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michaelmozina
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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>There are more comprehensive books out there that are a little more useful to me. </DIV></p><p>That "depends". If Alfven was correct, then his book will be more long term "useful" to you than anything else you might ever read. He did afterall apply MHD theory to the larger universe and to the plasma between the stars and galaxies. If he was right, you should read his work.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Of course they all incorporate and mention Alfven's early work. </DIV></p><p>They only incorporate and mention Alfven's work on the "field" side of MHD theory. They never mention the particle side of MHD theory except in passing mention or in reference to the auroral activities themselves. They are never mentioned in relationship to any other events in space. </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>However, none of them treat things in terms of circuits.</DIV></p><p>Exactly. They *ignore* half of MHD theory!</p><p>Maxwell's equations describe the relationship between electricity and magnetism. They show us that they are related phenonon. Maxwell's equations can be simpliifed either for B or for E. Both simplification routes are possible because we can subsitute for each variable. Priest's approach in his paper attempted to simplify for B, leaving E out of the equation altogether. This created a problem at the point of reconnection, because it is the charged particles that actually do the energy transfer. He "improvised".</p><p>Birn was more to the point, He didn't "oversimplify". As a result, things worked pretty well, but the naming convention he chose was a 'field' orientation naming convention.</p><p>Alfven gracefully worked between both the field orientation of MHD and what he called the "particle" view of MHD theory, the B and E simpified variations of Maxwell's equations. In dense, non current carrying plasma he tended to favor a *field* oriented viewpoint. In light, hot, current carrying plasma however, he typically preferred the particle/circuit approach. The naming convetions he worked with were consistent with principles of electrical engineering and particle physics and it is an equally "valid" way of describing events in plasma. You need to accept this point. There is more than one way to simplify for any equation that contains E and B from the outset and both viewpoints are valid. </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> What my work will focus on is developing the physics involved in cold, dense star forming regions.</DIV></p><p>And if there is powerful current flowing through this plasma, do you think it will have any effect?</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>This has more to do with radiative transfer and chemistry(i.e. atomic->molecular gas transition, cooling curves, etc) than E&M. </DIV></p><p>Of course a consistent or even intermittent electrical current flow could have an an effect on "cooling" don't you think? My point here is that if Alfven/Birkeland's views of space are correct, it will have a direct effect upon these events.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>B fields do have a large effect on structuring the regions, so of course there will be some.</DIV></p><p>E fields on the other hand would have some noticiable and interesting effects on events in plasma.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> My intended implication was not that reading Alfven's entire body of work would not be useful, just that there are better, more modern and applicable books for what I will be studying. <br /> Posted by UFmbutler</DIV></p><p>Personally I think Perratt's work is an easier read, and somewhat modernized (includes computer software simulations) but his book is out of print and it's *extremely* expensive. Alfven's work however would have a direct effect on events in your area of expertize. The only real question is: Was Alfven right about current flows in space? If the answer is yes, his work has a direct effect on your work as well. If the answer is no, then you may be right. I personally think it's highly important to get both sides of any debate, and the "predictions" each theory makes will ultimately determine the validity of the theory. </p> <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>