A gas jet superposition model for CFD modeling of group-hole nozzle sprays

In the present study, a jet superposition modeling approach is explored to model group-hole nozzle sprays, in which multiple spray jets interact with each other. An equation to estimate the merged jet velocity from each of the individual jets was derived based on momentum conservation for equivalent gas jets. Diverging and converging group-hole nozzles were also considered. The model was implemented as a sub-grid-scale submodel in a Lagrangian Drop–Eulerian Gas CFD model for spray predictions. Spray tip penetration predicted using the present superposition model was validated against experimental results for parallel, diverging and converging group-hole nozzles as a function of the angle between the two holes at various injection and ambient pressures. The results show that spray tip penetration decreases as the group hole diverging or converging angle increases. However, the spray penetration of the converging group-hole nozzle arrangement is more sensitive to the angle between the two holes compared to diverging nozzle because the radial momentum component is converted to axial momentum during the jet–jet impingement process in the converging group-hole nozzle case. The modeling results also indicate that for converging group-hole nozzles the merged sprays become ellipsoidal in cross-section far downstream of the nozzle exit with larger converging angles, indicating increased air entrainment.     

Synthesis and properties of an ionic polyacetylene with aromatic heterocycles

A new ionic polyacetylene with two aromatic heterocycles (pyridyl and thienyl) was prepared by the activation polymerization of 2‐ethynylpyridine by using 3‐(6‐bromohexyloxy)methylthiophene without any additional initiator or catalyst. The activated acetylenic triple bond of N‐substituted‐2‐ethynylpyridinium bromide, formed at first quaternarization process, was susceptible to linear polymerization. The instrumental analysis data on the polymer structure revealed that the polymer have the conjugated polyene backbone structure with the designed two aromatic heterocycles. The photoluminescence peak is located at 510 nm corresponding to a photon energy of 2.43eV. The electrochemical properties of this ionic polyacetylene were also measured and discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5679–5685, 2007     

Growth and characteristics of hydrogenated In-doped ZnO thin films by pulsed DC magnetron sputtering

We investigated the role of hydrogen impurities in highly oriented In-doped ZnO (IZO:H) films. The conductivity of ZnO:H films exhibit small variation despite the increase of hydrogen ratio. The small variation of the carrier concentration in IZO:H films can be explained by the reduction of the oxygen deficiency for the charge neutrality and the increase of Vzn-H bonding for partially charge compensation in the films. The additional mode at 573 cm⁻¹ is interpreted as vacancy clusters. The discrepancy between the increase of vacancy clusters (573 cm⁻¹) and small variation of carrier concentration is attributed to the different physical characteristics of the IZO:H films due to the hydrogen existence between bulk and surface. The measured FT-IR peak at 3500 cm⁻¹ exhibits typical characteristic of O-H bonding.     

Aluminum phthalocyanine: an active and simple catalyst for cyanosilylation of aldehydes

Aluminum phthalocyanine (AlPc) in the presence of Ph₃PO acts as a highly effective catalyst for cyanosilylation of various aldehydes to the corresponding cyanohydrin trimethylsilyl ethers. The reaction proceeds smoothly with 5 mol% catalyst loading at room temperature, giving up to 96% yield. Copyright © 2007 John Wiley & Sons, Ltd.     

Reynolds stress modelling of rectangular open‐channel flow

A Reynolds stress model for the numerical simulation of uniform 3D turbulent open‐channel flows is described. The finite volume method is used for the numerical solution of the flow equations and transport equations of the Reynolds stress components. The overall solution strategy is the SIMPLER algorithm, and the power‐law scheme is used to discretize the convection and diffusion terms in the governing equations. The developed model is applied to a flow at a Reynolds number of 77000 in a rectangular channel with a width to depth ratio of 2. The simulated mean flow and turbulence structures are compared with measured and computed data from the literature. The computed flow vectors in the plane normal to the streamwise direction show a small vortex, called inner secondary currents, located at the juncture of the sidewall and the free surface as well as the free surface and bottom vortices. This small vortex causes a significant increase in the wall shear stress in the vicinity of the free surface. A budget analysis of the streamwise vorticity is carried out. It is found that both production terms by anisotropy of Reynolds normal stress and by Reynolds shear stress contribute to the generation of secondary currents. Copyright © 2006 John Wiley & Sons, Ltd.     

Polymeric photoacid generators for direct photochemical modification of surface

To achieve easy spin coating and enhanced efficiency in the photolithographic process for the direct photochemical modification of surface, we incorporated photoacid generator (PAG) into polymer backbone. Bis‐(4‐hydroxy‐phenyl)‐(4‐methoxy‐3,5‐dimethyl‐phenyl)‐sulfonium chloride was synthesized as a monomer, and was polymerized with sebacoyl chloride and terephthaloyl chloride. The resulting polymeric PAG in chloride salt form was converted to the p‐toluenesulfonate and 1‐naphthol‐5‐sulfonate forms with ion‐exchange reactions. By the photolithographic process with the polymeric PAG, the protecting groups of the linker molecules self‐assembled onto a glass plate were micropatterned to produce an amine pattern for the microarray of oligonucleotides. The acids generated from the polymeric PAG effectively deprotect the acid‐labile protecting groups of the linker molecules through a chemical amplification process in the exposed region. After the treatment of the patterned amino groups with a fluorescent dye, the pattern profiles were observed with a fluorescence scanner. The fluorescence image reveals a well‐defined pattern at a micro level, which clearly indicates that the polymeric PAGs have a great potential in photochemical surface modification for the microarray of oligonucleotides. Copyright © 2007 John Wiley & Sons, Ltd.     

Measurement of collision broadening of the P1(5) line of (0,0) band of OH AΣ←XΠ transition at high temperatures

Even for the well-studied and ubiquitous species, OH, the current state of theoretical development of broadening theory does not allow extrapolation from low-temperature laboratory measurements to the range of practical combustion devices. We performed a series of experiments at typical combustion conditions to determine the collision broadening of the P₁(5) line of the (0,0) band of OH A²Σ⁺←X²Π transition by Ar in shock-heated H₂-O₂-Ar mixtures and by air in H₂-air flames over a wide range of stoichiometry (φ=0.01-10.0), temperature (T=780-2440 K), and pressure (p=0.7-10.0 atm). The values of the collision width, Δν_C, were acquired by fitting Voigt profiles to the measured spectral line shapes in flames and to the peak absorption coefficients (k_ν0) in shock tube experiments. Collision broadening parameters (2γ_Ar, 2γ_N2, and 2γ_H2O) were then calculated assuming the linear dependence of Δν_C with pressure—the 2γ_N2 and 2γ_H2O values were inferred from 2γ_Air and the equilibrium concentration of N₂ and H₂O of a given flame. The temperature dependences of 2γ_i in our temperature range are, respectively, 1.0, 0.75, and 0.87 for Ar, N₂, and H₂O. The collision broadening cross sections (σ) deduced from 2γ_i values are expressed with an assumed form, σ_i(T)=σ_i,₀(T₀/T)^k, T₀=1000 K: for Ar, σ_Ar,0=63.3 (Ų), k=0.50; for N₂, σ_N2,0=68.0 (Ų), k=0.25; for H₂O, σ_H2O,0=188.8 (Ų), k=0.37.     

Biocatalytic cascades and intercommunicated biocatalytic cascades in microcapsule systems

Biomolecule-loaded nucleic acid-functionalized carboxymethyl cellulose hydrogel-stabilized microcapsules (diameter ca. 2 μm) are introduced as cell-like containments. The microcapsules are loaded with two DNA tetrahedra, T₁ and T₂, functionalized with guanosine-rich G-quadruplex subunits, and/or with native enzymes (glucose oxidase, GOx, and/or β-galactosidase, β-gal). In the presence of K⁺-ions and hemin, the T₁/T₂ tetrahedra constituents, loaded in the microcapsules, assemble into a hemin/G-quadruplex bridged tetrahedra dimer DNAzyme catalyzing the oxidation of Amplex Red to Resorufin by generating H₂O₂. In the presence of co-loaded GOx or GOx/β-gal, the GOx//T₁/T₂ hemin/G-quadruplex cascade catalyzing the glucose-mediated oxidation of Amplex Red to Resorufin, and the three-biocatalysts cascade consisting of β-gal//GOx//hemin/G-quadruplex bridged T₁/T₂ catalyzing the lactose-driven oxidation of Amplex Red to Resorufin proceed in the microcapsules. Enhanced biocatalytic transformations in the microcapsules, as compared to the performance of the reactions in a homogeneous phase, are observed, due to the proximity of the biocatalysts in a confined volume. As the synthetic methodology to prepare the microcapsules yields boundaries functionalized with complementary nucleic acid tethers, the dynamic association of different microcapsules, loaded selectively with biomolecular catalysts, proceeds. The dynamic dimerization of GOx-loaded microcapsules and hemin/G-quadruplex bridged T₁/T₂ DNAzyme-loaded microcapsules yields effective intercommunicated microcapsules driving the GOx//hemin/G-quadruplex bridged T₁/T₂ DNAzyme cascade. In addition, the dynamic dimerization of GOx-loaded microcapsules with β-gal//hemin/G-quadruplex bridged T₁/T₂-loaded microcapsules enables the bi-directional intercommunicated operation of the lactose-stimulated three catalysts β-gal//GOx//hemin/G-quadruplex bridged T₁/T₂ DNAzyme cascade. The guided separation and formation of dynamic supramolecular dimer microcapsular containments, and the dictated switchable operation of intercommunicated biocatalytic cascades are demonstrated.

Dynamic dimerization of GOx-loaded microcapsules with β-gal//hemin/G-quadruplex-bridged T₁/T₂-loaded microcapsules guides the bi-directional intercommunication of the three catalysts cascade.     

Preparation of a Macroporous Poly(L‐lactide) Scaffold by Liquid‐Liquid Phase Separation of a PLLA/1,4‐Dioxane/Water Ternary System in the Presence of NaCl

A novel method for preparing regular and highly interconnected macroporous poly(L ‐lactic acid) (PLLA) scaffolds is presented. Scaffolds with pore sizes ranging from 50 to 300 μm were fabricated from a PLLA/1,4‐dioxane/water ternary system via a thermally induced phase separation (TIPS) in the presence of small amounts of NaCl (⩽0.1 wt.‐%). The addition of salt had the following effects. The cloud‐point temperature was raised because of a salt‐out effect. Spinodal decomposition was induced at a higher temperature with a large quench depth. Gelation due to the crystallization of PLLA was prevented to a large extent, which led to the creation of the highly interconnected macropores required for effective cell penetration.