Wikipedia:Reference desk/Archives/Science/2016 June 14

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June 14

Woodward effect/Mach effect

is Mach effect thruster (MET) a anti gravity device? 81.216.64.211 (talk) 12:19, 14 June 2016 (UTC)

see Woodward effect 81.216.64.211 (talk) 12:20, 14 June 2016 (UTC)

No. The claimed thrust of the Woodward effect is as difficult to show as nett power from a Brownian ratchet. AllBestFaith (talk) 23:26, 14 June 2016 (UTC)

Clicker training yourself

Is it possible to use clicker training on yourself? Is there anyone who has tried this? What if you make a robot that recognizes and rewards the desired behaviour? (((The Quixotic Potato))) (talk) 13:37, 14 June 2016 (UTC)

At least some people think so. Usually I hear about snapping a rubber band on your wrist to help create an aversion to the targeted behavior, see e.g. [1]. I'll see if I can find any real science on efficacy. SemanticMantis (talk) 14:41, 14 June 2016 (UTC)

Oh wait our article says clicker training is only used for positive reinforcement. I think that's too narrow, and clicker training is also used as positive punishment in the real world, even if that's not best practice. But anyway, the rubber band thing I link is definitely an attempt to get self-applied operant conditioning to work on humans. SemanticMantis (talk) 14:45, 14 June 2016 (UTC)

For the more general scientific perspective, here [2] is a book chapter on self-management methods, giving an overview of some theory and empirical research, many more refs therein. It seems to address some of your questions, but maybe no specific evidence based on experiments with a rewarding robot. SemanticMantis (talk) 14:57, 14 June 2016 (UTC)

Awesome, thank you! I've been thinking about writing some software to train myself to do certain things (and stop doing other things). Unfortunately I am not yet able to build a cool robot, but that might be a project for the future. (((The Quixotic Potato))) (talk) 21:36, 14 June 2016 (UTC)

The click sound in clicker training has no intrinsic meaning and is a "bridging stimulus" whose perceived value (to reinforce or deter behaviour) has to be trained by context. Its practical value is that the click can be given so quickly within an animal's short span of attention to a single action that the animal becomes conditioned to identify the action with the (desirable or undesirable) significance of the click. Neither a human nor a potato has both the insight needed to conceive a click training discipline and an inability to know what is happening, so self training efforts must involve more complex mental assumptions than clicker training. It is trivial to program a robot to collect either maximum or minimum number of signals, which may be clicks, but both the robot and its programmer have much more to learn before self-intelligent evaluation of behaviour can be possible. AllBestFaith (talk) 23:15, 14 June 2016 (UTC)

@AllBestFaith: True, the clicks are meaningless, but theoretically I can replace the sound of the click with a "ping"-sound, and display the score somewhere (perhaps with some pretty graphs to show my progress over time). Perhaps I can even use some gamification, donate money to charity per X points earned, or have a system where I can exchange points for treats/stuff I like. (((The Quixotic Potato))) (talk) 03:21, 18 June 2016 (UTC)

Hydrogen Vs Earth

Newton had stated in his universal law of gravitation that every body in this universe attracts every other body by a force that is directly proportional to the product of masses and is inversely proportional to the distance between their centers. But why the hydrogen gas goes upward from earth's surface and doesn't get stuck at the earth surface? If you opine that it is due to the less mass of hydrogen, then you should think about the gravity of such great mass of Earth . Can't the Earth pull the Hydrogen on it's Surface ? Please You Can Give The Answer From Any Angle. — Preceding unsigned comment added by Achyut Prashad Paudel (talk • contribs) 15:13, 14 June 2016 (UTC)

The Earth is not a black hole. You leave fast enough, you escape. Sagittarian Milky Way (talk) 16:38, 14 June 2016 (UTC)

Is it reasonable to suppose that if the entire atmosphere of the earth were hydrogen, that at least some would "stick" near earth's surface? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:45, 14 June 2016 (UTC)

I'm pretty sure there was a lot of hydrogen in Earth's first atmosphere and it's now down to 0.000055%. Sagittarian Milky Way (talk) 17:42, 14 June 2016 (UTC)

Less than 4% hydrogen is not flammable if the remainder is a fine 2016 vintage air. Buy a bottle today! Recently coming with notes of extra CO₂, fallout, and a bouquet of various CFCs, the air of this upstart sentience in the Orion Arm is a unique addition to the collection of any imported air connoisseur. Are you an alien hipster? Want something to show how obscure you are? While everyone else drinks common nitrogen you could be drinking the liquified air of a hypertropical world no one's ever heard of called Earth. Buy your expensive craft brew today! Sagittarian Milky Way (talk) 17:50, 14 June 2016 (UTC)

Is it organic? (((The Quixotic Potato))) (talk) 10:34, 15 June 2016 (UTC)

Actually... Tevildo (talk) 18:09, 15 June 2016 (UTC)

Fabulous. I wonder how full of hot air these jars are? (^_^) Double sharp (talk) 05:46, 17 June 2016 (UTC)

Maybe I am wrong but since China exports loads of stuff I expect that it imports less than it exports which probably means that at least some of the containers returning to China are empty... ehm... I mean full of valuable clean air. (((The Quixotic Potato))) (talk) 03:26, 18 June 2016 (UTC)

Gravitation is not the only force acting between the Earth and the atmospheric hydrogen, atmospheric pressure is acting in opposition to it. Also, gravitation is a comparatively weak force – consider, for example, that the gravitation of the entire mass of the Earth pulling on a piece of metal can be overcome by a small hand-held magnet.

For more details, see the article Atmospheric escape. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 17:28, 14 June 2016 (UTC)

Also, solar wind. If he earth was stationary and in the middle of deep space, then the hydrogen would probably float up to the very top of the atmosphere and gravity would probably hold it there. But the earth isn't stationary and it isn't in deep space. We are fortunate enough to have a magnetic field which deflects most of the solar wind away from the bulk of our atmosphere, something which mars is not lucky enough to have which is the main reason mars has 1/10th the atmosphere of earth. Vespine (talk) 23:14, 14 June 2016 (UTC)

Hydrogen floats for the same reason a boat floats - because something else is being pulled down more. The heavier atoms crowd in underneath it, and eventually it rises. Indeed, it may be lost entirely from the exosphere - each stray molecule, depending on its particular speed, which is a random function of temperature, might reach escape velocity with some low probability. Heavier molecules move more slowly and are far less likely to have escape velocity at the usual exosphere temperatures. Wnt (talk) 23:57, 14 June 2016 (UTC)

The Earth's atmosphere is quite warm, almost 300K, depending on altitude, and at the highest altitudes it becomes less well defined as there are too few collisions to get thermodynamic equilibrium. The molecules in the atmosphere have a kinetic energy of, on average, the temperature times Boltzmann's constant. Hydrogen molecules are much lighter than nitrogen molecules (by a factor of 13.9), so they move on average 3.7 times as fast. That makes is far more likely for hydrogen molecules to reach escape velocity than for nitrogen molecules. Effectively, the hydrogen molecules are kicked out of the atmosphere by collisions with other molecules. Photo-ionisation, magnetic fields and fast atoms from the solar wind give an extra notch. Next the hydrogen molecules fly through space until they hit something cold enough or massive enough to keep a hold on them. PiusImpavidus (talk) 12:01, 15 June 2016 (UTC)

Minimum forward current for Infrared LED

My understanding is that there's no such thing as a minimum forward current for LEDs; that as long as the V_f of LED is met, the LED will operate in forward bias mode and emit light, however little of it. These pages seems to support this[3][4].

But I came across this part, QRE1113[5], where on page 5 of its datasheet， "Fig.6. Forward Current vs. Forward Voltage" seems to show the forward current, I_f, being cut off at 10 mA. Does that mean that this part won't operate with a I_f less than 10 mA? Or am I reading the graph somehow? Johnson&Johnson&Son (talk) 17:39, 14 June 2016 (UTC)

The datasheet is for a reflective object sensor that consists of a LED plus a phototransistor. The graph in Fig. 6 is simply incomplete and there is no reason to expect unusual behaviour at LED currents I_F below 10 mA. However the datasheet implies I_F = 20 mA is normal operation and the spread of forward voltage at that current (1.2V typical, 1.6V maximum) is much wider than the "typical" graph might suggest. Fig. 1 shows that the sensor can be used at I_F = 10 mA and it probably works at lower I_F but such operation is outside the range that the data sheet supports. AllBestFaith (talk) 22:40, 14 June 2016 (UTC)

Thanks!Johnson&Johnson&Son (talk) 02:09, 15 June 2016 (UTC)

Engineering - problem solving

Classically, engineering has been about solving problems in creative ways through the application of engineering principles, but have some engineering disciplines, other than in research, become more about following codes and paperwork? I believe in electronics, medical or automotive engineering, innovation and problem solving is still at the heart of engineering but is this still the case in infrastructure, buildings or building services and systems? 2A02:C7D:B965:6200:C4BA:9A78:DF03:CD7F (talk) 21:13, 14 June 2016 (UTC)

Adhering to codes, standards and legislation, and making written records, are found in all engineering disciplines; just as problem solving and creativity are found in all engineering disciplines. Different levels of both will be found in different projects and different workplaces but to suggest significant differences exist across whole engineering disciplines is too broad a generalisation to be worthy of serious consideration. Dolphin (t) 21:42, 14 June 2016 (UTC)

I certainly hope that following the relevant codes is a big part of medical and automotive engineering. I don't want my pacemaker or car brakes designed by some guy who just had a wacky new idea. CodeTalker (talk) 23:46, 14 June 2016 (UTC)

There's a big difference between the disciplines where prototypes are common, and those where the final products tend to be built direct from plans. In the latter case the engineer follows a fairly standardised way of designing a particular device. In the former, we have stringent sets of tests that must be passed, so the wacky idea has to prove it is robust and useful. I must admit neither of the answers above impress me overmuch, in terms of insight or accuracy. Greglocock (talk) 00:14, 15 June 2016 (UTC)