Simulation of a turbulent premixed open V-shaped flame using contour advection with surgery

Despite its capability of high spatial resolution, simulation of turbulent flows with traditional Lagrangian (front tracking) scheme is often discouraged by numerical instability caused by clustering of marker nodes and topological changes of fronts. Contour advection surgery (CAS), being a robust front tracking scheme, can limit the growth of front complexity during simulation without jeopardizing accuracy or efficiency. This allows it to open up an advantage over traditional front-tracking schemes. It has already been demonstrated that CAS, with incorporation of the reaction sheet model, can accurately simulate the propagation and advection of a turbulent premixed V-shaped flame. In this study, it is further tested with 10 values of vortex circulation. A range of upstream turbulence levels of 1.8–19.8% was obtained. Results indicate that upstream turbulence increase the average flame length, flame zone area and the overall burning rate. Flame surface density Σ was also estimated. Maximum values of Σ obtained lie in the range 0.1–1.4 mm⁻¹. Skewness towards the burnt region was observed in all profiles of Σ. Similar to results from laboratory experiments, it was found that Σ values decreases with upstream turbulence. From this study, the ability of CAS to cope with intense turbulence is demonstrated and a better quantitative understanding on the scheme has also been acquired.     

Magic neutrino mass matrix and the Bjorken–Harrison–Scott parameterization

Observed neutrino mixing can be described by a tribimaximal MNS matrix. The resulting neutrino mass matrix in the basis of a diagonal charged lepton mass matrix is both 2–3 symmetric and magic. By a magic matrix, I mean one whose row sums and column sums are all identical. I study what happens if 2–3 symmetry is broken but the magic symmetry is kept intact. In that case, the mixing matrix is parameterized by a single complex parameter U_e3, in a form discussed recently by Bjorken, Harrison, and Scott.     

Enantioselective separations by capillary GC on derivatized cyclodextrins. Part 2: Determination of enantiomeric excess of some racemic 2,3-isopropylidene-1,2,3-cyclohexanetriol derivatives on permethyl α-, β-, and γ-cyclodextrins

Capillary GC on permethyl α-, β-, and γ-cyclodextrins has been applied to separate and quantify the enantiomers of some 2,3-iso-propylidene-1,2,3-cyclohexanetriol derivatives. Quantitative CGC data are compared to those obtained with chiral shift ¹H NMR.     

Application of ODMR to the study of DNA complexes of bisintercalating antibiotics and their biosynthesized derivatives

The DNA complexes of triostin A, echinomycin, and the monoquinoline (1QN) and bisquinoline (2QN) biosynthesized derivatives of echinomycin were investigated by optical detection of triplet-state magnetic resonance (ODMR) spectroscopy, with the quinoxaline and quinoline moieties of the DNA-binding peptides used as intrinsic probes. Plots of zero-field splitting (zfs)D parameter versus monitored wavelength revealed heterogeneity in the phosphorescence emission of echinomycin, triostin A, and 2QN ascribed to the occurrence of major and minor forms of the peptides in aqueous solution. ODMR results, in conjunction with findings from phosphorescence studies, indicate that the quinoxaline and quinoline chromophores of the major forms of the peptides are involved in aromatic stacking interactions in complexes with the natural DNAs fromMicrococcus lysodeikticus, Escherichia coli, and calf thymus as evidenced by red shifts in the phosphorescence 0,0 bands of the drugs, reductions in the phosphorescence lifetimes and zfsD andE parameters, and polarity reversal of the ODMR slow passage signals upon drug complexation. The reversal in ODMR signal polarity of echinomycin and 2QN is a consequence of changes in the triplet-state sublevel decay constants upon peptide binding to the natural DNAs. The extent of reduction of theD parameter for the major form of echinomycin, 2QN, and the quinoline moiety of 1QN upon complexation with polymeric DNAs was found to correlate with the binding affinities measured for these targets [1], but no correlation was found for the quinoxaline moiety of 1QN. Preliminary studies of triostin A-DNA complexes also revealed no correlation between the reduction in zfsD-value upon complexation and binding affinity, although the largest reductions inD-value among the peptides investigated in this report were exhibited by the poly(dG-dC)·poly(dG-dC) and natural DNA complexes of triostin A.     

Grid‐free surface vorticity method applied to flow induced vibration of flexible cylinders

In order to study cross flow induced vibration of heat exchanger tube bundles, a new fluid–structure interaction model based on surface vorticity method is proposed. With this model, the vibration of a flexible cylinder is simulated at Re=2.67 × 10⁴, the computational results of the cylinder response, the fluid force, the vibration frequency, and the vorticity map are presented. The numerical results reproduce the amplitude‐limiting and non‐linear (lock‐in) characteristics of flow‐induced vibration. The maximum vibration amplitude as well as its corresponding lock‐in frequency is in good agreement with experimental results. The amplitude of vibration can be as high as 0.88D for the case investigated. As vibration amplitude increases, the amplitude of the lift force also increases. With enhancement of vibration amplitude, the vortex pattern in the near wake changes significantly. This fluid–structure interaction model is further applied to simulate flow‐induced vibration of two tandem cylinders and two side‐by‐side cylinders at similar Reynolds number. Promising and reasonable results and predictions are obtained. It is hopeful that with this relatively simple and computer time saving method, flow induced vibration of a large number of flexible tube bundles can be successfully simulated. Copyright © 2004 John Wiley & Sons, Ltd.     

Improved estimation of a covariance matrix in an elliptically contoured matrix distribution

In this paper, the problem of estimating the covariance matrix of the elliptically contoured distribution (ECD) is considered. A new class of estimators which shrink the eigenvalues towards their arithmetic mean is proposed. It is shown that this new estimator dominates the unbiased estimator under the squared error loss function. Two special classes of ECD, namely, the multivariate-elliptical t distribution and the ε-contaminated normal distribution are considered. A simulation study is carried out and indicates that this new shrinkage estimator provides a substantial improvement in risk under most situations.     

Some New uniform frames with block size four and index one or three

In this paper, some new uniform frames with block size four and index one or three are obtained. The known existence results for (4,1)‐frames and (4,3)‐frames are both improved to the extent that only a finite number of possible exceptions remain. © 2003 Wiley Periodicals, Inc.