Recent comments in /f/askscience

rootofallworlds t1_j1d17zo wrote

Reply to Do we have to account for motion when receiving transmissions for things life planes and sattelites? by Acceptable-Lemonade

The Doppler shift in the frequency from a satellite transceiver is measurable and needs to be taken into account. In ham radio use this means adjusting the frequency on the ground transceiver during the satellite pass. Commercial systems will automate such corrections.

https://n1aae.com/visualizing-satellite-doppler-shift/

https://upcommons.upc.edu/handle/2117/123510

What will help is something in the signal that the receiver can "lock on" to in order to tolerate slight mistuning. With analogue modulation that's a "carrier" frequency which has no data but provides a frequency reference the receiver can "lock on" to. AM, FM, and analogue TV include such a carrier. By contrast single sideband with no carrier, popular in ham radio, will give the receiver an audible pitch shift if they are not precisely tuned. For digital modulation things are more complicated but there are still ways to handle that mistune, and indeed devices don't give the user control over the precise frequency.

https://en.wikipedia.org/wiki/Carrier_wave

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PropOnTop t1_j1d0z27 wrote

Reply to Do we have to account for motion when receiving transmissions for things life planes and sattelites? by Acceptable-Lemonade

I tried to calculate the shift as a joke and came to the conclusion that it's about 1/38038th of a second IF both objects move at the greatest relative speed to each other (17600mph - disregarding triangulation and relative angles). This is on the order of 26000 nanoseconds of shift (7867 metres per second, 0.19m is the wavelength of the GPS L1 signal@1575MHz, so about 41405 wavelenghts to 7867 metres, or 1/38038th of a second - same calculation if speed of light is used).

However, apparently general relativity plays a bigger role here (https://www.avionicswest.com/Articles/howGPSworks.html) and due to it the faster moving clocks on the satellites need to be slowed down, and by a relatively substantial amount too:

"... The physics of general relativity states that space-time is warped in the presence of massive bodies (the earth) with the result that clocks run slower as they are brought closer to that body. Satellite clocks at 4 earth radii are influenced less than the same (atomic) clock running on the surface of the earth. So the atomic clocks on the satellites must be slowed down to stay in sync with clocks in your GPS receiver. The frequency is reduced from 10.23 MHz by 4.547 milli-Hertz (a half a part in one billion) to stay in sync with earth clocks. While small, the error if not corrected would accumulate to a 38 ms advance per day, or a distance error of 10 km."

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derKestrel t1_j1d0x4n wrote

Reply to which is more efficient, using the sun to boil water and generate electricity from team or using solar panals? by Phat_Potatoes

If you concentrate sunlight and shine it directly into the water or on items absorbing sunlight which are inside the water, apart from refraction, reflection, and lens heating losses, all energy from sunlight should be transferred into the water. You lose some more from radiation of heat from the water vessel and the pipes.

In this case I think your efficiency is mainly ruled by your turbine efficiency: around 65 to 90 %, bigger turbines and hotter steam tend to be more efficient.

For the solar panels on the other hand, we look at 17 to 25ish %.

I guess steam power is still good.

I do have no idea about cost efficiency. The steam solution will have much higher maintenance costs and probably also setup costs.

You might also want to look at molten salt solar solutions.

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derpderp3200 OP t1_j1cpaij wrote

Reply to comment by Triabolical_ in How and why do diet and lifestyle changes reverse insulin resistance? by derpderp3200

I never really had hypoglycemia after an actual meal(I know you can get the adrenergic subset of hypoglycemia symptoms without objective hypoglycemia, but it doesn't seem to fit the bill), and my fatigue seems independent of glucose levels- sometimes it hits while they're still high, sometimes after they go back down, sometimes minimal symptoms start before it reaches the peak. I get hours of horrid brain fog, restlessness, anxiety, overwhelming desire to lie down, spend 45-90min in a food coma, and be groggy for several hours afterwards. It gets lighter in the evening, and it's bad enough that I'm afraid of eating during the day. But I'll have to force myself since science suggests that skipping breakfast and one meal a day worsen glucose tolerance, which tracks with my symptoms getting worse after I switched to this.

I'm trying to limit my carb intake, but it's very difficult. For one I'm vegetarian, for two, between ADHD, Sleep Disordered Breathing, and the part of fatigue I now presume to by dysglycemia related, I'm an extremely low functioning person and taking care of myself stretches my capacity very thin.

A lot of the time it's a choice between having some bread and going hungry, and I've been going hungry for a longer time now, which is also bad for my energy levels.

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seven_tech t1_j1coweo wrote

Reply to comment by samskiter in Why do we use phase change refrigerants? by samskiter

Mmm, kind of? 2 stroke has its place though. It's reliable, cheap to build and easy to maintain vs 4 stroke. Which makes it perfect for simple engines like lawn mowers and yard trimmers.

Gas-gas refrigeration doesn't really have any advantages over liquid-gas. So we don't really use it since perfecting the gas-liquid version. They used to use air refrigeration cycles. But not really anymore because it's so bulky due to the sheer amount of space/gas needed.

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askscience-ModTeam t1_j1cnzmu wrote

Reply to Why must closing tags in HTML and XML contain the name of the tag being closed, if the tag being closed can be determined by the order they were opened? by Throwawayingaccount

Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):

  • This question is based on fundamentally flawed premises. Please conduct some background research and revise your question if you wish to resubmit.
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