, a forte reatividade às variações de temperatura e umidade relativa do ar e a migração de surfactantes higroscópicos, adicionados às suas formulações, para a superfície da camada pictórica. Esse comportamento suscita preocupações sendo a principal delas a maneira como respondem aos tratamentos de limpeza, que podem resultar no aparecimento de manchas, áreas de abrasão ou de irregularidade do brilho da camada pictórica, alterações estas particularmente problemáticas em pinturas monocrômicas de grandes dimensões. Outro motivo de preocupação decorre da vulnerabilidade dos filmes acrílicos a solventes: rapidamente incham e dissolvem-se sob a ação de compostos polares. Também incham sob a ação de soluções aquosas. Como essas tintas são usadas há relativamente pouco tempo, os Conservadores-Restauradores tem pouca experiência para basear suas opiniões sobre o sucesso relativo de diferentes tratamentos. Muito preocupante é a tendência à adoção de procedimentos consagrados para a conservação-restauração de pinturas a óleo, tendência esta decorrente, em parte, da pouca disponibilidade de literatura específica. Por esse motivo, no último capítulo deste trabalho, foi feita a compilação de procedimentos utilizados por alguns profissionais para a conservação-restauração de pinturas acrílicas em nosso país

Forecasting the Student–Professor Matches that Result in Unusually Effective Teaching

Background. Two important influences on students’ evaluations of teaching are relationship and professor effects. Relationship effects reflect unique matches between students and professors such that some professors are unusually effective for some students, but not for others. Professor effects reflect inter-rater agreement that some professors are more effective than others, on average across students. Aims. We attempted to forecast students’ evaluations of live lectures from brief, video-recorded teaching trailers. Sample. Participants were 145 college students (74% female) enrolled in introductory psychology courses at a public university in the Great Lakes region of the United States. Methods. Students viewed trailers early in the semester and attended live lectures months later. Because subgroups of students viewed the same professors, statistical analyses could isolate professor and relationship effects. Results. Evaluations were influenced strongly by relationship and professor effects, and students’ evaluations of live lectures could be forecasted from students’ evaluations of teaching trailers. That is, we could forecast the individual students who would respond unusually well to a specific professor (relationship effects). We could also forecast which professors elicited better evaluations in live lectures, on average across students (professor effects). Professors who elicited unusually good evaluations in some students also elicited better memory for lectures in those students. Conclusions. It appears possible to forecast relationship and professor effects on teaching evaluations by presenting brief teaching trailers to students. Thus, it might be possible to develop online recommender systems to help match students and professors so that unusually effective teaching emerges

Pseudomonas aeruginosa toxin ExoU induces a PAF-dependent impairment of alveolar fibrin turnover secondary to enhanced activation of coagulation and increased expression of plasminogen activator inhibitor-1 in the course of mice pneumosepsis

<p>Abstract</p> <p>Background</p> <p>ExoU, a <it>Pseudomonas aeruginosa </it>cytotoxin with phospholipase A₂activity, was shown to induce vascular hyperpermeability and thrombus formation in a murine model of pneumosepsis. In this study, we investigated the toxin ability to induce alterations in pulmonary fibrinolysis and the contribution of the platelet activating factor (PAF) in the ExoU-induced overexpression of plasminogen activator inhibitor-1 (PAI-1).</p> <p>Methods</p> <p>Mice were intratracheally instilled with the ExoU producing PA103 <it>P. aeruginosa </it>or its mutant with deletion of the <it>exoU </it>gene. After 24 h, animal bronchoalveolar lavage fluids (BALF) were analyzed and lung sections were submitted to fibrin and PAI-1 immunohistochemical localization. Supernatants from A549 airway epithelial cells and THP-1 macrophage cultures infected with both bacterial strains were also analyzed at 24 h post-infection.</p> <p>Results</p> <p>In PA103-infected mice, but not in control animals or in mice infected with the bacterial mutant, extensive fibrin deposition was detected in lung parenchyma and microvasculature whereas mice BALF exhibited elevated tissue factor-dependent procoagulant activity and PAI-1 concentration. ExoU-triggered PAI-1 overexpression was confirmed by immunohistochemistry. In <it>in vitro </it>assays, PA103-infected A549 cells exhibited overexpression of PAI-1 mRNA. Increased concentration of PAI-1 protein was detected in both A549 and THP-1 culture supernatants. Mice treatment with a PAF antagonist prior to PA103 infection reduced significantly PAI-1 concentrations in mice BALF. Similarly, A549 cell treatment with an antibody against PAF receptor significantly reduced PAI-1 mRNA expression and PAI-1 concentrations in cell supernatants, respectively.</p> <p>Conclusion</p> <p>ExoU was shown to induce disturbed fibrin turnover, secondary to enhanced procoagulant and antifibrinolytic activity during <it>P. aeruginosa </it>pneumosepsis, by a PAF-dependent mechanism. Besides its possible pathophysiological relevance, <it>in vitro </it>detection of e<it>xoU </it>gene in bacterial clinical isolates warrants investigation as a predictor of outcome of patients with <it>P. aeruginosa </it>pneumonia/sepsis and as a marker to guide treatment strategies.</p

Evidence for Periciliary Liquid Layer Depletion, Not Abnormal Ion Composition, in the Pathogenesis of Cystic Fibrosis Airways Disease

The pathogenesis of cystic fibrosis (CF) airways infection is unknown. Two hypotheses, "hypotonic [low salt]/defensin" and "isotonic volume transport/mucus clearance," attempt to link defects in cystic fibrosis transmembrane conductance regulator–mediated ion transport to CF airways disease. We tested these hypotheses with planar and cylindrical culture models and found no evidence that the liquids lining airway surfaces were hypotonic or that salt concentrations differed between CF and normal cultures. In contrast, CF airway epithelia exhibited abnormally high rates of airway surface liquid absorption, which depleted the periciliary liquid layer and abolished mucus transport. The failure to clear thickened mucus from airway surfaces likely initiates CF airways infection. These data indicate that therapy for CF lung disease should not be directed at modulation of ionic composition, but rather at restoring volume (salt and water) on airway surfaces

Relation of exaggerated cytokine responses of CF airway epithelial cells to PAO1 adherence

In many model systems, cystic fibrosis (CF) phenotype airway epithelial cells in culture respond to P. aeruginosa with greater interleukin (IL)-8 and IL-6 secretion than matched controls. In order to test whether this excess inflammatory response results from the reported increased adherence of P. aeruginosa to the CF cells, we compared the inflammatory response of matched pairs of CF and non CF airway epithelial cell lines to the binding of GFP-PAO1, a strain of pseudomonas labeled with green fluorescent protein. There was no clear relation between GFP-PAO1 binding and cytokine production in response to PAO1. Treatment with exogenous aGM1 resulted in greater GFP-PAO1 binding to the normal phenotype compared to CF phenotype cells, but cytokine production remained greater from the CF cell lines. When cells were treated with neuraminidase, PAO1 adherence was equalized between CF and nonCF phenotype cell lines, but IL-8 production in response to inflammatory stimuli was still greater in CF phenotype cells. The polarized cell lines 16HBEo-Sense (normal phenotype) and Antisense (CF phenotype) cells were used to test the effect of disrupting tight junctions, which allows access of PAO1 to basolateral binding sites in both cell lines. IL-8 production increased from CF, but not normal, cells. These data indicate that increased bacterial binding to CF phenotype cells cannot by itself account for excess cytokine production in CF airway epithelial cells, encourage investigation of alternative hypotheses, and signal caution for therapeutic strategies proposed for CF that include disruption of tight junctions in the face of pseudomonas infection

Potential mechanisms underlying the acute lung dysfunction and bacterial extrapulmonary dissemination during Burkholderia cenocepacia respiratory infection

<p>Abstract</p> <p>Background</p> <p><it>Burkholderia cenocepacia</it>, an opportunistic pathogen that causes lung infections in cystic fibrosis (CF) patients, is associated with rapid and usually fatal lung deterioration due to necrotizing pneumonia and sepsis, a condition known as cepacia syndrome. The key bacterial determinants associated with this poor clinical outcome in CF patients are not clear. In this study, the cytotoxicity and procoagulant activity of <it>B. cenocepacia </it>from the ET-12 lineage, that has been linked to the cepacia syndrome, and four clinical isolates recovered from CF patients with mild clinical courses were analysed in both <it>in vitro </it>and <it>in vivo </it>assays.</p> <p>Methods</p> <p><it>B. cenocepacia-</it>infected BEAS-2B epithelial respiratory cells were used to investigate the bacterial cytotoxicity assessed by the flow cytometric detection of cell staining with propidium iodide. Bacteria-induced procoagulant activity in cell cultures was assessed by a colorimetric assay and by the flow cytometric detection of tissue factor (TF)-bearing microparticles in cell culture supernatants. Bronchoalveolar lavage fluids (BALF) from intratracheally infected mice were assessed for bacterial proinflammatory and procoagulant activities as well as for bacterial cytotoxicity, by the detection of released lactate dehydrogenase.</p> <p>Results</p> <p>ET-12 was significantly more cytotoxic to cell cultures but clinical isolates Cl-2, Cl-3 and Cl-4 exhibited also a cytotoxic profile. ET-12 and CI-2 were similarly able to generate a TF-dependent procoagulant environment in cell culture supernatant and to enhance the release of TF-bearing microparticles from infected cells. In the <it>in vivo </it>assay, all bacterial isolates disseminated from the mice lungs, but Cl-2 and Cl-4 exhibited the highest rates of recovery from mice livers. Interestingly, Cl-2 and Cl-4, together with ET-12, exhibited the highest cytotoxicity. All bacteria were similarly capable of generating a procoagulant and inflammatory environment in animal lungs.</p> <p>Conclusion</p> <p><it>B. cenocepacia </it>were shown to exhibit cytotoxic and procoagulant activities potentially implicated in bacterial dissemination into the circulation and acute pulmonary decline detected in susceptible CF patients. Improved understanding of the mechanisms accounting for <it>B. cenocepacia</it>-induced clinical decline has the potential to indicate novel therapeutic strategies to be included in the care <it>B. cenocepacia</it>-infected patients.</p

Outcomes of respiratory viral-bacterial co-infection in adult hospitalized patients

Background: Viral infections of the respiratory tract represent a major global health concern. Co-infection with bacteria may contribute to severe disease and increased mortality in patients. Nevertheless, viral-bacterial co-infection patterns and their clinical outcomes have not been well characterized to date. This study aimed to evaluate the clinical features and outcomes of patients with viral-bacterial respiratory tract co-infections. Methods: We included 19,361 patients with respiratory infection due to respiratory viruses [influenza A and B, respiratory syncytial virus (RSV), parainfluenza] and/or bacteria in four tertiary hospitals in Hong Kong from 2013 to 2017 using a large territory-wide healthcare database. All microbiological tests were conducted within 48 h of hospital admission. Four etiological groups were included: (1) viral infection alone; (2) bacterial infection alone; (3) laboratory-confirmed viral-bacterial co-infection and (4) clinically suspected viral-bacterial co-infection who were tested positive for respiratory virus and negative for bacteria but had received at least four days of antibiotics. Clinical features and outcomes were recorded for laboratory-confirmed viral-bacterial co-infection patients compared to other three groups as control. The primary outcome was 30-day mortality. Secondary outcomes were intensive care unit (ICU) admission and length of hospital stay. Propensity score matching estimated by binary logistic regression was used to adjust for the potential bias that may affect the association between outcomes and covariates. Findings: Among 15,906 patients with respiratory viral infection, there were 8451 (53.1%) clinically suspected and 1,087 (6.8%) laboratory-confirmed viral-bacterial co-infection. Among all the bacterial species, Haemophilus influenzae (226/1,087, 20.8%), Pseudomonas aeruginosa (180/1087, 16.6%) and Streptococcus pneumoniae (123/1087, 11.3%) were the three most common bacterial pathogens in the laboratory-confirmed co-infection group. Respiratory viruses co-infected with non-pneumococcal streptococci or methicillin-resistant Staphylococcus aureus was associated with the highest death rate [9/30 (30%) and 13/48 (27.1%), respectively] in this cohort. Compared with other infection groups, patients with laboratory-confirmed co-infection had higher ICU admission rate (p < 0.001) and mortality rate at 30 days (p = 0.028), and these results persisted after adjustment for potential confounders using propensity score matching. Furthermore, patients with laboratory-confirmed co-infection had significantly higher mortality compared to patients with bacterial infection alone. Interpretation: In our cohort, bacterial co-infection is common in hospitalized patients with viral respiratory tract infection and is associated with higher ICU admission rate and mortality. Therefore, active surveillance for bacterial co-infection and early antibiotic treatment may be required to improve outcomes in patients with respiratory viral infection