Wikipedia:Reference desk/Archives/Science/2013 December 29

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December 29

Can vegetables be grown in Zhejiang & Jiangxi during winter?

Can vegetables grow in Zhejiang and Jiangxi province, China during the winter? What kind of vegetables can be grown there or is it too cold to grow any vegetable over there in the winter? 173.32.117.240 (talk) 02:07, 29 December 2013 (UTC)

From: Xie, Dr Kaiyun (2008) THE STATUS OF ORGANIC POTATO PRODUCTIONIN CHINA in: Workshop to commemorate the International Year of the Potato - 2008 ISBN 97892106

"In the subtropical and tropical regions from north latitude 33 degrees, [...] a number of crops can be planted in the winter season, such as rapeseed, wheat, potatoes, minor grain crops, forage crops, melons and vegetables."

(Zhejiang & Jiangxi marginally fall within this region) ~:71.20.250.51 (talk) 02:45, 29 December 2013 (UTC)

They may fall within that region. but sometimes winter can be very harsh over there. Right? Do Zhejiang and Jiangxi have a lot arable lands to grow vegetables or are those provinces too mountainous to grow a lot of vegetables in the winter? 173.32.117.240 (talk) 03:20, 29 December 2013 (UTC)

The "Climate of Zhejiang" section here:[1] might be useful (?). As that potato book mentions, there's plenty of fallow rice-paddies (terraced) in the winter that could provide winter crops. Also from our Zhejiang article: Zhejiang has a humid subtropical climate with four distinct seasons'. ~E:71.20.250.51 (talk) 04:33, 29 December 2013 (UTC)

But the Southern province such as Guangdong Province is even warmer, and it would be good for more winter crops. Right? 173.32.117.240 (talk) 14:03, 31 December 2013 (UTC)

It's certainly warm and wet enough to grow vegetables there in the winter. However, it may be that people prefer to prepare the fields for the first rice crop rather than waste time on luxuries like vegetables. Matt's talk 06:51, 2 January 2014 (UTC)

What is the reason behind this?

The black object in this picture is hanging in air against gravity. What is the physics behind this? Concepts of Physics (talk) 04:39, 29 December 2013 (UTC)

See Meissner effect as it says in the file info. Dismas|^(talk) 04:46, 29 December 2013 (UTC)

Bricklaying stacked bonding and stretcher bonding

I read the brickwork article but I don't really understand a few things.
1- Why does stretcher bonding provide better strength than stacked bonding. Both have vertical stability by taking load axially. My only guess is that the stacked bonding provides a continuous weakness plane where the mortar is and the axial loads aren't distributed equally across the bricks as a result. Is this correct?
2 - Which is stronger in terms of lateral stability (e.g. from wind) and why? I would have thought it would be the same.
3 - Which is stronger when brick is used as paving slabs and why? In this case, I wouldn't have thought there's any difference at all. Clover345 (talk) 12:36, 29 December 2013 (UTC)

Your "guess" is on the right track. I'm attempting to find sources, but my understanding relates to the pyramidal distribution (angle of repose) of vertical loads; and breaking this up by using various pattern schemes allowing for a more even distribution of force (lateral). [edit: See also, Influence line & Structural load] 71.20.250.51 (talk) 17:12, 29 December 2013 (UTC) And... "Compressive strength of masonry is much higher than its tensile or flexural strength."^[2] ←This source has good info relating to the physics (which our brickwork article lacks). ~E:71.20.250.51 (talk) 15:40, 29 December 2013 (UTC)

Harmonic loading (see: Harmonic resonance) is also a factor (especially during earthquakes). See: A Study of the Progressive Degradation of Masonry Shear Walls Subjected to Harmonic Loading Harmonic resonance is also important in relation to wind. For an example of what can happen if you don't take this into consideration, see: Tacoma Narrows Bridge (1940) (Although not a masonry bridge, the same principle applies to various structures, see: Vortex-induced vibration). ~E:71.20.250.51 (talk) 16:18, 29 December 2013 (UTC)

Re: #3, You're probably right; but certain patterns might interlock better, preventing individual pavers from "wiggling loose"; resonance might also apply here. We don't have an appropriate article, Road surface#Other surfaces is the closest I could find. ~:71.20.250.51 (talk) 16:38, 29 December 2013 (UTC)

Wasnt Tacoma Narrows more to do with the fluid dynamics of the interaction between te wind and the structure than the dynamic loading from the wind? Clover345 (talk) 19:31, 29 December 2013 (UTC)

Yes, but it is a case study relating to the harmonic resonance (and wind can cause building to "vibrate", as well as sway tall structures resonantly) — Not directly related to OP's query, though. (Sometimes I get a little carried away with "teaching moments"). ~:71.20.250.51 (talk) 20:08, 29 December 2013 (UTC)

Your first posit is correct, though I don't have a reference at hand. Stack bond has both horizontal and vertical weakness planes, and since gravity isn't assisting the vertical plane, it results in a weak wall when subjected to lateral forces like wind load. It's also more prone to cracking from mortar shrinkage, and it's very hard to lay stack bond for any height: you can see the vertical joints snaking very easily. Acroterion (talk) 01:32, 30 December 2013 (UTC)

ISS

I just want to know how long the ISS is in direct sunlight and how dark it gets when they are in the shadow of the earth. — Preceding unsigned comment added by 70.251.192.181 (talk) 16:54, 29 December 2013 (UTC)

This is not as easy to answer as it sounds -- I was hoping to find an answer on the internet (no luck). There are many factors involved, mainly: The radius of orbit (in relation to Earth's radius). -&- The orbital speed. It is in sunlight more than 50% of the time, since r_iss > r_earth "How dark" is relative, and relates to umbra and ambient light from the Earth's albedo. Not to mention starlight and the light from the moon (depenending on its phase). ~E:71.20.250.51 (talk) 19:01, 29 December 2013 (UTC)

The Vortex Coils

What is it?What their relation the anti-gravity? 37.238.191.216 (talk) 17:49, 29 December 2013 (UTC)

A vortex coil is essentially a perpetual motion device. It's related to anti-gravity in that both are bullshit. Red Act (talk) 18:08, 29 December 2013 (UTC)

(edit conflict)

I'm not finding anything from scientific sources relating vortex coils to "anti-gravity" (only pulsed-field electromagnetism, and the like). However, the pseudo-science crowd tout magical properties relating to Free energy. Claims for "Electrogravitics" have not been verified, but "electromagnetic thrust" can be acheived (by ionizing air using electrohydrodynamics) as with Ionocraft. ~Eric:71.20.250.51 (talk) 18:23, 29 December 2013 (UTC):edit:71.20.250.51 (talk) 19:12, 29 December 2013 (UTC)

High tonnage on masonry arch bridges

I know that in terms of static loading, heavy tonnage creates unfavourable stress states on the masonry arch structure but what happens in terms of dynamic loading? Why are heavy loads damaging to the masonry arch structure in terms of dynamic loading? I assume its something to do with resonance but I assume its more complicated than this and would probably depend on the type of heavy load. For example, I assume a long freight train would be more of a problem than lorries or pedestrians, but I want to understand why. Clover345 (talk) 20:00, 29 December 2013 (UTC)

I haven't read this, but it seems relevant:

• Line of thrust and theoretical load of masonry arch bridge

Generally speaking, masonry is much better with static rather than than dynamic loading, due to its rigidity. (If you're building a bridge, consider a catenary arch.) ~:71.20.250.51 (talk) 20:31, 29 December 2013 (UTC)

I can see where the OP is coming from. Soldiers break step when crossing bridge so that resonance does not build up but this is more for light bridges. A resent example was the London Millennium Bridge. As for steam locomotives. They had a Coupling rod connecting the wheels. Although the wheels had counter weights, the upward and downward motion coursed a side to side rocking motion with forces that were considerably more than the engine's dead weight when stationary.--Aspro (talk) 20:44, 29 December 2013 (UTC)

The go-to article in this case is Hammer blow. {The poster formerly known as 87.81.230.195} 90.204.16.14 (talk) 01:21, 30 December 2013 (UTC)

Note that arches tend to push outwards, so they are best placed between cliffs or some other massive objects which can take that force. As for resonance, some type of soft material to absorb the vibrations would help here. For example, if the base of the arches is in sand (with bedrock at the very bottom), then that would help to limit vibrations, and hence resonance. StuRat (talk) 02:32, 30 December 2013 (UTC)

I wouldn't build a masonry bridge on sand. Some sort of damper would be better. (Damper is a disambiguation, closest match: shock absorber -- hardly adequate!). Anyway, there are many types of dampers. ~E:71.20.250.51 (talk) 05:44, 30 December 2013 (UTC)

No, not on sand, but on bedrock, with sand around the sides of the lower portion of the arch, to act as the damper. Sorry if I didn't make that clear in my first response.StuRat (talk) 14:02, 30 December 2013 (UTC)

See the Parable of the Wise and the Foolish Builders. Alansplodge (talk) 12:22, 2 January 2014 (UTC)