Ion, models for

Sun et al. (1985) found that replacement of Nd by Y, La or Ce does not have a pronounced effect on Tc. From an analysis of the anisotropy field JIA in the system (Nd1 xYx)2Fe14B, the same authors found evidence of the validity of the single-ion model for describing the magnetic anisotropy. The methodology of a multi-ion crystal-field analysis was discussed by Boltich (1988) and applied to the system ErxPr xFe14B. 

As discussed above, whereas for open structures the zero-pressure structures are calculated more accurately with the distorted ion model than with the spherical ion model, for close-packed systems the zero-pressure structures are calculated just as well with the spherical ion model. In the same way, the distorted ion model leads to improvements in the compression at high pressures for open structures but not for close-packed structures. Although the agreement with experiment is reasonable for calculated changes in volume with pressure, the calculated structures are generally less compressible than observed experimentally (i.e.,the bulk moduli are too high). 

Rapidly equilibrating classical car-bocation (carbenium ion) model for 2-norbornyl cation. 

The polarizable ion model for the monomeric alkali metal halides... 

Concentration-dependent diffusion coefficients for Sr + in ion-exchanged NaCl were determined by using a sectioning method. Isothermal diffusion annealing was performed at 448 to 683C. The saturation diffusion coefficients, enthalpies and entropies of impurity-vacancy associations were calculated by using the common-ion model for the simultaneous diffusion of divalent ions in alkali halides. The saturation diffusion data could be described by ... 

In case of (Er, Gd )2pei4B compounds a single-ion model for the free energy explains the magnetocrystalline anisotropy and describes qualitatively the... 

Fig. 28.16 Theoretical charge distribution of (A) C21H23 ion (model for charged soliton) and (B) push-pull polyene with strong polar end groups (V). The values reported are partial charges on the CH units obtained from ab initio calculation according to the definition of corrected Mulliken charges (see Ref. 149). Basis set used are 6-31 G in (A) and 3-21 G in (B). Units are electrons.

The Rigid-Ion Model for Ionic Crystals 4.2.1 Definition of the Model and Dynamical Matrix... 

The flow can be radial, that is, in or out through a hole in the center of one of the plates [75] the relationship between E and f (Eq. V-46) is independent of geometry. As an example, a streaming potential of 8 mV was measured for 2-cm-radius mica disks (one with a 3-mm exit hole) under an applied pressure of 20 cm H2 on QT M KCl at 21°C [75]. The i potentials of mica measured from the streaming potential correspond well to those obtained from force balance measurements (see Section V-6 and Chapter VI) for some univalent electrolytes however, important discrepancies arise for some monovalent and all multivalent ions. The streaming potential results generally support a single-site dissociation model for mica with Oo, Uff, and at defined by the surface site equilibrium [76]. 

Dynamic models for ionic lattices recognize explicitly the force constants between ions and their polarization. In shell models, the ions are represented as a shell and a core, coupled by a spring (see Refs. 57-59), and parameters are evaluated by matching bulk elastic and dielectric properties. Application of these models to the surface region has allowed calculation of surface vibrational modes [60] and LEED patterns [61-63] (see Section VIII-2). 

Stahlberg has presented models for ion-exchange chromatography combining the Gouy-Chapman theory for the electrical double layer (see Section V-2) with the Langmuir isotherm (. XI-4) [193] and with a specific adsorption model [194]. 

The interaction between ions of the same sign is assumed to be a pure hard sphere repulsion for r < a. It follows from simple steric considerations that an exact solution will predict dimerization only if i < a/2, but polymerization may occur for o/2 < L = o. However, an approximate solution may not reveal the fiill extent of polymerization that occurs in a more accurate or exact theory. Cummings and Stell [ ] used the model to study chemical association of uncharged atoms. It is closely related to the model for adliesive hard spheres studied by Baxter [70]. 

The solute-solvent interaction in equation A2.4.19 is a measure of the solvation energy of the solute species at infinite dilution. The basic model for ionic hydration is shown in figure A2.4.3 [5] there is an iimer hydration sheath of water molecules whose orientation is essentially detemiined entirely by the field due to the central ion. The number of water molecules in this iimer sheath depends on the size and chemistry of the central ion ... 

Within the framework of the same dielectric continuum model for the solvent, the Gibbs free energy of solvation of an ion of radius and charge may be estimated by calculating the electrostatic work done when hypothetically charging a sphere at constant radius from q = 0 q = This yields the Bom equation [13]... 

Lin C Y and Dunbar R C 1994 Time-resolved photodissociation rates and kinetic modeling for unimolecular dissociations of iodotoluene ions J. Rhys. Chem. 98 1369-75... 

Wheland intermediate (see below) as its model for the transition state. In this form it is illustrated by the case mentioned above, that of nitration of the phenyltrimethylammonium ion. For this case the transition state for -nitration is represented by (v) and that for p-substitution by (vi). It is argued that electrostatic repulsions in the former are smaller than in the latter, so that m-nitration is favoured, though it is associated rvith deactivation. Similar descriptions can be given for the gross effects of other substituents upon orientation. 

Heterogeneity Adsorbents and ion exchangers can be physically and chemically heterogeneous. Although exceptions exist, solutes generally compete for the same sites. Models for adsorbent heterogeneity have been developed for both discrete and continuous distributions of energies [Ross and Olivier, On Physical Adsorption, Interscience, New York, 1964 Jaroniec and Madey, Rudzinsld and Everett, gen. refs.]. 

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

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