Crystal field analysis of dysprosium ennea-aqua ethysulphate

The inadequacy of the available sets of crystal field parameters in explaining simultaneously the spectroscopic, magnetic and thermal properties of dysprosium ethylsulphate is brought out and a new optimum set is proposed to unify these characteristics.     

Rank procedures for testing subhypotheses in linear regression

Summary In the linear regression modelX _i=α+βc_i+Z_i, we consider the problem of testing the subhypothesis that some (but not all) components of β are equal to 0. A class of asymptotically distribution-free tests based on a quadratic form in aligned rank statistic is studied and the asymptotic relative efficiencies of the proposed tests with respect to the general likelihood ratio test and the test based on least-squares estimates of regression parameters are derived. Asymptotic optimality (à la Wald) is also discussed. Work done under the National Science Foundation Grant MCS 8301409 and NATO Grant 1465.     

Numerical modelling of subcritical open channel flow using the K-ε turbulence model and the penalty function finite element technique

A numerical model has been developed that employs the penalty function finite element technique to solve the vertically averaged hydrodynamic and turbulence model equations for a water body using isoparametric elements. The full elliptic forms of the equations are solved, thereby allowing recirculating flows to be calculated. Alternative momentum dispersion and turbulence closure models are proposed and evaluated by comparing model predictions with experimental data for strongly curved subcritical open channel flow. The results of these simulations indicate that the depth-averaged two-equation k-ε turbulence model yields excellent agreement with experimental observations. In addition, it appears that neither the streamline curvature modification of the depth-averaged k-ε model, nor the momentum dispersion models based on the assumption of helicoidal flow in a curved channel, yield significant improvement in the present model predictions. Overall model predictions are found to be as good as those of a more complex and restricted three-dimensional model.     

Mass-transport models with multiple-chipping processes

We study mass-transport models with multiple-chipping processes. The rates of these processes are dependent on the chip size and mass of the fragmenting site. In this context, we consider k-chip moves (where k = 1, 2, 3, ...); and combinations of 1-chip, 2-chip and 3-chip moves. The corresponding mean-field (MF) equations are solved to obtain the steady-state probability distributions, P(m) vs. m. We also undertake Monte Carlo (MC) simulations of these models. The MC results are in excellent agreement with the corresponding MF results, demonstrating that MF theory is exact for these models.     

Phase Separation in Confined Geometries

The kinetics of phase separation or domain growth, subsequent to temperature quenches of binary mixtures from the one-phase region into the miscibility gap, still remains a challenging problem of nonequilibrium statistical mechanics. We have an incomplete understanding of many aspects of the growth of concentration inhomogeneities, including the effect of surfaces on this process, and the interplay with wetting phenomena and finite-size effects in thin films. In the present paper, an overview of the simulation approaches to this problem is given, with an emphasis on solutions of a diffusive Ginzburg-Landau model. We also discuss two recent alternative approaches: a local molecular field approximation to the Kawasaki spin exchange model on a lattice; and molecular dynamics simulations of a fluid binary Lennard-Jones mixture. A brief outlook to open questions is also given.     

Novel class of hybrid natural products derived from lupeol as antimalarial agents

Thirty-four novel hybrid lupeol derivatives (4-18) were prepared and evaluated for antimalarial activity in vitro against Plasmodium falciparum. Three compounds (13d, 16a and 17a) have shown antimalarial activity at lower dose (10 microg mL(-1)) than lupeol.     

Reduced order fully coupled structural–acoustic analysis via implicit moment matching

A reduced order model is developed for low frequency, undamped, fully coupled structural–acoustic analysis of interior cavities backed by flexible structural systems. The reduced order model is obtained by applying a projection of the coupled system matrices, from a higher dimensional to a lower dimensional subspace, whilst preserving essential properties of the coupled system. The basis vectors for projection are computed efficiently using the Arnoldi algorithm, which generates an orthogonal basis for the Krylov Subspace containing moments of the original system. The key idea of constructing a reduced order model via Krylov Subspaces is to remove the uncontrollable, unobservable and weakly controllable, observable parts without affecting the transfer function of the coupled system. Three computational test cases are analyzed, and the computational gains and the accuracy compared with the direct inversion method in ANSYS.     

Characterization of two epimers, 4alpha and 4beta, of a novel podophyllotoxin-4-O-(D)-6-acetylglucopyranoside from Podophyllum hexandrum by LC-ESI-MS-MS

High-performance liquid chromatography (HPLC) with diode array detection interfaced to electrospray ionization (ESI) mass spectrometry (MS) is applied to identify the two epimers of a novel and minor constituent, podophyllotoxin-4-O-(D)-6-acetylglucopyraniside from high-altitude Podophyllum hexandrum for the first time. This is done by matching the structural information from the tandem MS data with the reported lignan markers. The results show that LC-MS-MS is the method of choice for fast detection and detailed chemical analysis of mixtures in the crude extracts of Podophyllum. The method can be employed in the absence of reference standards for the markers and is particularly useful in view of the scarcity of these rare chemical standards.