Structure and dynamics of CH2O,OH, and the velocity field of a confined bluff-body premixed flame,using simultaneous PLIF and PIV at 10 kHz.

This study characterizes the structure and dynamics of a confined, bluff-body-stabilized turbulent premixed flame by simultaneously employing formaldehyde (CH₂O) and hydroxyl (OH) planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV), at a rate of 10?kHz. The large field-of-view (>170 cm²) CH₂O-PLIF is enabled by use of a burst-mode laser delivering 10-kHz pulse trains of 355-nm at 350 mJ/pulse, resulting in a CH₂O signal-to-noise of 47:1 during PIV seed flow. Two cases illustrative of the CH₂O dynamics are presented. A statistically stationary turbulent combustion case highlights the development of the CH₂O layers in space and time. Notably, presumed CH₂O-vortex dynamic interactions are observed where the CH₂O accumulates broadly near the Kelvin–Helmholtz vortex core and remains thin near the vortex braid, contributing to a distribution of CH₂O preheat zone thickness from 1 to 10 times of the calculated laminar value. The second case highlights the CH₂O dynamics during a self-excited combustion instability. Two short-duration increases in CH₂O are produced during the elevated velocity portion of the acoustic cycle. The first CH₂O increase is caused by the reactant mass flux impulse as the velocity starts to increase. The second CH₂O increase is the result of the upper and lower shear layers merging downstream and entraining fresh reactants that burn in intense, distributed regions inside the wake. Estimating the time delay between the CH₂O and the heat release, it is suggested that the secondary CH₂O increase may contribute to damping of the acoustic instability, because of its out-of-phase relationship with pressure, while the first CH₂O increase appears to drive the instability.     

Gas‐phase structure and new vibrational study of methyl trifluoroacetate (CF3C(O)OCH3)

The molecular structure of methyl trifluoroacetate (CF₃C(O)OCH₃) has been determined in the gas phase from electron‐diffraction data supplemented by ab initio (MP2) and DFT calculations using different basis sets. Experimental data revealed an anti conformation with a dihedral angle θ (CCOC) = 180°. Quantum mechanical calculations indicate the possible existence of two conformers, differing by a rotation about the C(O) O bond. The global minimum represents a C_s‐symmetric structure in which the CF₃ group has the anti orientation with respect to the CH₃ group, but there is another potential minimum, much higher in energy, representing a C_s‐symmetric structure with a cis conformation. The preference for the anti conformation was studied using the total energy scheme and the natural bond orbital (NBO) partition scheme. Additionally, the total potential energy has been deconvoluted using a six‐fold decomposition in terms of a Fourier‐type expansion, showing that the electrostatic and steric contributions are dominant in stabilizing the anti conformer. Infrared spectra of CF₃C(O)OCH₃ were obtained for the gaseous and liquid phases, while the Raman spectrum was recorded for the liquid phase. Harmonic vibrational frequencies and a scaled force field have been calculated, leading to a final root mean‐square deviation of 9 cm⁻¹ when comparing experimental and calculated frequencies. Copyright © 2009 John Wiley & Sons, Ltd.     

Stimulated-emission-depletion microscopy with a multicolor stimulated-Raman-scattering light source

We describe a subdiffraction-resolution far-field fluorescence microscope employing stimulated emission depletion (STED) with a light source consisting of a microchip laser coupled into a standard single-mode fiber, which, via stimulated Raman scattering (SRS), yields a comb-like spectrum of seven discrete peaks extending from the fundamental wavelength at 532 nm to 620 nm. Each of the spectral peaks can be used as STED light for overcoming the diffraction barrier. This SRS light source enables the simple implementation of multicolor STED and provides a spectral output with multiple available wavelengths from green to red with potential for further expansion.     

Congruences on an inverse Bruck-Reilly monoid Part I: Non-group congruences

Communicated by N. R. Reilly     

Existence and asymptotic behavior of a functional differential equation in Banach space

Existence and asymptotic behavior of solutions are given for the equation u′(t) = ?A(t)u(t) + F(t,u_t) (t ? 0) and u₀ = ? ? C([?r,0]; X)  C. The space X is a Banach space; the family $\text{{A(t) ¦ 0 ? t ? T}}$ of unbounded linear operators defined on D(A) ? X → X generates a linear evolution system and F: C → X is continuous with respect to a fractional power of A(t₀) for some t₀ ? [0, T].     

Dramatic structural effects of a single hydrogen atom in HNPBu t 3

The molecular structure of tri-tert-butylphosphine imide has been re-determined using the recently developed DYNAMITE method, which allows all assumptions about local symmetry to be removed without increasing the number of refining structural parameters excessively. The imide hydrogen causes the NPBu(t)(3) group to deviate hugely from local C(3) symmetry, with N-P-C angles returned as 99.2(9), 110.9(7), and 111.5(11) degrees, while the C-P-C angles also deviate from symmetry, being 109.8(8), 110.5(9), and 113.9(9) degrees, so that the NPC(3) fragment is close to C(s) rather than C(3) symmetry. The application of the DYNAMITE method to HNPBu(t)(3) also allows the methyl groups to be asymmetric, which has been shown to be important by ab initio methods. The re-determination of this structure using these more sophisticated methods has also resulted in a much shorter P-N bond than was previously determined, and is consistent with the molecule being regarded as HN=PBu(t)(3), rather than HN(-)-P(+)Bu(t)(3).