Irreversible adsorption on nonuniform surfaces: the random site model

1993 ◽  
Vol 97 (17) ◽  
pp. 4256-4258 ◽  
Author(s):  
Xuezhi Jin ◽  
N. H. Linda Wang ◽  
Gilles Tarjus ◽  
Julian Talbot
Keyword(s):  
Irreversible Adsorption ◽  
Site Model ◽  
Random Site ◽  
Nonuniform Surfaces

Global analysis of phase states in a random-site model

1993 ◽  
Vol 47 (12) ◽  
pp. 7576-7579
Author(s):  
Jun Ni ◽  
Binglin Gu
Keyword(s):  
Global Analysis ◽  
Site Model ◽  
Random Site

Irreversible adsorption of hard spheres at random site (heterogeneous) surfaces

2002 ◽  
Vol 116 (11) ◽  
pp. 4665-4672 ◽  
Author(s):  
Zbigniew Adamczyk ◽  
Paweł Weroński ◽  
Elizeusz Musiał
Keyword(s):  
Hard Spheres ◽  
Heterogeneous Surfaces ◽  
Irreversible Adsorption ◽  
Random Site

The phase diagrams of an Ising spin-1 random site model for ternary alloy

1994 ◽  
Vol 206 (3-4) ◽  
pp. 454-462 ◽  
Author(s):  
Binglin Gu ◽  
Jun Ni ◽  
Janwei Wan ◽  
Jialin Zhu
Keyword(s):  
Phase Diagrams ◽  
Ternary Alloy ◽  
Site Model ◽  
Ising Spin ◽  
Random Site

Controlling the Chemical Order in PMN-Type Relaxors

1998 ◽  
Vol 541 ◽  
Author(s):  
P. K. Davies ◽  
M. A. Akbas
Keyword(s):  
Solid Solution ◽  
Thermal Treatment ◽  
Dielectric Response ◽  
Random Distribution ◽  
Domain Growth ◽  
Site Model ◽  
Charge Model ◽  
Random Site ◽  
Space Charge Model ◽  
The Stability

AbstractInvestigations of pure and chemically substituted tantalate and niobate members of the Pb(Mg1/3 Nb2/3)O3 (PMN) family of perovskite relaxors demonstrate that the degree of cation ordering and size of the chemically ordered domains can be extensively modified by thermal treatment. These observations and refinements of the cation occupancies in well ordered samples conflict with the predictions of the widely accepted “space charge model”, and instead support a “random site” model for the 1:1 B-site ordering. In this model one of the positions in the ordered structure is occupied by Ta (or Nb) and the other contains a random distribution of Mg and the remaining Ta cations. The stability of the order and magnitude of the domain growth can be enhanced by relatively small concentrations of selected solid solution additives (e.g. Zr in Pb(Mg1/3Ta2/3)O3 (PMT); Th or Sc in PMN). Correlations between the stability of the 1:1 order and the size of the solid solution additive can be used to understand the different responses of the cation order in PMN and PMT to thermal treatment. Results are also presented for the dielectric response of fully ordered relaxors in the (l–x) Pb(Mg1/3Ta2/3)O3 – (x) Pb(Sc1/2 Ta1/2)O3 system. While large domain samples of PMT-rich compositions exhibit a relaxor response, a crossover to normal ferroelectric behavior is observed for x = 0.5. The change in the dielectric response can be rationalized in terms of the effect of the chemistry of the random site sub-lattice on the correlation length of the ferroelectric coupling.

Irreversible adsorption of particles at random-site surfaces

2004 ◽  
Vol 120 (23) ◽  
pp. 11155-11162 ◽  
Author(s):  
Zbigniew Adamczyk ◽  
Katarzyna Jaszczółt ◽  
Barbara Siwek ◽  
Paweł Weroński
Keyword(s):  
Irreversible Adsorption ◽  
Random Site

A Phenotype–Genotype Codon Model for Detecting Adaptive Evolution

2019 ◽  
Vol 69 (4) ◽  
pp. 722-738 ◽  
Author(s):  
Christopher T Jones ◽  
Noor Youssef ◽  
Edward Susko ◽  
Joseph P Bielawski
Keyword(s):  
Positive Selection ◽  
Adaptive Evolution ◽  
Evolutionary History ◽  
Life History Trait ◽  
Molecular Adaptation ◽  
Simulation Studies ◽  
Site Model ◽  
Branch Site ◽  
A Site ◽  
Post Hoc

Abstract A central objective in biology is to link adaptive evolution in a gene to structural and/or functional phenotypic novelties. Yet most analytic methods make inferences mainly from either phenotypic data or genetic data alone. A small number of models have been developed to infer correlations between the rate of molecular evolution and changes in a discrete or continuous life history trait. But such correlations are not necessarily evidence of adaptation. Here, we present a novel approach called the phenotype–genotype branch-site model (PG-BSM) designed to detect evidence of adaptive codon evolution associated with discrete-state phenotype evolution. An episode of adaptation is inferred under standard codon substitution models when there is evidence of positive selection in the form of an elevation in the nonsynonymous-to-synonymous rate ratio $\omega$ to a value $\omega > 1$. As it is becoming increasingly clear that $\omega > 1$ can occur without adaptation, the PG-BSM was formulated to infer an instance of adaptive evolution without appealing to evidence of positive selection. The null model makes use of a covarion-like component to account for general heterotachy (i.e., random changes in the evolutionary rate at a site over time). The alternative model employs samples of the phenotypic evolutionary history to test for phenomenological patterns of heterotachy consistent with specific mechanisms of molecular adaptation. These include 1) a persistent increase/decrease in $\omega$ at a site following a change in phenotype (the pattern) consistent with an increase/decrease in the functional importance of the site (the mechanism); and 2) a transient increase in $\omega$ at a site along a branch over which the phenotype changed (the pattern) consistent with a change in the site’s optimal amino acid (the mechanism). Rejection of the null is followed by post hoc analyses to identify sites with strongest evidence for adaptation in association with changes in the phenotype as well as the most likely evolutionary history of the phenotype. Simulation studies based on a novel method for generating mechanistically realistic signatures of molecular adaptation show that the PG-BSM has good statistical properties. Analyses of real alignments show that site patterns identified post hoc are consistent with the specific mechanisms of adaptation included in the alternate model. Further simulation studies show that the covarion-like component of the PG-BSM plays a crucial role in mitigating recently discovered statistical pathologies associated with confounding by accounting for heterotachy-by-any-cause. [Adaptive evolution; branch-site model; confounding; mutation-selection; phenotype–genotype.]

scholarly journals Gas Porosimetry by Gas Adsorption as an Efficient Tool for the Assessment of the Shaping Effect in Commercial Zeolites

Nanomaterials ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 1205
Author(s):  
Alejandro Orsikowsky-Sanchez ◽  
Christine Franke ◽  
Alexander Sachse ◽  
Eric Ferrage ◽  
Sabine Petit ◽  
...  
Keyword(s):  
Ir Spectroscopy ◽  
Strong Interaction ◽  
Gas Adsorption ◽  
Co2 Adsorption ◽  
Adsorption Properties ◽  
Preparation Process ◽  
Pore Filling ◽  
Irreversible Adsorption ◽  
Efficient Tool ◽  
4A Zeolite

A set of three commercial zeolites (13X, 5A, and 4A) of two distinct shapes have been characterized: (i) pure zeolite powders and (ii) extruded spherical beads composed of pure zeolite powders and an unknown amount of binder used during their preparation process. The coupling of gas porosimetry experiments using argon at 87 K and CO2 at 273 K allowed determining both the amount of the binder and its effect on adsorption properties. It was evidenced that the beads contain approximately 25 wt% of binder. Moreover, from CO2 adsorption experiments at 273 K, it could be inferred that the binder present in both 13X and 5A zeolites does not interact with the probe molecule. However, for the 4A zeolite, pore filling pressures were shifted and strong interaction with CO2 was observed leading to irreversible adsorption of the probe. These results have been compared to XRD, IR spectroscopy, and ICP-AES analysis. The effect of the binder in shaped zeolite bodies can thus have a crucial impact on applications in adsorption and catalysis.

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