Wikipedia:Reference desk/Archives/Science/2017 December 28

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December 28

Exact value of the strong interaction (constant)?

For the electric and gravitational field constants we have the equations ~8.98x10^9 N m^2 C^-2 and ~6.67x10^-11 m^3 kg^-1 s^-2, respectively. But what about the strong nuclear force? I can't find a reference anywhere as to it's exact value or dimensions. As of yet unknown or am I just looking for it in the wrong places? Earl of Arundel (talk) 01:01, 28 December 2017 (UTC)

Does Fundamental interaction help you? Else it will surely help to learn all the "basics" first that we humans always think we can skip when we "only want to understand that detail, not trying to become a professional". --Kharon (talk) 19:46, 28 December 2017 (UTC)

I'm simply asking if the strong nuclear force does or does not have an analog to the gravitation proportionality constant (G), and if so what its value and dimensions are. Earl of Arundel (talk) 01:05, 29 December 2017 (UTC)

Until proven otherwise I'll assume that any field can be reduced to individual factual statements. Either the strong force isn't a force or else it has a value. My first search turned up a Stack Exchange set of answers on this at [1] (no two the same) which say the following. I don't pretend to be able to identify errors reliably...

• The exact formula for the interaction is a Lagrangian in quantum chromodynamics.

• In quantum hadron dynamics the strong force can be approximated by the derivative in $r$ of the Yukawa potential, said to be (I quote)

$V(r)=-{\frac {g^{2}}{4\pi c^{2}}}{\frac {e^{-mr}}{r}}$

where $m$ is roughly the pion mass and $g$ is an effective coupling constant. If I am not mistaken that should be

${\frac {g^{2}}{4\pi c^{2}}}{\frac {e^{-mr}}{r^{2}}}+{\frac {mg^{2}}{4\pi c^{2}}}{\frac {e^{-mr}}{r}}$

by a simple application of the chain rule.

• The most-upvoted answer says (quote) $V(r)=-{\dfrac {4}{3}}{\dfrac {\alpha _{s}(r)\hbar c}{r}}+kr$ where the constant $k$ determines the field energy per unit length and is called string tension. For short distances this resembles the Coulomb law, while for large distances the $k\,r$ factor dominates (confinement). It is important to note that the coupling $\alpha _{s}$ also depends on the distance between the quarks. (unquote) This gives us a derivative that depends on $\alpha _{s}(r)$ plus a constant k (force at any distance).

I can't help but observe some difference between the form of these equations... A comment notes that the "breaking of the flux tube has no classical counterpart" and calls the calculation handwaving (by "flux tube", read QCD string). Another comment suggests the equations are invalid because they imply action at a distance, faster than light, and action on a quantum scale that cannot be modelled classically. Nonetheless, there seems here a useful starting point for coming to some sort of understanding. Wnt (talk) 01:22, 29 December 2017 (UTC)

Our article on strong force provides some illuminating specifics. It says the strong force is 137 times more powerful than electromagnetic force at distances of 1 fm or less -- which is consistent with an inverse r^2 term, for small r. It also says the force is 10,000 newtons at any distance, which is consistent with a k term. I assume that ratio has something to do with the fine structure constant, and suggests you might simply multiply the universal gravitational constant by that for your answer, where short ranges are concerned. But that's perhaps a mistaken inference on my part. Wnt (talk) 01:34, 29 December 2017 (UTC)

Spot on, that's exactly what I was looking for. Can't comment specifically on much else though...it'll take some time to digest all of that! Anyhow, thanks so much for the most excellent effort. Cheers! Earl of Arundel (talk) 01:56, 29 December 2017 (UTC)

It depends on what you mean by nuclear force. If you mean the force that acts on nucleons in a nucleus, its depends on distance. On small distances <1 fm it is strongly repulsive and is actually strong enough to keep neutron stars from collapsing. At the intermediate distances of a few fm it is strongly attractive -- around 100 times stronger than the electrostatic repulsion of protons at the same distance. It keeps nuclei bounded. At larger distances it vanishes completely. As to interaction of quarks inside nucleons, it is difficult to express its force in easily understandable numbers. However at very small distances (or high energies) it vanishes. This is called asymptotic freedom. At large distances (small energies) it becomes in some sense infinitely strong. Ruslik_Zero 19:54, 29 December 2017 (UTC)

What do aircraft throttle numbers above 100 mean?

In a flight simulator I've seen the throttle go to 108 and 114 on a newer plane (the Boeing 777?) Is 100 maximum sustainable setting or maximum cruising or what? How much above 100 has an airliner or aircraft in general gone? Sagittarian Milky Way (talk) 02:23, 28 December 2017 (UTC)

There are no numbers on the throttle of the 777. The closest numbers are the flap angle. What numbers are you referring to? 71.85.51.150 (talk) 02:44, 28 December 2017 (UTC)

I seem to remember the throttles going from the idle number (0?) to 108 or 114 (not on the throttle levers themselves nor analogous to the tick marks on a mercury thermometer). That was BS? Or maybe it was on a green heads-up/projected onto windshield display or omniscient on-monitor stats display that wouldn't be there in the real aircraft (there were so many stats they'd intrude into the windscreen if you showed them all, things like odometer to the meter, thrust to the newton, mass to the pound and other stuff better then the real instruments). The Hindenburg's altimeter had a clock face from 0 to 9 (10=0), two hands for hundreds and thousands respectively and the face behind the hands would rotate 10 times slower than the slow hand (the ceiling was low enough that the letters couldn't get upside down). Was that not historically accurate too? Sagittarian Milky Way (talk) 04:24, 28 December 2017 (UTC)

It depends on the exact setting or gauge you're looking at, but it's almost certainly one of the turbine speeds (most likely N1, the turbofan speed). Instead of displaying a raw RPM value, the display is scaled against some 'nominal' speed, and the readout is expressed as a percentage of that value. Generally, the nominal speed is chosen to be somewhere near or at an engine's rated or designed maximum.

What subsequently happens is that a manufacturer will determine that certain components are more (or less) durable than projected, or make minor tweaks to their design. Heck, sometimes this happens before the first jet is delivered to a customer. Instead of changing that nominal calibration number for converting RPMs to percent (which can cause all kinds of paperwork and maintenance issues), the manufacturer and certifying authorities say, "Okay, you can take N1 up to 105% with these engines on this aircraft."

See here for a definition of N1 and N2; here and here for various discussions of N1 greater than 100% and how it comes about. TenOfAllTrades(talk) 05:24, 28 December 2017 (UTC)

Many jet engined-aircraft use engine pressure ratio (EPR) as an indicator of engine output. It is rare for the limiting EPR for take-off to be exactly 1.00 or 100%. It is likely that the numbers in question were EPR. Dolphin (t) 06:00, 28 December 2017 (UTC)

See also Airbreathing jet engine#Terminology. --47.157.122.192 (talk) 07:34, 28 December 2017 (UTC)

Many correct answers are already posted, but here's a few references!

Consider reading Chapter 15 of the Airplane Flying Handbook: Transition to Jet-Powered Airplanes.

That's not a throttle on a 777 - it's a thrust lever, because jets don't have a throttle!

Piston pilots control for RPM, and monitor the resulting power using other instruments (or computing the power by hand). Piston planes have a throttle control, and sometimes have other controls for manifold pressure, fuel rate, and so on.

Jet pilots usually control for "percent power," or "percent thrust," or "engine pressure ratio." They use RPM and temperature as an indicator of engine health and operating condition.

So - if you saw a lever in a simulator for a large jet, you were looking at a thrust lever and it is probably marked in either "percent power" or "EPR" (engine pressure ratio). On some aircraft, those values can exceed 100%.

If you were looking at an accurate 777 simulator, there should be no markings on the thrust levers. Pilots of 777 must monitor engine instruments. Here's Boeing's internal magazine article on the 767-400 and 777 flight deck: Aero Magazine, (described); here's a photo of the actual thrust lever used on 767-400 and 777. Here's the assembled control stand. Here's another issue all about the 777 flight deck (unfortunately, featuring fewer close-up photos than the very similar 767-400 deck). And here's Aviation Week's sneak-peek at the 777X flight deck, replete with five full 15.1-inch Rockwell-Collins touchscreens, and still no marking on the thrust lever or control stand.

A few weeks ago I had the privilege of visiting the flight-deck of an MD-11. The thrust lever on that aircraft is a lot if fun: if you throw it full-forward (for maximum thrust), you even get an audible voice-alert in the cockpit that reminds you if full thrust is inappropriate for the airplane's present configuration. Intelligent!

Nimur (talk) 08:15, 28 December 2017 (UTC)

Flying is special because of all the security needed. So the technology in play is never maxed out in practice. If you have a car that the producer sells as 240Km/h fast, that is really its max speed. When the engine becomes to hot you simply stop on the sideway. That is never an option for the pilot of a 777. He will always try to fly in the technical save zone of maybe 70% of the max the plane could do. In some planes that is probably the "100" marker. --Kharon (talk) 19:18, 28 December 2017 (UTC)

Perhaps I am unadventurous, but I've never taken my car anywhere near the nominal limits. The closest I get might be one or two trips to the higher end of the RPM scale, and as it happens, when that happens I am never moving anywhere at all! And it is invariably winter. You do make me wonder whether the MD-11 has a fancy steering wheel that complains if you aim it at the new World Trade Center. ;) Wnt (talk) 01:42, 29 December 2017 (UTC)

Köppen climate classification in the US

This map, ultimately derived from [2], is in line with the Humid subtropical climate article's statement that this climate zone extends only as far north as "far southern portions of Illinois, Indiana and Ohio." However, sources such as Weatherbase, used in tons of locality articles to determine climate, disagree; Bloomington is hardly far south, and Indianapolis is almost exactly in the center (well north of what you see highlighted on this map), but as you can see at [3] and [4], Weatherbase lists both of them in humid subtropical. What's the difference? Is it a matter of varying definitions? Nyttend (talk) 13:30, 28 December 2017 (UTC)

Well, the article gives the definitions used for the current map, and it has been revised historically. I have linkified the title of this section to increase its usefulness. I find of specific interest the fact that southwestern New Jersey is classified as humid subtropical, and this area corresponds very closely with a change in the dominant climax forest vegetation that is quite obvious (at least to those of us who've studied plant ecology) as one travels from the Pine Barrens westward into lowlands that drain into the Delaware Bay. In other words, that map does seem quite relevant and accurate for that local boundary in New Jersey. μηδείς (talk) 18:05, 28 December 2017 (UTC)

The article mentions (cite) However, while some climatologists have opted to describe this climate type as a "humid subtropical climate", Köppen himself never used this term.. In the end its just a silly category and that is where some science communities go nuts on Scientific formalism. Rock solid Pluto is no Planet anymore since some Astronomers Assembly decided so in 2006 but Saturn, which is believed to be only gases, is? Just take it as it is. Discussing or arguing about disputed scientific categorization is a waste of time unless you also like to discuss or argue about Roman Catholic Dogmatics (which some argue is a science too!). --Kharon (talk) 18:55, 28 December 2017 (UTC)

Saturn only has a thin skin of gas, it's average density is as substantial as 0.7x water and the density barely inside the gas is only an order of magnitude from water but two from air. Sagittarian Milky Way (talk) 20:26, 28 December 2017 (UTC)

I prefere planets to be solid rock. :) --Kharon (talk) 14:36, 29 December 2017 (UTC)

So if aliens added water till the ocean covered everything would Earth stop being a planet? Sagittarian Milky Way (talk) 18:19, 29 December 2017 (UTC)

The temperature threshold for dividing the C and D Koeppen primary classifications (i.e., mean temperature of the coldest month) sometimes is taken as 0 C and sometimes as -3 C. This can produce noticeable differences in geographic extent of the classifications. The article you linked states that for Bloomington "the coolest month on average is January, with an average temperature of 30.0°F (-1.1°C)." Thus if a threshold of -3 C is used Bloomington will be Koeppen type Cf (so-called "humid subtropical") and if 0 C is used the type will be Df (sometimes called severe mid-latitude or other names). Shock Brigade Harvester Boris (talk) 20:01, 28 December 2017 (UTC)

Didn't the -3 climatologists choose it to try to follow the limit of semi-persistent snowcover on the coldest month? At least for Earth and the time it was chosen? (who knows about other geological epoches and planets) Maybe non-zero snow depth 50% of the time?. While 0 might be the best Celsius integer for some other line(s) (50% liquid precip? sharpest cutoff in snowfall?) there's just too much time >0, rain and sun there to avoid a fairly high no snowdepth percentage. Sagittarian Milky Way (talk) 21:43, 28 December 2017 (UTC)

• To address a question about the earth being covered in water, were it not due plate tectonics, the continents would not have formed and once plate tectonics grinds to a halt the ocean, if it still exists, will erode most of the existing elevated areas of the earth below see level. One exception would be volcanic hot spots like Hawaii which would still poke above the waves as long as there were mantle upwellings to produce them. According to this study there was little continental crust before 1.4 billion years, and a google search for "early earth little land surface" provides such things as Quora answers saying the early earth was mostly ocean, as well as the NIH study I first linked to. This paper on visualizing the land surface compares the relief profiles of Venus, Earth, Luna, and Mars, and shows how the earth has much higher and lower peaks due to plate tectonics, although Olympus Mons, another hot spot volcanic formation skews the Martian relief map away from flat. μηδείς (talk) 17:32, 1 January 2018 (UTC)

Modern equivalents of chief engineers such as Brunel

I know these days major infrastructure projects involve hundreds of people from several companies but would the closest thing to Brunel these days, on a major project, be a consultant who is employed by a client to design and develop their project? Clover345 (talk) 20:04, 28 December 2017 (UTC)

Many large companies bestow the title "senior engineer," "distinguished engineer," "engineering director," and other such accolades, with various career implications. University scholars are sometimes awarded a "named chair" or similar accolade. Depending on the company or institution, this type of title can be a serious privilege and honor. For example, I have often observed that a named chair at a prestigious university commands more ears and eyes than a corporate executive.

It can be instructive to have a look at the actual job titles held by such greats who pioneered and transitioned engineering into its modern era: individuals such as Claude Shannon, Alan Turing, Frederick Terman; Douglas Engelbart, Paul Allen, William Boeing; Cecil Howard Green, William Shockley, Gordon Moore... Edwin Aldrin, Vint Cerf, Grace Hopper.

Among such individuals, we have pilots, admirals, entrepreneurs; scientists, engineers, businesspeople; CEOs, professors, individual contributors; capitalists, innovators, and heirs.

Perhaps the hardest thing to recognize is that modern technology is all about miniaturization - so today's great engineers often build invisible things - things that we can't point at and attribute. Contrast our understanding of global navigational satellite technology, and the great engineers who built it - shall we point at the vague direction of space? ... or a cheap commodity hand-held electronic device? ...and compare to pointing at the Brooklyn Bridge, and saying it was "built" by Roebling ("with the help of others"). Both narratives are a summary-abstraction.

One of my favorite documentary series, Connections (1978), incisively explores whether it is appropriate to look at history as the well-orchestrated accomplishments of a few geniuses. Many episodes study famous scientists and engineers, and surrounds each historical story with much-needed context. In particular, historian James Burke explores the transition to modern science and engineering, where every discovery is widely-regarded to be the cumulative effort of many thousand-individuals, rather than a single genius; and he analyzes whether this is because engineering is different today, or if it is only a difference in the narrative that we construct about engineering. By now, surely all educated individuals know about "great man theory," and its strengths and serious weaknesses; any actual survey of the history of science and engineering will deconstruct the conventional narrative; and reconstruct it, or replace it.

So, do we even have a 21st-century equivalent of a 19th-century "Chief Engineer"? And if you can forgive the academic question, which story-book concoction is the more fictitious plot device: the 19th-century Chief Engineer, or the 24th-century version?

Nimur (talk) 21:17, 28 December 2017 (UTC)

Paul MacCready springs to mind, and perhaps more like Brunel (some failures, well quite a lot really) Jim Bede, Colin Chapman Greglocock (talk) 05:18, 30 December 2017 (UTC)