MRI machines use superconducting coils to generate a 1T magnetic field over a volume sufficient for a human body
Andy www.g4jnt.com On Tue, 26 Jan 2021 at 21:47, Tom Holmes <[email protected]> wrote: > I was told that one of the killers of superconductivity is magnetic > fields. I guess they 'fixed' that. > > Tom Holmes, N8ZM > > -----Original Message----- > From: time-nuts <[email protected]> On Behalf Of Mike Feher > Sent: Tuesday, January 26, 2021 1:07 PM > To: 'Discussion of precise time and frequency measurement' < > [email protected]> > Subject: Re: [time-nuts] "Q for dummies" > > I recall back in the late 60’s visiting some friends at BNL. One of them > took me through the cryogenic lab. In one they had an LC running at near 0 > and it could be heard in a receiver. We know for L, Q in its simplest form > is Xl/R. At superconductor temperatures R approaches 0 and therefore Q > approaches infinity. Consequently the circuit oscillated by itself. I was > amazed. Slightly different, but in the same lab they showed me an > electromagnet in a superconductor cooled environment. I noticed it was > wound with uninsulated wire. I inquired about that and was told that > contact resistance is so much higher than the superconductor resistance, > and they could get more turns without insulation. Regards – Mike > > > > Mike B. Feher, N4FS > > 89 Arnold Blvd. > > Howell NJ 07731 > > 848-245-9115 > > > > -----Original Message----- > From: time-nuts <[email protected]> On Behalf Of Dana > Whitlow > Sent: Tuesday, January 26, 2021 9:36 AM > To: Discussion of precise time and frequency measurement < > [email protected]> > Subject: Re: [time-nuts] "Q for dummies" > > > > If anybody can even approach doing justice to the Q concept, including why > it matters, in just two sentences, that person will have definitely earned > the "Qulitzer prize" in technical journalism. > > > > Here's my entry: > > > > "A circuit's Q is closely related to its internal energy losses compared > to external energy exchanges. A high Q can mean better efficiency, better > conformance with expected performance (especially in filter applications), > longer ringdown times (wineglass compared to milk glass) and > (unfortunately) higher price." > > > > Dana > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
