A tapered channel microfluidic device for comprehensive cell adhesion analysis, using measurements of detachment kinetics and shear stress-dependent motion

We have developed a method for studying cellular adhesion by using a custom-designed microfluidic device with parallel non-connected tapered channels. The design enables investigation of cellular responses to a large range of shear stress (ratio of 25) with a single input flow-rate. For each shear stress, a large number of cells are analyzed (500–1500 cells), providing statistically relevant data within a single experiment. Besides adhesion strength measurements, the microsystem presented in this paper enables in-depth analysis of cell detachment kinetics by real-time videomicroscopy. It offers the possibility to analyze adhesion-associated processes, such as migration or cell shape change, within the same experiment. To show the versatility of our device, we examined quantitatively cell adhesion by analyzing kinetics, adhesive strength and migration behaviour or cell shape modifications of the unicellular model cell organism Dictyostelium discoideum at 21 °C and of the human breast cancer cell line MDA-MB-231 at 37 °C. For both cell types, we found that the threshold stresses, which are necessary to detach the cells, follow lognormal distributions, and that the detachment process follows first order kinetics. In addition, for particular conditions’ cells are found to exhibit similar adhesion threshold stresses, but very different detachment kinetics, revealing the importance of dynamics analysis to fully describe cell adhesion. With its rapid implementation and potential for parallel sample processing, such microsystem offers a highly controllable platform for exploring cell adhesion characteristics in a large set of environmental conditions and cell types, and could have wide applications across cell biology, tissue engineering, and cell screening.     

The lived experiences of orphaned learners in South Africa: implications for the provision of quality education

Learners living in impoverished communities and subjected to the kind of disadvantage in operation in their home environment are at risk of receiving education of an inferior quality. The situation is worse for orphans, especially those residing in poor communities in that they bring to school peculiar attributes which poses challenges for the South African government in its endeavour to provide quality education for all. This paper presents constructed narratives of four primary-school learners living in a poor community in South Africa. The narratives are presented from the perspectives of the learners themselves, teachers and caregivers. These narratives reveal that following the death of parents, orphaned learners experience emotional changes, increased responsibilities, safety concerns as well as absence of learning support in the case of sibling-headed households. We argue that the challenges they experience in their home environment impact negatively on learning at school. We, therefore, propose that the extended family and the community serve as resources in providing needed support for promoting positive educational experiences to these learners.     

Teachers’ dilemmatic decision-making: reconciling coexisting policies of increased student retention and performance

In recent years, many countries within the Organisation for Economic Co-operation and Development have formulated educational policies aimed at providing better education to more students. However, this may be perceived as constituting dilemmatic spaces, where teachers must make efforts to reconcile coexisting political demands in their everyday work. The purpose of this article is to provide insight into how teachers handle coexisting educational policies of increased student retention and performance. Empirical findings from a one-year field study at a Danish vocational school explore how teachers’ decision-making as response to coexisting demands of increased student retention and performance involves the development of various pedagogical approaches to the students: an active ‘caring’ approach, a passive ‘wait until this class is over’ approach, an active ‘vocational gate-keeping’ approach, and a passive ‘wait and see whether they drop out’ approach. Based on the findings, it is argued that the various pedagogical approaches are developed through social negotiations with leaders, students, and other teachers. Moreover, these pedagogical approaches lead to the development of further negotiated, dilemmatic decisions to be made. Thus, a dynamic approach to teachers’ dilemmatic decision-making is proposed.     

NURTURING EARLY CHILDHOOD PROFESSIONALISM: THE RHODE ISLAND EARLY CHILDHOOD SUMMER INSTITUTE

This article describes the independent study project of a student who was a graduate assistant in a child development laboratory preschool when Hurricanes Katrina and Rita struck the Gulf Coast area. Through her experiences with “Project Katrina” she deepens her understanding of developmentally appropriate practices as she learns firsthand about the project approach and writing an article for publication in a professional journal.     

An Instructional Strategy to Introduce Pedagogical Content Knowledge Using Venn Diagrams

This paper describes the use of a three-circle Venn diagram as a vehicle for introducing pre-service elementary teachers to pedagogical content knowledge (PCK). Each circle of the diagram represents pedagogy, content and context individually. The overlap of any two circles represents the interaction between the circles. For example, the overlap of pedagogy and context relates to the ways that each of these general topics influences the other. The overlap of all three circles represents a complete lesson that is an integration of the three major components of PCK. The Venn diagram is an easily remembered graphic illustration of PCK that can be useful in planning lessons. The use of this graphic organizer in a science capstone course required of all pre-service elementary teachers is described.     

马桶座圈——真的是你家里最脏的地方吗?

马桶座圈背负着一个不公平的污名,那就是被认为是一般家庭中最脏的物件。但科学家们称,我们的家里其实有更为污秽的地方,有些地方还是最令人意想不到的。你会在马桶座圈上切菜吗?我想基本上所有人都说不会。但或许我们得重新考虑一下了。