Science desk
< March 13	<< Feb \| March \| Apr >>	March 15 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 14[edit]

Condensation trails from airplane props?[edit]

I was driving by the airport today and I saw a Douglas DC-3 looking like it was about ready to take off. I grabbed my camera. When the plane was facing me, I saw circles at the end of the propellers that I thought were afterimages from the stripes on the props. But they show up on photos, see this dropbox link. The temperature was around 60F and the humidity was high. The contrail article has a great photo of contrails from a prop airplane. Is that what is in the photos? Bubba73 ^{You talkin' to me?} 01:13, 14 March 2015 (UTC)[reply]

Looks like it. The only way the plane would make a motion effect (from the stripes) like after images that is similar to your pictures is if it was moving, and it is clearly not. The shapes even look similar to the article. -- Orduin ^Discuss 01:35, 14 March 2015 (UTC)[reply]

There's one way you could get an appearance like that in a photo, from the markings on the propeller. Say the prop was turning at 1800 rpm, which is 30 revolutions per second. Say it was a dull day and the photo was taken with an exposure of 1/15 second, and the camera flash also fired for say 1/3,000 second. Then the photo would capture two full revolutions of the prop (giving the outside ring effect, and if the plane was taxiing slowly, the rings could separate in a helical appearance); but it would also freeze 1/100 of a revolution (giving the slightly blurred but clearly visible prop blades). Now, a close look at the photo shows that this isn't what happened. The ring doesn't match the stripes that the propeller tips would make, but has a puffy appearance like how a contrail looks if you see it up close from another airplane; and the light levels aren't consistent with a flash on the camera contributing. So having mentioned this possibility, I would rule it out. The rings are real. --65.94.48.86 (talk) 20:35, 14 March 2015 (UTC)[reply]

Yes. I took these at 1/1250 second, no tricks. Bubba73 ^{You talkin' to me?} 00:25, 15 March 2015 (UTC)[reply]

Contrails contain the exhaust from the jet engines, which "seeds the clouds", causing moisture in the air to from droplets. Pressure differences can have the same effect. Supersonic aircraft are known to cause vapor cones, for example. StuRat (talk) 09:04, 14 March 2015 (UTC)[reply]

In this case, though, the condensation has more in common with wingtip vortices - except instead of forming around a wing, the airfoil is the propeller blade itself.

Very nice photographs! Which airfield still has an operational DC-3 near you? Nimur (talk) 15:44, 14 March 2015 (UTC)[reply]

Thanks. It was on St. Simons Island, Georgia. I knew they had a DC-3 there. I was driving by and saw it out of the hanger. I have my old camera in the trunk for such emergencies, and I started taking photos by sticking the lens up to the gaps in the fence. (The photo above has info about the tail number and serial number.) As I was doing that, they cranked it up and then moved to another area and revved up the engines to a high rate. I thought they were preparing to take off, but then they throttled down and put it in the hanger. A guy was driving around it in a golf cart, so maybe he is thinking about buying it or something. Bubba73 ^{You talkin' to me?} 00:31, 15 March 2015 (UTC)[reply]

Fascinating. The DC-3 is probably the least interesting aircraft in that hangar. Don't get too close to the man in the golf cart, he'll probably be disinclined to share more than a minimum exchange of sensitive information. Nimur (talk) 14:46, 15 March 2015 (UTC)[reply]

Soil and nutrient source[edit]

What are the long term and short term effects of using organic nutrient in soil?
What are the long term and short term effects of using inorganic nutrient in soil?

Learnerktm 01:36, 14 March 2015 (UTC)[reply]

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Roger (Dodger67) (talk) 05:24, 14 March 2015 (UTC)[reply]

(Assuming it's not a homework Q.) I'm guessing you aren't using "organic" and "inorganic" in the chemistry sense, but rather with the "organic = natural" meaning. In this case, you're talking about chemical fertilizers versus manure, compost, etc. One problem with the natural method is that you risk bacterial contamination of both the food and, due to run-off, of nearby rivers and lakes. StuRat (talk) 08:59, 14 March 2015 (UTC)[reply]

Run-off from chemical fertilizers also causes problems in rivers and lakes (see Algal bloom). There might be some hints (but not direct answers to your homework) in Soil biology and Organic farming. Dbfirs 09:04, 14 March 2015 (UTC)[reply]

You can find some details about organic and inorganic nutrients in Soil fertility: Soil fertilization. See also Organic fertilizer and fertilizer. Basically inorganic (in the chemical sense) nutrients can be taken up directly by the plants, organic nutrients have to be broken down first. So inorganic are fast acting but can be rapidly depleted, organic are slower acting but stay available longer. Ssscienccce (talk) 07:37, 15 March 2015 (UTC)[reply]

What is the biggest / largest cell in human body and what is the biggest eukaryotic cell?[edit]

5.28.161.253 (talk) 03:56, 14 March 2015 (UTC)[reply]

In the female human body a mature ovum is pretty big, as cells go. StuRat (talk) 08:55, 14 March 2015 (UTC)[reply]

The largest eukaryotic cell currently to be found is the egg of an ostrich, although larger birds in the past (the Moa, for example) will have had larger eggs. Tevildo (talk) 09:45, 14 March 2015 (UTC)[reply]

My lecturer said it's a neuron somewhere in the body. I don't remember well what the specific name of this neuron is. 5.28.161.253 (talk) 12:32, 14 March 2015 (UTC)[reply]

According to neuron, there are sensory neurons with axons that run from the toes to the posterior column of the spinal cord, reaching 1.5 meters in length.--Wikimedes (talk) 13:11, 14 March 2015 (UTC)[reply]

Or about 5 feet in length. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:22, 14 March 2015 (UTC)[reply]

, Actually, that's 3 feet, 24 inches. μηδείς (talk) 16:22, 14 March 2015 (UTC)[reply]

The largest single-celled organisms are the Xenophyophores, here are some google images. μηδείς (talk) 16:22, 14 March 2015 (UTC)[reply]

Sorry, what does "3 feet, 24inches" refer to? Richard Avery (talk) 07:49, 15 March 2015 (UTC)[reply]

I will forgive Medeis everything if her source for that joke is the same as mine. Tevildo (talk) 09:23, 15 March 2015 (UTC)[reply]

Harley? Dbfirs 12:19, 15 March 2015 (UTC) [reply]

I doubt my source is yours. I just read in obscure biography that the producer of The Godfather was 6'5", and when asked how tall he was, would respond, Only 5'17". μηδείς (talk) 15:50, 15 March 2015 (UTC)[reply]

Ahh, close but no cigar. We'll have to remain in a state of enmity for now. Mine is from Myra Breckinridge via Mike Myers. Dbfirs' solution is far better, though - I should use that in future. Tevildo (talk) 20:43, 15 March 2015 (UTC)[reply]

5'17" is the rueful self-description of a character (Coby Clay?) in Leo Rosten's 1961 novel Captain Newman M.D.. The novel is based on real experiences, but I don't know if that character is. I wonder whether Ruddy's use of the phrase preceded 1961. --ColinFine (talk) 22:15, 17 March 2015 (UTC)[reply]

Ruddy said it was the answer he gave Ayn Rand (who looked half his height) when they were negotiating an adaptation of one of her books in the 1970's. He strikes me as the kind to reuse a good line when he sees one. μηδείς (talk) 00:57, 18 March 2015 (UTC)[reply]

Naval equipment mystery[edit]

This is a piece of naval equipment spotted on a Valour-class frigate of the South African Navy. It obviously includes optical instruments (camera, rangefinder, etc) and the "blank" flat panels suggest the possibility of a radar antenna. Does anyone recognise it? Roger (Dodger67) (talk) 07:34, 14 March 2015 (UTC)[reply]

Yes it would be flat panel phased array antennas. The panels may not be electronically steerable since it has manual steering. Graeme Bartlett (talk) 11:49, 15 March 2015 (UTC)[reply]

It looks like part of a fire control system for an anti-aircraft or dual-purpose gun, but I cant figure out what it is. I looked at the website for Reutech Radar Systems that supplied some systems for the Valour-class but didn't find anything like it. Sjö (talk) 12:00, 15 March 2015 (UTC)[reply]

This gizmo bears some similarity to the central part of the array in question. It is described as an "electro-optical tracking and fire control system". It seems to be made by Thales Group. Alansplodge (talk) 17:47, 16 March 2015 (UTC)[reply]

H₃O₂ ?[edit]

Is this "structured water" real or just a scam from the new age crowd ? StuRat (talk) 08:53, 14 March 2015 (UTC)[reply]

See Gilbert Ling and Association induction hypothesis (currently up for AfD) for our material on the subject. Pathological science might be a better term than "scam", but it's safe to say that Ling's hypothesis is not accepted by the wider scientific community. Tevildo (talk) 09:51, 14 March 2015 (UTC)[reply]

Seeing this discussion I have to ask: What are the objective reasons and not subjective ones for this hypothesis not having a wider acceptance as an alternative hypothesis?--94.53.199.249 (talk) 19:38, 14 March 2015 (UTC)[reply]

It doesn't save the appearances. It depends on the behaviour of water in an organic system being radically different from its behaviour in the laboratory, with no theoretical explanation and (at best) very borderline and non-conclusive experimental support. It's not consistent with established and well-tested theories of solvation and the equally well-established properties of water. See Polywater for a very similar example from a few decades ago. Scientific method and Scientific theory may also be useful - from the latter article, "[A scientific theory] is consistent with pre-existing experimental results and at least as accurate in its predictions as are any pre-existing theories." This is where Ling's hypothesis has its difficulties. Tevildo (talk) 22:59, 14 March 2015 (UTC)[reply]

As an interesting side note, a molecule with that formula is known. It exists transiently as a reactive intermediate in the reaction between water and the hydroxyl radical. In this molecule two hydroxyl groups are bridged by a hydrogen atom, joining to the oxygen centers in a Three-center two-electron bond. Plasmic Physics (talk) 06:56, 16 March 2015 (UTC)[reply]

It's also been detected as an intermediate in the oxidation of H atoms by O₂ on a catalyst surface (see doi:10.1021/nn8008245). The full route was found as:

O₂ → HO₂ → H₂O₂ → H₃O₂ → [H₂O]₂

That same type of step, addition of H to H₂O₂ to give H₃O₂, has been proposed as part of the Fenton step of the biochemical Haber–Weiss reaction (see doi:10.1007/BF01858251). DMacks (talk) 07:45, 16 March 2015 (UTC)[reply]

Thanks all. StuRat (talk) 05:17, 19 March 2015 (UTC)[reply]

Chemistry of obtaining energy[edit]

When humans and vehicles obtain energy from stuff, oil, for example, do they basically perform the same chemical reaction, but at a different pace? --Llaanngg (talk) 15:42, 14 March 2015 (UTC)[reply]

Every chemical reaction is either oxidation or reduction, if you're willing to abuse terminology and reduce everything to an incredibly oversimplified version.

What are you trying to understand? Perhaps you should start with a book on basic chemistry, or spend some hours perusing the fine resources on Energy Sources provided by the U.S. Department of Energy. Nimur (talk) 15:49, 14 March 2015 (UTC)[reply]

(ec) Not every chemical reaction is oxidation or reduction -- double displacement is a one that is not. (Athough if you are willing to abuse terminology enough, you could claim double displacment is not "really" a chemical reaction.) - On the original question, it's true that from an end-to-end view the reactions are very similar: "fuel" + oxygen => carbon dioxide + water, but that's true only in a very rough view. The first major difference is that the fuel is different in both cases. Humans can't digest gasoline or diesel, and putting sugar in a vehicle's fuel tank is a notoriously bad idea. The oils used by vehicles and humans are actually rather different chemically, and can't be directly substituted, despite both being called "oil". Ethanol, though, is one fuel both humans and some vehicles can use, but the way they use them is very different. Vehicles burn ethonol directly though combustion. That is, in a very high temperature environment molecular oxygen becomes activated enough to directly attack the carbon-hydrogen and carbon-carbon bonds in ethanol. This results in carbon dioxide and water directly, and a bunch of heat, which is then used to expand the combustion gasses and drive a piston which turns the wheels. (See internal combustion engine for more details.)

How humans use ethanol, on the other hand, is *much* more complex. One major difference is that all the reactions happen at low to moderate temerature (37 C). This means oxygen isn't activated enough to directly attack the ethanol. Instead, the body uses enzymes to slowly convert the ethanol. First alcohol dehydrogenase converts the ethanol into acetaldehyde and a "reducing equivalent" (NADH), with absolutely no involvement of molecular oxygen. The acetaldehyde is then converted to acetate via acetaldehyde dehydrogenase, again with the generation of a "reducing equivalent". The enzyme acetyl—CoA synthetase then converts the acetate into acetyl-CoA, deriving the energy needed to do so from a "high energy" molecule (ATP), rather than from surrounding heat. The Acetyl-CoA can then go into a multi-step reaction cascade known as the TCA cycle, the result of which is generation of a number of "reducing equivalents" and carbon dioxide. Note that in contrast to regular combustion, the oxygens in the carbon dioxide don't come directly from molecular oxygen, but instead come from water.

So how does oxygen come into the picture? Well, you still have all those "reducing equivalents" hanging around. Those are used by a multi-enzyme process called oxidative phosphorylation to pump hydrogen ions from one side of a membrane to the other. Only at the very end of the electron transport chain do the electrons that originally "came from" the ethanol get transfered to the oxygen, converting it to water. So the point in humans is not to drive a piston, but to pump hydrogen ions. Those hydrogen ions are then let back across the membrane by ATP synthase, which couples the movement to production of the "high energy" compound ATP, which is then used by the cell when it needs energy. -- 162.238.240.55 (talk) 16:31, 14 March 2015 (UTC)[reply]

Neutralization is undeniably a chemical reaction and is neither oxidation nor reduction. That doesn't really address the original question. Robert McClenon (talk) 02:40, 15 March 2015 (UTC)[reply]

The metabolism of fats and oils in most animals (including humans) is described at beta oxidation. Basically the last two carbon atoms are cleaved of the monoglyceride, and sent into the citric acid cycle (aka Krebs' cycle) — LongHairedFop (talk) 16:11, 14 March 2015 (UTC)[reply]

Note that there are many sources of energy which don't require a chemical reaction: hydropower, tidal power, passive solar power, wind power, nuclear power (nuclear reactions, not chemical), to name a few. StuRat (talk) 17:10, 14 March 2015 (UTC)[reply]

Additional question on this topic: I buy a package of food which contains 10% cellulose and 10% of sugar and no other source of energy. The label says 90 Calories per serving. Would the same amount served to a cow which is able to utilize the cellulose say 180 Calories per serving (cow)? Is the label taking this difference in biochemistry into account?

This could depend on precisely what country's laws the nutrition information panel is intended for. That said, AFAIK and as per our articles most countries use something derived from the Atwater system to determine Food energy. The proportion of the various common components which will provide energy are determined in some way (either chemically or from standard listings for the ingredients), and these are then used to calculate the food energy [1] [2] [3]. The whole system is targeted at humans and normal human foods, so it may work somewhat okay (although as our articles attest, it's far from perfect) for humans, not so much for cows or anything else. Nil Einne (talk) 12:47, 15 March 2015 (UTC)[reply]

Thanks for the answer, tis was exactly what I was searching for!!--Stone (talk) 15:31, 15 March 2015 (UTC)[reply]

Technical reports[edit]

If both the methods and evaluation sections of a technical report are longer than the analysis section, has something gone wrong? 194.66.246.37 (talk) 19:43, 14 March 2015 (UTC)[reply]

Depends on the subject matter. There are no strict size expectations that could be applied to all possible technical reports. Dragons flight (talk) 19:47, 14 March 2015 (UTC)[reply]

One possibility is not that something has gone wrong but that not enough analysis has been done (not enough right). As Dragons flight noted, there is no universal rule on technical reports. Robert McClenon (talk) 02:37, 15 March 2015 (UTC)[reply]