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V. N. Pavlechko - One of the best experts on this subject based on the ideXlab platform.
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Relationship between Murphree and Complex Model mass transfer efficiencies
Journal of Engineering Physics and Thermophysics, 2011Co-Authors: V. N. PavlechkoAbstract:Graphical comparison of the Murphree mass transfer efficiency with the efficiency of the Complex Model has been made. We have proved and illustrated the expediency of using the Murphree mass transfer efficiency determination in the vapor and the liquid phases for the parallel flow, the counterflow, and the crossflow at phase equilibrium coefficients close to 1; at its other values it is recommended to use the efficiency of the Complex Model. The impossibility of using the Murphree efficiency in a liquid for analyzing the mass transfer in the counterflow of the phases, which in this case is equal to zero, has been proved.
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Motive Force in a Complex Model of Mass Transfer
Journal of Engineering Physics and Thermophysics, 2004Co-Authors: V. N. PavlechkoAbstract:Relations for determining a motive force in a Complex Model of mass transfer as applied to concurrent, countercurrent, and cross motion of the vapor and liquid phases have been introduced. These forces have been compared for different forms of organization of the flow, and their comparison with similar quantities from the known Murphree and Hausen Models is presented.
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Analysis of the boundary conditions of the Complex Model of mass exchange in rectification processes
Journal of Engineering Physics and Thermophysics, 2003Co-Authors: V. N. PavlechkoAbstract:Boundary conditions of applicability of the Complex mass‐exchange Model to forward, backward, and cross motions of the vapor and liquid phases in rectification have been found. Four variants of mass exchange which are the limits of the Complex Model have been considered. The limiting values of the distances h and h1 from the site of injection of the phases at which the compositions in ideal and real plates are equalized have been computed. The relations between the basic technological parameters of the rectification process under the boundary conditions have been obtained.
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Comparison of the efficiency of mass exchange in the Complex Model for highly volatile and nonvolatile components
Journal of Engineering Physics and Thermophysics, 2003Co-Authors: V. N. PavlechkoAbstract:The efficiencies of mass exchange in the Complex Model have been compared for two variants of representation of the running equation of the equilibrium line: y = mx and y = ax + b. Based on the processing of experimental data on separation of the benzene–toluene mixture in cross motion of the flows, it has been shown that the first equation is adequate only for small variations in the concentrations at the step of mass‐exchange while the second equation has a more universal character.
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Complex Model of the Efficiency of Rectification Plates. 6. Some Features of Applicability of Calculational Dependences
Journal of Engineering Physics and Thermophysics, 2001Co-Authors: V. N. PavlechkoAbstract:The author assumes the interrelation of the distances from the site of injection of a vapor h and a liquid h _1 to the surface of equality of the concentrations on ideal and real plates with a degree of deviation from the Raoult law that is characterized by the activity coefficient γ. If the activities of the components of ideal and real solutions coincide (γ = 1), then h = 0.5 and h _1 = 0.5. With a positive deviation of a highly volatile component from the Raoult law (γ > 1), h > 0.5 and h _1 > 0.5, with a negative deviation (γ < 1) — h < 0.5 and h _1 < 0.5. The influence of the activity of a poorly volatile component and of both components on the indicated distances is also analyzed. In order to eliminate the negative values of the efficiency in calculational procedures, especially in countercurrent flow, it is proposed that the coefficient of equilibrium be found from the slope of a tangent to an equilibrium line to the X axis and that the length of a segment cut off by this tangent on the Y axis be taken into account. Some modifications of new dependences for concurrent flow, countercurrent flow, and cross flow with mixing and without it are given.
Frederick J. Ehlert - One of the best experts on this subject based on the ideXlab platform.
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Cooperativity Has Empirical and Ultimate Levels of Explanation
Trends in pharmacological sciences, 2016Co-Authors: Frederick J. EhlertAbstract:Controversy over the meaning of pharmacological parameters often arises because of a lack of appreciation of different hierarchical levels of analysis. In a recent letter in Trends in Pharmacological Sciences, Zhang and Kavana [1] concluded that my two-state Model for allosterism lacks cooperativity, even though Figures 5 and 6 in my review [2] illustrate examples of how the two-state Model yields specific cooperativity values. Here, I explain how the two-state Model (receptor-state analysis) gives rise to the cooperativity parameter (α) of the allosteric ternary Complex Model (receptor-population analysis).
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two state Models and the analysis of the allosteric effect of gallamine at the m2 muscarinic receptor
Journal of Pharmacology and Experimental Therapeutics, 2008Co-Authors: Frederick J. Ehlert, Michael T GriffinAbstract:We measured the influence of gallamine on the functional responses and binding properties of selected agonists at the M2 muscarinic receptor and analyzed the data within the context of the allosteric ternary Complex Model. Our analysis showed that gallamine modified agonist affinity without influencing efficacy. To explain this behavior, we investigated the allosteric ternary Complex Model at a deeper level of analysis to assess allosterism in terms of the differential affinity of gallamine for ground and active states of the receptor. Our simulations showed that two-state Models based on a single orthosteric site for the agonist linked to an allosteric site for gallamine could not account for affinity-only modulation, even if multiple conformations of ground and active states were considered. We also expanded the tandem two-site Model ( J Biol Chem 275:18836–18844, 2000) within the context of the allosteric ternary Complex Model and analyzed the resulting hybrid Model at the level of receptor states. This Model posits that the agonist first binds to a relay site and then shuttles to the activation site to turn on the receptor. If it is assumed that allosterism occurs at the relay site and not the activation site, then this Model can account for affinity-only modulation in a manner consistent with the allosteric ternary Complex Model.
Hansjoachim Freund - One of the best experts on this subject based on the ideXlab platform.
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reaction kinetics on Complex Model catalysts under single scattering conditions
Journal of Physical Chemistry B, 2002Co-Authors: Jorg Libuda, Hansjoachim FreundAbstract:To approach a microscopic understanding of the reaction kinetics on Complex surfaces of heterogeneous catalysts, we combine multimolecular beam techniques and a supported Model catalyst approach. The Model systems are prepared under ultrahigh vacuum (UHV) conditions and have been characterized in detail with respect to their geometric and electronic structure. To probe the kinetics of catalytic reactions on these systems, we have developed a molecular beam instrument, which allows us to cross up to three beams on the sample surface. The simultaneous detection of reaction products and surface species is established by a combination of angle- and time-resolved gas-phase detection and in situ time-resolved IR reflection absorption spectroscopy. In this paper, we review a variety of representative experiments, illustrating the experimental possibilities of the molecular beam approach. As a Model surface, we focus on alumina supported palladium particles. We cover the adsorption and desorption kinetics of smal...
Robert J Lefkowitz - One of the best experts on this subject based on the ideXlab platform.
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a mutation induced activated state of the beta 2 adrenergic receptor extending the ternary Complex Model
Journal of Biological Chemistry, 1993Co-Authors: P Samama, Susanna Cotecchia, Tommaso Costa, Robert J LefkowitzAbstract:We have replaced the C-terminal portion of the third intracellular loop of the beta 2-adrenergic receptor (residues 266-272) with the homologous region of the alpha 1B-adrenergic receptor. In a fashion analogous to the reciprocal mutations of the alpha 1B receptor previously described (Cotecchia, S., Exum, S., Caron, M. G., and Lefkowitz, R. J. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 2896-2900), this conservative substitution leads to agonist-independent activation of adenylyl cyclase. In addition, the constitutively active mutant receptor exhibits: (i) an increased affinity for agonists (even in the absence of guanine nucleotide-binding regulatory protein (G protein)) but not antagonists, with the extent of affinity increase being correlated with the intrinsic activity of the ligand; (ii) an increased potency of agonists for stimulation of adenylyl cyclase; and (iii) an increased intrinsic activity of partial agonists. We document that our experimental findings with the mutant receptor cannot be adequately rationalized within the theoretical framework of the Ternary Complex Model (De Lean, A., Stadel, J. M., and Lefkowitz, R. J. (1980) J. Biol. Chem. 255, 7108-7117) which postulates that receptor activation requires the agonist-promoted formation of an active, "ternary" Complex of agonist, receptor, and G protein. We show, through extensive computer simulations, that an extended version of this Model that includes an explicit isomerization of the receptor (R) to an active state (R*) closely Models all our findings for both the mutant and the wild-type receptors. Study of such constitutively active mutant G protein-coupled receptors should help elucidate the molecular nature of the processes involved in receptor activation.
Michael T Griffin - One of the best experts on this subject based on the ideXlab platform.
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two state Models and the analysis of the allosteric effect of gallamine at the m2 muscarinic receptor
Journal of Pharmacology and Experimental Therapeutics, 2008Co-Authors: Frederick J. Ehlert, Michael T GriffinAbstract:We measured the influence of gallamine on the functional responses and binding properties of selected agonists at the M2 muscarinic receptor and analyzed the data within the context of the allosteric ternary Complex Model. Our analysis showed that gallamine modified agonist affinity without influencing efficacy. To explain this behavior, we investigated the allosteric ternary Complex Model at a deeper level of analysis to assess allosterism in terms of the differential affinity of gallamine for ground and active states of the receptor. Our simulations showed that two-state Models based on a single orthosteric site for the agonist linked to an allosteric site for gallamine could not account for affinity-only modulation, even if multiple conformations of ground and active states were considered. We also expanded the tandem two-site Model ( J Biol Chem 275:18836–18844, 2000) within the context of the allosteric ternary Complex Model and analyzed the resulting hybrid Model at the level of receptor states. This Model posits that the agonist first binds to a relay site and then shuttles to the activation site to turn on the receptor. If it is assumed that allosterism occurs at the relay site and not the activation site, then this Model can account for affinity-only modulation in a manner consistent with the allosteric ternary Complex Model.