Tuesday, April 26, 2011

If we only had the Parom tug

The russians are uncertain about letting the Dragon too close to the ISS.  Dragon has had only one test flight after all.  If we only had a reliable and proven Parom tug it could go get the Dragon (or other cargo capsules) from a safe distance.  Only a time proven technology would then approach the ISS. (It would also be useful for delta IV, delta IV heavy, or atlas V launched payloads.)

Thursday, April 21, 2011

Does Falcon 9 Heavy have too many engines?

When people discuss the difficulties with the N-1 rocket they frequently cite its 30 engines. (This number was used to help keep the price of the N-1 down.)  Certainly no airplane would be fitted with 30 engines.  On the other hand the R-7 became a very reliable launcher with its 20 main engines. (After some number of failures during development.) Are 27 engines (Falcon 9 Heavy) just too many?  I guess time will tell.

Wednesday, April 20, 2011

The Nature of Science

Tony Rothman has criticized physics teaching for not emphasizing the approximate character of physical theory (and science in general and knowledge of all sorts). (The Man Behind the Curtain, American Scientist, vol. 99, pg 186, May-June 2011)
In my general education classes I begin with a handout that contains the quote from Einstein that Rothman cites: "When mathematical propositions refer to reality they are not certain; when they are certain, they do not refer to reality" (1921) I also quote Stephen Jay Gould  "Science does not deal in certainty, so 'fact' can only mean a proposition affirmed to such a high degree that it would be perverse to withhold one's provisional assent." (Time magazine, 23 Aug. 1999) and Bertrand Russell  "All knowledge is in some degree doubtful, and we cannot say what degree of doubtfulness makes it cease to be knowledge, any more than we can say how much loss of hair makes a man bald." (Human Knowledge, Simon and Schuster, 1948,  pg 497)
For many years I have been giving this handout.  Throughout my course I then try to point out as many of the assumptions and approximations as I can. I hope other teachers will follow suit.

Thursday, April 14, 2011

Debye Shielding

We usually expect that a biased electrode in contact with a plasma will affect only its immediate surroundings.  The plasma will tend to shield itself from the applied electric potential.  The characteristic shielding distance being the Debye length. 

This is not the case for biased gun electrodes which can project a nonneutral plasma beam relatively long distances across a magnetically confined plasma (Controlling the plasma potential across a magnetic field, Trans. Kansas Acad. Sci., vol 93, pg 125, R. Jones, 1990)

Some G.O.F.A.I.

Schank proposed scripts for dinner parties, restaurant dining, and airports.  If we were to hope to formalize all of human experience we had better not need too many such scripts.  Gerard de Nerval "Having early desired to know the exact number of actions possible to the theater...found...twenty-four." (The thirty-six
dramatic situations, Georges Polti, The editor company, 1917)  Gozzi expanded this to 36 and Schiller and Goethe tried to find more but failed. Universal scripts based on Polti's list would include such things as:
loss,  misfortune/disaster,  pursuit,  obtaining,  imprudence,  ambition,  sacrifice,  rivalry some of which I know how to formalize as code.

Wednesday, April 13, 2011

Robert E. Lee's Biggest Mistake

Robert E. Lee should have accepted command of the Union army and so shortened the civil war. He had mistaken loyalties.

Turbulent Pinch

Back in 1983  I demonstrated that turbulence could improve plasma confinement in an internal ring machine. (Plasma Physics, vol. 25, pg 901, 1983 and other publications, see http://www.robert-w-jones.com/, publications)
At that time I couldn't get funding to continue the work but now MIT (and others) are pursuing the "turbulent pinch" (PSFC/JA-10-22, Boxer, et al, Dec. 2010 and Nature Physics, 6, pg 207, 2010).  Better late than never.  We still have an energy problem.

Monday, April 11, 2011

Is Information Energy?

I was presenting a poster on Saturday at the Kansas Academy of Science meeting (on my theory of thought) when a colleague said to me he had heard that "information IS energy." (Taking the old adage "knowledge is power" very literally.)  Perhaps he had in mind the "Information Converted to Energy" article of Nov. 19, 2010 posted on Physicsworld.com. But if information IS energy then, by relativity, it IS mass and, furthermore, a flashdrive (or other memory device) when travelling at high speeds would have more mass and information (and different amounts of information as seen by different observers).  This seems like a good counter argument against the idea that information IS energy.

Monday, April 4, 2011

Little Problems, Big Problems, and Reductionism

Small, simple problems can be solved completely.  A "hello world" program can be written that is bug free. An application in propositional logic is not subject to Godel's incompleteness theorem and may be provably correct.
The operation of a Turing machine, however, may prove inconsistent and typical real world computer programs contain bugs.
We can try, then, to decompose big problems into a set of small, simple ones which can be solved independently and then combined (reductionism).  Of course, the interconnections between the little pieces can not be too complex and numerous or we may fail during the recombination step. 
Large, difficult problems that are NOT decomposable may have to be APPROXIMATED by some decomposition that we hope is "close enough."  There may be several such approximations that give different answers to the original problem.

Saturday, April 2, 2011

Notes and Note taking

So what CAN we do to boost student learning?  Some years ago I had to teach an introductory physical science course.  In order to force students to take notes I had them keep notebooks which I then periodically collected and graded.  I found these to be quite poor.  I know that I was never taught to take notes and I suspect our current crop of students weren't either.  Probably more time should be devoted to notes and note taking.  (By the way, student notes are not the same thing as teachers notes.  My notes for my lectures remind me WHAT to talk about, the ORDER in which I want to talk about things, and the details of some difficult topics, but they would not be good STUDENT notes.  What you record when you are first learning a subject is something rather different. My notes are more about how to present things.  Student notes should be more content oriented. My research notes and files might be a better model for what student lecture notes should look like.)