tag:blogger.com,1999:blog-13869903.post1453175342797436827..comments2021-05-14T12:50:22.568-05:00Comments on nanoscale views: Noise IIDouglas Natelsonhttp://www.blogger.com/profile/13340091255404229559noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-13869903.post-67443458305673735652011-03-15T01:16:24.496-05:002011-03-15T01:16:24.496-05:00As we know that according to fluctuation dissipati...As we know that according to fluctuation dissipation theorem, the response of a system in thermodynamic equilibrium to a small applied force is the same as its response to a spontaneous fluctuation. So, the linear response relaxation of a system from a prepared non-equilibrium state to its statistical fluctuation properties in equilibrium. Often the linear response takes the form of one or more exponential decays.fashion accessorieshttp://www.ettika.com/noreply@blogger.comtag:blogger.com,1999:blog-13869903.post-87726447225220351122009-12-17T03:56:54.767-06:002009-12-17T03:56:54.767-06:00Anonymous, I'm guessing that Weber, who had a ...Anonymous, I'm guessing that Weber, who had a PhD in electrical engineering, knew his stuff. (I certainly don't know anything about antennas.) I remember 50 ohms, <a href="http://en.wikipedia.org/wiki/Dipole_antenna" rel="nofollow">but maybe it was 75 ohms</a> as that is what wikipedia is using to illustrate a short dipole antenna.<br /><br />His calculation invovled assuming that the antenna cross section was equal to lambda^2 / 4 pi, after integration over all directions, a fact which is well known to EEs. Lambda is wavelength, see wiki article on antenna aperture.<br /><br />The students were stuck on computing aperture from integrating over the antenna pattern, all done from first principles.CarlBrannenhttps://www.blogger.com/profile/17180079098492232258noreply@blogger.comtag:blogger.com,1999:blog-13869903.post-86055082679375225642009-12-15T22:46:21.470-06:002009-12-15T22:46:21.470-06:00Shouldn't it be a 377 Ohm resistor?
http://en....Shouldn't it be a 377 Ohm resistor?<br />http://en.wikipedia.org/wiki/Impedance_of_free_spaceAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-13869903.post-45253099505359194402009-12-13T23:07:54.271-06:002009-12-13T23:07:54.271-06:00I had the fluctuation dissipation theorem in a gra...I had the fluctuation dissipation theorem in a graduate statistical mechanics (sort of) class taught by <a href="http://en.wikipedia.org/wiki/Joseph_Weber" rel="nofollow">Joe Weber</a>.<br /><br />He assigned us the almost impossible homework problem of showing that the energy absorbed by a short dipole antenna in a black body region with temperature T, matched that emitted by a 50 ohm resistor (at temperature T). They're connected by a 50 ohm coaxial cable. Thus the power out of and into the antenna matched and no violation of the laws of thermodynamics ensues.<br /><br />Then in class, he solved it in three lines by happening to know the total cross section of an antenna is always 4 pi or something like that.CarlBrannenhttps://www.blogger.com/profile/17180079098492232258noreply@blogger.com