Biology Reference
In-Depth Information
2
/
d
for the dif-
ferent myelin periods. These properly scaled structure factors sample the
continuous structure factor
F
(
R
) given by Eq. (5).
It is also possible to derive the electron density on an absolute scale
by using two fluids having different densities
f
1
and
f
2
. The Fourier trans-
form of
subsequently be scaled by assuming a constant
Σ
|
F
obs
(
h
/
d
)|
∆ρ
(
r
) gives
D
FR
()
=
F R
()
-
0
rf
in(
c rR
p
,
(6)
i
0
(
r
) within
|r|<r
0
/2
,
and is independent of the fluid density
f
. For myelin lattices having two
different fluid densities, the structure factors
where
F
i
(
R
) is the Fourier transform of the bounded
ρ
∆
F
1
(
R
) and
∆
F
2
(
R
) are
expressed as
D
FR
()
-
D
F R
()
=
r
in(
c rR f
p
(
-
f
.
(7)
1
2
0
0
2
1
When the structure factors are measured at
R
=
h/d
, it follows that
h
d
h
d
c
rh
d
Ê
Á
p
ˆ
˜
Ê
Á
ˆ
Ê
Á
ˆ
0
KF
˜
-
KF
˜
=
r
sin
(
f
-
f
),
(8)
11
2 2
0
21
obs
obs
where
K
1
, and
K
2
are scale factors for the observed structure factors
F
1
obs
and
F
2
obs
. Because these structure amplitudes, and
d
,
f
1
and
f
2
are known in
Eq. (8), the unknown phases of the structure factors, and
K
1
,
K
2
and
r
0
may
be obtained by searching for the values satisfying Eq. (8) (Fig. 3). The
electron density
(
r
) and
F
(
R
) on an absolute scale are then derived
according to Eqs. (3) and (5) (Fig. 3).
ρ
Chemical Interpretation of the Electron Density and
Neutron Scattering Length Density Profiles
Method
The electron density distribution and the neutron scattering length density
are compared with the chemical dispositions of phospholipids, cholesterol,
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