Wikipedia:Reference desk/Archives/Science/2017 January 23

= January 23 =

syphilis among first peoples in south america, north america, and nearby islands, etc.
Do the descendants of first peoples exhibit more immunity and better tolerance to syphilis infections than most other people? I think if their bodies did fight syphilis better, it wold support the theory that the 1400s and 1500s european explorers brought it back from the americas after having sex with first peoples. But if so, where did the first peoples get it? Did their ancestors bring it over the bering strait 30000 years ago in a prior form that europe and asia previously had and may still have?Thanks144.35.45.33 (talk) 19:42, 23 January 2017 (UTC)
 * Wikipedia has an article titled History of syphilis. It would be a good starting place for your research.  -- Jayron 32 19:54, 23 January 2017 (UTC)
 * Yes, I had already read that. It does not address my question.144.35.45.63 (talk) 16:07, 24 January 2017 (UTC)
 * The article states that there are two competing hypotheses, the Columbian and pre-Columbian. We do not know at present which is correct, so I'm afraid there's no answer to your question at present. --47.138.163.230 (talk) 01:00, 25 January 2017 (UTC)
 * Your answer is only superficially logical, but it enables you to dispose of my question.144.35.45.62 (talk) 19:24, 25 January 2017 (UTC)

Dehumidifier performance when the coils develop a coating of ice
When I read about why dehumidifier performance can deteriorate sources say that ice on the coils stops dehumidification and completely glosses over why this should be. Ice is at a cold temperature so water in the air should condense onto it just as it would onto metal. I don't see why this defrost period should be less effective than the usual cycle provided the fan continues to run (and it does). --78.148.97.148 (talk) 19:56, 23 January 2017 (UTC)


 * Ice blocks airflow between the coils, which reduces the amount of moisture in the air that has the chance to condense. Reduced airflow also slows the air moving past the coils, which leads to more ice buildup, which reduces airflow, which leads to more ice, which eventually blocks all airflow and system is not effective in any way. You can create this on your own (but I highly advise against it) if you have central air conditioning. Block at least half of the main air return duct. That reduces airflow to the main unit. The air moisture will begin freezing on the coils and, eventually, completely ice up the coils and block all air flow. Because the ice can cause severe damage to the unit, I strongly advise against going this, but if you really really really want to see it happen, it is possible. I did it inadvertently one summer by moving the trash can in front of the return duct while cleaning and it iced up the unit and cracked the coil, releasing all the coolant. Expensive mistake. 209.149.113.5 (talk) 20:09, 23 January 2017 (UTC)


 * Dehumidifiers work because of the difference between absolute humidity (water content of the air) and relative humidity (current water content as a proportion of the maximum water content possible). Absolute humidity is constant, unless water is added or removed. The maximum humidity (the carrying capacity) though is temperature dependent and decreases with falling temperature. So if the air is cooled, the relative humidity does change: it increases, not because the water content has increased, but because the potential carrying capacity is less at reduced temperature. When the max humidity is reached, water condenses out.
 * This leads to the main problem with dehumidifiers: they don't work efficiently in cold weather. If the air is already cold, cooling it down further has only a small difference of carrying capacity to work with. They still work (if the temperature is still anything above the refrigerator temperature) but increasingly less efficiently: the electrical cost of running the refrigerator compressor is much the same, but the water yield is less. A well-designed dehumidifier should not become encased in ice; if it does, that may indicate that it is being operated at a low starting temperature.
 * Ice (so long it's dry, not wet) is also a good insulator. Refrigerator evaporator coils coated with it are no longer so effective. If they increase in size, they may also block airflow through them. This is less significant an effective than the humidity aspects, but it also makes a dehumidifier less effective in cold weather. Andy Dingley (talk) 00:09, 24 January 2017 (UTC)