8,667 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 71
visits member for 3 years, 10 months
seen 1 hour 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.


1h
comment Why does an image form at the intersection of light rays?
@user132522: Don't call your English bad. It's far better than my Spanish, and that's far better than my French, German, Portugues, Greek, Korean, etc. We hosted students learning English. A Brazilian woman wanted to speak English with no accent. I told her no - your accent is charming. Keep it.
2h
comment Why does an image form at the intersection of light rays?
@user132522: I guess English is difficult. Yes "right side up" means "upright. The lens of your eye forms an image on your retina. The image is "upside down" or "inverted", meaning the sky is in the lower part of the retina, and your shoes are in the upper part. Left-right is also swapped. But your optic nerves twist it so it looks upright.
3h
comment Why does an image form at the intersection of light rays?
@user132522: I'm not sure what you're asking.When a light ray strikes an interface plane between two transparent media having different indices of refraction, the light beam will change direction, and if the angle is shallow enough, it will reflect off the interface plane, just like off a mirror. You can easily see this in a table-top aquarium filled with water.
4h
revised Why does an image form at the intersection of light rays?
added 49 characters in body
4h
answered Why does an image form at the intersection of light rays?
Jul
28
comment What stops giant cruise ships toppling over in rough seas?
@Acid: Every such boat is designed by engineers and you can be absolutely sure they've thought of that. You can be sure they have written a user's manual saying things like: putting more weight than XXX on decks YYY will "void the warranty". They know what they're doing.
Jul
28
comment What stops giant cruise ships toppling over in rough seas?
They look top-heavy, but they are not. Suppose you took a row-boat, and put a few hundred pounds of cement bags in it. Then pile cardboard boxes on top several feet high. Same idea. It might look top-heavy, but if you try to push it over, the weight in the bottom will bring it back up.
Jul
27
comment Why is not the entropy of earth increasing?
@Acid: I disagree with your last paragraph. The second law applies to closed systems, which the earth is not.
Jul
27
comment Why is not the entropy of earth increasing?
@pentane: Entropy can be defined as the integral of $dQ/T$, so it's not unreasonable to say sunlight at high temperature is energy at low entropy, and radiational cooling is the opposite. No?
Jul
27
comment What's the max speed a man-made satellite can travel in space before its circuitry stopped working?
Nice, but I would have said something like 1 - 2e-14 or 1 - 2e-7, rather than string a bunch of 9s and make me count them :)
Jul
26
comment Breaking the sound barrier underwater
Google supersonic torpedoes.
Jul
23
comment What is (theoretically) the most efficient shape for an aircraft, assuming you don't have to carry any cargo?
What matters is the lift/drag ratio. If drag is zero, the plane can't even come down! (They can point the nose down, but all that does is make them go faster, increasing lift, making them go back up.) Airplanes with high L/D are sailplanes (30:1). They minimize drag by traveling slowly and having long skinny wings (as well as being aerodynamically "slippery"). Efficient aircraft need spoilers and/or speed brakes, without which their glide is simply too shallow to be useful when landing. They have to get to the landing zone while missing the trees.
Jul
23
comment Finding minimum time to raise a bucket
It's good that you tried to solve it yourself and showed your approach.
Jul
22
answered Trajectory of rolling billiard ball after collision with another billiard ball with same mass
Jul
21
comment Why and how strong are currents near ship side?
Good question. I assume the ship is anchored and aligned with the current. People often swim near large boats that are anchored, but maybe not in a river with current.
Jul
21
comment rotational springs
My favorite example - torsion bar suspension.
Jul
20
comment rotational springs
Torsion spring.
Jul
19
comment What's wrong with this argument that aerodynamic lift really does rely on Bernoulli?
I have to disagree with your last two paragraphs. You don't have to do piecewise analysis to understand that the wing pulls the air into a downwash because of Bernoulli's principle. The answer from BillOer, while he should have said more, points to the best explanation I've ever seen. (And I'm a pilot.)
Jul
16
comment What is the maximum speed of an object moving trough air?
Wasn't the Chelyabinsk meteor traveling at about 100k kmh?
Jul
15
comment Will the water go inside the moving water bottle?
@Vaggelis: Forget drag. Suppose the water is flowing and the bottle is stationary. Then the water outside the mouth of the bottle has to come to a stop. In order to do that, some pressure has to stop it, and that is the stagnation pressure. Then, you get into questions of how big is the nozzle, can some more water flow in while some water/air flows out, etc. That's a different question, depending on how big the nozzle is, and so on.