Recent comments in /f/askscience

jawshoeaw t1_j3usbqt wrote

Interestingly there is a limit to the bloods ability to transport proteins and it’s viscosity. Too many cells make the blood too thick and too may proteins make the blood too thick. And having antibodies doesn’t work if you have like one molecule-there’s a minimum amount required to work. That said, I’ve never heard of someone maxing out via vaccines.

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kilotesla t1_j3uolby wrote

>It's not glass compared to air that's the issue so much as compared to water or ice. The air is the environment in this situation so if the system is in a glass container the heat transfer to the air will be negligible compared to the surface area of the water and ice (which again depends on the shape of the container greatly).

In a series circuit with a very low resistance resistor, a medium value resistor, and a large resistor, fed by a voltage source, the voltage drop across the medium value resistor is affected a lot more by the large resistor than by the smallest resistor. If we have 1 ohm, 33 ohms, and 1000 ohms in series, the drop across the 33 ohm resistor is 3% of the source value, even if we drop the 1 ohm resistor to 0.1 ohms. We can't conclude that the 33 ohm resistor will have a lot of voltage drop because it is huge compared to 0.1 ohms. That doesn't work.

The glass outer surface will be very close to the same temperature as the water. The heat flow per unit area is determined by the temperature difference between the water and ambient. If the outer glass surface were at 1 C instead of zero, the temperature difference with respect to ambient would not change significantly. And the surface temperature wouldn't even be that high.

>Realistically, radiation is going to be a meager source of heat loss, even hot water radiators to heat houses only supply about 5% of their heat contribution through actual radiation, and that's at higher temperatures.

  1. 5% is way too low. Modern "radiators" have fins which enhance convection but not radiation, so convention is typically larger, but radiation is still about 25%, even just counting the outward facing surface.

  2. In the range of temperatures we are talking about, radiation is reasonably approximated by a linear function of temperature difference. Yes I know, that's counterintuitive with that fourth power, but it's T1^4 - T2^4 , not (T1-T2)^4. On the other hand, natural convection is nonlinear enough that it drops as a fraction of overall heat transfer when the temperature difference gets smaller.

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JamesTKierkegaard t1_j3ueydg wrote

It's not glass compared to air that's the issue so much as compared to water or ice. The air is the environment in this situation so if the system is in a glass container the heat transfer to the air will be negligible compared to the surface area of the water and ice (which again depends on the shape of the container greatly). If it's a thin metal container then water remaining will probably win in most configurations simply because it will act as a convective exchange surface. Realistically, radiation is going to be a meager source of heat loss, even hot water radiators to heat houses only supply about 5% of their heat contribution through actual radiation, and that's at higher temperatures.

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tdTomato_Sauce t1_j3u8q8u wrote

One thing to consider in this train of thought is that those antibodies and cells are not being constantly produced or maintained. This is the beauty of “immunological memory”.

These cells die off in massive numbers once you clear a pathogen (or following vaccination), leaving behind a tiny colony of memory cells that lies relatively dormant until you encounter the same pathogen (or vaccinate antigen) again.

When that happens, they multiply enormously and mount a whole new immune response, then repeat. This is basically what allows an enormous & diverse immune library.

Using the computing analogy, it’s like running a program vs storing program files. You can’t run all your programs at once, but you can store a lot of program files.

There is obviously a lot more happening in the grand scheme of immunity but hope this is easier to understand!

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root_over_ssh t1_j3u71oi wrote

Draining will be faster.

Let's assuming you have a glass of ice in a room with a constant air temperature.

The air will begin to melt the ice and soon you'll have a glass of ice water. The ice is no longer in contact with the air directly and is now submerged in a water that is only slightly above freezing temperatures. It takes a lot of energy at this point to keep warming, so now thay air has to heat the water first before there is a significant temperature gradient to melt the ice more.

Now, if you have the same amount of ice in a strainer, you have 2 changes going on - when the water is removed, they're now 2 separate systems in this constant air temperature exam, the ice doesn't impact the water and the water doesn't impact the ice. Since the water is being removed from the ice "system", you now have less mass to heat up as well and maintain a higher temperature gradient between the air and temperature of the ice.

While water is a better conductor of heat, heating ice with water that is heated by air is still far less efficient than heating the ice from the air directly.

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kilotesla t1_j3tzhd4 wrote

Those sound like valid results to me. One thing that I'd want to be a little bit careful of is the initial temperature of the bowl. If you had a bowl that started out at room temperature, and it was thick and heavy, it's thermal mass could contribute to the faster melting.

One other question is whether the ice was in the form of cubes, such that air could flow in between them in the strainer case, or whether it was perhaps frozen in the bowls so it was one solid hunk of ice

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kilotesla t1_j3tz1rk wrote

That's good advice that the specifics matter. Since there will be heat transfer by radiation as well as convection, the emissivity of the surface of the container also matters, and if it's polished metal, the low emissivity would retard melting. Also, if the thermal mass of the container is significant, its starting temperature would matter.

When considered in comparison to air, glass is not a poor conductor of heat. It's conductivity is 33 times higher than that of air, and it's likely pretty thin, such that the heat transfer through the air will be the dominant thermal resistance. Air of course has the advantage that it is moving and so carrying heat by convection, not just conduction but it's still going to be the dominant thermal resistance.

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