meta user
network profile
| bio | website | en.wikipedia.org/wiki/… |
|---|---|---|
| location | United States | |
| age | 68 | |
| visits | member for | 1 year, 8 months |
| seen | 6 hours ago | |
| stats | profile views | 417 |
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)
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6h |
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How to find outflow pressure/force of air through a pipe en.wikipedia.org/wiki/Pipe_flow |
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2d |
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What is the state of contempoary Quantum Physics as a discipline? Easy there! No need to jump off the diving board :) (BTW, I learned early on that there's no need on stackexchange for excitement-toned language. You're among friends.) There are plenty of people on this site who know this stuff well enough that they aren't wracked with uncertainty, so you could follow them. |
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2d |
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How would a change in ambient temp affect a radiator? @Gk3Biz: Think of it like an electrical resistor being fed a constant current (heat power). Then a constant voltage (temperature difference) will appear across it. If you up your fan speed, that's like reducing the resistance, giving you less voltage (temperature) difference. Generally, electric equipment like motors have a rated temperature rise above ambient, in order to shed the heat they produce. |
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2d |
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How large can planets or moons appear? John Rennie's answer is right on, but keep in mind the Roche limit is due to tidal forces overcoming the satellite's own gravity. That means the closer the main planet comes to subtending 45 degrees of sky, the closer the moon (and its inhabitants, its atmosphere/ocean, and its liquid core) come to being ripped off into their own orbits. |
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May 19 |
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Radio antennas that are much shorter than the wavelength FWIW: en.wikipedia.org/wiki/Fractal_antenna |
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May 14 |
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Definition of entropy @Ben: Right. Reading too fast. |
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May 14 |
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Why can't supersonic planes “just fly higher” to go faster while maintaining cost? @Jim: There are variations of what's called "class Alpha" between countries, but there are no altitudes reserved for international flights. It generally refers to heights from 18kft to 60kft, above mean sea level, with standard altimeter setting. When divided by 100ft, these are called "flight levels". Airspace class |
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May 14 |
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Definition of entropy You point 2 is only true if all values are equally likely. For example, if there are two outcomes, and one outcome has probability 1/1024, while the other has 1023/1024, then the entropy is 10/1024 + ~0 = ~0.01 bits, not 1 bit. |
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May 14 |
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Definition of entropy Don't think of it as disorder. Think of it as what you don't know, and of what, on average, you will learn if you find out what the value of the variable is. |
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May 14 |
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Why can't supersonic planes “just fly higher” to go faster while maintaining cost? Conventional subsonic aircraft have to contend with the coffin corner. |
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May 14 |
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Why can't supersonic planes “just fly higher” to go faster while maintaining cost? The heat is not just skin friction. Where the air hits a forward-facing surface it has to stop, which compresses it, which makes it very hot (stagnation temperature). Even if it's very low density, it still gets very hot. That's what spacecraft re-entry is all about. |
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May 10 |
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Equal Transit Time Fallacy Brandon's right. IMHO, that av8n link is the best, most accessible, explanation I've seen. It all has to do with the fact that air cannot reverse direction at the trailing edge of the wing. This results in an overall rotary circulation, which is at the heart of the explanation of lift. |
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May 10 |
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Repulsion does not exist; Gravity assist slingshot as a repulsive force Thank you for trying to ask a question in English, but I had difficulty understanding it. Certainly the slingshot effect would be about the same if gravity were repulsive. |
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May 5 |
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Lifting house with balloons @Someone: It's better if you put some thought into it. This site is to help people learn from each other, and that doesn't work if your brain doesn't kick in. |
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May 4 |
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Will a helicoper which is hovering inside a closed box move with the box when we move it? It depends on the size of the box, whether it is a 1m cube or a 10km cube. The hovering helicopter will try to have zero velocity w.r.t the air mass it is in, not perfectly of course, but over time. This is easy to see if an updraft hits it. (I'm sure you know it has nothing to do with bouyancy - i.e. floation :-) |
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May 4 |
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Why do focal lengths affect magnification? @articlestack: Suppose you have two stars, where the angular distance between them is .01 radian. Then if you have an objective lens that focuses them to an image plane, how big is the image of the two stars? It will be .01 times the focal length, right? 10cm -> .1cm, 100cm->1cm, 1000cm -> 10cm. So then if you look at that image plane with a keplerian eyepiece (magnifying glass), you're examining a small piece of a bigger image. |
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May 4 |
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Will a helicoper which is hovering inside a closed box move with the box when we move it? The helicopter is not independent of the air - it is suspended in it. (Pilots care about that, needless to say.) If the air accelerates upward (say) the air will soon have an upward velocity, creating more lift, causing the helicopter to accelerate upward after a time lag. Same goes for acceleration in any direction, but you're right that if the box is small the 'copter will probably hit the wall in that time lag. |
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May 3 |
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Solving a simple equation Sounds like you need the quadratic formula. |
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May 3 |
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I read a book saying bernoulli's flight equations didn't have as much impact on lift as most people think @user1247: Please read. |
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May 3 |
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Why do focal lengths affect magnification? @articlestack: Wikipedia |
