6,281 reputation
1322
bio website en.wikipedia.org/wiki/…
location United States
age 69
visits member for 2 years, 7 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.


Feb
2
answered When is the stress on an airplane the highest?
Jan
31
comment $\Delta T$, temperature units. How to use fahrenheit in this formula
Looks cool! Good luck.
Jan
31
comment $\Delta T$, temperature units. How to use fahrenheit in this formula
Multiply by 5/9
Jan
31
comment Why does a flat clover-like shape fall slower when it is rotating?
@DiomidisSpinellis: There's a video here (and there are many more like it) illustrating the concept of AoA and wing stall.
Jan
30
comment Why does a flat clover-like shape fall slower when it is rotating?
@DiomidisSpinellis: If you are a tiny person attached to the end of a blade, and if the motion downward is 1 m/s, and since the toy is spinning you also have a tangential motion forward of, say, 10 m/s, then the air is coming toward you at an angle of roughly 6 degrees below the horizon, at a speed of roughly 10 m/s. Even if the blade you are attached to has zero pitch (i.e. perfectly flat), that blade will be functioning as a wing, not a parachute, i.e. it will be flying, not stalled, therefore seeing appreciable lift. Stall AoA is between 10 & 20 degrees.
Jan
30
comment Why does a flat clover-like shape fall slower when it is rotating?
@Olin: Yeah, helicopters do not reverse rotation direction when they autorotate, they pitch the blades down. Regarding the "whole disk" acting like a parachute, I'm sure you've seen this. As a sometime pilot myself, I'm very aware of the essential importance of angle of attack. A parachute (not a paraglider) is essentially stalled (90 degree AoA). Rotor blades are flying, not stalled (AoA < 20 degrees). The airflow follows both upper and lower surfaces. So calling the spinning toy basically a circular parachute doesn't hold water, I think.
Jan
29
comment Why does a flat clover-like shape fall slower when it is rotating?
"Approximate a disk for the purpose of air resistance"? "rotor end up spinning opposite of how the engine was driving it"? Sure you don't want to reconsider those?
Jan
29
revised Why does a flat clover-like shape fall slower when it is rotating?
added 156 characters in body
Jan
29
answered Why does a flat clover-like shape fall slower when it is rotating?
Jan
29
comment pressure in fluid mechanics of incompressible liquid
Keep in mind that the Bernoulli relation is simply energy conservation. Ignoring gravity, the only way the fluid can change speed is if there is a pressure gradient for it to fall through.
Jan
29
comment Physics and Linear Differential Equations
@RoopamSinha: I would be careful of the term "linear", if what you mean is that only first powers of state elements, not multiplied by other state elements, appear on the right hand sides. In my experience in pharma, nonlinear differential equations appear all the time.
Jan
27
answered Centre of instantaneous rotation problem
Jan
24
comment How physical objects (e.g. Earth and Apple) are aware and do computation about each other?
@Yasser: Another way is to simply accept not knowing! We don't know now, and maybe we will in the future, maybe not. Does a blank piece of paper need an explanation? Look, hundreds of years ago, there was no conflict between science and theology, because scientists saw themselves as trying to understand more about creation. Theology was not seen as a substitute for science, until some hard-nosed people insisted it was, and we still see that trouble today. Personally, I keep those issues entirely separate and private, and I wish more people would do the same :)
Jan
24
comment How physical objects (e.g. Earth and Apple) are aware and do computation about each other?
@KeithThompson: Totally agree. In one of Feynman's paperbacks, he tells the story of his father being asked, if there's a pumpkin in a wagon, and the wagon is pulled, why does the pumpkin roll to the back? His father said, basically, everybody knows it does, but nobody knows why.
Jan
24
comment How physical objects (e.g. Earth and Apple) are aware and do computation about each other?
@Yasser: Newton couldn't answer that question, so he assumed God did it. Einstein actually made a theory of it, which helps us understand it, regardless of any deity, but it does not not require the physical objects to know that theory.
Jan
24
revised According to relativity, can a statement be true and false in same time?
added 66 characters in body
Jan
24
answered According to relativity, can a statement be true and false in same time?
Jan
24
comment How physical objects (e.g. Earth and Apple) are aware and do computation about each other?
If you put one block on top of another, do the blocks need to know math to know they are 2 blocks tall? No. Maybe we do.
Jan
24
comment Does rotation cause gravity?
Just to be light-hearted, some children were once asked what causes wind. The answer: the trees waving their leaves.
Jan
22
comment Who popularized $E=mc^2$?
6 August, 1945, is when the world became aware.