7,425 reputation
1628
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 1 month
seen 18 hours ago

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.


Jun
2
comment Are there any substances that allow sound to travel better then air?
A lot depends on dimensions. If the medium is fully 3d over long distances, energy falls off as $1/r^2$. If it's 2d, like a temperature layer in air or water, it is $1/r$, so sound can carry a lot farther. If it's 1d, like a tin-can string, pipe, or iron rail, the sound can go very far without dissipating.
Jun
2
comment Are there any substances that allow sound to travel better then air?
+ Air isn't so bad either, at low frequencies.
Jun
2
comment Quick question on parallax and parsec
There is a background of relatively fixed stars. You see a pair of stars 3" apart. Six months later they are still 3" apart, but the pair of them together appear to have moved 1" against the background. The movement against the background is the parallax.
May
30
comment Does the lift created by a wing change when the slats are deployed?
What slats and flaps do is increase the effective camber, or curve angle of the wing. Then the definition of AoA gets a bit fuzzy. What is a chord line that everyone could agree on?
May
30
comment Why do clouds fly?
@user2820052: NP. The air has a temperature, which is just the air molecules moving around excitedly, bumping into themselves and everything else. That bumping is what pressure is. If you're teeny-tiny and weigh nothing (or practically nothing) you will just bump around in the general chaos. Now, take a cubic liter of water - it has 100 square cm area on a side, and weighs 1kg. Now take a cubic cc of water, it has 1 square cm area on a side, and weighs 1 gram. 100 times less area, 1000 times less weight. Keep going. That's why dust motes fly and mountains don't.
May
29
comment Why do clouds fly?
@user2820052: forget the density and temperature. What matters is the ratio of volume to area. If a droplet has a diameter of 10^-4 cm, then its ratio of volume to surface area is 10^-4 that of a cc of water. In other words, its weight becomes insignificant compared to its area, so gravity has no more effect on it than a hair on your head.
May
28
comment Why do clouds fly?
@user2820052: If you were your present size, but you only weighed 1 gram, and if air molecules kept bumping into you like bouncing bowling balls on all sides, you'd fly too. And if there was a region of fewer bowling balls up ahead, it would attract many of them, and you'd be carried along.
May
26
comment Why do turbine engines work?
@Nathaniel: The torque exerted by the exhaust on the turbine is equal to the torque exerted by the compressor on the incoming air and, a little bit, on the pressure in the combustion chamber. (The vane area at the last stage of the compressor is small compared to the vane area of the turbine.)
May
25
comment Why do turbine engines work?
@Nathaniel: What do you mean "push more"?
May
17
comment Double slit experiment and single particles. Is the wave function just a mathematical model?
@Overloaded_Operator: It's not that photons don't have location, it's that they have a very specific definite location in every different world they are in. Are there actually many worlds - who knows? but nature seems to behave as if there are. Einstein objected to nature being probabilistic (I'm sure you know), so you're in good company. But that's where we are.
May
16
comment What was the Law of Gravity better explained by?
@JFA: Sure. They're lengthy, and by rights, you should work the math along with him, pausing as necessary. I get too many interruptions, myself. But nobody can make it clearer than he does.
May
16
comment What was the Law of Gravity better explained by?
You need patience to understand this stuff, but Lenny Susskind's lectures can't be beat!
May
13
comment Fluid mechanics of aircraft at 10000 m
Usually we try not to make answers so complete that the OP can turn them in as if he himself did the work. That would short-circuit the education process. Whether you've done that here, I'm not sure.
May
12
comment Flight time Toronto to Moscow the same
Right. If you've ever use a flight simulator to re-create a flight like that, you realize the winds aloft can be quite strong. 70 nautical miles per hour is typical.
May
12
comment Calculating the rate at which a car turns
No need to start from scratch. Just straighten out your differential equations. In terms of vectors, it's simple. You have position P, velocity V, and acceleration A. P += Vdt, V += Adt. A is the sum of the two components at right angles, tangential and radial, as I said. If you don't understand me, learn up on vector algebra.
May
12
comment Calculating the rate at which a car turns
There are two components to acceleration, tangential, due to the thrust/weight ratio at the driving wheels, and radial, due to the angle of the steering wheels, causing the car to travel in a circle. The radial acceleration is $V^2/R$, and the $R$ depends on the angle of the front wheels and the wheelbase.
May
12
comment Calculating the rate at which a car turns
airResistance should affect the tangential acceleration, not the velocity, and your way of linking velocity, acceleration, and turning angle do not look right to me.
May
11
comment What is the exact cause of flow separation in a viscous fluid?
Are you asking about the Kutta condition?
May
9
comment Why doesn't this model plane fly?
@Pranav: Good point.
May
9
comment Why doesn't this model plane fly?
@Pranav: This video shows what happens when the loading shifts aft.