The Channeling Effect

The enhancement of ion or damage penetration in ordered materials along certain 

There exist two main reasons for this effect  

The channeling effect is illustrated experimentally by letting protons penetrate through a thin aligned gold crystal. The proton current, a measure of the transmission probability, is a strong function of the orientation of the crystal. In Fig. 10 the transmitted ion cunent is plotted as a function of the rotation of the crystal around the (111) axes  

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Fig. 8 at an RH of 65%. This difference demonstrates the channelling effect of the orientation distribution during a tensile test. 

As shown in Figure 16b, the 2-D rib models deal with how the existence of a solid rib affects fuel-cell performance. They do not examine the along-the-channel effects discussed above. Instead, the relevant dimensions deal with the physical reality that the gas channeFdiffusion media interfaces are not continuous. Instead, the ribs of the flow-channel plates break them. These 2-D models focus on the cathode side of the fuel-cell sandwich because oxygen and water transport there have a much more significant impact on performance. This is in contrast to the along-the-channel models that show that the underhumidification of and water transport to the anode are more important than those for the cathode. 

Taftp, J. (1982) The cation-atom distribution in a (Cr,Fe,Al,Mg)304 spinel as revealed from the channeling effect in electron-induced X-ray emission. J. Appl. Crystallogr., 15, 378-81. 

Spence, J. C. H., Tafto, J. (1982). Atomic site and species determination using the channelling effect in electron diffraction. In Scanning Electron Microscopy 1982, II, pp. 523-31. Chicago SEM Inc., AMF O Hare. 

When individual membranes are stacked into a column, it is advisable to use at least 30 membranes on top of each other to average out the membrane heterogeneities and the channeling effects. The pressure drop over the membrane stack should be as low as possible. Therefore, producers like Sartorius, Millipore, and Pall advise not to apply pressures >4 bar. 

An increase in dose slowly destroys the ordered crystal structure, leading to a distribution similar to the amorphous case. The channeling effect in polycrystalline material is much smaller compared with single crystals, b) At elevated temperature the diffusion of the implanted atoms very often leads to a broadening of the profile. In addition diffusion processes play a role at low temperatures during the irradiation, leading to radiation enhanced diffusion (Sect. 2.6). Fig. 7 illustrates the effect. 

The binary collision approximation (BCA) model was the first to be used in computer simulations of ion-solid interactions (Bredov et al, 1958). The usefulness of computer simulations was further demonstrated by Robinson and Oen (1963) during their discovery of the channeling effect. Computer simulations based on the BCA model in essence fall into two categories, those that assume a crystalline structure of the solid and those that, as in calculations based on the TRIM code, assume a randomized or structureless target. 

In practice, the target is usually deliberately misaligned with respect to the major axes of the crystal. This misalignment angle is typically 7 to 10 degrees off-axis. This quenches the channeling effect and simulates an amorphous target. 

The channeling effect can be seen most clearly in tungsten, which is characterized by small-ampUtude thermal vibrations of atoms. Consequently, dechanneUng of particles wiU be weak. In this case, the three sections corresponding to the three types of trajectory shown in Fig. 8.5 are quite pronounced on the concentration distribution curve, as shown in Fig. 8.5. Particles scattered by angles on... 

Neurospora is similar to yeast in having two separate enzymes for the synthesis of CP, but it differs in that the CP formed by either one is not available for the other pathway. The complexities of this system have been thoroughly reviewed by Davis [80,81] and may be summarized as follows. Mutational loss of one or the other of the two enzymes leads to an absolute requirement for either arginine or uracil. This has been interpreted as a channeling effect whereby the two modes for CP synthesis give rise to two spatially separate pools of CP in the intact cell. Each pool is specific for one of the two pathways and unavailable for the other. This becomes conceptually acceptable if the CP product remains boimd to its specific synthetase and is directly coupled in its substrate role with its corresponding transcarbamylase. The channeling effect may be disturbed by mutational events which alter the reciprocal... 

Blends prepared in different mixing equipment showed some slight differences in blend morphology. The blends prepared with the Buss Co-Kneader-type extruder exhibited the finest dispersion of LCP phases. In contrast, the channeling effect and phase separation were most pronounced for the counterrotating twin-screw extruder, in particular for blends whose components had totally different melt viscosities. 

Where a is a constant, d is the distance between successive atoms along the column direction (zone axis), z is atomic number, B is the Debye-Waller factor. Since HREM image is a phase contrast image, a high-resolution TEM image should reflect phase information induced by the channeling effect for each column. By tuning focus and sample thickness, one can obtain reverse contrast for different atomic columns. 

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