Wikipedia:Reference desk/Archives/Science/2020 December 1

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December 1

Is it warmer to wear 2 medium sweater vests or a large and a medium?

2 mediums is somewhat tight and a medium over the large is tighter and very stiff and hard to compress by sweater standards (it's better to replace an overcoat with this before being punched in the chest probably) which should increase conduction and squeeze out most insulating inter-layer air. The large over a medium is neither tight nor loose.

2. Is it worth it to buy a light jacket in an overweight people size - whichever one's the right tightness or looseness to minimize heat loss when worn over your winter coat?Sagittarian Milky Way (talk) 02:50, 1 December 2020 (UTC)

You might find info at Layered clothing, although the article is mostly unsourced. Zindor (talk) 03:09, 1 December 2020 (UTC)

Indeed, see also here. Count Iblis (talk) 14:43, 1 December 2020 (UTC)

What is "power for an average home" in journalism?

One frequently encounters, in newspapers and other media, sentences like "The Zorch Project will supply enough electricity for 170 thousand average homes." Sometimes no other information is given. My question is whether there is a standard in journalism for converting standard power units, like megawatts, and maybe capacity factor, in coming up with that kind of statement. I'm not asking for statistics on actual household power consumption, just whether are any standards or guidelines for making such assertions. I did find a reference from the U.S. NRC What is a megawatt?, but again I'd like to know if the use of the phrase "power for an average home" has any consistent basis in journalism.--agr (talk) 18:47, 1 December 2020 (UTC)

That is a great question which I unfortunately don't know the answer to, but I did want to point out that "170 thousand average homes" is at least a better descriptor than the "light up a city the size of Los Angeles" short hand, which is almost aggressively unhelpful. Matt Deres (talk) 18:55, 1 December 2020 (UTC)

Can't we use a conversion-factor like "Japan-populations per Rhode-Island-area" to find the number of homes in LA? DMacks (talk) 19:11, 1 December 2020 (UTC)

Probably depends on the country; electric heating and aircon will push it it. It might be around 500W. LongHairedFop (talk) 19:16, 1 December 2020 (UTC)

Around 500W sounds ok for EU average (4000KWh/Year). --Stephan Schulz (talk) 21:41, 1 December 2020 (UTC)

There is also peak demand versus demand averaged over 24 hour periods. If the daily demand is 11KWh, 500W will not be enough to meet peak demand.  --Lambiam 09:46, 2 December 2020 (UTC)

In this context, of course no sensible power distributor or government administration would choose to power a significant number of customers exclusively by a single source (solar, wind, hydroelectric or whatever).

I note that, as of this moment, Great Britain's National Grid System is distributing 42.37GW of power from nine different sources, ranging from Combined Cycle Gas Turbines (49.71% of current demand), through Wind (15.37%), Nuclear (15.13%), Biomass (6.82%), Coal (5.78%), Solar (2.62%), Hydro (1.37%), Pumped (0.37%), down to Open Cycle Gas Turbines (0.33%).

For completeness, we're also drawing 1.18% of the demand from Eire and 0.76% from Northern Ireland, but are supplying 2.05% to Belgium, 1.82% to France and 1.79% to The Netherlands.

Obviously, the balances of these figures (and the actual demand) vary greatly over the time of day, day of the week and time of the year, and any of the overseas links may be positive or negative in value as required to balance the needs of, and availabilities and prices from, the respective grid systems involved.

If anyone's interested, the site from which this data comes is here. {The poster formerly known as 87.81.230.195} 90.197.26.5 (talk) 14:18, 2 December 2020 (UTC)

When I looked at 90.197's link, I saw that the biomass gauge was at 3 and in the red. What does that mean and does it matter? -- SGBailey (talk) 16:08, 4 December 2020 (UTC)

To be clearer, it's currently at 3.00 GW as an absolute power measurement, and 6.99% of current total demand of 42.92GW.

The 3 GW is just a current measurement, which happens to be the maximum value representable by that gauge (though not on the associated graphs). I don't know what the orange and red sectors on some (not all) of the various gauges mean, but suspect that they indicate a proximity to maximum capacity for that particular source. The actual maximum reading on the gauges are probably arbitrary to an extent, based on what was expected when the site display was last reprogrammed, since when some facilities may have been dismantled or repurposed (such as old coal-fired plants being converted to biomass (i.e. wood), and some expanded (e.g. wind, since additional new turbines are regularly commissioned). The parent site linked as Elexon Portal may have further details, but requires a log-in I'm not going to try to investigate it; the Sheffield University link might be worth exploring.

[NB: I have no involvement with the site, I just happen to enjoy checking it in conjunction with https://earth.nullschool.net (configured to my own location), because like many Brits I'm obsessed with the weather.] {The poster formerly known as 87.81.230.195} 90.197.26.5 (talk) 16:43, 4 December 2020 (UTC)

To be precise, the 'Pumped' source is not a source at all. It is just an accumulator, which is used to store energy from other sources at the time of low demand and then supply it back to the grid at a peak time. So, whatever power the Pump category lists, it actually comes from Nuclear, Gas, Biomass, Wind etc. --CiaPan (talk) 17:06, 4 December 2020 (UTC)

Claimed efficacy of disinfectants

Disinfectants commonly claim that they are effective against "99.9% of all known household germs". Or even 99.9999% or whatever.

Just exactly what is being measured here? The number of types of germs, or the number of actual germs? And what about the germs that survive? How are we supposed to protect ourselves against them? -- Jack of Oz ^{[pleasantries]} 20:07, 1 December 2020 (UTC)

For your latter question, generally speaking, you protect yourself from the survivors with your immune system. That may seem simplistic, but the issue is basically one of infectious load. If you touch a surface covered in Staphylococcus aureus, then the of live bacteria transferring to you will be high, meaning your initial infection population will also be high. If 99.9% of the bacteria were killed by a disinfectant before you touched the surface, that means the amount of bacteria you will come into contact with will be 1:1000th what you would have without the disinfectant. That lower infectious dose is much easier for your immune system to combat and stop before you ever get sick. This is similar to how we classify the efficacy of antibiotics. See antibiotic sensitivity testing, where the efficacy of an bacteria being classified as "susceptible" to an antibiotic is based on the number of colony forming units as measured after exposure to the antibiotic. A threshold is set, and it isn't 0 colony forming units per millimeter, for example. However, that low number that still survive are low enough for your immune system to take care of the rest. --OuroborosCobra (talk) 21:01, 1 December 2020 (UTC)

They are going by Log reduction. Abductive (reasoning) 09:46, 2 December 2020 (UTC)

One brand claims to kill "all known germs". I guess they're ignoring the unknown ones.--Shantavira|^{feed me} 09:43, 2 December 2020 (UTC)

Perhaps because they are unknown unknowns. --Jayron32 13:03, 2 December 2020 (UTC)

I've sometimes mused to myself, only half-jocularly, why we can't just spray the entire inhabited world with household disinfectant, and hey presto, Covid-19 gone! -- Jack of Oz ^{[pleasantries]} 21:17, 2 December 2020 (UTC)

Early on in the pandemic there were plenty of news reports with videos of people (in full PPE usually) doing just that on streets in China, India and elsewhere. Mike Turnbull (talk) 11:50, 3 December 2020 (UTC)

We had a president who encouraged people to drink bleach to cure themselves of the disease, so your proposal is not as outrageous in comparison. --Jayron32 13:22, 3 December 2020 (UTC)

News flash: You still have him for the next 7 weeks, and yesterday's windy pronouncement showed that anything is yet possible. Do not remove your seat belts just yet. (Mind you, with over 3,000(!!!) people dying every day from Covid in the USA, his supporter base must be rapidly dwindling.) -- Jack of Oz ^{[pleasantries]} 20:14, 3 December 2020 (UTC)