Search results for "Viscosity."
showing 10 items of 537 documents
Mechanistic investigation of food effect on disintegration and dissolution of BCS class III compound solid formulations: the importance of viscosity
2012
A negative food effect, i.e. a decrease in bioavailability upon the co-administration of compounds together with food, has been attributed particularly with high solubility/low permeability compounds (BCS class III). Different mechanisms have been proposed including intestinal dilution leading to a lower concentration gradient across the intestinal wall as well as binding of the active pharmaceutical ingredient to food components in the intestine and thereby decreasing the fraction of the dose available for absorption. These mechanisms refer primarily to the compound and not to the dosage form. An increase in viscosity of the dissolution fluid will in particular affect the absorption of BCS…
Molekülgrößenbestimmungen an makromolekularen Stoffen (Kritik und Vergleich der Methoden)
1952
A survey is given of the most important methods for determination of molecular weight (osmotic pressure, ultracentrifuge and diffusion, light scattering, viscosity). All the methods require an extrapolation to zero concentration in order to use equations valid for ideal solutions. Furthermore the polymolecularity of the examined substance must be considered, since each method yields a characteristic average of molecular weight differing from the others. The present limits of the methods are given and their results compared.
Hemorheologic profile of hyperlipidemic patients treated with gemfibrozil
1996
Abstract We measured the plasma lipid levels and the macrorheologic (whole-blood, plasma, and serum viscosity levels; fibrinogen; hematocrit; mean erythrocyte aggregation; and whole-blood filterability) and microrheologic (erythrocyte membrane fluidity and red cell membrane protein lateral mobility) determinants in a group of 19 hyperlipidemic patients (Fredrickson's classification phenotype IIa, 12 patients; phenotype IV, 4; phenotype IIb, 3) at baseline and after 45 and 90 days of treatment with gemfibrozil (900 mg orally once a day). At baseline we noted statistically significant increases in plasma viscosity level, fibrinogen, and mean erythrocyte aggregation, as well as a statistically…
Phase transitions in a colloidal dispersion flowing through a cylindrical capillary
2008
The flow of a charged-stabilized colloidal dispersion of crystalline equilibrium structure through a cylindrical capillary is investigated. The simultaneous existence of up to three differently ordered states is observed under conditions of stationary flow. The evolution of their concentric arrangement along the capillary is determined by Bragg microscopy. For sufficient low fluxes, stationary phase distributions are obtained. While the apparent viscosity is non-monotonous and non-Newtonian, the corresponding velocity profiles are found to be piecewise parabolic and are compatible to numerical calculations. Furthermore, we test the assumption of a constant yield stress determining the radia…
Temperature dependence of η/s of strongly interacting matter: Effects of the equation of state and the parametric form of (η/s)(T)
2020
We investigate the temperature dependence of the shear viscosity to entropy density ratio $\ensuremath{\eta}/s$ using a piecewise linear parametrization. To determine the optimal values of the parameters and the associated uncertainties, we perform a global Bayesian model-to-data comparison on $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=200$ GeV and $\mathrm{Pb}+\mathrm{Pb}$ collisions at 2.76 TeV and 5.02 TeV, using a $2+1\mathrm{D}$ hydrodynamical model with the Eskola-Kajantie-Ruuskanen-Tuominen (EKRT) initial state. We provide three new parametrizations of the equation of state (EoS) based on contemporary lattice results and hadron resonance gas, and use them and t…
Sound absorption prediction of linear damped acoustic resonators using a lightweight hybrid model
2019
International audience; A lightweight numerical method is developed to predict the sound absorption coefficient of resonators whose cross-section dimensions are significantly larger compared to the viscous and thermal boundary layer’s thicknesses. This method is based on the boundary layer theory and on the perturbations theory. According to the perturbations theory, in acoustical domains with large dimensions, the fluid viscosity and thermal conductivity only affect the boundary layers. The model proposed in this article combines the lossless Helmholtz wave equation derived from a perfect fluid hypothesis, with viscosity and thermal conductivity values of a real fluid to compute the sound …
Ab initiosimulations of accretion disc instability
2003
We show that accretion disks, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behavior has been obtained by performing a set of time-dependent 2D SPH simulations of accretion disks with different values of alpha and accretion rate. In this study, to avoid any influence of the initial disk configuration, we produced the disks injecting matter from an outer edge far from the central object. The period of oscillations is 2 - 50 s respectively for the two cases, and the variation amplitude of the disc luminosity is 10^38 - 10^39 erg/s. An explanation of this luminosity behavior is proposed in terms o…
Numerical Simulations of the Thermal Instability Collapse in Radiation Pressure Dominated Disks
2005
We show that accretion disks, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behavior has been obtained by performing a set of time‐dependent 2D SPH simulations of accretion disks with different values of α and accretion rate. An explanation of this luminosity behavior is proposed in terms of limit‐cycle instability: the disk oscillates between a radiation pressure dominated configuration (with a high luminosity value) and a gas pressure dominated one (with a low luminosity value). The origin of this instability is the difference between the heat produced by viscosity and the energy emitted as r…
Nonlinear Critical Layers in Barotropic Stability
1991
Abstract Applying the method of matched asymptotic expansions (MAE) to the shallow water equations on a rotating sphere, the structure of critical layers that occur in the linear and inviscid analysis of neutral disturbances of barotropic zonal flows is investigated, assuming that the critical layers are controlled by nonlinearity rather than viscosity or nonparallel flow effects. It turns out that nonlinearity is insufficient to resolve the critical layer singularity completely. It suffices however to connect linear and nondissipative solutions across critical latitudes.
Critical Dynamics in a Binary Fluid: Simulations and Finite-Size Scaling
2006
We report comprehensive simulations of the critical dynamics of a symmetric binary Lennard-Jones mixture near its consolute point. The self-diffusion coefficient exhibits no detectable anomaly. The data for the shear viscosity and the mutual-diffusion coefficient are fully consistent with the asymptotic power laws and amplitudes predicted by renormalization-group and mode-coupling theories {\it provided} finite-size effects and the background contribution to the relevant Onsager coefficient are suitably accounted for. This resolves a controversy raised by recent molecular simulations.