Effect of Particle Concentration and AC Electric Field Strength on Particle Trapping in Rapid Electrokinetic Patterning (REP)

Rapid Electrokinetic Patterning (REP) is an optoelectric technique for trapping and translating micro- and nanoparticles non-invasively. It uses a combination of laser-induced AC electrothermal flow and particle-electrode interactions in the presence of a uniform AC electric field. The trapping is governed by laser power, electric field strength, AC frequency and dielectric properties of the particle and the medium. A REP trap has an AC frequency, termed critical frequency, above which particles cannot be trapped. It is expected to be dependent on dielectric properties of the particle and the medium. However, we propose that the particle concentration and AC field strength also influence the critical frequency. In our experiments, we test 1 µm polystyrene microspheres in REP under the condition of three particle concentrations and two electric field strengths while keeping the laser power fixed at 25mW. We find that as the particle concentration increases, the critical frequency increases. Besides, by lowering the AC field strength, the critical frequency decreases. To our best knowledge, this is the first study revealing the effect of particle concentration on critical frequency. Based on these results, by selecting proper parameters, we can separate the smaller particles and hold the larger particles in the trap, opposite to what has been achieved by other researchers. The ability to separate smaller particles will make REP a more prominent and powerful particle trapping method

Open optoelectrowetting droplet actuation

We present experimental realization of an open optoelectrowetting (o-OEW) device for liquid droplet manipulations. The o-OEW device is realized by coplanar electrodes and a photoconductor. The local switching effect for electrowetting resulting from illumination is based on the tunable impedance of the photoconductor. Dynamic virtual electrodes are created using projected images, leading to free planar movements of droplets. Basic operations such as transporting and merging were demonstrated. Translational speed up to 3.6 mm/s was measured. Equivalent circuit analysis shows that the operational frequency for the current setup ranges from 100 to 800 Hz. (C) 2008 American Institute of Physics

Extracting the Past from the Present: Exotic Prizes, Empty Wilderness, and Commercial Conquest in Two Oil Company Advertisements, 1925–2012

This article undertakes a comparative analysis of two oil company advertisements—British Petroleum’s (BP) “Persian Series”, published in London in 1925, and Cenovus Energy’s “Canadian Ideas at Work”, published across Canada in 2012. These advertisements are separated by eighty-seven years, and were produced in different countries, by different companies, and for different audiences. Yet, a closer reading of these documents reveals that they are two sides of the same coin: both narrate the extraction of oil as a great game of commercial conquest, whereby exotic prizes trapped beneath wild and empty landscapes are unlocked by oil companies. How could two advertisements that appear so radically distant feel so close? In what ways do the oil cultures of the past inflect those of the present? This article engages with such questions by critically deconstructing and comparing the imagined worlds of oil presented in BP and Cenovus’ advertisements, tracing the ways in which the resource is represented through the binaries of ancient and modern, empty and urban, wild and civilized. By configuring oil as a constellation of ideas rather than a system of things, this investigation reveals how the colonial legacies of the past continue to seep through the oil cultures of the present

Volitional code switching: Is there a cost?

Bilinguals commonly commingle their languages when speaking among other bilinguals in a process known as code switching (CS). Previous studies have been equivocal on whether CS is cognitively demanding, as measured by a time cost. This study sought to identify and compare time cost in CS across two experimental paradigms: naturalistic conversation and self-paced reading. Eighteen participants of similar linguistic background (English-dominant second language learners of French) were recruited and completed both tasks. Results identified a time cost for CS in the conversation task, but not the self-paced reading task. The data were also analyzed for effect of CS direction (either L1 to L2 or vice versa). In the conversation task only, there was a greater time cost for switching from L1 into L2. These results suggest that, while time cost for CS exists, it is limited to tasks that require selection of lexical and syntactic schemas

Real-time particle dispersion from a DPI using image velocimetry – Evaluation of powder adhesion, impact, and collision

Dry powder inhaler (DPI) is a dosage form for delivering fine drug powders to the respiratory tract. Particle size and size distribution, proportion of fines, particle shape, particle surface roughness, flow rate and adhesion force have been reported to affect the aerosolization process. Several mechanisms for particle dispersion in DPI have been considered; a proposed mechanism to explain the particle dispersion phenomenon is the active site theory. However, there have been several conflicting reports, therefore, an agglomeration/fracture hypothesis has been also proposed. Particle dispersion is associated with events such as impact, acceleration, shear stress, and turbulent flow. The aim of this study is to use high-speed video imaging to provide direct experimental observation of the particle dispersion process in order to unveil a mechanism for particle dispersion. Mixture of micronized lactose and coarse lactose carrier was placed in a model inhaler device, a high speed video imaging was used to capture the dry powder inhalation process. The flow pattern was found to be turbulent. Particles were observed to collide with one another, causing detachment of micronized particles from the surfaces of the coarse lactose particles. Impact of the powder agglomerates on the device grid also contributed to deaggregation and dispersion of the particles. The findings suggest that collision and impact are important mechanisms for the dispersion of DPI particles

Analysis of fly fishing rod casting dynamics

Abstract. An analysis of fly fishing rod casting dynamics was developed comprising of a nonlinear finite element representation of the composite fly rod and a lumped parameter model for the fly line. A nonlinear finite element model was used to analyze the transient response of the fly rod, in which fly rod responses were simulated for a forward casting stroke. The lumped parameter method was used to discretize the fly line system. Fly line motions were simulated during a cast based on fly rod tip response, which was used as the initial boundary condition for the fly line. Fly line loop generation, propagation, and line turn-over were simulated numerically. Flexible rod results were compared to the rigid rod case, in which the fly tip path was prescribed by a given fly rod butt input. Our numerical results strongly suggest that nonlinear flexibility effects on the fly rod must be included in order to accurately simulate casting dynamics and associated fly line motion