Kinetics of rich ammonia flames

We report laser absorption measurements of NH₃ decay within the flame front region of rich, atmospheric pressure ammonia flames. These data are combined with earlier OH, NH, and NH₂ measurements to obtain new estimates for the oscillator strength of NH₂. This value, f_i = 6.4 × 10^?5 for the ^PQ_1,7 line in the (0,9,0) ← (0,0.0) vibrational band of the A²A₁ ← X²B₁ transition, suggests ΔH(NH) ? 87 kcal/mol. The ammonia profiles were also combined with previous data on NO, NH, NH₂, and OH to provide an extensive database at fuel equivalence ratios (ø) of 1.28, 1.50, and 1.81 for comparison to our kinetic model predictions. This modeling used a one-dimensional flame code which explicitly accounts for the diffusional component in our flame experiments. Modeling results using a conventional mechanism predicted concentration profiles which deviated markedly from our observations. It was possible to obtain much more satisfactory fits by postulating reactions between various NH_i (i = 1, 2) species to form N—N bonds. The N₂H_j (j = 1–3) species could then lose H atoms via dissociation to ultimately form N₂. Inclusion of these reactions in the mechanism allowed us to predict concentration—distance profiles for five different species at three different equivalence ratios that are in good agreement with experiment. The most important component of this mechanism is the recognition that the NH_i + NH_i reactions dominate the kinetics in rich flames. A most satisfying aspect of these calculations is that the key rate constants in the NH_i + NH_i sequence were estimated using simple RRK theory.     

A novel synthesis of cis-dihydro-rose oxide and related stereochemistry

A new synthesis of cis-dihydro-rose oxide from elsholtzia oil is presented. The stereochemistry of catalytic hydrogenation of elsholtziol is discussed, and configurations of the diastereoisomers of the resulting tetrahydroelsholtziol have been deduced with the aid of gas chromatography, infrared spectroscopic analysis and conformational analysis. Stereochemical study of catalytic dehydration of tetrahydroelsholtziols indicates that the dehydration-rearrangement reactions follow a (trans-elimination process.     

Nonlinear multiwavelength conversion based on an aperiodic optical superlattice in lithium niobate

We have demonstrated what is to our knowledge the first successful achievement of multiwavelength conversion in an aperiodic optical superlattice (AOS) lithium niobate crystal with equalized gain. The two AOS devices in our experiment, numerically synthesized from 2857 crystal blocks with a unit block thickness of 3.5 microm, have fundamental wavelengths of 1540 and 1545 nm for double-wavelength second-harmonic generation (SHG) and of 1540, 1545, and 1553 nm for triple-wavelength SHG at 50 degrees C. Our experiment and simulation show that the output spectrum of an AOS wavelength converter is fairly insensitive to typical fabrication errors.     

Structure determination of the Si3N4/Si(111)- (8 x 8) surface: a combined study of Kikuchi electron holography, scanning tunneling microscopy, and ab initio calculations

A comprehensive atomic model for the reconstructed surface of Si3N4 thin layer grown on Si(111) is presented. Kikuchi electron holography images clearly show the existence of adatoms on the Si3N4(0001)/Si(111)-(8x8) surface. Compared with the ab initio calculations, more than 30 symmetry-inequivalent atomic pairs in the outmost layers are successfully identified. Scanning tunneling microscopy (STM) images show diamond-shaped unit cells and nine adatoms in each cell. High-resolution STM images reveal extra features and are in good agreement with the partial charge density distribution obtained from total-energy calculations.     

First symmetry tests in polarized Z0 decays to bbg

We have made the first direct symmetry tests in the decays of polarized Z0 bosons into fully identified bbg states, collected in the SLD experiment at SLAC. We searched for evidence of parity violation at the bbg vertex by studying the asymmetries in the b-quark polar- and azimuthal-angle distributions, and for evidence of T-odd, CP-even or CP-odd, final-state interactions by measuring angular correlations between the three-jet plane and the Z0 polarization. We found results consistent with standard model expectations and set 95% C. limits on anomalous contributions.     

Anomalous splittings of torsional sublevels induced by the aldehyde inversion motion in the S1 state of acetaldehyde

The G6 group-theoretical high-barrier formalism developed previously for internally rotating and inverting CH3NHD is used to interpret the abnormal torsional splittings in the S1 state of acetaldehyde for levels 14(0-)15(0), 14(0-)15(1), and 14(0-)15(2), where 14(0-) denotes the upper inversion tunneling component of the aldehyde hydrogen and 15 denotes the methyl torsional vibration. This formalism, derived using an extended permutation-inversion group G6m, treats simultaneously methyl torsional tunneling, aldehyde-hydrogen inversion tunneling and overall rotation. Fits to the rotational states of the four pairs of inversion-torsion vibrational levels (14(0+)15(0A,E), 14(0-)15(0A,E)), (14(0+)15(1A,E), 14(0-)15(1A,E)), (14(0+)15(2A,E), 14(0-)15(2A,E)), and (14(0+)15(3A,E), 14(0-)15(3A,E)) are performed, giving root-mean-square deviations of 0.003, 0.004, 0.004, and 0.004 cm(-1), respectively, which are nearly equal to the experimental uncertainty of 0.003 cm(-1). For torsional levels lying near the top of the torsional barrier, this theoretical model, after including higher-order terms, provides satisfactory fits to the experimental data. The partially anomalous K-doublet structure of the S1 state, which deviates from that in a simple torsion-rotation molecule, is fitted using this formalism and is shown to arise from coupling of torsion and rotation motion with the aldehyde-hydrogen inversion.     

CeO2-promoted W-Mn/SiO2 catalysts for conversion of methane to C3-C4 hydrocarbons at elevated pressure

A CeO2-doped Na-Mn-W/SiO2 catalyst for oxidative conversion of methane has been studied in a micro-stainless-steel reactor under elevated pressure; a CH4 conversion of 47.2% with a C3-C4 selectivity of 47.3% (C2:C3:C4 = 1:1:3.3) was obtained at 983 K with 1.0 x 10(5) ml g-1 h-1 GHSV, CH4/O2 = 2.5 and P = 0.6 MPa.     

The weak closure of the set of left translation operators

It is known that for an amenable locally compact group , is not in the weak closure of of . In this paper, it is proved that the converse of this is true. In other words, if is a non-amenable locally compact group, then is in the weak closure of . This answers several questions of Ülger. Applications to the algebra and the dual of the reduced group -algebra are obtained.