Comparison between the classical and QELSS determination of diffusion coefficients. Sharp polymer fractions

1989 ◽  
Vol 54 (7) ◽  
pp. 1808-1820
Author(s):  
Simon King ◽  
Lars-Olof Sundelöf ◽  
Bedřich Porsch
Keyword(s):  
Concentration Dependence ◽  
Exponential Decay ◽  
Diffusion Coefficients ◽  
Diffusion Constant ◽  
Suggested Model ◽  
Model Calculations ◽  
Simple Modification ◽  
Error Limit

Simple modification of the method of cumulants for an evaluation of QELSS data within the error limit of 2% in the case of narrow polymers is suggested. Model calculations of the deviations from the exponential decay due to polydispersity are presented, criteria of applicability of the 1st and 2nd cumulant fit at a given accuracy are derived and verified experimentally. The required agreement between the classical and QELSS diffusion constant is achieved if the QELSS measurements are made at concentrations where the effect of concentration dependence of the diffusion constant may be neglected.

scholarly journals Quantifying the concentration dependence of sedimentation coefficients for globular macromolecules: a continuing age-old problem

2021 ◽  
Author(s):  
Donald J. Winzor ◽  
Vlad Dinu ◽  
David J. Scott ◽  
Stephen E. Harding
Keyword(s):  
Concentration Dependence ◽  
Diffusion Coefficients ◽  
Sedimentation Coefficient ◽  
Sedimentation Velocity ◽  
Translational Diffusion ◽  
Optical Systems ◽  
Coefficient Measurement ◽  
Retrospective Investigation ◽  
Linear Concentration

AbstractThis retrospective investigation has established that the early theoretical attempts to directly incorporate the consequences of radial dilution into expressions for variation of the sedimentation coefficient as a function of the loading concentration in sedimentation velocity experiments require concentration distributions exhibiting far greater precision than that achieved by the optical systems of past and current analytical ultracentrifuges. In terms of current methods of sedimentation coefficient measurement, until such improvement is made, the simplest procedure for quantifying linear s-c dependence (or linear concentration dependence of 1/s) for dilute systems therefore entails consideration of the sedimentation coefficient obtained by standard c(s), g*(s) or G(s) analysis) as an average parameter ($$ \overline{s} $$ s ¯ ) that pertains to the corresponding mean plateau concentration (following radial dilution) ($$ \overline{c} $$ c ¯ ) over the range of sedimentation velocity distributions used for the determination of $$ \overline{s} $$ s ¯ . The relation of this with current descriptions of the concentration dependence of the sedimentation and translational diffusion coefficients is considered, together with a suggestion for the necessary improvement in the optical system.

The Calculation of Turbulent Diffusion Coefficients in Aquatic Ecosystems

2019 ◽  
Vol 70 (11) ◽  
pp. 3903-3907
Author(s):  
Galina Marusic ◽  
Valeriu Panaitescu
Keyword(s):  
Transport Equation ◽  
Turbulent Diffusion ◽  
Diffusion Coefficients ◽  
Aquatic Ecosystems ◽  
Specific Area ◽  
Left Bank ◽  
The Right ◽  
Prut River

The paper deals with the issues related to the pollution of aquatic ecosystems. The influence of turbulence on the transport and dispersion of pollutants in the mentioned systems, as well as the calculation of the turbulent diffusion coefficients are studied. A case study on the determination of turbulent diffusion coefficients for some sectors of the Prut River is presented. A new method is proposed for the determination of the turbulent diffusion coefficients in the pollutant transport equation for specific sectors of a river, according to the associated number of P�clet, calculated for each specific area: the left bank, the right bank and the middle of the river.

scholarly journals Migration of mineral oil in elastomers

2021 ◽  
Author(s):  
Tobias Förster ◽  
Artur Blivernitz
Keyword(s):  
Diffusion Coefficients ◽  
Mineral Oil ◽  
Activation Energies ◽  
Concentration Profiles ◽  
Small Reservoir ◽  
Experimental Procedure ◽  
Mineral Oils ◽  
The Absolute ◽  
Suitable Measure

AbstractThis work describes a newly introduced experimental procedure to quantify the diffusion progress of mineral oils locally resolved in NBR. Diffusion of reference oils IRM 901, IRM 902 and IRM 903 in NBR with various acrylonitrile contents was investigated. Classical sorption experiments were performed as a basic characterization and compared to the newly introduced method. Here, elastomer specimens are only being dipped with the bottom in a relatively small reservoir of mineral oil. This provides a determination of locally resolved concentration profiles of mineral oils, and the calculation of diffusion coefficients. These diffusion coefficients follow the same trends like those determined via sorption experiments. Despite differences in the absolute numbers, activation energies of diffusion can be applied as a suitable measure for the compatibility of elastomers and fluids.

Statistical Description of Isotope Exchange Processes: A Multisite Model for the 18O Exchange

1982 ◽  
Vol 37 (11-12) ◽  
pp. 1161-1169 ◽  
Author(s):  
Paul Rösch
Keyword(s):  
Active Site ◽  
Isotope Exchange ◽  
Analytical Procedure ◽  
Matrix Formalism ◽  
Model Calculations ◽  
Exchange Processes ◽  
Reaction Solution ◽  
Different Types ◽  
Refinement Procedure

Abstract An analytical procedure has been developed for the determination of isotope exchange processes as exemplified by the 18O exchange catalysed by enzyme-nucleotide complexes. The model is able to handle more than one type of active site per reaction solution and is also able to distinguish between different types of inequivalence of the oxygens of enzyme bound Pi. Use of transition matrix formalism and basic statistical considerations lead directly to the simple model. A data refinement procedure is introduced and model calculations are shown.

Direct determination of the concentration dependence of diffusivities using combined model-based Raman and NMR experiments

2009 ◽  
Vol 277 (2) ◽  
pp. 96-106 ◽  
Author(s):  
E. Kriesten ◽  
M.A. Voda ◽  
A. Bardow ◽  
V. Göke ◽  
F. Casanova ◽  
...  
Keyword(s):  
Concentration Dependence ◽  
Direct Determination ◽  
Combined Model ◽  
Model Based
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