Wikipedia:Reference desk/Archives/Science/2014 March 16

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March 16

Practical magnetics problem

If a magnetic material is fully saturated, will it exhibit any loss to an applied alternating magnetic field? In other words, what is the value of u when the material is magnetically saturated?--31.55.104.196 (talk) 00:20, 16 March 2014 (UTC)

That didnt come out right. I meant mu prime prime. Wiki markup seems to put that inti italcs.--31.55.104.196 (talk) 00:40, 16 March 2014 (UTC)

Try this: μ''. StuRat (talk) 01:17, 16 March 2014 (UTC)

You can apply "nowiki" to itself:  <nowiki>μ''</nowiki>  —71.20.250.51 (talk) 01:34, 16 March 2014 (UTC)

Try this: μ″. —Tamfang (talk) 08:06, 16 March 2014 (UTC)

Certainly a material can become "saturated," but in view of the exacting language in "any loss," I wonder about "fully saturated" since the B field approaches an asymptote, but can always increase a tiny amount if the H field increases, according to Saturation (magnetic). Edison (talk) 22:43, 16 March 2014 (UTC)

Should have mentioned its fairly square loop ferrite. So can I assume negligible core loss in a ferrite material if it is fairly heavily saturated? I think so but Im not sure. Im not talking about resistive losses due to eddy currents.--86.179.250.140 (talk) 15:14, 17 March 2014 (UTC)

Philip experiment

Philip Experiment. Philip experiment on youtube. I know it is probably a hoax, but I still don't understand what was really going on even after I read the article? The group probably imagined all the noises. My question is was the table really moving by itself? Was the table actually floating above the ground by itself? If the floating table was just the participants' hallucinations then how can I see it in the video? How could they capture their hallucination on video? Or was there some kind of trick behind the scenes? 75.168.134.220 (talk) 06:52, 16 March 2014 (UTC)

That video is a documentary about the experiment, as the description says: "A story about this experiment done in the early 1970's". None of it is actual footage. --140.180.249.239 (talk) 07:41, 16 March 2014 (UTC)

Is that mean all of the things happened in the footage were made up? — Preceding unsigned comment added by 75.168.134.220 (talk) 16:37, 16 March 2014 (UTC)

It means they were "reenactments," not footage from the original experiments. — The Hand That Feeds You:^Bite 20:16, 16 March 2014 (UTC)

Self-defense

It's widely known that when protecting yourself against a man, kicking his testicles is a good way to cause extreme pain. What about women? Where should one strike to cause the most pain for the least force? --140.180.249.239 (talk) 07:31, 16 March 2014 (UTC)

Considering that men are generally stronger than women, they may simply restrain women without the need to hit them. But in extreme cases and when you don't know any submission hold, my bet would be celiac plexus, as in addition to pain hitting it induces temporary breathing problems (but even then - do not hit by knee!). Brandmeister^talk 11:19, 16 March 2014 (UTC)

Note also that the groin is a very hard area to hit effectively if the opponent expects an attack. We have very good reflexes that way. --Stephan Schulz (talk) 12:15, 16 March 2014 (UTC)

A blow to the kidneys is extremely painful, but you have to hit a person on the back (to the side, just above belt level). That's not particularly useful for self-defense, though. Looie496 (talk) 14:00, 16 March 2014 (UTC)

Women (among many others) hate it when you gouge their eyes, and even a baby can do it. InedibleHulk (talk) 14:15, 16 March 2014 (UTC)

"kicking his testicles is a good way to cause extreme pain." One who has studied judo might question that it is a "good way" for an attacker without training, since anyone with a little training in judo might be able to dodge the kick and grasp the attackers foot, leaving the attacker very vulnerable to the defender's move of sweeping the attacker's other foot out from under her, causing her to fall on her back. It would be a good way for someonewell trained in martial arts to attack a man. Edison (talk) 00:46, 18 March 2014 (UTC)

There's a simple solution for that. Seriously though, every move has a counter. Can't let that dissuade you from trying. Natural kick/knee to aim, and all one really needs to remember is "hard as possible".On your back isn't the worst place for continued nutkicking, anyway. Worth the risk, in a serious situation. Unless you've some unblockable strike you're not telling us about. InedibleHulk (talk) 21:38, 19 March 2014 (UTC)

Waist–hip ratio

What is meant when a person has a "high waist–hip ratio"? (as seen in "Lifestyle" section of Diabetes mellitus type 2). Don't understand what that mean. Please link to my user page when you reply. HYH.124 (talk) 08:26, 16 March 2014 (UTC)

HYH.124, are you asking how to obtain the ratio? It's very simple: just measure the waist, then measure the hips (at positions shown in the article you link), then divide the first by the second. Ideally your answer should no more than 0.7 or 0.9, depending on your gender. Please clarify if you were asking about something else. Dbfirs 09:42, 16 March 2014 (UTC)

User:Dbfirs: I was asking how many is considered high. Also I am actually asking how one would shape/look like if one has "high waist-hip ratio". HYH.124 (talk) 09:44, 16 March 2014 (UTC)

The right-hand example in the picture of waist–hip ratio illustrates a high ratio. Also from the article "abdominal obesity is defined as a waist–hip ratio above 0.90 for males and above 0.85 for females". Dbfirs 10:10, 16 March 2014 (UTC)

Thanks for explaining. HYH.124 (talk) 12:18, 16 March 2014 (UTC)

Aircraft wing deformation

Do aircraft wings gradually bend and deform due to engines suspended below them? What is used to prevent that? --93.174.25.12 (talk) 11:11, 16 March 2014 (UTC)

There are two relevant types of deformation:

1) Elastic deformation. This is the type of deformation where the object returns to it's original shape once the force (engine weight, in this case) is removed.

2) Plastic deformation. This is the type of deformation that does not return to it's original shape.

Most materials first undergo elastic deformation with a small force and then plastic deformation with a larger force, although how much of the total occurs in each range varies wildly (with elastic having a larger elastic deformation range and plastic having a larger plastic deformation range). Metals have moderate amounts of deformation in both ranges. So, as long as the force (engine weight) is kept below the line where plastic deformation will occur, then the sagging under the engine weights won't bend the wings permanently.

If this was an issue, I'd expect supports to be mounted under plane wings while on the ground (I do expect they would add supports when doing work on the wings which lessens their strength for a while). Also note that aerodynamic lift causes the wings to bend upwards while in flight. This bending down when on the ground and back up in the air could also lead to metal fatigue, but that's another issue. StuRat (talk) 15:13, 16 March 2014 (UTC)

While not the engines the Learjet 25 and the Learjet 35 that were/are stationed at Cambridge Bay Airport are never fuelled up until the destination was known. According to the operators this was to reduce the stress on the wings. Of course there is no point in putting fuel in to go to Edmonton International Airport (969 nautical miles (1,795 km; 1,115 mi)) if you are only going to Gjoa Haven Airport (204 nautical miles (378 km; 235 mi)). CambridgeBayWeather (talk) 17:01, 16 March 2014 (UTC)

The weight of engines on the wing, fuel in wing tanks, and weight of the wing structure cause the wing to deflect but the wing does not deform. Permanent deformation is prevented simply by building the wing strong enough to avoid permanent deformation, even under the most severe loads likely to be imposed on the aircraft in service. This is no different to designing a bridge or a multi-storey building so that it can withstand all loads likely to be imposed on it in service.

Locating engines on the wing is actually much better from a structural perspective than locating them on the fuselage, such as on the Boeing 727 and Hawker Siddeley Trident! When the aircraft is in flight, the lift on each half-wing (the left half-wing and the right half-wing) is pushing the half-wing upwards, creating a substantial bending moment that reaches its maximum at the wing root, next to the fuselage. If an engine is located on each half-wing, the weight of the engine is pushing downwards and causing a reduction in the bending moment at the wing root. This phenomenon is called bending moment relief and it allows the airframe designer to use less metal in the wing structure and this leads to a lighter airframe. In contrast, the engines in the Boeing 727, Trident etc provide no bending moment relief. Engines buried in the wing root, adjacent to the fuselage, as seen in the De Havilland Comet and the V bombers, provide a little bending moment relief but not as much as engines located further outboard on the wing. Four-engine aircraft such as the Boeing 747 achieve substantial bending moment relief, especially from the outer engines. The maximum bending moment relief is achieved by moving some of the aircraft's weight to the tip of each half-wing; this explains the fuel tanks on the wing tips of some aircraft such as the Learjets and Mitsubishi MU-2. Dolphin (t) 23:37, 16 March 2014 (UTC)

See stress-strain curve: in theory, a material will undergo pure elastic deformation up to the yield point, then pure plastic deformation until failure. With real-world materials, however, there's an overlap between plastic and elastic deformation. --Carnildo (talk) 01:30, 19 March 2014 (UTC)

Which plant is this ?

which plant ? http://i.imgur.com/ODXwL9s.jpg — Preceding unsigned comment added by 182.185.191.116 (talk) 12:36, 16 March 2014 (UTC)

Hard to say from that picture. Maybe a Phlox of some kind? --Jayron32 02:36, 17 March 2014 (UTC)

Which insect is this ?

Which insect is this ? the legs are orange/red coloured.

Superior view http://i.imgur.com/tpVz3cP.jpg

Lateral view http://i.imgur.com/TcUnn4M.jpg — Preceding unsigned comment added by 182.185.191.116 (talk) 12:41, 16 March 2014 (UTC)

It's a moth, for starters. Not sure of the specifics, but I'm almost certain the same kind are on my house every August in Northern Ontario. Might help. Of course, lepidopterists are a picky bunch. May have a slightly different cousin there. InedibleHulk (talk) 13:31, 16 March 2014 (UTC)

Actually, the antennae are different. That might be an ugly butterfly. Or whichever gender mine aren't, maybe. InedibleHulk (talk) 13:34, 16 March 2014 (UTC)

Comparison of butterflies and moths makes me think I was right the first time. InedibleHulk (talk) 13:39, 16 March 2014 (UTC)

SO, this is a moth ? How can I determine it's gender ? which other views are needed for species determination ? — Preceding unsigned comment added by 182.185.191.116 (talk) 14:30, 16 March 2014 (UTC)

Yes, a moth. That dude looks like a lady. Mine have those feathery ones. Shorter, too. I think the views are good (high detail, too), if someone smarter on moths than I sees them. If nobody like that shows up here, you can try sharing the picture with BugGuide. InedibleHulk (talk) 14:42, 16 March 2014 (UTC)

I have always found What's That Bug very helpful, you may have to wait for a while but the 5 or 6 times I have used it they came up trumps. Richard Avery (talk) 14:43, 16 March 2014 (UTC)

This photo reminds me of a wooly bear (Isabella Tiger Moth), but the black markings are much weaker than those in [1] and the coloration seems more orange. Either it's simply a color phase from a region not often represented in this photo collection, or some other species, likely somewhat closely related. Wnt (talk) 15:44, 16 March 2014 (UTC)

The original question was posted from Pakistan, so not likely. Alansplodge (talk) 18:28, 17 March 2014 (UTC)

Oh! I was hunting for something in northern Ontario... since that wasn't shown, it might even have been the wooly bear. I should see what related species exist in Pakistan... Wnt (talk) 01:53, 19 March 2014 (UTC)

It turns out that there are a lot of types of Spilarctia that might have ranges in the area, and have an appearance somewhat similar to this one, but not quite right [2]. But I'm not finding good photos for most of the species in the web searches. Trying to identify a lepidopteran from photo comparisons is already unreliable enough, but take away the photos and it's quite a problem! Wnt (talk) 02:12, 19 March 2014 (UTC)

If I remember in August, I'll snap a shot of mine. InedibleHulk (talk) 20:28, 19 March 2014 (UTC)

Main Battle Tank (Maintenance)

It is always mentioned by many military experts that Russian tanks require more maintenance than western why ? and what are the maintenance requirements generally in a tank ? Tank Designer (talk) 13:36, 16 March 2014 (UTC)

Russian main battle tanks are more likely to be used close to home (say for invading the Ukraine), so sending them home for maintenance is more feasible than US tanks, unless the US plans to invade Canada or Mexico. This fact may have affected the maintenance specs for each. StuRat (talk) 15:24, 16 March 2014 (UTC)

Or Cuba? But first, I'd like to see these "military experts". For many kinds of equipment, Russian/Soviet designs are more rugged and require less maintenance than the Western equivalent. Compare AK-74 and M16, or, historically, Panther tank and T-34. --Stephan Schulz (talk) 15:31, 16 March 2014 (UTC)

I don't see the US invading Cuba, as it's simply not militarily important enough to warrant an invasion anymore (unless they offer to host Russian nukes again). And if the US did invade, they could do tank maintenance at Gitmo. StuRat (talk) 16:55, 16 March 2014 (UTC)

I think the main concern for US tank crews is what CDs to take with them. KägeTorä - (^影_虎) (Chin Wag) 15:54, 16 March 2014 (UTC)

You can't go wrong with Clash's Combat Rock — Ahhh, the good-ol'days!  —71.20.250.51 (talk) 16:25, 16 March 2014 (UTC)

Can anyone tell me what are the maintenance aspects in the tank engine or give me a link so I can read it alone ? Tank Designer (talk) 17:01, 16 March 2014 (UTC) I′m not bigoted to western weapons , most of my information is derived from English documentary videos which are almost bigoted to their countries,sorry for my weak English I′m Arabian .Tank Designer (talk) 17:11, 16 March 2014 (UTC)

Which tank? They all have some distinctions, notably: M1A1 Model TGA1500 Lycoming Turbine —71.20.250.51 (talk) 20:22, 16 March 2014 (UTC)

I meant Diesel Engine tanks as they are the most common tanks but thank you for help . Tank Designer (talk) 20:35, 16 March 2014 (UTC)

Not Diesel but petrol, but here is the Panther Fibel (unfortunately in German, but a real hoot). --Stephan Schulz (talk) 21:36, 16 March 2014 (UTC)

Thanks everyone .Tank Designer (talk) 03:36, 17 March 2014 (UTC)

Here is a maintenance manual for the M1 Abrams. KägeTorä - (^影_虎) (Chin Wag)

Thank you Tank Designer (talk) 10:15, 18 March 2014 (UTC)

The major difference is philosophical rather than technical: Russian doctrine calls for military vehicles to be used for a certain number of operating hours with no field maintenance, then returned to the factory or a maintenance depot for a major overhaul regardless of need: this lets them operate a large number of vehicles with a small number of skilled maintenance personnel. Western doctrine calls for military vehicles to be maintained in the field by skilled personnel, only returned to a depot in the event of major damage: this requires more skilled personnel, but has fewer vehicles unavailable due to maintenance at any given time. --Carnildo (talk) 01:42, 19 March 2014 (UTC)

Two Port Network

Are the cell phone charger and laptop charger two port networks.117.194.239.211 (talk) 18:10, 16 March 2014 (UTC)By the way can adapters be regarded as two port network.117.194.239.211 (talk) 18:12, 16 March 2014 (UTC)

A charger adapter like this has two ports, mains input and dc output, but it is not a linear two port amenable to electrical network analysis. 84.209.89.214 (talk) 22:47, 16 March 2014 (UTC)

Visual acuity in the human retinal periphery.

Approximation of the acuity of the Human eye, horizontal cross section

I want to get hold of a curve describing how visual acuity changes when a test object moves from the center (fovea) to the periphery. Anybody knows where to get this information?

Thanks, - --AboutFace 22 (talk) 19:15, 16 March 2014 (UTC)

Something like this graph from Fovea centralis?  : [71.20.250.51 (talk) 21:18, 16 March 2014 (UTC)] →

Thank you, --AboutFace 22 (talk) 21:55, 16 March 2014 (UTC)