Saturation trapping

In the examples considered above traps B were assumed to serve as sinks of the infinite capacity. Its simple modification for the case of saturable traps (the policeman who caught some toper is no longer on his post but is bringing him to the police station) leads us immediately to the new class of reactions known as A + B —> C (C is a neutral reaction product - the policeman bound to a toper is out of his duty) or A+B —> 0 (reaction product leaves the system). This latter reaction is typical for the so-called Frenkel defects in solids when complementary defects A and B (interstitial atoms and vacancies) annihilate each other, thus giving no products and restoring the perfect crystalline lattice. 

Let us consider the reaction in which particles P of a chemical substance diffuse in the medium, containing random located static non-saturated traps (growing macromolecular coils) T. At the contact of particle P with a trap T the particle disappears. It is usually considered that if the concentration of particles and traps is large or the reaction occurs with intensive stirring, the process can be considered as the classical reaction of the first order. In this case it can be assumed that the concentration of particles c(t) decay law will be the following [136] ... 

Table 1. Nonwetting phase saturations trapped in random packings of equal spheres at various Bond and capillary numbers. (Ap = 0.748, O = 23.19 dyne/cm). 

Behar F, Vandenbroucke M. (1988) Characterization and quantitation of saturates trapped inside kerogen network implications for pryolysate composition. Org Geochem 13 927-938... 

Vc) = 0 (D diffusion coefficient, c H-atoms per unit volume ), is limited to some rare cases (e.g. to steels with saturated traps resulting from low density of defects or high H-content). In fact, a source term must be added to the right side of the equation, which was firstly developed by McNabb and Foster, (McNabb Foster, 1963), and later by Oriani assuming local equilibrium, (Oriani, 1970). Thus, the following equations hold for diffusion of hydrogen under the presence of local stress fields (c << 1), (Serebrinsky et al., 2004) ... 

The NSR catalyst operates in fast lean/rich transients. During the lean steps of approximately 1 min, the gas phase is constituted by the standard exhaust gas from the lean burn engine. NO is then oxidized into NO2 over the precious metals and further trapped as nitrite/nitrate on the basic components of the catalyst. The saturated trap is then regenerated during short incursions in rich media for few seconds in order to reduce the stored NOx into N2. In fact, the rich phases are... 

On the other hand 7i = 5% represents the minimum relative intensity of the free positron component that can be resolved in the PL spectrum. We then find, using the same procedure as shown above, that the maximum detectable vacancy concentration 10 at. This means that if c v > c , almost all positrons will be trapped at monovacancies (saturated trapping) and it will be possible to determine the vacancy concentration. 

Of particular interest is the concentration of defects as a function of the irradiation dose and the thermal treatment used. Generally, these effects can be explored in positron studies only if the bulk lifetime can be resolved from the shortest lifetime, which is attributed to annihilation from defects. In the present case of saturation trapping, this proved impossible. Therefore, based on the individual lifetime spectra, we can only conclude that the total trapping rate k is larger than about 10 ° s . ... 

However, using the variation of the mean lifetime rav as a function of positron implantation energy, we can even estimate k in the case of saturation trapping. The problem was fully analysed in [188,189]. Based on this theory, the total defect concentration can be estimated as ... 

Figures 4.53 and 4.54 present results for k (the trapping rate) obtained using the procedure described above. The plausible value of 10 s [129] was assumed for the specific trapping rate Kspec- Because of slight surface oxidation, this evaluation of K results in a systematic underestimate. A lower limit of 10 ns for k may be derived within the framework of the STM, since we have observed saturation trapping at defects.

Figure 4.53 The total trapping rate k versus the HoUomon-Jtiffe parameter in isochronally annealed (step 25 °C) specimens of base (ZM) and weld ZK) alloys after one year of iiradiation in the reactor (neutron fluence 7.8 x 10 m ). The lower limit for k, as derived from saturation trapping according to the STM, is 10ns ...

In order to compensate the initially proposed interfacial electron traps on the Si02 dielectric, Ahles et al. [62] introduced traces of Ca to the Si02 dielectric interface. As a low work function metal, Ca was believed to act as an electron donor saturating traps in the interface near pentacene layer. The capability to accumulate mobile charge carriers at the newly engineered interface can again be examined by MIS diode experiments. The result of impedance measurements on a MIS diode... 

E. V. Kornelsen, A. A. Van Gorkum, Attachment of Mobile Particles to Non-Saturable Traps II. The Trapping of Helium at Xenon Atoms in Tungsten, Rad. Effects 42 (1979) 113. 

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