Wikipedia:Reference desk/Archives/Science/2019 April 13

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April 13

Mean corpuscular hemoglobin concentration (MCMH)

Normal range Mean corpuscular hemoglobin concentration (MCMH) is listed by MedlinePlus as 320 to 360 grams per liter (g/L), meanwhile the UK National Health Service system i'm looking at states the normal range 290-350. That's 30 to the downside and 10 to the upside in terms of variation in normal range. Ostensibly a result which would be considered "normal" by the United States National Library of Medicine can be flagged as "abnormal" in overseas healthcare systems. My questions are:

1) are there any reasons for this variation in normal range?
2) is the "normal range" typically benchmarked against the range of the domestic population?
3) do normal ranges for this parameter vary dependent on variables such as age, gender, ethnicity, or is it a "one-size fits all range"?
4) the result i am looking at specifically is a read of 357, where all other blood test parameters are normal range. This is certainly not medical advice, but scientifically speaking can any deductions or conclusions be drawn from this outlier 357 read in isolation (assuming the data is reliable)? Uhooep (talk) 00:16, 13 April 2019 (UTC)

Hemispatial neglect, and turning 180 degrees

I have heard of patients with hemispatial neglect who only "noticed" one side of their room: for example, they might keep all their things on the right-hand side, and fail to perceive the left-hand side of the room. But "left" and "right" and relative. When the person turns around 180 degrees to leave the room, what happens? Do they think all their stuff has vanished? Equinox ◑ 02:22, 13 April 2019 (UTC)

In your own life you can only see things that are roughly in front of you, and unless you have eyes on the back of your head like my sixth grade teacher had you cannot see things when the back of your head is "facing" them. Do the things in front of you disappear when you turn around 180 degrees? --Guy Macon (talk) 02:34, 13 April 2019 (UTC)

Our article cites research: Left of what? The role of egocentric coordinates in neglect, (1997).

Human perception, and non-normal conditions therein, (including disease and illness) makes for a fascinating field; I think we can safely say that our best research sometimes finds and describes elements of human behavior that we cannot really explain, nor can we easily ascertain a physiological cause. Nimur (talk) 02:37, 13 April 2019 (UTC)

Heat from heat lamps vs heat from heaters

Besides the fact that maybe it's directional, does the heat from those heat lamps (looks like a light bulb, emits almost only IR and some red light) have anything that makes it therapeutic or in any way different from the heat of another common household heater? I notice it emits some red light, which the heater doesn't, so I wonder whether it is at a higher frequency or concentrated around a different wavelength? --Doroletho (talk) 12:31, 13 April 2019 (UTC)

Do our articles on Black-body radiation, Color temperature, and Heat therapy answer your question? --Guy Macon (talk) 13:00, 13 April 2019 (UTC)

Penetration depth of infrared radiation in our skin depends on its wavelength. IR-A (from 0.78 to 1.4 μm) is the most penetrating. For this reason the infrared lamps used for therapeutic purposes produce mainly IR-A radiation. DroneB (talk) 13:39, 13 April 2019 (UTC)

• Depends on the wavelength, depends on the age of the lamp. The wavelength can be chosen to optimise for therapeutic use. Older (1930s-1950s) lamps looked like "lamps" and were sold as therapeutic, but didn't yet have this under control, so they'd also make things uncomfortably hot on the surface. The more specific ones started to appear (as domestic products) in the 1960s. Andy Dingley (talk) 16:36, 13 April 2019 (UTC)
• The heat from an ordinary heater is not at any "frequency"; it's just heat, which is random motion of molecules. If it's an electric heater and you see some light, that's a secondary effect (although it does contribute slightly to heating things as well). It warms the air in the room, which in turn warms your skin (and other objects) by conduction. On the other hand, an IR lamp warms your skin (and other objects) directly by radiation, and as Drone said, the IR may penetrate a little way into your skin, but it does not warm the air. In short, you may feel the heat in a slightly different place in the two cases. That's all. --76.69.46.228 (talk) 02:25, 14 April 2019 (UTC)

  I guess there is a typo in that reply: heater resistance to air and air to skin heat transfer is convection, not conduction. Tigraan^{Click here to contact me} 11:00, 15 April 2019 (UTC)

  An electric heater is also glowing super bright, just in the infrared, which you can't see. Any object at a temperature above absolute zero radiates heat. The amount of heat it radiates at specific wavelengths is dependent on temperature, so only certain temperature objects will give off visible light. As already noted above, see blackbody radiation. The difference between an electric space heater and a heat lamp is that the heat lamp also gives off radiation in the visible range. --Jayron32 11:35, 15 April 2019 (UTC)

  Well, the real question is how much (for a given heating power) is dissipated in radiation vs. convection for the heating lamp (vs. the heater). Time for the math!

For the heating lamp, I will assume the fraction is somewhat close to 100% (I cannot find specs online).

For the heater, let's compute the blackbody radiation vs. convection by assuming a temperature of about 127°C (clearly that is more than the outside temperature of the heater, though it may be less than the temperature of the resistance inside - I did not find any specs online here either). The value is conveniently taken to have a 100K difference in the convection computation and a 400K absolute temperature in the radiation computation. The blackbody radiation is $\sigma T^{4}=5.67\times 10^{-8}W/m^{2}/K^{4}*(400K)^{4}\approx 1.5kW/m^{2}$. For convection, assuming a heat transfer coefficient of about $10W/K/m^{2}$ (highly debatable, but that's the rough ballpark for natural convection), we have about $h\Delta T=10W/K/m^{2}\times 100K=1kW/m^{2}$ of convection.

Both values are kind of close, so the fraction is somewhere in the middle, but keep in mind that the computation assumes blackbody radiation. If the outside of the heater is painted "white", the radiation drops proportionnally to the emissivity. Scare quotes around "white", because what will actually matter is the emissivity around peak emission in the infrared, and I highly doubt that visible-white paint is infrared-white. The dominant transfer in that case could be resistance → walls by radiation then walls → air by convection, rather than resistance → air by convection directly. Tigraan^{Click here to contact me} 16:02, 15 April 2019 (UTC)