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Constant Independent (constant + independent)
Selected AbstractsOn the possibility of self-induction of drug protein bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Leonid M. Berezhkovskiy Abstract The equilibrium unbound drug fraction (fu) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that fu can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation. For several drugs, though, a seemingly unusual sharp decrease of the unbound drug fraction with the increase of total drug concentration (Ro) in the interval 0,<,Ro,,,5,µM was experimentally observed. A possible explanation of this apparently strange phenomenon is presented. The explanation is based on the consideration of a two-step mechanism of drug protein binding. The first step occurs as a drug binding to the site with relatively low affinity. Consequently this binding leads to the activation of a high affinity site, which otherwise is not available for binding. The suggested binding scheme yields the curves for fu dependence on the total drug concentration that are in good agreement with experimental measurements. The interpretation of pharmacokinetic data for the drugs with such unusual concentration dependence of fu appears to be a formidable problem. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4400,4405, 2010 [source] Empirical Equation for Calculating the Density of Oxide GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Seiji Inaba The density of oxide glass including silicate, borate, phosphate, tellurite, and germanate glasses were measured using the Archimedes method. On the assumption that the ionic packing ratio is approximately a constant independent of chemical composition, an empirical equation for estimating the density from chemical composition was proposed. The calculated values are in reasonable agreement with the corresponding measured ones. [source] An investigation of human brain tumour lipids by high-resolution magic angle spinning 1H MRS and histological analysisNMR IN BIOMEDICINE, Issue 7 2008Kirstie S. Opstad Abstract NMR-visible lipid signals detected in vivo by 1H MRS are associated with tumour aggression and believed to arise from cytoplasmic lipid droplets. High-resolution magic angle spinning (HRMAS) 1H MRS and Nile Red staining were performed on human brain tumour biopsy specimens to investigate how NMR-visible lipid signals relate to viable cells and levels of necrosis across different grades of glioma. Presaturation spectra were acquired from 24 adult human astrocytoma biopsy samples of grades II (8), III (2) and IV (14) using HRMAS 1H MRS and quantified using LCModel to determine lipid concentrations. Each biopsy sample was then refrozen, cryostat sectioned, and stained with Nile Red, to determine the number of lipid droplets and droplet size distribution, and with Haematoxylin and Eosin, to determine cell density and percentage necrosis. A strong correlation (R,=,0.92, P,<,0.0001) was found between the number of Nile Red-stained droplets and the ,1.3,ppm lipid proton concentration by 1H MRS. Droplet sizes ranged from 1 to 10,µm in diameter, and the size distribution was constant independent of tumour grade. In the non-necrotic biopsy samples, the number of lipid droplets correlated with cell density, whereas in the necrotic samples, there were greater numbers of droplets that showed a positive correlation with percentage necrosis. The correlation between 1H MRS lipid signals and number of Nile Red-stained droplets, and the presence of lipid droplets in the non-necrotic biopsy specimens provide good evidence that the in vivo NMR-visible lipid signals are cytoplasmic in origin and that formation of lipid droplets precedes necrosis. Copyright © 2008 John Wiley & Sons, Ltd. [source] Two-grid methods for banded linear systems from DCT III algebraNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 2-3 2005R. H. Chan Abstract We describe a two-grid and a multigrid method for linear systems whose coefficient matrices are point or block matrices from the cosine algebra generated by a polynomial. We show that the convergence rate of the two-grid method is constant independent of the size of the given matrix. Numerical examples from differential and integral equations are given to illustrate the convergence of both the two-grid and the multigrid method. Copyright © 2004 John Wiley & Sons, Ltd. [source] Failure prediction for Titanium alloys using a superplastic forming limit diagram approachMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4-5 2008S.B. Leen Abstract Superplastic forming limit diagrams (SPFLDs) are presented for both Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys. FE-predicted ,1 - ,3 -,eq paths for key points on the forming blank are then plotted on the SPFLD to predict failure. A key factor for reliable SPF forming limit prediction is the incorporation of a mechanisms-based constitutive model, which includes microstructural effects, such as static and dynamic grain growth and associated hardening, and with material constants independent of the forming strain-rate. The sinh model of Dunne and co-workers is thus employed. Results from forming trials for both materials are used to assess the failure predictions. [source] Artificial boundary conditions for viscoelastic flowsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2008Sergueï A. Nazarov Abstract The steady three-dimensional exterior flow of a viscoelastic non-Newtonian fluid is approximated by reducing the corresponding nonlinear elliptic,hyperbolic system to a bounded domain. On the truncation surface with a large radius R, nonlinear, local second-order artificial boundary conditions are constructed and a new concept of an artificial transport equation is introduced. Although the asymptotic structure of solutions at infinity is known, certain attributes cannot be found explicitly so that the artificial boundary conditions must be constructed with incomplete information on asymptotics. To show the existence of a solution to the approximation problem and to estimate the asymptotic precision, a general abstract scheme, adapted to the analysis of coupled systems of elliptic,hyperbolic type, is proposed. The error estimates, obtained in weighted Sobolev norms with arbitrarily large smoothness indices, prove an approximation of order O(R,2+,), with any ,>0. Our approach, in contrast to other papers on artificial boundary conditions, does not use the standard assumptions on compactly supported right-hand side f, leads, in particular, to pointwise estimates and provides error bounds with constants independent of both R and f. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||