Thermodynamic Description (thermodynamic + description)

Distribution by Scientific Domains


Selected Abstracts


Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003
Maria Bercea
Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source]


Comprehensive Thermodynamic Description of the Quasiternary System PbTe,GeTe,SnTe.

CHEMINFORM, Issue 24 2006
Lada V. Yashina
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


Thermodynamic Modeling of High-Temperature Fe-Ni-Heazlewoodite

ADVANCED ENGINEERING MATERIALS, Issue 11 2006
P. Waldner
The thermodynamic modeling of key sub-systems as the iron-nickel-sulfur system is a contribution to the development of extended databases for multicomponent metal-sulfur systems. A further extension of a recent thermodynamic modeling of the Fe-Ni-S system is presented. A two-sublattice approach in the framework of the Compound Energy Formalism is used for a consistent integration of a second ternary high,temperature heazlewoodite phase within a complete thermodynamic description of the Fe-Ni-S system. [source]


Multiple steady states in distillation: Effect of VL(L)E inaccuracies

AICHE JOURNAL, Issue 5 2000
Nikolaos Bekiaris
Output multiplicities in heterogeneous azeotropic distillation columns were studied. The accuracy of the thermodynamic description is a key factor that determines if multiplicities can be observed in numerical simulations. The descriptions used in the multiplicity-related literature are analyzed. The ,/, analysis of Bekiaris et al. (1996) was used to check implications of inaccuracies in the reported thermodynamics on the existence of multiplicities in azeotropic distillation. On this basis, guidelines are derived concerning what features of thermodynamic descriptions need special attention for use in multiplicity prediction and simulation. Secondly, numerical studies on output multiplicities in heterogeneous azeotropic distillation in the literature were compared to the ,/, predictions wherever possible. The ,/, analysis was used to derive the relations between the reported multiplicities and to identify the physical phenomena causing them. [source]


Lessons in stability from thermophilic proteins

PROTEIN SCIENCE, Issue 7 2006
Abbas Razvi
Abstract Studies that compare proteins from thermophilic and mesophilic organisms can provide insights into ability of thermophiles to function at their high habitat temperatures and may provide clues that enable us to better define the forces that stabilize all proteins. Most of the comparative studies have focused on thermal stability and show, as expected, that thermophilic proteins have higher Tm values than their mesophilic counterparts. Although these comparisons are useful, more detailed thermodynamic analyses are required to reach a more complete understanding of the mechanisms thermophilic protein employ to remain folded over a wider range of temperatures. This complete thermodynamic description allows one to generate a stability curve for a protein that defines how the conformational stability (,G) varies with temperature. Here we compare stability curves for many pairs of homologous proteins from thermophilic and mesophilc organisms. Of the basic methods that can be employed to achieve enhanced thermostability, we find that most thermophilic proteins use the simple method that raises the ,G at all temperatures as the principal way to increase their Tm. We discuss and compare this thermodynamic method with the possible alternatives. In addition we propose ways that structural alterations and changes to the amino acid sequences might give rise to varied methods used to obtain thermostability. [source]


Multiple steady states in distillation: Effect of VL(L)E inaccuracies

AICHE JOURNAL, Issue 5 2000
Nikolaos Bekiaris
Output multiplicities in heterogeneous azeotropic distillation columns were studied. The accuracy of the thermodynamic description is a key factor that determines if multiplicities can be observed in numerical simulations. The descriptions used in the multiplicity-related literature are analyzed. The ,/, analysis of Bekiaris et al. (1996) was used to check implications of inaccuracies in the reported thermodynamics on the existence of multiplicities in azeotropic distillation. On this basis, guidelines are derived concerning what features of thermodynamic descriptions need special attention for use in multiplicity prediction and simulation. Secondly, numerical studies on output multiplicities in heterogeneous azeotropic distillation in the literature were compared to the ,/, predictions wherever possible. The ,/, analysis was used to derive the relations between the reported multiplicities and to identify the physical phenomena causing them. [source]