Transport dispersive

Fig. 5. Various current transients obtained by a time-of-fligbt method (a) nondispersive transport (b) dispersive transport and (c) analysis of disperse...

Global AMI.5 sun illumination of intensity 100 mW/cm ). The DOS (or defect) is found to be low with a dangling bond (DB) density, as measured by electron spin resonance (esr) of - 10 cm . The inherent disorder possessed by these materials manifests itself as band tails which emanate from the conduction and valence bands and are characterized by exponential tails with an energy of 25 and 45 meV, respectively the broader tail from the valence band provides for dispersive transport (shallow defect controlled) for holes with alow drift mobiUty of 10 cm /(s-V), whereas electrons exhibit nondispersive transport behavior with a higher mobiUty of - 1 cm /(s-V). Hence the material exhibits poor minority (hole) carrier transport with a diffusion length <0.5 //m, which puts a design limitation on electronic devices such as solar cells. 

DOS and, concomitantly, on p [63-66], and, (iv) the temporal features of TOF signals, notably the universality of non-dispersive signals at variable sample length and electric field, and the transition to dispersive transport which, remarkably, does not bear out universality [67]. 

Here

l and Dy are the coefficients of hydro-dynamic dispersion (cm2 s-1) in the longitudinal (along the flow) and transverse (across the flow) directions. Parallel equations are written for components w, k, and m, in terms of Cw, Q, and Cm, as defined in the previous section. By these equations, we see that dispersion transports a component from areas of high to low concentration, working to smooth out the component s distribution. 

In this situation, transport equations similar to those discussed previously can be applied. For example, by assuming sorption to be essentially instantaneous, the advective-dispersion equation with a reaction term (Saiers and Hornberger 1996) can be considered. Alternatively, CTRW transport equations with a single ti/Ci, t) can be applied or two different time spectra (for the dispersive transport and for the distribution of transfer times between mobile and immobile—diffusion, sorption— states can be treated Berkowitz et al. 2008). 

Typical photocurrent transients are shown in Fig. 6 for electrons and in Fig. 7 for holes. The shape of these curves is representative for all transients observed in the study and is characteristic of dispersive transport [64-68]. The carrier mobility p was determined from the inflection point in the double logarithmic plots (cf. Fig. 6b and Fig. 7b) [74]. TOF measurements were performed as a function of carrier type, applied field, and film thickness (Fig. 8). As can be seen from Fig. 8, the drift mobility is independent of L, demonstrating that the photocurrents are not range-limited but indeed reflect the drift of the carrier sheet across the entire sample. Both the independence of the mobility from L, and the fact that the slopes of the tangents used to determine the mobility (Fig. 6 and Fig. 7) do not add to -2 as predicted by the Scher-Montroll theory, indicate that the Scher-Montroll picture of dispersive transients does not adequately describe the transport in amorphous EHO-OPPE [69]. The dispersive nature of the transient is due to the high degree of disorder in the sample and its impact on car-... 

Market and environment parameters. The market parameters include application areas, sales volume, price, and growth potential. The environment parameters include environmental dispersion, transportation and transformation, areas of concentration, safety, health, and environmental impact. 

However, one should be cautious about overinterpreting the field and temperature dependence of the mobility obtained from ToF measurements. For instance, in the analyses of the data in [86, 87], ToF signals have been considered that are dispersive. It is well known that data collected under dispersive transport conditions carry a weaker temperature dependence because the charge carriers have not yet reached quasi-equilibrium. This contributes to an apparent Arrhenius-type temperature dependence of p that might erroneously be accounted for by polaron effects. 

The phenomenon, which has come to be termed anomalously dispersive transport, was characterized during this period with respect to the following properties ... 

We see that the transit signal does not change appreciably with temperature. Also note that at the final stage (t > 1 ), the TOF signal exhibits a power-law decay and appears to be dispersive. According to the Scher-Montroll theory [33], in the case of the dispersive transport process, I(t) should exhibit power-law dependences rd-a) and 7 d+a) fpj. j respectively, where a is the disorder parameter. The... 

Dispersive transport in PVC was investigated. The results of Pfister and Griffits obtained by the transit method are shown in Fig. 6. The hole current forms at temperatures > 400 K clearly show a bend corresponding to the transit time of the holes. At lower temperature the bend is not seen and transit time definition needs special methods. The pulse form shows the broad expansion during transition to the opposite electrodes. This expansion corresponds to the dispersive transport [15]. The super-linear dependence of the transit time versus sample thickness did not hold for pure PVC. This is in disagreement with the Scher-Montroll model. There are a lot of reasons for the discrepancy. One reason may be the influence of the system dimensions. It is quite possible that polymer chains define dimension limits on charge carrier transfer. 

The influence of the light intensity on the hole transfer was marked [36]. The good agreement between experimental and theoretical data for dispersive transport was observed only for a low intensity of the exciting light. 

The dependence of the drift mobility p on the electric field is represented by formula p (p-E1/2/kTcf) which corresponds to the Pool-Frenkel effect. The good correspondence between experimental and theoretical quantity for Pool-Frenkel coefficient 3 was obtained. But in spite of this the interpretation of the drift mobility in the frame of the Coulombic traps may be wrong. The origin of the equal density of the positive and negative traps is not clear. The relative contribution of the intrinsic traps defined by the sample morphology is also not clear [17,18]. This is very important in the case of dispersive transport. A detailed analysis of the polymer polarity morphology and nature of the dopant molecules on mobility was made by many authors [55-58]. 

The dispersive transport processes were discovered in the first molecule doped systems. The experimental data are shown in Fig. 53 for lexan films with... 

ANOMALOUS STOCHASTIC PROCESSES IN THE FRACTIONAL DYNAMICS FRAMEWORK FOKKER-PLANCK EQUATION, DISPERSIVE TRANSPORT, AND NON-EXPONENTIAL RELAXATION... 

Paints may also need to contain antifoaming and/or defoaming components since air can become incorporated into a paint during any or all of dispersing, transportation, mixing, filling, and application steps [483,780], Hydrophobic components, such as treated (hydrophobic) silicas or waxes, may be added to water-based paints in accordance with the principles described in Section 7.2.2, although there is a tendency to use quite specific antifoams for specific paints [780]. 

Separation is the art and science of maximizing separative transport relative to dispersive transport. In pursuit of this goal, work of recent decades has increasingly amplified the former. However, without a concomitant effort to reduce the latter—to suppress the universal thermodynamic inclination toward dispersion and randomization—modern analytical tech-... 

In this book the mechanisms of both separative and dispersive transport are discussed, with an emphasis on their role in analytical separation processes. 

Mean or median values should not be given for the whole bowel transit since most of the dissolved and/or undissolved drug traverses the entire gastrointestinal tract. The complex nature of transit involving normal and dispersive transport [195] as well as periods of stasis would be better expressed by reporting the range of the experimental values. 

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