Single cell rheometry with a microfluidic constriction: Quantitative control of friction and fluid leaks between cell and channel walls

We report how cell rheology measurements can be performed by monitoring the deformation of a cell in a microfluidic constriction, provided that friction and fluid leaks effects between the cell and the walls of the microchannels are correctly taken into account. Indeed, the mismatch between the rounded shapes of cells and the angular cross-section of standard microfluidic channels hampers efficient obstruction of the channel by an incoming cell. Moreover, friction forces between a cell and channels walls have never been characterized. Both effects impede a quantitative determination of forces experienced by cells in a constriction. Our study is based on a new microfluidic device composed of two successive constrictions, combined with optical interference microscopy measurements to characterize the contact zone between the cell and the walls of the channel. A cell squeezed in a first constriction obstructs most of the channel cross-section, which strongly limits leaks around cells. The rheological properties of the cell are subsequently probed during its entry in a second narrower constriction. The pressure force is determined from the pressure drop across the device, the cell velocity, and the width of the gutters formed between the cell and the corners of the channel. The additional friction force, which has never been analyzed for moving and constrained cells before, is found to involve both hydrodynamic lubrication and surface forces. This friction results in the existence of a threshold for moving the cells and leads to a non-linear behavior at low velocity. The friction force can nevertheless be assessed in the linear regime. Finally, an apparent viscosity of single cells can be estimated from a numerical prediction of the viscous dissipation induced by a small step in the channel. A preliminary application of our method yields an apparent loss modulus on the order of 100 Pa s for leukocytes THP-1 cells, in agreement with the literature data.     

Adolescents‘ Self-Efficacy to Overcome Barriers to Physical Activity Scale

This paper describes a revised measure of self-efficacy to overcome barriers to moderate and vigorous physical activity in a sample of 484 high school students in Toronto, Ontario. The students had a mean age of 15.3 years. Principal axis factoring with oblique rotation yielded five factors: self-efficacy to overcome internal, harassment, physical environment, social environment, and responsibilities barriers. Two problematic items were removed, which resulted in a 22-item measure. Subsequent analyses were conducted on responses to this shortened measure. Confirmatory factor analysis supported the five-factor model and demonstrated age- and sexinvariance. The subscales had good internal consistency reliability. Structural regressions demonstrated a strong relationship between the resulting factors and a physical activity measure (energy expenditure), showing predictive validity.     

Professional learning community process in the United States: conceptualization of the process and district support for schools

Abstract

As the Professional Learning Community (PLC) process becomes embedded within schools, the level of district support has a direct impact on whether schools have the ability to re-culture and sustain highly effective collaborative practices. The purpose of this article is to share a professional learning community conceptual framework from the US, and to highlight recent findings relating to district level support for the PLC process in schools. The professional learning community conceptual model is organized around five dimensions: shared and supportive leadership, shared values and vision, collaborative learning and application, shared personal practice, and supportive conditions. The overarching question guiding this qualitative research study is: How do school district personnel (central office staff) support schools in the professional learning community process? Findings reveal the importance of transformative and proactive district involvement, and the use of transparency, trust, accountability, and autonomy in school re-culturing. It was also found that developing leadership capacity, embedding professional development, and focusing the culture on student success were critically important. As districts provide support for the PLC dimensions and themes, school leaders will have a foundation of curricular strategies, collaborative skills, and necessary resources to serve teachers and students through continuous school improvement.     

Avoidance differences between rats and gerbils

Gerbils and rats learned equally well to discriminate the lighted, safe arm from the unsafe arm during Y-maze avoidance trials. Gerbils, however, were inferior to rats in initiating this response in time to avoid shock. Two subsequent experiments on passive avoidance did not support the interpretation of these data based on a greater incidence of shock-induced activity suppression in gerbils. In both experiments, gerbils required more shocks than rats to learn a staying response, indicating a pronounced locomotor response bias in gerbils that is not compatible with the required passive avoidance response. A fourth experiment, using a shuttlebox, found that the relative active avoidance performance by these species depends upon whether intertriai responses are permitted and punished. When they are, gerbils are inferior to rats, since their high level of locomotor responding is not compatible with the behavior required, i.e., staying during the intertrial interval and running during the CS-US interval. On the other hand, gerbils are not inferior when intertrial responses are prohibited, since their locomotor bias is not punished and is compatible with the required avoidance response.     

Turning thinking on its head: How bodies make up their minds

The assumption that bodies have little to do with thinking – other than to be the vehicle that gets a mind to a classroom – deeply underpins the traditional model of schooling. Lessons and seminars are designed on the premise that thinking happens best when people are pretty still, their bodies are quiet and undemanding of attention, and they are writing or talking. Unless it is interfering, the physical body has little to do with cognition. This paper offers an overview of the emerging field of ‘embodied cognition’ that profoundly challenges this model of the mind, and therefore undermines many of the assumptions that underlie the dominant sedentary and disembodied approach to the high-status bits of education.