Biomedical Engineering Reference
In-Depth Information
Fig. 1.46
(
a
) A schematic snapshot of the simulation system in side view (the
xz
-plane). The
Y-SWNT features a main tube (MT) and two branch tubes (BT
1
,BT
2
) positioned in the same plane
(the
xz
-plane). The angle between each two neighboring SWNTs is 120
ı
. Small angular changes
do not affect the results. The single-walled CNTs are represented by
gray lines
. Water molecules
are shown with oxygen in
red
and hydrogen in
gray
. Water molecules outside the nanotubes are
omitted in the figure. The
green sphere
represents the imposed charge. The lengths of MT, BT
1
,
and BT
2
are 1.44, 1.21, and 1.21 nm, respectively. (
b
) The average dipole angle
'.t/ of the water
orientations inside the MT, BT
1
,andBT
2
for a negative charge (
left
) and a positive charge (
right
).
(
c
) The probabilities of the dipole orientations
P
(
t
) in different tubes for a negative charge (
solid
lines
) and a positive charge (
dashed lines
).
P
(
t
) for a negative charge converges to about 1.0 within
a few nanoseconds (reprinted from [
59
]. Copyright 2009 National Academy of Science, USA)
adopted the similar approach that an external charge
q
is attached at the center of
a second carbon ring of the MT (see Fig.
1.46
) to initiate a signal of water dipole
orientations. Similar to the single channels, the water molecules in the MT have
the upward and downward concerted dipole orientation for
q
D
e
and
q
DC
e
,
respectively. Remarkably, the water orientations in both the BTs follow the water
orientations in the MT when water orientations in the MT are downward, while the
water orientations in both the BTs fluctuate between upward and downward when
the water orientations in the MT are upward. This can be seen more clearly from the
time-dependent behavior of '.t/ asshowninFig.
1.46
. Therefore, from the water
orientations in each branch tube of the Y-shaped channel, we can easily distinguish
the sign of the imposed charge at the MT. In other words, the charge signal at the
bottom of the MT is “converted” into water dipole signal and then transmitted to the
two Y-branch tops and “multiplied” (from one signal to two).
