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Curious to know if this capacitance discussion concerning nerve cells has s=
ome bearing on why we have not yet figured out how to fix a severed human s=
pine..=20
> Date: Fri=2C 31 Aug 2012 00:12:27 -0300
> From: srshaw@DAL.CA
> To: naturens@chebucto.ns.ca
> Subject: Re: [NatureNS] wind power storage
>=20
> The following is bit too detailed=2C perhaps=2C but ...
> ... the undersea cable problem was investigated conceptually I think =20
> first by Lord Kelvin in the late 1800s. This is casually known to =20
> later physiologists=2C because of the close parallel to nerve conduction =
=20
> along 'passive' nerve axons (ones without nerve impulses). In both =20
> cases there is a certain significant capacitance per unit length=2C in =20
> the cable because (as Chris says) there is a significantly thick =20
> insulation with a finite dielectric constant=2C necessary to prevent =20
> current from leaking out of the conducting core into the surrounding =20
> sea water (at roughly ground potential). In the nerve fiber=2C the =20
> membrane around the nerve cell (or any animal cell) comprises a =20
> molecular bilayer about 5-7 nanometers thick=2C made largely of =20
> phospholipids. The dielectric constant of these lipids is relatively =20
> constant=2C similar to olive oil=2C so all animal cell membranes have a =
=20
> specific capacitance close to 1 =B5F/cm^2=2C pretty much a biological =20
> constant (one microfarad per a one centimeter square of membrane =20
> surface).
>=20
> If a DC current step is applied between one end of the nerve/cable and =20
> the fluid outside=2C the voltage inside changes quasi-exponentially to =20
> the voltage of the source. As it proceeds along the cable=2C the =20
> voltage gets smaller because of leakage through the 'resistance' of =20
> the membrane=2C as ions move through actual molecular protein channels =20
> embedded in it. It also gets slower=2C because the initial current has =
=20
> to discharge even more capacitance as distance increases. The current =20
> flows both through the leakage resistance R and the capacitance C =20
> (according to the product of the two=2C R*C)=2C charging the cable or =20
> membrane depending on whether -V or +V is applied. The result is that =20
> a signal (say +V) put in at one end of the cable declines inexorably =20
> to background noise level over a certain definable distance=2C so the =20
> cable or nerve would no longer be useful beyond that. So capacitance =20
> is a bad thing because it both reduces and slows down signals being =20
> transmitted=2C and smears them out.
>=20
> The solution is similar in both cases=2C to put a series of repeater =20
> amplifiers into the cables at determined distances=2C to periodically =20
> boost the signals. These boosters are the nodes of Ranvier in =20
> vertebrate myelinated nerve fibers=2C or a continuous 'doping' of active =
=20
> channels into the unmyelinated giant nerve axons of Loligo pealii =20
> mentioned recently. Invertebrates missed out on 'discovering' =20
> myelination. In squid axons=2C a large fraction of the current flowing =
=20
> down the inside of the axon is used to discharge the =20
> already-charged-up membrane capacitance=2C so the influence of =20
> capacitance in slowing signal transmission is a very important factor =20
> limiting impulse conduction velocity.
>=20
> A complementary 'clever trick' vertebrate axons use is to have up to =20
> ~100 accessory myelin membranes wind around the axon=2C which does two =20
> things. It increases the leakage resistance by a factor of ~100=2C but =20
> less widely appreciated=2C it decreases the capacitance per unit length =
=20
> by the same factor. Much less charge is then needed to discharge the =20
> lowered capacitance by the advancing impulse=2C so a boosted impulse can =
=20
> 'jump' from node 1 to node 2 etc much more quickly than otherwise. As =20
> a result=2C vertebrate axons only 10 microns in diameter use much less =20
> ATP energy to conduct ~6 times faster that squid axons even 500 =20
> microns in diameter=2C cutting central costs more that even Harper =20
> dreamed about.
>=20
> I'm less sure about the limitations of a copper cable suspended in air =20
> at least several inches from the nearest ground reference (present =20
> close to the insulators=2C on the metal pylons). In this case=2C the =20
> capacitors must be large air gaps with consequently very little =20
> capacitance. At a very low frequency of 50-60 hertz in AC =20
> transmission=2C I imagine that capacitative losses are relatively small=
=2C =20
> but this could be wrong. Most losses presumably would come because =20
> even a copper cable has a very significant resistance to current owing =20
> to the large distances it covers=2C plus the inevitable losses caused by =
=20
> the current heating the cable. In any case=2C as Dave Webster says=2C th=
e =20
> capacitance must be very small=2C so charging it to a certain voltage =20
> won't recover much charge if the cable is then allowed to discharge.
> Steve (Hfx)
>=20
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Quoting David & Alison Webster <dwebster@glinx.com>:
>=20
> > Hi Chris=2C Steve & All=2C Aug 30=2C 2012
> > Yes the capacitance of the cable would store electricity but =20
> > (and here I venture onto thin ice) the magnitude of this storage =20
> > would be vanishingly small.
> [agreed]
> >
> > From here onward the ice is even thinner--
> > As a first approximation=2C when the DC source is removed then the =
=20
> > voltage between the two ends of the cable would not decrease to zero =20
> > immediately but would fall asymptotically as charge is drained from =20
> > the coaxial sheath.
> [you'd normally charge the inside at one end relative to the nearby =20
> juice outside=2C not between the two ends]
> >
> > The charge delivered to the destination/sec=2C before removal of =
=20
> > the DC source=2C would be roughly 3 x 10^10 times as great as the =20
> > charge delivered by discharge of the cable.
> [when the cable is charged at one end as above=2C the time course is not =
=20
> exactly exponential because the capacitance is distributed along the =20
> cable=2C and is governed by a more complicated 'bent' function (an error =
=20
> function=2C concocted from a series of exp functions). The discharge =20
> process is the complementary function.]
>=20
> > Yt=2C DW=2C Kentville
> ################################
> > ----- Original Message -----
> > From: Christopher Majka
> > To: naturens@chebucto.ns.ca
> > Sent: Thursday=2C August 30=2C 2012 10:14 AM
> > Subject: Re: [NatureNS] wind power storage
>=20
> > Hi Steve=2C
> > "Long undersea / underground high voltage cables have a high =20
> > electrical capacitance compared with overhead transmission lines=2C =20
> > since the live conductors within the cable are surrounded by a =20
> > relatively thin layer of insulation (the dielectric)=2C and a metal =20
> > sheath. The geometry is that of a long co-axial capacitor. The total =20
> > capacitance increases with the length of the cable. This capacitance =20
> > appears in parallel with the load."
> >
> > Does this indicate that the capacitance of cable itself can store =20
> > electricity or am I completely off-base? =3B~>
>=20
>=20
=
--_8243996e-f23c-4886-ad40-06204737588c_
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<body class=3D'hmmessage'><div dir=3D'ltr'>Curious to know if this capacita=
nce discussion concerning nerve cells has some bearing on why we have not y=
et figured out how to fix a severed human spine.. <br><br>> Date:=3B Fri=
=2C 31 Aug 2012 00:=3B12:=3B27 -0300<br>> From:=3B srshaw@=3BDA=
L.CA<br>> To:=3B naturens@=3Bchebucto.ns.ca<br>> Subject:=3B Re=
8=3B [=3BNatureNS]=3B wind power storage<br>> <br>> The following is =
bit too detailed=2C perhaps=2C but ...<br>> ... the undersea cable problem =
was investigated conceptually I think <br>> first by Lord Kelvin in the la=
te 1800s. This is casually known to <br>> later physiologists=2C because o=
f the close parallel to nerve conduction <br>> along '=3Bpassive'=3B=
nerve axons (=3Bones without nerve impulses)=3B. In both <br>> cas=
es there is a certain significant capacitance per unit length=2C in <br>> =
the cable because (=3Bas Chris says)=3B there is a significantly thic=
k <br>> insulation with a finite dielectric constant=2C necessary to preve=
nt <br>> current from leaking out of the conducting core into the surround=
ing <br>> sea water (=3Bat roughly ground potential)=3B. In the ner=
ve fiber=2C the <br>> membrane around the nerve cell (=3Bor any animal =
cell)=3B comprises a <br>> molecular bilayer about 5-7 nanometers thick=
=2C made largely of <br>> phospholipids. The dielectric constant of these =
lipids is relatively <br>> constant=2C similar to olive oil=2C so all anim=
al cell membranes have a <br>> specific capacitance close to 1 µ=3BF/c=
m^=3B2=2C pretty much a biological <br>> constant (=3Bone microfarad=
per a one centimeter square of membrane <br>> surface)=3B.<br>> <br>> =
If a DC current step is applied between one end of the nerve/cable and <br=
>> the fluid outside=2C the voltage inside changes quasi-exponentially to =
<br>> the voltage of the source. As it proceeds along the cable=2C the <b=
r>> voltage gets smaller because of leakage through the '=3Bresistance&#=
39=3B of <br>> the membrane=2C as ions move through actual molecular prote=
in channels <br>> embedded in it. It also gets slower=2C because the init=
ial current has <br>> to discharge even more capacitance as distance incre=
ases. The current <br>> flows both through the leakage resistance R and t=
he capacitance C <br>> (=3Baccording to the product of the two=2C R*=
=3BC)=3B=2C charging the cable or <br>> membrane depending on whether -=
V or +=3BV is applied. The result is that <br>> a signal (=3Bsay &#=
43=3BV)=3B put in at one end of the cable declines inexorably <br>> to =
background noise level over a certain definable distance=2C so the <br>> c=
able or nerve would no longer be useful beyond that. So capacitance <br>>=
is a bad thing because it both reduces and slows down signals being <br>>=
transmitted=2C and smears them out.<br>> <br>> The solution is similar in =
both cases=2C to put a series of repeater <br>> amplifiers into the cables=
at determined distances=2C to periodically <br>> boost the signals. Thes=
e boosters are the nodes of Ranvier in <br>> vertebrate myelinated nerve f=
ibers=2C or a continuous '=3Bdoping'=3B of active <br>> channels int=
o the unmyelinated giant nerve axons of Loligo pealii <br>> mentioned rece=
ntly. Invertebrates missed out on '=3Bdiscovering'=3B <br>> myelinat=
ion. In squid axons=2C a large fraction of the current flowing <br>> down=
the inside of the axon is used to discharge the <br>> already-charged-up =
membrane capacitance=2C so the influence of <br>> capacitance in slowing s=
ignal transmission is a very important factor <br>> limiting impulse condu=
ction velocity.<br>> <br>> A complementary '=3Bclever trick'=3B verte=
brate axons use is to have up to <br>> ~=3B100 accessory myelin membra=
nes wind around the axon=2C which does two <br>> things. It increases the =
leakage resistance by a factor of ~=3B100=2C but <br>> less widely app=
reciated=2C it decreases the capacitance per unit length <br>> by the same=
factor. Much less charge is then needed to discharge the <br>> lowered c=
apacitance by the advancing impulse=2C so a boosted impulse can <br>> '=
=3Bjump'=3B from node 1 to node 2 etc much more quickly than otherwise. =
As <br>> a result=2C vertebrate axons only 10 microns in diameter use muc=
h less <br>> ATP energy to conduct ~=3B6 times faster that squid axons=
even 500 <br>> microns in diameter=2C cutting central costs more that eve=
n Harper <br>> dreamed about.<br>> <br>> I'=3Bm less sure about the lim=
itations of a copper cable suspended in air <br>> at least several inches =
from the nearest ground reference (=3Bpresent <br>> close to the insula=
tors=2C on the metal pylons)=3B. In this case=2C the <br>> capacitors =
must be large air gaps with consequently very little <br>> capacitance. At=
a very low frequency of 50-60 hertz in AC <br>> transmission=2C I imagine=
that capacitative losses are relatively small=2C <br>> but this could be =
wrong. Most losses presumably would come because <br>> even a copper cabl=
e has a very significant resistance to current owing <br>> to the large di=
stances it covers=2C plus the inevitable losses caused by <br>> the curren=
t heating the cable. In any case=2C as Dave Webster says=2C the <br>> cap=
acitance must be very small=2C so charging it to a certain voltage <br>> w=
on'=3Bt recover much charge if the cable is then allowed to discharge.<b=
r>> Steve (=3BHfx)=3B<br>> <br>> ~=3B~=3B~=3B~=3B&#=
126=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=
=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B=
~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B~=3B=
26=3B~=3B<br>> Quoting David &=3B Alison Webster <=3Bdwebster@=
=3Bglinx.com>=3B:=3B<br>> <br>> >=3B Hi Chris=2C Steve &=3B All=
=2C Aug 30=2C 2012<br>> >=3B Yes the capacita=
nce of the cable would store electricity but <br>> >=3B (=3Band here=
I venture onto thin ice)=3B the magnitude of this storage <br>> >=
=3B would be vanishingly small.<br>> [=3Bagreed]=3B<br>> >=3B<br>>=
>=3B From here onward the ice is even thinner--<br>> >=3B As=
a first approximation=2C when the DC source is removed then the <br>> =
2=3B voltage between the two ends of the cable would not decrease to zero =
<br>> >=3B immediately but would fall asymptotically as charge is draine=
d from <br>> >=3B the coaxial sheath.<br>> [=3Byou'=3Bd normally =
charge the inside at one end relative to the nearby <br>> juice outside=2C=
not between the two ends]=3B<br>> >=3B<br>> >=3B The charge d=
elivered to the destination/sec=2C before removal of <br>> >=3B the DC=
source=2C would be roughly 3 x 10^=3B10 times as great as the <br>> &#=
62=3B charge delivered by discharge of the cable.<br>> [=3Bwhen the cabl=
e is charged at one end as above=2C the time course is not <br>> exactly e=
xponential because the capacitance is distributed along the <br>> cable=2C=
and is governed by a more complicated '=3Bbent'=3B function (=3Ba=
n error <br>> function=2C concocted from a series of exp functions)=3B.=
The discharge <br>> process is the complementary function.]=3B<br>> <=
br>> >=3B Yt=2C DW=2C Kentville<br>> #=3B#=3B#=3B#=3B#=
=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B&#=
35=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B#=3B=
#=3B#=3B#=3B#=3B#=3B#=3B<br>> >=3B ----- Original Me=
ssage -----<br>> >=3B From:=3B Christopher Majka<br>> >=3B To&=
#58=3B naturens@=3Bchebucto.ns.ca<br>> >=3B Sent:=3B Thursday=2C=
August 30=2C 2012 10:=3B14 AM<br>> >=3B Subject:=3B Re:=3B &=
#91=3BNatureNS]=3B wind power storage<br>> <br>> >=3B Hi Steve=2C<b=
r>> >=3B "=3BLong undersea / underground high voltage cables have a=
high <br>> >=3B electrical capacitance compared with overhead transmis=
sion lines=2C <br>> >=3B since the live conductors within the cable are=
surrounded by a <br>> >=3B relatively thin layer of insulation (=3B=
the dielectric)=3B=2C and a metal <br>> >=3B sheath. The geometry is=
that of a long co-axial capacitor. The total <br>> >=3B capacitance in=
creases with the length of the cable. This capacitance <br>> >=3B appea=
rs in parallel with the load."=3B<br>> >=3B<br>> >=3B Does this =
indicate that the capacitance of cable itself can store <br>> >=3B elec=
tricity or am I completely off-base?=3B ;=3B~=3B>=3B<br>> <br>=
> <br> </div></body>
</html>=
--_8243996e-f23c-4886-ad40-06204737588c_--
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