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Stability Diagram (stability + diagram)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Assessment of algorithms for the no-slip boundary condition in the lattice Boltzmann equation of BGK model

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008
Yong Kweon Suh
Abstract Three kinds of algorithms for the lattice Boltzmann equation of the BGK model in the implementation of the no-slip boundary condition on the wall are assessed by using the analytical formula for the slip velocity of the fully developed pressure-driven channel flow. It is shown that the bounce-back algorithm results in the spatial accuracy of 1st order, except for the case when the wall is located at half way between the two grid lines. The interpolation scheme proposed by Yu et al. (Prog. Aerospace Sci. 2003; 39:329,367) and the similar one by Bouzidi et al. (Phys. Fluids 2001; 13(11):3452,3459) are of 2nd order, but the error increases quadratically with the relaxation time. The extrapolation scheme of Guo et al. (Phys. Fluids 2002; 14(6):2007,2010) is also shown to be of 2nd order, and the error level increases linearly with the relaxation time, but it turns out that this scheme is unstable for a certain range of parameter values. Numerical experiments with various parameter sets have been performed to obtain the stability diagram. Three algorithms are then applied to a circular-Couette flow and their performance is also studied in terms of the numerical accuracy and stability. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Fine structure of the stability diagram and the amplitude of ion oscillation within hyperboloidal mass spectrometers

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2002
Ernst P. Sheretov
This article shows that the dependence of the amplitude of ion oscillation within a hyperboloidal mass spectrometers (HMS) as a function of working point location on the stability diagram (in this case all working points lie at one scan line) exhibits a structure with spikes: the amplitude decreases drastically in some points and these dips look like ,reversed spikes'. It is shown that the dips appear at particular values of the stability parameter, ,0, that correspond to intersections of the scan line with lines of parametric resonances (quasi-stability lines) described by us previously. This effect governs the trapping efficiency of ions injected into a radio-frequency ion trap from an external source. Copyright © 2002 John Wiley & Sons, Ltd. [source]

On the Temperature,Pressure Free-Energy Landscape of Proteins

CHEMPHYSCHEM, Issue 4 2003
Revanur Ravindra Dr.
Abstract We studied the thermodynamic stability of a small monomeric protein, staphylococcal nuclease (Snase), as a function of both temperature and pressure, and expressed it as a 3D free-energy surface on the p,T -plane using a second-order Taylor expansion of the Gibbs free-energy change ,G upon unfolding. We took advantage of a series of different techniques (small-angle Xray scattering, Fourier-transform infrared spectroscopy, differential thermal analysis, pressure perturbation calorimetry and densitometry) in the evaluation of the conformation of the protein and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The calculated results of the free-energy landscape of the protein are in good agreement with experimental data of the p,T -stability diagram of the protein over a temperature range from 200 to 400 K and at pressures from ambient pressure to 4000 bar. The results demonstrate that combined temperature,pressure-dependent studies can help delineate the free-energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. The approach presented may also be used for studying other systems with so-called re-entrant or Tamman loop-shaped phase diagrams. [source]