Combined Effect of Temperature and Ternary Mobile Phase Composition on the Retention in Ternary Isocratic and Gradient Elution RP-LC under Isothermal Conditions. Application to the Retention Prediction of Four Macrolide Antibiotics

Retention models considering simultaneously ternary mobile phase organic contents and column temperature (T) were developed by a direct combination of equations expressing separately the dependence of the retention upon each of these factors. Thus, a combination of a linear dependence of the logarithm of the solute retention factor, ln k (T), against 1/T, i.e. ln k (T) = a + b/T, and of either a linear or a quadratic dependence of ln k upon the compositions of a binary mobile phase, gave two different expressions for the logarithm of the solute retention factor in terms of both temperature and organic contents in the ternary mobile phase. The effectiveness of the above models was tested in the prediction of isothermal retention of a mixture of four macrolide antibiotics under ternary isocratic and gradient elution conditions using mobile phases modified by methanol and acetonitrile. The limiting case of using ternary eluents with constant ratio of the concentrations of the two organic modifiers was also tested.     

Impact of Statistical Multiplexing on Voice Quality in Cellular Networks

This paper examines the quality of transmission of voice over cellular, packet-switched networks. The medium access mechanism in the uplink is simulated under various statistical multiplexing scenarios in order to assess the effect of front-end clipping on voice quality. Moreover, the simulation is implemented in a real-time demonstration platform utilized to acquire subjective indicators of voice quality by performing Mean Opinion Score (MOS) tests. Results from the MOS tests are reported, and an analysis of the obtained speech samples is presented. Finally, the results are summarized and potential further directions for the simulation tool and the speech models are discussed.     

High resolution multigrid cross-correlation digital PIV measurements of a turbulent starting jet using half frame image shift film recording

This paper describes a novel approach of acquiring two single-exposed, non-overlapping images using half frame image shift (HFIS) recording on photographic film. This technique permits the recording of two single-exposed, non-overlapping images of seed particles in a flow plane on high spatial resolution film with any arbitrary time delay between exposures. A new multigrid CCDPIV (MCCDPIV) analysis method is used to analyse the single-exposed, non-overlapping sequential images resulting in PIV measurements with a larger velocity dynamic range, lower random error and better spatial resolution than standard CCDPIV analysis. HFIS recording followed by MCCDPIV analysis was employed to measure the spatio-temporal evolution of the in-plane velocity vector and the out-of-plane vorticity fields of a turbulent starting jet at Reynolds numbers based on the orifice diameter and piston velocity of 10,780 and 13,860.     

Magnetohydrodynamics and Plasma Cosmology

We study the linear magnetohydrodynamic (MHD) equations, both in the Newtonian and the general-relativistic limit, as regards a viscous magnetized fluid of finite conductivity and discuss instability criteria. In addition, we explore the excitation of cosmological perturbations in anisotropic spacetimes, in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m) and fast-magnetosonic modes, propagating normal to the magnetic field, can be excited, resulting in several implications of cosmological significance.     

Dynamic K-L analysis of coherent structures based on DNS of turbulent Newtonian and viscoelastic flows

Earlier work [1, 2], using Karhunen-Loeve (K-L) analysis, demonstrated a dramatic enhancement of the importance of large scale motions with increased viscoelasticity and an equally dramatic decrease in the K-L dimension of the flow (an order of magnitude) as viscoelasticity increases versus similar Newtonian results. In this work we look into dynamics of viscoelastic turbulent flows by projecting the DNS data in time into a selected set of K-L modes. The dynamics of the coherent structures embedded in turbulent flows were investigated through calculations of mode auto and cross correlations. This allows for a more systematic examination of the role of large-scale structures in turbulence and drag reduction. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Extensional behavior influence on viscoelastic turbulent channel flow

In this work we use in the simulation of a viscoelastic turbulent channel flow a modification of the finitely extensible of non-linear elastic dumbbells with the Peterlin approximation (FENE-P) constitutive model for dilute polymer solutions, applicable to high extensional deformations. The new feature introduced by this modification is that the free energy of the polymer (since it is assumed to be entirely entropically driven) remains always bounded (FENE-PB). The characteristics of the model under steady shear flow, pure elongational flow and transient extensional behavior are presented. It is found that the FENE-PB model is more shear thinning than FENE-P. Most importantly, it also shows a higher extensional viscosity than the FENE-P model. Although the steady-state Trouton ratio asymptotically reaches at high extensional rates the same limit as the FENE-P model, the transition from the Newtonian value is sharper and faster. We use the FENE-PB model in direct numerical simulations (DNS) of viscoelastic turbulent channel flow using spectral approximations. The results for various statistics of the flow and the polymer conformation, when compared against those obtained with the original FENE-P model and the same rheological parameters, show an enhanced polymer-induced drag reduction effect and enhanced deformation of the polymer molecules. This indicates that it is not only the asymptotic but also details from the extensional rheological behavior that matter in quantitatively specifying turbulent viscoelastic flow behavior.