164
Even with relatively narrow size distribution for each of these populations (see Morel and
Ahn, 1991), there are only a few remnants of oscillations. Also figure 4 exemplifies the large
span of the lateral scattering (around () = 90 0) with respect to the forward lobe. This
property is largely used in flow cytometry techniques to identify and characterize various
particles according to their scattering capabilities. In this perspective, Eq. 13 has been
integrated between the angular limits 2-18° and 72-108°, respectively, in view of simulating
the near forward-scatter and the side-scatter detectors of a flow cytometer. Before integrations,
the individual VSF were computed for increasingly discrete a-values (from 2 to 1000) and
various values given to the index of refraction n (real, between 1.01 and 1.09). The results
are shown in two different ways: in Fig. 7a the side scatter (SS) and forward scatter (FS) are
separately plotted as a function of the size parameter and for only two n - values (1.01 and
1.07); in Fig. 7b, SS is plotted as a function of FS, and each "rod" in this representation
corresponds to a single a - value with varying n value, between 1.03 (bottom end) and 1.06
(top end).
For very small a - values (say below 1.5), FS and SS are both increasing as a 6
domain (left hand side of Fig. 7b, where the slope is 1), there is an ambiguity between the
effects of the size and of the index upon the SS and FS values (note these particles are
excessively small, in the range of 0.1 - 0.2 ~m). When a exceeds 2, SS starts to experience
oscillations (see Fig. 7a) around a general trend which corresponds to an a 2 (i.e. d 2 )
dependency, whereas FS continues to increase according to a 6 • In this domain, which extends
up to a = 20 (d..:::.. 2-3 mm) or more (depending on the index), FS is the signal which is the
most sensitive to the size (through approximately d 6 , progressively becoming d 4 ). In principle,
separate knowledge of SS and FS, provided that they are transcribed in absolute units (via
calibrating beads), allow the size and index to be separately determined in many occasions.
The restriction comes from the "folds" which are clearly seen in Fig. 7b. The enlargments
of such folds show, however, that a couple of SS-FS values leads to a plausible domain of size
and index which remains rather restricted (under the proviso of sphericity; see also Spinrad
and Brown, 1986 and Ackleson and Spinrad, 1988). With reduced oscillations in SS for
greater a, the situation tends to simplify. As soon as a exceeds 50 or 60 (d > 6-7 mm), FS
as well as SS become proportional to a 2 • In Fig. 7a it can be noticed that within this domain
Even with relatively narrow size distribution for each of these populations (see Morel and
Ahn, 1991), there are only a few remnants of oscillations. Also figure 4 exemplifies the large
span of the lateral scattering (around () = 90 0) with respect to the forward lobe. This
property is largely used in flow cytometry techniques to identify and characterize various
particles according to their scattering capabilities. In this perspective, Eq. 13 has been
integrated between the angular limits 2-18° and 72-108°, respectively, in view of simulating
the near forward-scatter and the side-scatter detectors of a flow cytometer. Before integrations,
the individual VSF were computed for increasingly discrete a-values (from 2 to 1000) and
various values given to the index of refraction n (real, between 1.01 and 1.09). The results
are shown in two different ways: in Fig. 7a the side scatter (SS) and forward scatter (FS) are
separately plotted as a function of the size parameter and for only two n - values (1.01 and
1.07); in Fig. 7b, SS is plotted as a function of FS, and each "rod" in this representation
corresponds to a single a - value with varying n value, between 1.03 (bottom end) and 1.06
(top end).
For very small a - values (say below 1.5), FS and SS are both increasing as a 6
domain (left hand side of Fig. 7b, where the slope is 1), there is an ambiguity between the
effects of the size and of the index upon the SS and FS values (note these particles are
excessively small, in the range of 0.1 - 0.2 ~m). When a exceeds 2, SS starts to experience
oscillations (see Fig. 7a) around a general trend which corresponds to an a 2 (i.e. d 2 )
dependency, whereas FS continues to increase according to a 6 • In this domain, which extends
up to a = 20 (d..:::.. 2-3 mm) or more (depending on the index), FS is the signal which is the
most sensitive to the size (through approximately d 6 , progressively becoming d 4 ). In principle,
separate knowledge of SS and FS, provided that they are transcribed in absolute units (via
calibrating beads), allow the size and index to be separately determined in many occasions.
The restriction comes from the "folds" which are clearly seen in Fig. 7b. The enlargments
of such folds show, however, that a couple of SS-FS values leads to a plausible domain of size
and index which remains rather restricted (under the proviso of sphericity; see also Spinrad
and Brown, 1986 and Ackleson and Spinrad, 1988). With reduced oscillations in SS for
greater a, the situation tends to simplify. As soon as a exceeds 50 or 60 (d > 6-7 mm), FS
as well as SS become proportional to a 2 • In Fig. 7a it can be noticed that within this domain