Hole distribution

The reformer feeds and combustor air flow in a counter current manner as shown in Fig. 2. In order to transfer heat to the reformer evenly throughout the interface between reformer and combustor, the combustor is designed to feed the fuel through the holes distributed over the combustor. In this manner, the feed will mix with air incrementally and generate heat throughout the combustor plate evenly. The combustor plate is packed with a Pd catalyst and the reformer uses a Ni/Al203 catalyst. 

The broken line indicates the interface between bulk and SCR. The dots represent the hole distribution. After [Le 21],... 

We shall assume that the electron and hole distributions in the respective bands as well as on the impurity levels in the bulk are Maxwellian. In addition, we shall consider for simplicity s sake that the entire surface charge is due to the chemisorbed particles, i.e., that the clean surface of the semiconductor is electrically neutral. We shall thus neglect the structural defects of the surface, which are always present to some degree on a real surface and act as additional traps for the electrons and holes. With these assumptions we may take expression (10) for [Pg.248]

Figure 6.17 Schematic illustration of electron and hole distribution for a /rw-rectifying junction for (a) no applied electrical potential, (b) forward bias, and (c) reverse bias. Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 631. Copyright 2000 by John Wiley Sons, Inc.

Essentially, it is determined by the combined density-of-states of the conduction and valence bands and by the difference of the electron and hole distribution functions. In fact, the effect of the band structure is two-fold. On one hand a large combined density-of-states is beneficial for a large optical gain, and on the other hand large densities-of-state correspond to large carrier densities in order to achieve inversion. 

In practice the lifetime distributions are usually obtained using a computer program such as the MELT [21] or CONTIN [22, 23] programs. The reliablity of these programs for measurring the o-PS lifetime distribution in polymers was shown by Cao et al [24]. A detailed description of these methods of data analysis is presented in Chapter 4. The advantage of the continuous lifetime analysis is that one can obtain free volume hole distributions rather that the average values obtained in the finite analysis. 

The affect of polymer stereoregularity in the chains on the PAL data has also been studied. Hamielec et al [56] found what appears to be an increased lifetime (hole size) with increased randomness of the chain configuration in a series of polyvinlychloride (PVC) polymers, despite the large degree of scatter in the sample (probably due to the fact that a series of commercially available products were used.). They however found little correlation with tacticity in polypropylene. More recently a PAL study on a series of very well characterized polystyrene and poly(p-methlystyrene) samples of differing tacticity [57] was performed. In addition to finding that the polystyrene samples have smaller free volume holes than the poly(p-methylstyrene) samples, they found that the syndiotactic samples had broader hole distributions than the attactic samples. 

There is much still to be understood about the photoconductivity of a-Si H. However, the measurements confirm that recombination through defects is the main mechanism, particularly when their concentration is high. Extrinsic effects further complicate the interpretation of photoconductivity. For example, surface recombination can dominate when the bulk recombination rate is low. These effects can arise from either the excess defects at the surface or from the band bending, which causes a field induced separation of the electron and hole distributions. Contacts, which are almost invariably non-ohmic, also modify the photoconductivity, in particular, the response time. 

Figure 19. A typical HTOF signal from the photorefractive polymer composite PVK/0.1 wt.% TNF and 40 wt.% 4-(hexyloxy)nitrobenzene electro-optic chromophore, reproduced with permission from [42]. A clear peak is observed which represents the transit time of holes across half a grating period. Eventually a steady state is reached due to the spatial hole distribution being smeared out by dispersive transport and hole recombination.

To obtain the spin-Hall current, it is necessary to analyze the hole distribution function. Within the linear response regime, we find that the linear electric field part of the helicity-basis distribution function, j(p), can be written as a sum of two terms,... 

NQR/NMR measurements have been carried out in an attempt to reveal the hole distribution under pressure and its relevance to the change of Tc.63,64 In YIE ChuOg,63 it was found that vq(Cu) decreases in the CuO chain but increases in the CUO2 plane (Fig. 21), which indicates that the number of holes decreases at the chain site but increases at the plane site. A similar result was... 

Effect of hole distribution on superconducting characteristics of multilayered... 

Fig. 9.11. Dynamical calculations of the thickness profiles of electron diffraction intensities for different hole distributions assuming fully ionic bonding in (a) and (b) and with 76% and 56% of the holes in the Cu02 plane, respectively. In (c) there is partly covalent bonding assigning the charge - -3, +1, -1-1.62, and —1.69 to the Y, Ba, Cu, and O ions, respectively (from Ref. [9.3]), and with an additional charge transfer of 0.08 holes per unit cell from the chains to the planes in (d).

The air-lift circulator is shown in Fig. 11.3. There are 152 j-in-diameter holes distributed over a 6-in-diameter face plate of the diffuser cone. The vertical air supply line supports an 18-in-diameter outer pipe. Figure 11.3 demonstrates how this device works. There are 22 air-lift circulators, to provide for vertical mixing of the waste solution. 

Real barriers contain crooked, noncircular holes distributed in size about a mean radius in the range of 0.005 to 0.03 pm. Molar velocity throu most barrier materials is found experimentally to depend on pressures as in Eq. (14.10) ... 

An ingenious approach to the autoionization process was suggested by Tomelini and Fanfoni [32]. They examined diffraction processes in the framework of autoionization, i.e., a second-order process. More exactly, they studied only the second stage of autoionization, namely, the secondary electron emission from the intermediate state where the core hole is coherently distributed over the crystal. With such an approach it was shown that in crystals this diffraction contribution enhances fine structure as compared to the amorphous substance. However, the applicability of such a model is determined by the probability of the occurrence of the core hole distributed coherently over the crystal. More conventional... 

Jean, Y. C., and Deng, Q., Direct measurements of free-volume hole distributions in polymers by using a positronium probe, J. Polym. Sci. B, 30, 1359-1364 (1992). 

Figure 8. Change of the o-Ps hole distribution before ( ) and after (O, A) crystallization of poly(ethylene terephthalate) by heat treatment. It is clearly shown that the small size holes have disappeared due to the crystallization. (Adopoted from ref 29)...

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