Jobst approximations

In lieu of these expressions, Jobst (76) derived values for Kgca, the effective scattering eflBciency of a particle, from the Mie equations for four special particle size-refractive index regimes. The values of and the restrictions on their application caused by approximations to the Mie eflBciencies are listed in Table I. The Jobst approximations provide simple analytical solutions for particles with the dimensions and composition of bacteria, since a is quite large (a = 27t(0.65)/0.41 = 10), yet... 

Table I. Jobst Approximations to Mie Scattering Efficiencies Ksca for Selected Size—Refractive Index Regimes ...

In summary, the diflBculties in determining aggregate form factors, particle form factors, phase shifts, and distribution functions combine to make the Rayleigh-Debye approach too complicated for practical application. On the other hand, the coalesced-sphere approach using the Jobst approximations to the Mie scattering eflBciencies allows rapid correlation of turbidity with particle size distributions. Consequently, a coalesced-sphere approach was adopted for experimentation in the E. coli-PEI system. 

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