• Canada
• Publicationsclose
• 01 natural sciences close
• 010405 organic chemistry close
• Natural Sciences and Engineering Research Council of Canada close

Magnetic actuation is a droplet manipulation mechanism in digital microfluidics (DMF), where droplets can be actuated over a (super)hydrophobic surface with a magnetic force. Superparamagnetic particles or ferromagnetic liquids are added to the droplets to provide a “handle” by which the magnet can exert a force on the droplet. In this study, we present a novel method of magnetic manipulation, where droplets instead contain paramagnetic salts with molar magnetic susceptibilities (χm) approximately ≈10 000× < that for superparamagnetic particles. Droplet actuation is facilitated by low surface friction on fluorous silica nanoparticle-based superhydrophobic coatings, where <2 μN is required for reproducible droplet actuation. Different paramagnetic salts with χm from ≈4500 to 72 000 (× 10–6 cm3 mol–1) were used to make aqueous solutions of different concentration and tested for droplet actuation and sliding angle using permanent magnets (1.8–2.1 kG). Paramagnetic salts are compared in terms of solubility, m...

AbstractIn this study, the 3D printability of a series of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly(lactic acid) (PLA) blends were investigated using fused filament fabrication (FFF). The studied blends suffered from poor 3D printability due to differences in compatibility and low thermal resistance. These shortcomings were addressed by incorporating a functionalized styrene-acrylate copolymer with oxirane moieties as a chain extender (CE). To enhance mechanical properties, the synergistic effect of 3D printing parameters such as printing temperature and speed, layer thickness and bed temperature were explored. Rheological analysis showed improvement in the 3D printability of PHBV:PLA:CE blend by allowing a higher printing temperature (220 °C) and sufficient printing speed (45 mm s−1). The surface morphology of fractured tensile specimens showed good bonding between layers when a bed temperature of 60 °C was used and a layer thickness of 0.25 mm was designed. The optimized printing samples shown higher storage modulus and strength, resulting in stiffer and stronger parts. The crystallinity, morphology and performance of the 3D printed products were correlated to share key methods to improve the 3D printability of PHBV:PLA based blends which may be implemented in other biopolymer blends, and further highlight how process parameters enhance the mechanical performance of 3D printed products.

The Bethe-Salpeter (BS) amplitude for $\pi N$ scattering is evaluated at the off mass shell points corresponding to the Low Energy Theorems (LET) based on PCAC and current algebra. The results suggest a way of maintaining consistency between BS equation and LET. Comment: 3 pages, 1 Figure, Contribution to QNP2002 Conference, Juelich June 2002

The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss and rotation are the main drivers of stellar evolution. Binarity and magnetic field may also significantly affect the fate of massive stars. Our goal is to investigate the evolution of single O stars in the Galaxy. For that, we use a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We rely on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We perform spectral modelling with the code CMFGEN. We determine the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen and oxygen. Most of our sample stars have initial masses in the range 20 to 50 Msun. We show that nitrogen is more enriched and carbon/oxygen more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More massive stars, within a given luminosity class, appear to be more chemically enriched than lower mass stars. We compare our results with predictions of three types of evolutionary models and show that, for two sets of models, 80% of our sample can be explained by stellar evolution including rotation. The effect of magnetism on surface abundances is unconstrained. Our study indicates that, in the 20-50 Msun mass range, the surface chemical abundances of most single O stars in the Galaxy are fairly well accounted for by stellar evolution of rotating stars. Comment: 15 pages, 12 figures. Accepted in Astronomy & Astrophysics

Elemental copper and potassium are immiscible under ambient conditions. It is known that pressure is a useful tool to promote the reaction between two different elements by modifying their electronic structure significantly. Here, we predict the formation of four K–Cu compounds (K3Cu2, K2Cu, K5Cu2, and K3Cu) under moderate pressure through unbiased structure search and first-principles calculations. Among all predicted structures, the simulated x-ray diffraction pattern of K3Cu2 perfectly matches a K–Cu compound synthesized in 2004. Further simulations indicate that the K–Cu compounds exhibit diverse structural features with novel forms of Cu aggregations, including Cu dimers, linear and zigzag Cu chains, and Cu-centered polyhedrons. Analysis of the electronic structure reveals that Cu atoms behave as anions to accept electrons from K atoms through fully filling 4s orbitals and partially extending 4p orbitals. Covalent Cu–Cu interaction is found in these compounds, which is associated with the sp hybridizations. These results provide insights into the understanding of the phase diversity of alkali/alkaline earth and metal systems.

AbstractWe study the well-posedness and regularity of the generalized Navier–Stokes equations with initial data in a new critical space Qα;∞β,−1(Rn)=∇⋅(Qαβ(Rn))n, β∈(12,1), which is larger than some known critical homogeneous Besov spaces. Here Qαβ(Rn) is a space defined as the set of all measurable functions withsup(l(I))2(α+β−1)−n∫I∫I|f(x)−f(y)|2|x−y|n+2(α−β+1)dxdy<∞ where the supremum is taken over all cubes I with edge length l(I) and edges parallel to the coordinate axes in Rn. In order to study the well-posedness and regularity, we give a Carleson measure characterization of Qαβ(Rn) by investigating a new type of tent spaces and an atomic decomposition of the predual for Qαβ(Rn). In addition, our regularity results apply to the incompressible Navier–Stokes equations with initial data in Qα;∞1,−1(Rn).

In this work, significant enhancement in absorption, especially in the near infra-red region, is achieved for ultra-thin crystalline silicon of various thicknesses using a photonic crystal structure. This is realized by patterning the silicon with close-packed inverted pyramid structuring, wherein the lattice spacing is comparable to the wavelength of the near infra-red light, which results in strong wave-interference-based light trapping. Absorption enhancement of more than a factor of two in the spectral range of 1000–1100 nm is achieved without any other optical enhancments. Details on the techniques used to realize the ultra-thin silicon, the fabrication of the inverted pyramids using standard photolithography and a complete optical analysis are reported in this work.

A comprehensive characterization of ``local operations assisted by classical communication'' shows that pure multipartite entangled states cannot be transformed into other similar states, an important insight in entanglement theory.