Crowding effect

Fig. 14. Schematic representation of the influence on water exchange rate (at 298.15 K) of the crowding effect around the metal due to the elongation of the acetate arm or the amine backbone of DTPA . ...

The effective parking area of the adsorbed molecule may vary with the extent of adsorption. As more molecules are adsorbed, the area occupied by each may decrease due to a crowding effect. 

The concentration effects. This term describes variations in Vr of the polymer samples due to changes of injected concentration, Cj. The retention volumes as a rule increase with raising Cj in the area of practical concentrations [104-107]. This is mainly due to the crowding effects when the concentration of macromolecules is high enough so that they touch each other in solution and shrink due to their mutual repulsive interactions. The concentration effects in SEC are expressed by the slopes k of the mostly linear dependences of Vr on c,. K values rise with the molar mass of samples up to the exclusion limit of the SEC column. 

Due to the lack of a shallow acceptor level in 4H-SiC and a relatively low hole mobility, the intrinsic base resistance of a 4H-SiC BJT is very high for example, a base epilayer sheet resistance of 46 kQ per square was reported for a 4H-SiC BJT in [6]. The high intrinsic base resistance in 4H-SiC BJTs results in a very severe emitter current crowding effect [7], which limits most of the current flow to within 1 jum from the edge of the emitter regions [8]. This indicates that tight cell pitches are necessary to achieve a low specific on-resistance, as shown in Figure 6.2(a) [6]. 

Further compounds, such as gossypol 3, normally exist as atropisomers due to steric crowding effects. Hence, it is possible to prepare the compound in a homochiral state, provided that the experimental temperature is not raised sufficiently to overcome the restricted rotation energy barrier. If this does occur, then the outcome is a racemic mixture of (+)- and (—)-isomers. 

The level of infection in a host has a direct effect on the carbohydrate content of cestodes (796) and has been shown by Henderson (317) to affect glucose absorption by H. diminuta in vitro (Fig. 5.1). These are manifestations of the crowding effect, reported in Raillietina, H. microstoma, H. nana and, most notably, H. diminuta (697), which results in an inverse correlation between worm size and increasing population density. Competition for host dietary carbohydrate presumably plays a role in the crowding effect, but the phenomenon is complex and a number of other factors are probably involved (348, 697, 979, 980). This phenomenon is addressed further in Chapter 9. 

Fig. 9.6. The crowding effect in Hymenolepis diminuta. The growth is measured as dry weight at different worm loads. (After Roberts, 1961.)...

Other workers (325), however, found that when the crowding effect was assessed by measuring the egg output, an effect became evident even at the two-worm level. Thus, in a one-worm infection, the egg production per worm was found to be about three times that of a two-worm infection, and in 5-20-worm infections, each worm produced only about one-sixth to one-ninth of a two-worm infection, independent of the number of worms harboured (Fig. 9.7 Table 9.3). 

There is, however, increasing evidence that the crowding effect (at least in H. diminuta) cannot be explained simply in terms of interworm competition for carbohydrate. In rats given exclusively a diet containing 3% (w/w)... 

A crowding effect is also well documented for H. microstoma (373) and H. nana (254). In the latter, the worm burden which developed from cysticercoid-derived infections was greater than that from egg-derived infections (Fig. 9.8), although the crowding effect was similar in both. 

Ghazal, A. M. Avery, R. A. (1974). Population dynamics of Hymenolepis nana in mice fecundity and the crowding effect . Parasitology, 69 403-15. 

C chemical shifts are more sensitive to steric crowding effects and less sensitive to through-space effects of double bonds than 1H chemical shifts. Increasing the substitution of a carbon (CH3 to CH2 to CH to C) leads to downfield shifts of about 10 ppm in each step. 

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