Post #71,916
1/1/03 8:15:10 PM
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The world! is analog(ue).
'Digital' is a math contrivance of the homo-sap mind, a convention which permits certain Boolean operations. In the physical word, there is never 0 resistance or infinite resistance; nor can a delta-function exist (a pulse with 0-rise-time).
As your digital fab folk have learned via many co$tly errata: every 'switch' has a finite rise time, obeys abstruse physics laws, sees a virtual wave-guide where a designer thought s/he was using wires. Skin-depth in ground-planes is now as much a consideration as it ever was, in the design of electron linacs or other microwave constructs.
(And 'digital' sampling oscilloscopes are 'blind' for very much of their duty cycle - all those repetitive calcs. and such: whereas an analog scope is blind for a tiny fraction of a percent - merely to move the beam back to left side. Real engineers, especially while troubleshooting glitches caused by a PC-designer's ignorance of the above -- keep their Tek 'image intensifier' Ghz scopes around to find those glitches. Hey! your scope == Your Eyes. Another analog device.)
Those whose "electronics training" is via Pee Cee Auto-Circuit simulations - are no more 'electronics engineers' than is Billy an 'innovator'. Go read some Bob *Pease columns in Electronic Design for the corollary to your thesis.
* Chief Scientist at National Semiconductor, excellent writer and trekker in Nepal. Better yet, read his seminal book, Troubleshooting Analog Circuits. It's hilarious as well as concisely informative, from decades of experience. Check out his 'fuzzy logic' feedback control VS the classic designs, while at it.
Those 1s and 0s you imagine: are nothing Like That in a world of quantum-like level changes at EH frequencies. Very much basic Maxwell and Helmholtz underlies the tasks of approximating the theory.
Even in audio reproduction: your bit-streams tend to leave the ear cold. Old vinyl recordings (some produced with >20K BW) are the preferred medium of actual music lovers - at least those with the $ to feed the habit. The digital ADC/DAC degradations / artifacts the 'corpuscularizing' of actual ANALOG energy which the analog ear apparatus expects to 'hear':
sustains the illusion for.. Yanni, rap, synthesizers and amplified 'guitars' - but makes a sustained brass, violin tone ICY. Loses the spatial positioning of an orchestra, etc. (Yes, as with wine tasting - the vocabulary ever fails to transmit the experience of listening critically to familiar works, and the rare double-blind test of those perceptions). Nobody understands the mechanism of the cochlea's conversion to brain information (or the brain itself obv) - notwithstanding recent work with cochlear implants -- and the horrific noise which THE MIND learns to recognize as ~'speech, after a while.
But yes: the world imagines it is 'digital' - that I'll grant. 40% of Muricans aren't sure if the sun goes around the earth or..
Cheers,
Ashton
an analog type of device
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Post #71,919
1/1/03 8:34:33 PM
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Yes, alas, digitial does not actually exist . .
. . in our 100% analog universe. It can only be simulated, always imperfectly.
Anyone who designs hard disk drives can tell you plenty about the non-existance of digital anything.
[link|http://www.aaxnet.com|AAx]
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Post #72,031
1/2/03 11:59:44 AM
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What matters is the precision necessary and possible
With Fourrier transforms you can have as much precision as you need (and willing to pay for), and often more than possible with analog devices.
And hard drives actually illustrate my point: the analog electronics gone so far advanced as to be beyond the reach of any hobbyist, American or otherwise.
--
We have only 2 things to worry about: That
things will never get back to normal, and that they already have.
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Post #71,922
1/1/03 8:48:57 PM
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Be careful saying "never".
Ashton writes:
In the physical word, there is never 0 resistance or infinite resistance; nor can a delta-function exist (a pulse with 0-rise-time).
Emphasis added.
As I'm sure you're aware, [link|http://www.suptech.com/super101.html|superconductors] have 0 (zero), not "really, really small" resistance. :-) They're used in several real systems, e.g., [link|http://www.brown.edu/Administration/News_Bureau/2001-02/01-083.html|MRI machines] (as discussed in the link).
Cheers,
Scott.
(Pedants R Us. :-)
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Post #71,924
1/1/03 9:17:06 PM
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Methinks that "0 resistance"
does not transmit EMF across those er "frictionless outer valence electrons?" at precisely C - a velocity indistinguishable from that of the [also impossible to attain] "perfect vacuum". So, I'll take 'never' as a good approximation ;-)
You'll note that 'DC' is the preferred mode of operating superconducting magnets.. and as the electrons dribble FIFO, this question of degraded velocity only appears not-to matter. And it doesn't (!) in these primitive applications.
(And maybe hedge the bet. Given that the trend towards proliferation of a few of those kilotons of fissionable material which we have accumulated for our illusion of security: this fact + homo-sap suicidal tendency pretty much places a Species Survival Limit upon this species' imaginations of the word forever, and by implication never.)
My mere guess is that TANSTAAFL Rulez.
Ashton
[cackle]
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Post #71,941
1/1/03 10:41:32 PM
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Electrical resistance and *c* are different issues.
Electrical resistance of zero means that there's no power loss - i.e. P = IV = I^2R = 0. Thus, no heating of the material due to the current (no energy is lost to the material by phonons (lattice vibrations)).
As discussed [link|http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html#c1|here], the "drift velocity" or the net electron speed through a conductor is very slow - a few cm/hr to a few m/s - far less than c. They're [link|http://www.lns.cornell.edu/spr/2002-01/msg0038305.html|faster] in superconductors but still far less than c.
Superconductors aren't otherworldly. They're simply materials that have the proper combinations of electronic and lattice energy states such that conduction electrons can "pair", act as bosons, and have a forbidden "energy gap" such that they [link|http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html#c1|cannot lose energy to the lattice] when the material is kept below a certain characteristic temperature.
Cheers,
Scott.
(Who agrees that perfect vacuum, like "empty space", is ideal and doesn't exist. And who agrees that superconductors are lossy using AC.)
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Post #71,948
1/1/03 11:42:01 PM
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Well... DC resistivity does seem bulletproof
and like Newton's notes re fluxions, (IIRC he had an aside ~ "assuming mass remains constant" - which some take to be a prescience of Relativity ;-) I must eat the non-0 resistivity claim prima facie, since E=IR presumes 'DC'! :(
Now as to impedance and the analogues of capacitive or inductive reactance: looks as if we have here not much likelihood of superconducting transmission, rectification? for much beyond milliHertz frequencies. Also kinda amazing data point distributions in the experimental evidence: can one say "straight line"? (The EE ideal is of course, "the straight wire with gain", as some early transistorized amplifier mfgs. loved to spin.)
I have some experience of cryo-vacuum systems, incl. He reefers - but not with superconducting magnets (hands-on). Maybe.. had the SCSC gotten past the pork-barrel brigade, though moving to Texas would have cut it for me.
Now I shall have to imagine Bosons! in practical day-day application.
Nicely complete links. Thanks,
Ashton
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Post #71,950
1/2/03 12:15:07 AM
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A/C for runing a super conductor
The only reason I can see for any inefficiency is that the electrons have to slow down & reverse direction & the logistics required to do that are inefficient plus the beneficial effect of the magnetic flux provided by the electron flow through the superconductor material, gets reversed every cycle.
The 1st problem is losses due to latency in the collapse of the magnetic field then there is the effect of the revers polarity...
I mean can you imagine what the ride would be like in Shanghai's maglev supertrain if the field holding it up reversed 50 or so times per second.
That would be one brain scrambling ride <grin>
Cheers Doug
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