Search

As systems become more complex, demand for teaching systems thinking is increasing. To date, studies in undergraduate engineering education have not presented a pedagogical framework suitable for teaching systems thinking to first-year engineering students. We designed and applied such a framework, the System Architecture-Function-Purpose framework for technological systems, in a semester-long first-year remote course. Forty-four first-year students with undeclared majors studying at an engineering-centric university participated in this study. Participants practiced the framework as applied to multidisciplinary case studies. Participants carried out three in-class individual training assignments during weeks 4,5, and 6. Each training assignment was followed by an out-of-class team assignment which expanded on the same case study. These assignments comprised the intervention component of the study, intended to improve students' systems thinking. The effectiveness of this intervention was evaluated during weeks 1 and 7 based on self-rated systems thinking (a) knowledge and ability, and (b) systems thinking as expressed in examples provided by participants. While self-rating improved from week 1 to 7. example assignment performance scores remained the same. We discuss future efforts for framework validation and provide suggestions for instructors. [ABSTRACT FROM AUTHOR]

Abstract Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events. Methods Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD). Results Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa. Conclusions This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.

The article discusses photosynthetic microorganisms have key players in aquatic ecosystems with strong potential for bioenergy production. Topics include to facilitate the phenotyping of microalgae and cyanobacteria, developed "PhenoChip," and strain-specific thermal sensitivity thresholds and distinct pH optima for photosynthetic performance.

This work is concerned with the behavior of pulsatile flows over a backward-facing step geometry. The paper mainly focuses on the effects of the pulsation frequency on the vortex development of a 2:1 backward-facing step for mean Reynolds number of 100 and for 0.035 ⩽ St ⩽ 2.19. The dependence of the flow field on the Reynolds number (Re = 100 and 200) was also examined for a constant Strouhal number, St of 1. A literature survey was carried out and it was found that the pulsation modifies the behavior of the flow pattern compared to the steady flow. It was shown in the present work that the inlet pulsation generally leads to differences in the mean flow compared to the steady field although the inlet bulk velocity is the same due to energy redistribution of the large-scale vortices, which result in nonlinear effects. The particle-image velocimetry results show that the formation of coherent structures, dynamical shedding, and transport procedure are very sensitive to the level of pulsation frequencies. For low and moderate inlet frequencies, 0.4 ⩽ St ⩽ 1, strong vortices are formed and these vortices are periodically advected downstream in an alternate pattern. For very low inlet frequency, St = 0.035, stronger vortices are generated due to an extended formation time, however, the slow formation process causes the forming vortices to decay before shedding can happen. For high inlet frequencies, St ⩾ 2.19, primary vortex is weak while no secondary vortex is formed. Flow downstream of the expansion recovers quickly. For Re = 200, the pattern of vortex formation is similar to Re = 700. However, the primary and secondary vortices decay more slowly and the vortices remain stronger for Re = 200. The strength and structure of the vortical regions depends highly on St, but Re effects are not negligible. [ABSTRACT FROM AUTHOR]

The effects of non-uniform hydrodynamic conditions resulting from flow cell geometry (square and rectangular cross-section) on Pseudomonas aeruginosa 01 (PAO1) biofilm formation, location, and structure were investigated for nominally similar flow conditions using a combination of confocal scanning laser microscope (CSLM) and computational fluid dynamics (CFD). The thickness and surface coverage of PAO1 biofilms were observed to vary depending on the location in the flow cell and thus also the local wall shear stress. The biofilm structure in a 5:1 (width to height) aspect ratio rectangular flow cell was observed to consist mainly of a layer of bacterial cells with thicker biofilm formation observed in the flow cell corners. For square cross-section (1:1 aspect ratio) flow cells, generally thicker and more uniform surface coverage biofilms were observed. Mushroom shaped structures with hollow centers and wall breaks, indicative of 'seeding' dispersal structures, were found exclusively in the square cross-section tubes. Exposure of PAO1 biofilms grown in the flow cells to gentamicin revealed a difference in susceptibility. Biofilms grown in the rectangular flow cell overall exhibited a greater susceptibility to gentamicin compared to those grown in square flow cells. However, even within a given flow cell, differences in susceptibility were observed depending on location. This study demonstrates that the spanwise shear stress distribution within the flow cells has an important impact on the location of colonization and structure of the resultant biofilm. These differences in biofilm structure have a significant impact on the susceptibility of the biofilms grown within flow channels. The impact of flow modification due to flow cell geometry should be considered when designing flow cells for laboratory investigation of bacterial biofilms. [ABSTRACT FROM AUTHOR]