8,034 reputation
1728
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 6 months
seen 52 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
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.
Jan
22
answered Where does the loss of kinetic energy of the wind flowing over an airfoil go?
Jan
20
revised How does a supersonic flight speedometer work?
added 69 characters in body
Jan
20
answered How does a supersonic flight speedometer work?
Jan
20
comment Alternative air transportation and magneto-aerodynamics
There have been "flying saucer" aeronautical projects, of varying degrees of success.
Jan
20
comment Helicopter, Tricopter, Quadccopter - what's really happening here? Are there generalized advantages on a small scale?
For efficiency, the longer and thinner the blades, the better. Smaller rotors are less efficient, thus less flying duration. If you have an odd number of lifting rotors, you have net torque, so you need a tail rotor. Planes with lifting rotors can hover, but planes with wings have to fly in circles if they want to stay in one place. Put all those considerations together.
Jan
16
answered How size of objects lifted by the wind depends on the speed of the wind?
Jan
15
revised transfer of heat from lower to higher temperature
added 122 characters in body
Jan
15
answered transfer of heat from lower to higher temperature
Jan
14
comment Problem regarding Archimedes Principle
It's a spring-mass-dashpot system (ignoring the dashpot). You can figure out the amount of mass, and you can figure out the spring constant (dForce/dY). Then look up the equation.