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Figure 3
The effect of the contrast-transfer function on the projection of an enveloped virus is shown for Semliki Forest virus (Fuller et al., 1995BB17). (a) shows the projection of the three-dimensional density of the 700 Å diameter virion. Note the lipid bilayer separating the internal capsid from the external spikes. (b)–(f) show the application of the transfer functions displayed in Fig. 2[link] to the projected density in (a). Gaussian-distributed noise with σ equal to half the maximum density in (a) was added to each image to simulate the effect of the low signal-to-noise ratio in a low-dose image. Note that the use of underfocus and amplitude contrast change the sign of the density.

Journal logoBIOLOGICAL
ISSN: 1399-0047
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