7,738 reputation
1628
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 3 months
seen yesterday

BS Mechanical Engr.
PhD CS(AI)
CS Prof (4yr)
Numerous consulting jobs.
15 yr at http://www.pharsight.com
Published book on CS & several articles
4 kids, 2 grand
Pilot(student)

P.S. The picture is a Beta-prime distribution. It shows the program speedup factors you can get if you see a problem twice in 2, 3, 4, and 5 samples.


Jul
18
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
You could just have a stationary scaffold around the entire black hole, and stand on that.
Jul
17
comment Add weight in front or behind the moving wheel?
@user55493: I see kids do it all the time. They go up-hill on their skateboards in a series of S-turns. Each curve of the S-turn, they are pushing sideways. It doesn't matter how many wheels they do it on, or whether their weight is forward or back. What matters is the sideways push.
Jul
14
comment Does the Higgs boson give mass to ALL other particles?
Is it possible that the mass of nucleons is mostly the energy (over $c^2$) of the binding of their components, and not really anything to do with the Higgs field?
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: It's a great question you asked. In my pilot training, I was taught to be very aware of "wake turbulence" - those invisible vortices coming off heavy-plane wingtips.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: I just googled "vortex merging" and a ton of high-quality stuff turned up!
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Now I'm the one who's skeptical :) Any vortex has to have a central region of low pressure, so that the pressure gradient provides the radial acceleration keeping it circular, so when the vortices come close together, the pressure gradients have to superimpose, affecting the paths of particles. But the trouble is, if that were the only effect, then counterrotating vortices would also merge. Hmmm...
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Well, as I said, when they come close together there will be counter-rotation between them. This will divert flow from each vortex to the other. If you're after a mathematical description of this process, maybe you should research it or better yet, construct it. For the other case, counter-rotating vortices, they don't merge because the physics are obvious, as Floris pointed out.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Then check Floris' answer. It's a simple matter of conservation of vorticity (i.e. angular momentum), and kinetic energy.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Forget subsumption. They simply merge, because each little parcel of air follows a path.
Jul
11
comment Computing the force generated by a sail on a boat
@T.Kiley: I'm afraid you need to know how the sail functions as an airfoil - namely what is its chord, its angle of attack, and its coefficients of lift and drag as a function of those.
Jul
11
comment How effective is speeding?
It's more important to minimize time spent going slow than to go fast.
Jul
9
comment Problem understanding basic sail mechanics
+1 @T.Kiley: Don't confuse yourself with the Bernoulli kerfuffle. Just consider the centerboard of the boat as if it were a skate. Consider the sail as if it were a knife blade, and the air were jello. Then satisfy yourself that no matter how fast the boat is sailing downwind, there is a sail angle that can give it forward thrust. A simple physical analogy is a wet watermellon seed squeezed between thumb and forefinger. Here's a similar question.
Jul
3
comment Do airlocks in space decompress violently as they do in movies?
For the airlock, it depends how suddenly the air is released. People consist of lots of muscle, fat, bones, etc. plus liquid plasma in fairly strong tubes, plus air in lungs. If they don't try to hold their breath, there's not much to decompress.
Jul
3
comment How should I throttle my rocket to reach highest altitude?
Here is a *very worthwhile read: *
Jul
2
comment Paper airplane physics
@J...: The OP had some basic misconceptions that needed to be corrected. When that is done, the equations just fall out. I was trying to correct the misconceptions.
Jun
30
comment What does a wing do that an engine can't?
There are misconceptions in some of the answers here. Lift/Drag ratio is beside the point. Angle of the engine axis is beside the point. Gliders vs. rockets are beside the point. Falling plates are beside the point. The answers that are on point are the ones that talk about momentum vs. energy of the downwash.
Jun
22
comment Prerequisites for Halliday Resnick Walker
Khan Academy is hard to beat. Just be sure, when you take calculus in school, that you are humble, and take the material at the rate it is taught, even if you know it already.
Jun
12
comment Why air above airplane's wing moves faster?
It is a recurring, and absolutely wrong, conception that the air has to rejoin itself at the trailing edge. In fact, wings could not work if it did, because lift requires circulation. Check this very good explanation.
Jun
4
comment Why is the application of probability in QM fundamentally different from application of probability in other areas?
@TwoBs has it right. In QM, probabilities don't add, they interfere, because their amplitudes add. And if you're concerned about independence, just break down the cross-product, and consider each possibility independently.
Jun
3
comment What's the advantage of NASA's flying saucer over traditional aerodynamic models?
Currently they go from 1) a small aeroshell to 2) a large parachute. They want something in between, a 1.5