Secondary modules, presence

Most of the antibiotics commercially available nowadays are derivatives of natural compounds produced by bacteria or fungi. It is widely accepted that in nature these secondary metabolites can act as weapons for microbial cell defence, inhibiting the growth of competitors. However, it seems that antibiotics have, in nature, more sophisticated and complex functions [1-3]. Many environmental bacteria can not only cope with natural antimicrobial substances but also benefit from their presence. For instance, the use of antibiotics by bacteria as biochemical signals, modulators of metabolic activity or even carbon sources has been demonstrated [1, 2, 4]. In other cases, antibiotics can be tolerated because they have structures similar to the natural substrates of bacterial housekeeping enzymes and thus are inactivated, leading to a natural form of resistance [2]. These are just some... 

If we assume as we did before that the cell contains n vacancies, the probability of an atom s presence on a site is (N - n)/N and the diffracted intensity of each peak will be decreased by a factor corresponding to this term. Furthermore, secondary peaks associated with the atomic displacements appear. The structure factor and hence the diffracted intensity are modulated (see Figure 5.3a). 

Secondary effects can introduce small errors in this method of measuring twist. Dust and surface scatches can, of course, seriously affect local alignment. More subtle are perturbations apparently produced by variations in the flow pattern (hydrodynamic domains) of neutral molecules. In the cells used here hydrodynamic instabilities become quite pronounced at field frequencies around 5 Hz at 17v and resemble the patterns described by Sussman.9 They were not visible at 0.3 Hz and 17v but Fig. 11 shows evidence of their presence. In this case, the 0 orientation of the cell was fixed and the cell was translated relative to the beam while applying 17v at 0.3 Hz. A slow variation in polarity modulation amplitude is expected because of the effects discussed in connection with Fig. 3. Superimposed are local oscillations of modulation amplitude possibly attributable to hydrodynamic domains. It may be surprising that neutral molecule flow would not exhibit a more pronounced effect however, the flow adjacent to the cell walls must be parallel to the walls and exert a minor orienting force on the thin layer of molecules with significant homogeneous component at 17v. 

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