Recent comments in /f/askscience

Hannover2k t1_j35ir9s wrote

Reply to comment by masklinn in Where does all of the snot come from when you have a cold? by Dunkachin0

I'm guessing things like antihistamines suppress the production of this mucus? What would happen if this process was turned off completely? Is this mucus produced in response to something physically in the nose that it's trying to flush out? I could understand allergens and such as those are physical particles but what about when you have a cold/flu? What's actually being flushed out? I just got over a flu where I was blowing out tremendous amounts of liquid so I'd love to know what my nose thought it was flushing out, aside from what it was producing itself.

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ttkciar t1_j35gt9s wrote

Reply to Is it true that rubber gaskets in a dishwasher will crack if unused? by iamaparttimemonster

If the gaskets are made of natural latex rubber (without intensive cross-linking as seen in automobile tires), then they will grow brittle and crack if they dry out too much.

Gaskets are traditionally made from natural latex rubber, but nowadays PU and PVC are frequently used, which are not susceptible to drying out but can grow brittle eventually (several years) anyway.

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dmmaus t1_j359y61 wrote

Reply to comment by romxza in How close does one need to bring two coloured lights together to perceive a compound colour effect? by romxza

It's important to understand that colour sensation is entirely psychophysical. The colours we sense are a product of the construction of our eyes and nervous systems - they don't really exist outside the context of a human observer (or an observer with the same visual architecture).

A spectrometer can easily tell the difference between (light of wavelength 580nm) and (mix of light with wavelengths 480nm and 650nm). There is a physical difference. But human vision cannot tell the difference - our brains sense both these as "yellow". Which one is really yellow? Neither. "Yellow" has no physical reality outside a human brain - it's our label for a sensation that we have.

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Origin_of_Mind t1_j355ent wrote

Reply to How do you optimize a rocket or space vehicle liftoff? by seriousnotshirley

In practice, this is done by numerical optimization, using ready-made optimization software.

A theory which was applied for designing the trajectory for the first "civilian" US space rocket "Vanguard", was presented in an article "Satellite launching vehicle trajectories" by Joseph W. Siry, published in 1959. The article was published in "Orbit Theory, Proceedings of the Ninth Symposium in Applied Mathematics", which unfortunately is slightly difficult to get a hold of.

More recent publications are easy to find, from lecture slides, to NASA technical reports, to various academic publications.

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fliguana t1_j34yvei wrote

Reply to comment by ncc81701 in How do you optimize a rocket or space vehicle liftoff? by seriousnotshirley

Dropping unused fuel tanks is not unique to rockets, some military planes use it too.

In most cases, dropped stage also contains the engine(s), because replumbing inflight is hard, and because the next-stage thrust need is reduced. But not always. For example, the Space shuttle made do with oversized reusable engines and an add-on tank.

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ncc81701 t1_j34xdbc wrote

Reply to comment by fliguana in How do you optimize a rocket or space vehicle liftoff? by seriousnotshirley

I mean this is why rockets are staged and non single stage to orbit vehicles have been put into service. During early part of the flight you have massive engines/power and once you are at high speed and high altitude you drop your boost stage to dump the engine and Fuel/O2 tanks you don’t need anymore and continue to orbit using a much smaller second, 3rd or even 4th stage.

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