# Wikipedia:Reference desk/Archives/Science/2014 July 10

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# July 10

## Pressure drag not symmetric?

This is somewhat related to my question from two days back.

Given an object and an axis, it has pressure drag when moved in air along the axis. It has a different pressure drag when moved in the opposite direction. Is there a decomposition of pressure drag into symmetric and asymmetric components? That is, is there a known component of pressure drag that does not change when the direction is reversed? --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 15:46, 10 July 2014 (UTC)

By applying the Parallelogram of force one can always decompose the drag forces into a component parallel to the given axis and another component. 84.209.89.214 (talk) 17:06, 10 July 2014 (UTC)

To clarify my question: Is there a decomposition of pressure drag into two components, one independent of forward/reverse direction, and another that depends on forward/reverse? --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 17:55, 10 July 2014 (UTC)

Regarding drag as a function of a real variable (the velocity), yes, it always has. The decomposition is into a sum of even and odd functions. —Quondum 19:19, 10 July 2014 (UTC)
Apart from the cases of a planar cutout or a symmetrical object such as a sphere, No. Drag is in general a non-linear function of velocity that depends on viscosity, laminar/turbulent flow and possible shock waves. Reversing the flow direction past a 3-D object does not change the object's cross section but without symmetry the flow behaviours and consequent drags can be very different (as the Anemometer cups demonstrate). See also Aerodynamic drag and Drag equation. 84.209.89.214 (talk) 22:01, 10 July 2014 (UTC)

Thanks User:84.209.89.214.

Is there some overly simplistic model of fluid dynamics, in which it is guaranteed that reversing flow direction does not change the drag? --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 08:59, 11 July 2014 (UTC)

Well, the not-that-useful model is to treat fluid dynamics "normally", but demand that every object in the flow be symmetric along some appropriate axis. SemanticMantis (talk) 13:44, 11 July 2014 (UTC)

## The relation between diarreah and ear infaction

What is the relation between ear infection to diareah (not from aspect of asking advise, but from the aspect of biology aspect)מוטיבציה (talk) 21:50, 10 July 2014 (UTC)

None that I know of -- the ear and the intestines are not connected except through the circulatory system (and even in terms of circulation they're on different loops), so there's no way for an infection to travel between the two except through the bloodstream. 24.5.122.13 (talk) 21:54, 10 July 2014 (UTC)
Wikipedia spells this condition Diarrhea with an alternative spelling diarrhoea that is chiefly British. The Greeks had the word first: διάρροια from διά dia "through" and ῥέω rheo "flow". Presumably the OP wonders about a relation between diarrhea and an ear infection or Otitis but I know of none. 84.209.89.214 (talk) 22:21, 10 July 2014 (UTC)
Taking antibiotics for the ear infection could cause diarrhoea as they can upset the normal bacteria balance in the gut. Richerman (talk) 22:33, 10 July 2014 (UTC)

yes, but one of the symptoms of ear infection in babies is diarrhea. So what is the relation between the two? — Preceding unsigned comment added by מוטיבציה (talkcontribs) 00:07, 11 July 2014 (UTC)

I certainly haven't heard that before. Can you point us to a reliable source that tells us that "one of the symptoms of ear infection in babies is diarrhea"? HiLo48 (talk) 00:11, 11 July 2014 (UTC)
there are a lot of sources for that. By simple search in google you can find them. I'm on the phone, so it's difficult for me to put them here. Sorry. מוטיבציה (talk) 00:25, 11 July 2014 (UTC)
The University of Maryland says both the disease and the (medicinal) cure cause diarrhea. Babies can't catch a break. Doesn't say how, though. InedibleHulk (talk) 01:13, July 11, 2014 (UTC)
On a pedantic point the ear and the digestive system are connected, by the eustachian tubes, but I don't think that alters much the discussion above. Richard Avery (talk) 07:42, 11 July 2014 (UTC)
Well, throat infections can (and quite often do) travel up into the middle ear and can cause deafness in the long term; that's why we have ear, nose, and throat surgeons. Still don't see what would be likely to give one both diarrhea and a throat infection, tho! Whoop whoop pull up Bitching Betty | Averted crashes 09:10, 11 July 2014 (UTC)
I'd say the specific relationship between the two phenomena has been overstated, but when talking about pediatrics in general, infants in particular are very broadly susceptible to infection relative to those who have more developed immune responses, including higher occurrences of certain types of ear infection and of diarrhea both. It's worth noting that since infants cannot communicate the specific nature of the pain they are experiencing (be it an ear-ache or some other form of pain) but only general discomfort/pain, in some case a physician must attempt to diagnose the source of discomfort from context and probability and proceed with a physical examination accordingly. This rule of thumb may have been slightly simplified and misinterpreted via a game-of-telephone type effect that has associated it most closely with one of the "usual suspects" in such cases, when in reality it is simply the case that any infection an infant contracts is likely to have very acute systemic effects which the physician can rely upon in diagnosing a pre-verbal child. Snow talk 11:56, 11 July 2014 (UTC)
Yes, multiple seemingly unrelated infections can be a sign of a suppressed immune system, such as in AIDS patients. In the case of babies, poor hygiene practices by the baby, who doesn't know any better, may also play a role. Specifically they may put their hand in a diarrhea filled diaper, then put a finger it in their ear, spreading the infection that way. StuRat (talk) 13:22, 11 July 2014 (UTC)
-sigh- No... 1) In this scenario we are not talking about unrelated infections - diametrically the opposite, in fact. 2) We're also not talking about suppressed immune systems, but rather immune systems which are not yet developed through exposure to pathogens and the subsequent development of antibodies. 3) Your speculation on poor hygiene as the cause of such infections is just that - uninformed speculation and highly unlikely to be the major causal factor of otitis media -- infection and inflammation of the middle ear -- which is the more habitual form of ear infection in infants and more likely to have been caused by an infection moving into the ear systemically via the eustachian tubes than caused by bacteria crammed that far into the ear from the external orifice. Snow talk 20:22, 11 July 2014 (UTC)
1) I said "seemingly" unrelated. I think we can all agree that diarrhea and ear infections at first "seem" to be unrelated.
2) My suppressed immune systems example also applies to not having a fully developed immune systems, such as in the case of babies. The common factor is that a weak immune system makes multiple, "seemingly" unrelated infections more likely.
3) Not sure what you find wrong with this argument. Do you disagree that babies exhibit poor hygiene practices ? Do you not agree that poor hygiene practices can increase exposure to pathogens ? Do you not agree that increased exposure to pathogens can result in increased incidence of infection ? If you tell me specifically where you think that argument is wrong, I will look up sources to prove that point.
Your speculation that most middle ear infections originate in the eustachian tube seems reasonable, but note that the OP did not specify middle ear infections only. If you believe this is also true of the outer ear, then I'd like to see sources to support that. StuRat (talk) 15:56, 12 July 2014 (UTC)
It does seem to be the case that diarrhea and vomiting are symptoms of ear infections. WebMD says that the symptoms include vomiting and diarrhea (in infants only). MedlinePlus, confusingly, says that vomiting and diarrhea are symptoms of an acute ear infection in older children or adults. John M Baker (talk) 14:49, 11 July 2014 (UTC)
The phrase "symptom of" seems wrong to me. There may be a correlation between the two, but that does not make one a symptom of the other. For example, blacks are more at risk of developing sickle-cell anemia, but that does not make being black a "symptom" of sickle-cell anemia. StuRat (talk) 16:02, 11 July 2014 (UTC)
Diarrhea and ear infections can be caused by bacterial or viral infections. It's not that the ear infection causes diarrhea, it's that the bacteria can infect both the ear and intestine. It doesn't seem too difficult for bacteria to move from the ear to intestine or vice versa. --DHeyward (talk) 06:33, 12 July 2014 (UTC)
Diarrhea can also be triggered by stress, such as that an ignorant baby might feel from the unfamiliar pain. When we get older, wise up to the fact that things get better and generally become accustomed to pain, we may relax and stop shitting ourselves over it. Would explain the "infants only" bit. InedibleHulk (talk) 06:49, July 12, 2014 (UTC)
Take the Mayo Clinic's symptoms in children, subtract the adult symptoms, then compare to Mayo's stress symptoms. Children need to chill out. InedibleHulk (talk) 07:06, July 12, 2014 (UTC)
(Late answer, sorry I missed this one, מוטיבציה) There was an article right around the time of this discussion [1] that suggests that diarrhea from poor sanitation causes malnutrition on a widespread scale. And malnutrition of course can contribute to infections - in the case of ear infection, vitamin A deficiency is apparently a culprit associated with diarrhea. [2] Wnt (talk) 17:19, 1 August 2014 (UTC)

## Night vision device

In yesterday's discussion about night vision devices, Nimur said, quote, "Many people confuse thermal imaging with infrared imaging with near infrared with image intensification. These are each different types of night vision device." Which got me thinking: are there any night vision devices out there which combine two or more of these functionalities -- maybe even all four? 24.5.122.13 (talk) 21:50, 10 July 2014 (UTC)

Many years ago I used a thermal imaging device which had an IR detector which used a stream of some gas, likely Argon, and which had a moving mirror to scan the scene, with a red LED display. Edison (talk) 03:20, 11 July 2014 (UTC)
Early IR cameras in the US military worked that way. They used some very cold gas to cool the thing (so that heat produced within the device itself didn't mess things up) - then a column of single-pixel IR sensors - each one connected via a high-gain amplifier to an LED. By rotating this contraption back and forth over a few tens of degrees, they could both scan the field of view with the sensors, and produce a horizontally scanning visible-light image from the LED's. That image would be viewed by a video camera which was hooked up to a display in the aircraft's cockpit. That's a pretty seriously obsolete technology though. This approach was used (for example) in early versions of the Maverick missile. SteveBaker (talk) 18:27, 11 July 2014 (UTC)
That would be hyperspectral imaging and it is widely used in military surveillance and scientific imaging applications. Nimur (talk) 04:53, 11 July 2014 (UTC)
As a not-that-great analogy, hyperspectral imaging is similar to High_dynamic_range_imaging. In the former, several images made in different spectral bands, and combined in a way that reveals more information than any one of the base images. In the latter, a similar approach is used, but rather than combining images with different spectral bands, the images are based on different white balances, exposure values, and luminosities. I bring this up because many readers will be familiar with the HDR images that have recently become popular on the web. SemanticMantis (talk) 13:41, 11 July 2014 (UTC)