Biology Reference
In-Depth Information
From the observed structure amplitudes, the electron density on an
absolute scale is, therefore, given by
Â
1
h
d
i
2
p
h
= Ê
ˆ
˜
Ê
Á
ˆ
˜
Ê
Á
ˆ
˜
r
()
r
F
exp
-
Á
d
d
-•
h
F
d
()
02
h
d
2
p
rh
d
+ Ê
ˆ
˜
max
Ê
Á
ˆ
˜
Ê
Á
ˆ
˜
Â
ª
K
F
cos
(3)
Á
obs
d
h
=
1
and
F
()
0
=
D
F
()
0
+
fd
.
(4)
The values for F ( 0 ), K, and the phase of the structure factors should be
known in order to calculate the absolute electron density. F ( R ), which is
the continuous Fourier transform of
ρ
( r ), can be derived from Eqs. (1)
and (3) as
Â
Ê
Á
h
d
ˆ
˜
FR
()
=
F
in(
cdR
p
-
p
h
)
-•
D
FR
()
=
FR
()
-
fd
in(
c dR
p
)
and
Â
h
d
Ê
ˆ
˜
=
D
F
sin
cdR
(
p
-
p
h
).
(5)
Á
-•
Internodal myelin swells and compacts under different conditions of
pH and ionic strength, giving various myelin periods. To compare the
observed intensities with different myelin periods, the following scaling is
needed. Using discretely observed structure amplitudes and the scale fac-
tor K , the origin of the Patterson function of
ρ
( r ) at r
=
0 is given by
2
ª Ê
1
ˆ
˜
+ Ê
2
ˆ
˜
KF h
d
Ê
Á
ˆ
˜
2
2
Â
2
2
Ú
Ú
r ()
rdr
=
FR dR
( )
F
()
0
.
Á
Á
obs
d
d
When the fluid electron density is similar to that of the membrane,
then f
≈〈ρ
( r )
r 0
and
F (0)
0. The observed structure amplitudes can
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