8,087 reputation
1728
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 7 months
seen 41 mins 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.


Feb
27
comment What happens during gravitational collapse to cause the formation of a star?
My understanding of the fusion reaction is that the caloric density is actually quite low, like a compost pile. It's just that there's so much of it.
Feb
24
revised Can a thrown egg chip (or break) a car windshield?
spelling
Feb
16
comment Why does it take so long to get to the ISS?
@Dewi: The plane of any satellite's orbit is stationary, while the launch site is traveling east, so it is under the orbit twice a day, if the orbit is sufficiently inclined.
Feb
13
comment Can I tell where a leak is in a vertical water pipe based on the water pressure at the bottom?
@Skywalker answer is right. You can only get the height of the water. You can only get the height of the leak if you let the water drain down to it. So if you measure the pressure at the bottom, you need to wait until it stops falling. Actually, that will be an asymptote. It will slow down before it gets there. Actually, you might speed it up by letting some water out the bottom.
Feb
13
comment Why does NaCl (aq) conduct electricity but NaCl (s) does not?
and in solid, they are not even ionized.
Feb
13
comment Airfoils contradict the law of the lever?
@Floris answer is right. It's about energy, not force. The drag experienced by a wing is simply lost energy. A lever is a system that does not lose energy.
Feb
8
comment Application of Bernoulli's theorem
If it helps, I think the easiest way to understand Bernoulli is the simplest: to make a fluid accelerate (change speed), you need a difference in pressure. It's just $F = ma$ for fluid.
Feb
7
comment Why does the airflow in the mid-stratosphere of the northern hemisphere rotate FASTER than the earth?
@tpg2114: I appreciate what you're saying. I looked at the simulation, and the entire southern hemisphere has a broad easterly flow, and the equator is all westerly. This makes me doubt the simulation.
Feb
7
comment Why does the airflow in the mid-stratosphere of the northern hemisphere rotate FASTER than the earth?
If air moves toward the east at all, it is moving faster than the earth, if the reference is the earth's surface. But I agree, it is surprising. There's a lot about that simulation I don't understand. It seems to disagree with what I thought was basic circulation of air on the earth.
Feb
4
comment The stability of falling through a planet
As @docscience said, it looks like harmonic motion, because the gravitational force on you would be proportional to $r$. Basically the shell above you cancels out, leaving only what's below you. The mass of that goes as $r^3$, but the denominator goes as $r^2$, leaving the force proportional to $r$.
Feb
4
comment The stability of falling through a planet
Don't forget coriolis force. Unless you are at one of the poles, you are traveling toward the East at a high rate of speed, but at the center of the Earth you would not be, so on the way down, there would be a lot of rubbing. The gravity at the center of the Earth is actually zero. What you feel at the ocean bottom is not higher gravity, it is lower. What you feel is because you are holding up all the water above you.
Feb
4
revised What information do $|\psi(0)\rangle$ and $|\psi(t)\rangle$ represent?
added 653 characters in body
Feb
3
answered What information do $|\psi(0)\rangle$ and $|\psi(t)\rangle$ represent?
Feb
2
comment Can a nuclear reactor be used as a space-based weapon?
@Sofia: You're right, of course. That's no fun at all. I was just reacting to the Hollywood-style depiction of things blowing up :)
Feb
2
comment Can a nuclear reactor be used as a space-based weapon?
Nuclear reactors are slow-motion things. To make a nuclear explosion requires very careful design so that neutrons and other radiation that is generated is caught in just the right way to as to amplify the rate of the reaction.
Feb
2
comment Why are radians more natural than any other angle unit?
@supercat: I remember a debate some time back that would change the convention from 360 degrees to 400. That would have made it easier on aviators, who have to mentally calculate things like: "Given your current heading is $\alpha$, what heading would you turn to to make a 180 degree turn?" It's not the kind of thing where you want to make a mistake. Fortunately, if they have the presence of mind, they can just read it off their gyro-compass card.
Jan
28
comment Does Newton's 3rd Law apply to friction?
Newton's 3rd law says you can't push on something without its pushing back. Friction or not, it doesn't matter.
Jan
26
answered Is the buoyant force on an object is the reaction force?
Jan
26
comment Am i trying to fly by pulling myself up by my hair?
You might try a lever arrangement, so the downwash is not hitting the scale.
Jan
26
comment Can a car steer on a frictionless surface?
@EmilioPisanty: I don't think the front wheels on a car (on the frictionless surface) can change the car's pointing direction, because those wheels are not free to precess at right angles to the direction in which they are turned, because the car cannot bank (as a motorcycle can). You would need to have a gyroscope mounted in the vehicle, and it would need to be free to take on a bank angle. The amount it would need to bank would depend on its angular momentum.