Mobility model

Neurokinin-1 Receptor. A homology model of the neurokinin-1 (NKi) receptor was built from the X-ray structure of rhodopsin, using the MOBILE (modeling binding sites including ligand information explicitly) approach. In this procedure, a preliminary model is generated, which is afterwards refined... 

M 1) and the ratios of mobilities of electrons and ions. Theoretical analysis by Mozumder (1971) produced a higher value, 1.0 x 1012 M-1s 1. Later experiments of Beck and Thomas (1972) gave ks - (2.2-3.0) x 1012 M Is 1, which is consistent with a recent mobility model (Mozumder, 1995 see Sect. 10.3.3). 

PG Muijselaar, HA Claessens, CA Cramers. Migration behavior of monovalent weak acids in micellar electrokinetic chromatography mobility model versus retention model. J Chromatogr A 765 295—306, 1997. 

The GPCR process is commercially available as a fixed-facility, full-scale system a semi-mobile model and a portable demonstration unit. The technology has been used in full-scale cleanups. 

PROCESSING TOOL n frequency/time frequency dependent frequency/time molecular models impedance measurement molecular mobility models data base... 

The general conclusion to be drawn from the above discussion is that the dual gas sorption and mobility model has very useful predictive potential in the field of membrane gas separation. At the present stage, no comparable predictive capability is discernible in the alternative treatments so far published 33 >34 63). 

The dual mobility model expresses the concentration dependency of Deff(C) in terms of the local concentration of dissolved penetrant, CD, as shown in Eq (6) ... 

The only "small error", suggested in Assink s statement concerning the dual mode model s assumptions, deals with the earlier approximation by Vieth and Sladek (34) that was equal to zero. The work of Assink was performed prior to the formulation of the dual mobility model which eliminates this approximation and accomodates values of > 0 (17,18). 

The mechanical counterpart of this equation comes from a theory of the nonelastic deformations developed from a molecular mobility model. The parameters 5, h and k have precise physical meanings, taking into account the effectiveness of correlation effects exhibited during the molecular motions involved in the process. 

Campbell et al. [46] also compared their data with the mobility model. The mobility model showed a very steep rise in the current with voltage at low temperature, which is inconsistent with their data. More recently Berleb et al. [47] and Lupton et al. [48] have also measured the J-V curves of conducting organic semiconductors at different temperatures. Similar discrepancies between theory and their data are found. 

Fig. 3.20. (a) Calculated current density as a function of inverse temperature for V = 10 V for a conducting polymer sample with exponentially distributed traps. The values of the trap distribution parameter Tc are Tc = 2500 K (long dash line), Tc = 1800 K (dash-dot line), Tc = 1500 K (solid line), Tc = 1200 K (dotted line) and Tc = 1000 K (small dash line). The values of the other parameters are Hb = 3 x 1018 cm-3, Nv = 3 - 1020 cm-3, e=2 and /ip = 5 x 10 cm2 V 1 s 1. The inset shows the calculated effective activation energy, Eeb. as a function of the characteristic trap distribution energy ) = kTc. (b) J-V characteristics of a sample of MEH-PPV with a thickness of 94 nm on a log-linear scale. The symbols represent the data of Campbell et al. [46]. The lines represent calculated values using the mobility model. The figure is taken from [42],... 

Researchers have used various models to explain the charge carrier transport mechanism in organic semiconductors. Two models have been used frequently, (i) the trapping model, which assumes a certain distribution of traps in the energy space and (ii) the field dependent mobility model, which assumes an exponential dependence of mobility on square root of electric field. 

Fig. 3.26. J-V characteristics of the Alq3 electron only device at lower temperatures. The solid lines are the theoretical plots while the symbols are the experimental data. From these results the current was found to obey the mobility model [54].

The mobility model is based on the empirical fitting of the time-of-ffight data to obtain the observed mobility-field dependence [42, and references given therein]. In the mobility model the mobility p is assumed to vary with electric field F according to the formula... 

If we consider a sample with shallow Gaussian traps and include PEE, the sample behaves as if there are no traps and the mobility is field dependent given by Eq. (3.56) far as the dependence of J on V is concerned. The zero field mobility and its temperature dependence are different in the two equations. If the traps are at a single energy level, <7t = 0 and the temperature variation of the mobility also becomes the same in the two cases. Eq. (3.58) represents both the models, it reduces to the existing shallow trap model (without PEE) when = 0 and to the existing field dependent mobility model when 6 = exp(-EtfkT). 

Fig. 3.29(a) shows that the results of the unified model (based on shallow traps and with PEE) agree well with the 296 K J-V curve measured by Blom et al. [57], Blom et al. [57] found excellent agreement with the theory that does not assume the presence of traps but uses the field dependent mobility. The above discussion shows that the model with shallow traps plus PFE and the field dependent mobility model are equivalent. 

Several experimental J-V curves taken from the recent literature have been compared with the PFE model [39], We quote a few typical examples here. Extensive measurements of J(V) curves have been made by Crone et al. [59], They used both hole only Au/MEH-PPV/Al and electron only Ca/MEH-PPV/Ca devices. Crone et al. [59] used the mobility model to interpret their results. Comparison of their results for the electron devices with the Field Dependent Trap Occupancy (FDTO) model is shown in Fig. 3.33(a). The thicknesses of the samples are 25 nm (circles), 60 nm (diamonds) and 100 nm (plus symbols). The parameters used in calculations are Tc = 1420 K, //h = 7 x 1018 cm-3, ]Vt = 5x 1019 cm-3, JV, = 1 x 1020 cm-3, p, = 6.5 x 10-6 cm2 V-1 s 1 and e = 3. The agreement of the experimental results is satisfactory. The model has another advantage. The calculations have been made with the same parameters for all the three samples. With the mobility model, Crone et al. [59] had to use different values of the parameters for different samples. 

Barrer (1984) suggested a further refinement of the dual-mode mobility model, including diffusive movements from the Henry s law mode to the Langmuir mode and the reverse then four kinds of diffusion steps are basically possible. Barrer derived the flux expression based on the gradients of concentration for each kind of diffusion step. This leads to rather complicated equations, of which Sada (1987, 1988) proved that they describe the experimental results still better than the original dual-mode model. This, however, is not surprising, since two extra adaptable parameters are introduced. 

Thus treatment of the data with this alternative adsorption model yields a more negative enthalpy change by RT than the mobile model. 

As it can be seen from Fig. 5.22, when moving from the localized adsorption towards the mobile model, we can expect smooth decrease in the entropy of desorption. The entropy of the adsorbate which experiences lateral diffusion was discussed, in particular, by Patrikiejew, et al. [95]. They approached the problem by assuming that a fraction of the molecules is in completely mobile state, while the others are completely localized. Then they suggested that the canonical partition function (9ml... 

BJ Compton. Electrophoretic mobility modeling of proteins in free zone capillary electrophoresis and its application to monoclonal antibody microheterogeneity analysis. J Chromatography 559 357-366, 1991. 

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