An immersed boundary method for the incompressible Navier–Stokes equations in complex geometry

A nodally exact convection–diffusion–reaction scheme developed in Cartesian grids is applied to solve the flow equations in irregular domains within the framework of immersed boundary (IB) method. The artificial momentum forcing term applied at certain points in the flow and inside the body of any shape allows the imposition of no‐slip velocity condition to account for the body of complex boundary. Development of an interpolation scheme that can accurately lead to no‐slip velocity condition along the IB is essential since Cartesian grid lines generally do not coincide with the IB. The results simulated from the proposed IB method agree well with other numerical and experimental results for several chosen benchmark problems. The accuracy and fidelity of the IB flow solver to predict flows with irregular IBs are therefore demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.     

Measurement of the optical Stark effect in semiconducting carbon nanotubes

A strong optical Stark effect has been observed in (6,5) semiconducting single-walled carbon nanotubes by femtosecond pump-probe spectroscopy. The response is characterized by an instantaneous blueshift of the excitonic resonance upon application of pump radiation at photon energy well below the band gap. The large Stark effect is attributed to the enhanced Coulomb interactions present in these one-dimensional materials.     

No Fear of Perfluorinated Peroxides: Syntheses and Solid‐State Structures of Surprisingly Inert Perfluoroalkyl Peroxides

We report on the solid‐state structures of bis(nonafluoro‐tert‐butyl) peroxide [(F₃C)₃CO]₂ and bis(undecafluoro‐2‐methyl‐2‐butyl) peroxide [(C₂F₅)(F₃C)₂CO]₂. These peroxides were prepared from the corresponding hypofluorites and fluorinated silver wool. The solid‐state structures obtained after in situ crystallisation show unusual COOC dihedral angles of 180°, as well as elongated O?O bonds because of the bulky perfluorinated alkyl groups. The perfluorinated alkyl peroxides are insensitive to both impact (>40 J) and friction (>360 N), and resistant towards mineral acids (HX; X=F, Cl, Br) and elemental halogens (X₂). Ferrocene is oxidized by [(F₃C)₃CO]₂ to [Fe^IIICp₂][OC(CF₃)₃].     

Mathematical Modeling of Silica Anode Decomposition

The volatilization of quartz in a transferred arc plasma followed byquench and recondensation is a promising route to the production offumed silica. In this work, an existing model of a transferred arcwas modified and combined with a newly developed model of a moltensilica anode to predict the behavior of a transferred arc evaporatoras a function of current and plasma gas flow rate. The model predictstemperature, current, and flow fields in both the plasma and anode aswell as evaporation rates. Although quantitative agreement withexperimental results was not possible because of insufficient propertydata for silica at high temperature, the results were within an orderof magnitude of those measured experimentally. The model developed isuseful for the design and scaleup of this type of reactor.     

Enhanced fluorescence and chiral discrimination for tartaric acid in a dual fluorophore boronic acid receptor

The addition of D-tartaric acid to R,R- causes a large increase in fluorescence. While addition of L-tartaric acid to R,R- only produces small changes in fluorescence.     

Detection of anions using a fluorescent alizarin-phenylboronic acid ensemble

Selective anion-induced organization of phenylboronic acids and alizarin results in a new TURN-ON fluorescent sensor for anions in MeOH.     

Surfactant-mediated capillary electrochromatography with octadecyl-silica- packed capillary columns for the separation of nonpolar compounds. Case of pyrethroid insecticides

Capillary electrochromatography (CEC) with octadecyl-silica-packed capillary columns was evaluated in the separation of nonpolar compounds, e.g., pyrethroid insecticides, using surfactant-rich mobile phases. This novel concept is referred to as surfactant-mediated capillary electrochromatography (SM-CEC), and is based on including a charged surfactant, namely sodium di-2-ethylhexyl sulfosuccinate (DOSS), in the mobile phase. Under these conditions, DOSS plays the role of a slowly moving pseudostationary phase so that solutes are partitioned between a mobile phase, a fixed stationary phase and a slowly moving pseudostationary phase. The SM-CEC system was investigated with pyrethroid insecticides over a wide range of DOSS and acetonitrile concentrations in the mobile phase. Pyrethroid insecticides, which are very hydrophobic solutes consisting of geometric isomers and diastereomers, were better resolved in SM-CEC than in straight CEC.     

Analysis of ν2, ν4 Infrared Hot Bands of SO3: Resolution of the Puzzle of the ν1 CARS Spectrum

Further analysis of the high-resolution (0.0015 cm⁻¹) infrared spectrum of ³²S¹⁶O₃ has led to the assignment of more than 3100 hot band transitions from the ν₂ and ν₄ levels to the states 2ν₂ (l=0), ν₂+ν₄ (l=±1), and 2ν₄ (l=0,±2). These levels are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν₁ levels, which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed the solution of the unusual and complicated structure of the ν₁ CARS spectrum. This has been accomplished by locating over 400 hot-band transitions to levels that contain at least 10% ν₁ character. The complex CARS spectrum results from a large number of avoided energy-level crossings between these states. Accurate rovibrational constants are deduced for all the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm⁻¹ for ν₁, α₁^B, and α₁^C, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. In addition, new values for some of the anharmonicity constants have been obtained. Highly accurate values for the equilibrium rotational constants B_e and C_e are deduced, yielding independent, nearly identical values for the SO r_e bond length of 141.734 03(13) and 141.732 54(18) pm, respectively.