Magnetophoretic manipulation in microsystem using carbonyl iron-polydimethylsiloxane microstructures

This paper reports the use of a recent composite material, noted hereafter i-PDMS, made of carbonyl iron microparticles mixed in a PolyDiMethylSiloxane (PDMS) matrix, for magnetophoretic functions such as capture and separation of magnetic species. We demonstrated that this composite which combine the advantages of both components, can locally generate high gradients of magnetic field when placed between two permanent magnets. After evaluating the magnetic susceptibility of the material as a function of the doping ratio, we investigated the molding resolution offered by i-PDMS to obtain microstructures of various sizes and shapes. Then, we implemented 500 μm i-PDMS microstructures in a microfluidic channel and studied the influence of flow rate on the deviation and trapping of superparamagnetic beads flowing at the neighborhood of the composite material. We characterized the attraction of the magnetic composite by measuring the distance from the i-PDMS microstructure, at which the beads are either deviated or captured. Finally, we demonstrated the interest of i-PDMS to perform magnetophoretic functions in microsystems for biological applications by performing capture of magnetically labeled cells.     

Ice hockey skate starts: a comparison of high and low calibre skaters

The forward skating start is a fundamental skill for ice hockey players, yet extremely challenging given the low traction of the ice surface. The technique for maximum skating acceleration of the body is not well understood. The aim of this study was to evaluate kinematic ice hockey skating start movement technique in relation to a skater’s skill level. A 10-camera motion capture system placed on the ice surface recorded “hybrid-V” skate start movement patterns of high and low calibre male ice hockey players (n = 7, 8, respectively). Participants’ lower body kinematics and estimated body centre of mass (CoM) movement during the first four steps were calculated. Both skate groups had similar lower body strength profiles, yet high calibre skaters achieved greater velocity; skating technique differences most likely explained the performance differences between the groups. Unlike over ground sprint start technique, skating starts showed greater concurrent hip abduction, external rotation and extension, presumably for ideal blade-to-ice push-off orientation for propulsion. Initial analysis revealed similar hip, knee and ankle joint gross movement patterns across skaters, however, further scrutiny of the data revealed that high calibre skaters achieved greater vertical CoM acceleration during each step that in turn allowed greater horizontal traction, forward propulsion, lower double-support times and, accordingly, faster starts with higher stride rates.     

The role of technology standards in product innovation: Theory and evidence from UK manufacturing firms

This paper studies the role of technology standards in firms’ product innovation in terms of both incremental innovation (within a technology life cycle) and radical innovation (beyond the present technology cycle). We first develop a theoretical model which predicts that technology standards can be used by firms as an “insurance” hedging against the risky process of developing new products. This insurance mechanism fosters incremental innovation and product growth especially for those further away from the technological frontier. Using data from a weighted panel of UK manufacturing firms over seven years, we find that the use of technology standards over past years significantly enables a firm’s incremental innovation while also reducing its incentive to deliver radical innovation. Additionally, we show that this relationship is contingent on a firm’s R&D intensity in line with predictions of our theoretical model.     

Gold coated optical fibers as three-dimensional electrodes for microfluidic enzymatic biofuel cells: Toward geometrically enhanced performance

For the first time, we report on the preliminary evaluation of gold coated optical fibers (GCOFs) as three-dimensional (3D) electrodes for a membraneless glucose/O₂ enzymatic biofuel cell. Two off-the-shelf 125 μm diameter GCOFs were integrated into a 3D microfluidic chip fabricated via rapid prototyping. Using soluble enzymes and a 10 mM glucose solution flowing at an average velocity of 16 mm s⁻¹ along 3 mm long GCOFs, the maximum power density reached 30.0 ± 0.1 μW cm⁻² at a current density of 160.6 ± 0.3 μA cm⁻². Bundles composed of multiple GCOFs could further enhance these first results while serving as substrates for enzyme immobilization.     

A student's view of an engineering exchange scheme (1)

The idea of writing a short essay, comparing the English and French schools of engineering, largely owes its genesis to a conversation with Professor Sir Alan J. Harris of Imperial College, London. It was during this discussion that it became evident that the benefits to be gained from a greater intercourse between schools engaged in international exchange programmes are not always apparent to the layman. One form of such an interchange was first carried out between the Ecole Nationale des Ponts et Chaussées and Imperial College of Science and Technology in the form of an exchange of their respective third year and graduate students. The author was one of the original participants in this scheme and believes he has greatly benefited from the experience. He is, however, occasionally confronted with the question (in France as well as in England): “Why did you come/go to France to learn engineering? What more does the experience have to offer?” This question, at first, almost invariably provoked a reaction of surprise and bafflement on the part of the author, who wishes in no way to be conceited in the matter. It is only recently that the author has come to accept the esoteric nature of the whole affair and furthermore to accept with hindsight that he is beginning to appreciate and exploit fully his one year at E.N.P.C., the major part of his original doubts having been dissipated. It is after having lived through and thoroughly digested the experience that these reflections are now possible.     

Our Stories about Teaching and Learning: A Pedagogy of Consequence for Yukon First Nation Settings

In this study, First Nation community members in Canada’s Yukon Territory share their stories about teaching and learning, both in informal and formal settings, in an effort to identify practices that might serve teachers to be more responsive to their First Nation students. In all, 52 community members between the ages of 15 and 82 shared their stories and assisted in identifying eight categories of practice and thought associated with effective teaching practices for this First Nation. Based upon these categories of thought and practice, we present a pedagogical framework for teachers and, finally, illustrate how this profile and the stories about teaching and learning are being used for adjusting and improving teaching practice in this First Nation.     

Balancing the score: the financial impact of resource dependence on symphony orchestras

Expenses in the performing arts have historically increased at a rate faster than earned revenues due to the labour reliance of the sector. Flanagan (The perilous life of symphony orchestras: artistic triumphs and economic challenges. Yale University Press, New York, 2012) found that US symphony orchestras were able to avoid the negative consequences of this earning gap by fostering strong private support. In the present study, we find that, in contexts where private funding is not as readily accessible, like in Canada, arts organizations have more incentive to keep expenses under control. This can be understood in terms of resource dependence where government funding bodies, due to a homogeneous set of demands, put pressure on organizations to control their expenses and reach greater audiences. Using panel data covering a period of 8 years and forty-eight orchestras, the results show that Canadian orchestras, when compared to US ones, achieve a lower rate of expense increases over time and are more reactive to economic downturns.     

A miniaturized continuous dielectrophoretic cell sorter and its applications

There is great interest in highly sensitive separation methods capable of quickly isolating a particular cell type within a single manipulation step prior to their analysis. We present a cell sorting device based on the opposition of dielectrophoretic forces that discriminates between cell types according to their dielectric properties, such as the membrane permittivity and the cytoplasm conductivity. The forces are generated by an array of electrodes located in both sidewalls of a main flow channel. Cells with different dielectric responses perceive different force magnitudes and are, therefore, continuously focused to different equilibrium positions in the flow channel, thus avoiding the need of a specific cell labeling as discriminating factor. We relate the cells’ dielectric response to their output position in the downstream channel. Using this microfluidic platform that integrates a method of continuous-flow cell separation based on multiple frequency dielectrophoresis, we succeeded in sorting viable from nonviable yeast with nearly 100% purity. The method also allowed to increase the infection rate of a cell culture up to 50% of parasitemia percentage, which facilitates the study of the parasite cycle. Finally, we prove the versatility of our device by synchronizing a yeast cell culture at a particular phase of the cell cycle avoiding the use of metabolic agents interfering with the cells’ physiology.     

Ice hockey skating sprints: run to glide mechanics of high calibre male and female athletes

ABSTRACT

The skating acceleration to maximal speed transition (sprint) is an essential skill that involves substantial lower body strength and effective propulsion technique. Coaches and athletes strive to understand this optimal combination to improve performance and reduce injury risk. Hence, the purpose of this study was to compare body centre of mass and lower body kinematic profiles from static start to maximal speed of high calibre male and female ice hockey players on the ice surface. Overall, male and female skaters showed similar centre of mass trajectories, though magnitudes differed. The key performance difference was the male’s greater peak forward skating speed (8.96 ± 0.44 m/s vs the females’ 8.02 ± 0.36 m/s, p < 0.001), which was strongly correlated to peak leg strength (R ² = 0.81). Males generated greater forward acceleration during the initial accelerative steps, but thereafter, both sexes had similar stride-by-stride accelerations up to maximal speed. In terms of technique, males demonstrated greater hip abduction (p = 0.006) and knee flexion (p = 0.026) from ice contact to push off throughout the trials. For coaches and athletes, these findings underscore the importance of leg strength and widely planted running steps during the initial skating technique to achieve maximal skating speed over a 30 m distance.