6,281 reputation
1322
bio website en.wikipedia.org/wiki/…
location United States
age 69
visits member for 2 years, 7 months
seen 3 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.


Feb
15
comment How much weight can a person carry to avoid being blown over by wind?
It does get windy between the buildings in Boston (or anywhere). I would go with @Carl's suggestion of a cane, especially one that is adjustable and collapsible, and that has a strap or hook so you can free up both hands without dropping it. The trouble with a rolling bag is just that - it rolls, so it may not give as much stability as you'd like. Good luck. (Just thought of another possibility - a 4-wheel bag that you can lean on while it rolls - maybe?)
Feb
11
comment water in vacuum(or space) and temperature in space
Take a beaker of water out of the space station and remove the lid. First the water will float out, then it will boil away because of no pressure, and the vapor will fly away. If you kept it under pressure so it could not boil off, then it would either 1) get hot when the sun shone on it, or 2) get cold in the shade, because it would radiate its heat away to the sky, which is practically at absolute zero.
Feb
8
comment How can a fly be in the space of a roofless car, get out of the car space and get back in while the car is driving at the speed of 80mph?
Maybe relevant. My cousin is a long-time pilot. He has heard of people who wished to have their ashes spread from an airplane. What a mess! The dust blows everywhere and they have a big cleanup job.
Feb
6
comment Can you read and write a quantum state to a particle without collapsing its probability field?
Writing information to it before a computation is no problem. After it has started, you cannot touch it until it is finished, at which time you can read it. You may not get the right answer. You have to arrange the computation so that the right answer has an acceptably high probability.
Feb
4
comment Calculate work done in an inclined plane
@mc8: Then you're not elevating it, right? So you're not putting in any potential energy. You might give it kinetic energy, if you push it and it just keeps on moving. That's when your F=ma comes into play.
Feb
3
comment Calculate work done in an inclined plane
@mc8: Glad you got it. You're welcome.
Feb
3
comment Calculate work done in an inclined plane
@mc8: Because the work done is the same whether it is done in one minute or in one millenium. In the frictionless case, the weight rises through a distance, increasing its potential energy, and that is the work done. Please figure out the rest of it yourself.
Feb
3
comment Calculate work done in an inclined plane
@mc8: because you're not accelerating. It's a simple balance of forces.
Feb
3
comment Calculate work done in an inclined plane
Draw a vector diagram of the forces, and use a smidge of trig.
Feb
3
comment Calculate work done in an inclined plane
Sounds like homework. Figure out the force if it is frictionless, then add in the friction force, multiply by distance. Forget F=ma - you figure out why.
Feb
2
comment Why does the blade height goes on decreasing in a multi-stage axial flow compressor?
+ Right. As the air is squeezed, its volume decreases.
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
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
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 :)