Recent comments in /f/askscience

Redbiertje t1_je92cup wrote

Review papers are typically written by experts in the field (and even usually upon request from a journal), so this is not something you should aim for as a MSc student.

What I can recommend is that you email a few professors at your institute and say that you are orienting yourself for a possible future PhD, and you would like to ask if they have 15 minutes to talk about the current state of their field of research (or maybe they can direct you to one of their postdocs). That way, you get a basic idea about what the main questions are they are working on, and then you can decide which of those you find interesting.

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El_Sephiroth t1_je8y2on wrote

As I understand it, dielectric breakdown voltage is the energy necessary to disrupt an insulator into a conductor. Therefore, if you have a perfect vacuum, there is no matter to disrupt. But, a high enough voltage could still create electron-positron pairs out of the vacuum and therefore make a conductor in something empty. It's called schwinger effect. It is only a prediction of quantum electrodynamics.

So if there is nothing there, electricity could pass through when "matter" (here electron and positron) are created in it.

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mfb- t1_je8wf3w wrote

Permanent magnets have a saturation magnetization. Trying to apply stronger fields doesn't magnetize the material more, and if you drop the external field then the field of the magnet decreases, too. In practice you get around 1.3 T for neodymium magnets, theoretical values might be slightly higher. This publication calculates 1.32 to 1.38 T.

The size of the magnet doesn't matter, you just scale up everything linearly in space and the field gets larger but not stronger.

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ch1214ch OP t1_je8vds0 wrote

Okay, lets say the left and right retinas are like two laptop screens with all the pixels numbered/labeled the same. Does a corresponding position fall on the same numbered/labeled pixel for each eye, or would the correspondence fall on different numbered pixels?

Does that make sense? Like if the retinas were like battleship would the corresponding position be the same (b4 and b4) or would they be different (like b4 for the left eye and c4 for the right eye)

I want to know if they correspond in the sense that they are b4 b4. Or because they correspond to the same point in physical space but are in fact different "pixels", like b4 and e6

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Kyrsatile t1_je8ujy5 wrote

This is kind of both a physics and astronomy set of questions.

In Mass Effect 2, there's a planet called Hagalaz that is described as having a constant lightning storm happening right where the sun is setting where hot and cold air meet. This storm is caused by "the ocean boiling during the day, only to snap freeze 10 minutes after sunset." I understand it’s science fiction, but it’s been driving me crazy.

Here is all of the information about the planet I can find:

Hagalaz has a radius of 6,309 km, a day length of 98.3 Earth Days with an orbital period of 1 Earth year, an atmospheric pressure of 0.83 of Earth, an average surface temperature of 72 °C (day) and −64 °C (night), a surface gravity of 0.69 g, and a mass of 0.67 Earth Masses. It has an orbital distance of 0.95 AU around a star with a stellar mass of 1.01 compared to our sun. It is not specified if Hagalaz’s oceans are salt or fresh water, nor the temperature of the star, though it appears to be roughly half the size of our sun. Hagalaz has a nitrogen-oxygen atmosphere and is apparently a garden world capable of supporting life.

With all of the necessary information about the composition of the planet aside my questions are - would the storm that is supposedly spanning at least most of the circumference of the planet and constantly chasing the sunset even be possible? Would it be possible for water, any water, to boil at 72C and snap freeze in 10 minutes after sundown in these conditions? Would this planet even have any water left?

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wwjgd27 t1_je8nghy wrote

I thought ABAB stacking was for graphite and other graphitic structures since each stack of graphene is missing a carbon atom at the center of the hexagonal rings which would give it the symmetry allowing for ABCABC stacking in both HCP (0001) planes and FCC (111) planes? Interesting conversation by the way!

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Okonomiyaki_lover t1_je8hhs1 wrote

Spacetime is just the grid we exist on. Every object can have an x, y, z, and time coordinate to describe its location in the universe. While all mass warps space time, very massive objects produce enough warp to be easily seen.

The earth would fly off in a straight line if the sun disappeared. But the sun warps spacetime so the earth orbits this warped part of spacetime.

Spacetime is everywhere (except maybe inside the event horizon of a black hole). Even where matter is. If you had an x/y plane and put a point on it. That point is not separate from the grid.

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Weed_O_Whirler t1_je8e4g9 wrote

So I'm honestly curious - is 1-2 T the theoretical max for how strong a neodymium magnet can be? Or is there an easy, back of the envelope, way of calculating it? I tried to scale up a small one to the mass of the Earth, but couldn't find any easy way of doing it, but my estimate made it quite large.

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Indemnity4 t1_je8byp8 wrote

We are running out of cheap, easily available, high-purity commercial helium.

Helium mostly comes from natural gas / fracking. The US gas reserves are naturally rich in helium, which is why they are the largest global producer. It will be something like 1-4% of the gas in a given gas well, but can be up to 10% of the gas well by volume. Before they put it in the pipeline and send natural gas to your house, they separate out all the other gases such as carbon dioxide, oxygen, nitrogen, and helium.

What USA government used to do was require the few giant mega gas producers to separate the helium and send it to a central facility. Now that gas producing regions have relocated and split into multiple smaller units it is no longer financial sense to do the separation and transport.

Unfortunately, helium is still really cheap. It's only $7 cubic meter! It is not worth the cost of running the separator and a bottling plant just for helium. Instead, it gets released to the atmosphere.

Future developments include the price of helium increasing to the point it does make financial sense to separate helium from smaller gas wells. Also, potentially direct helium mining. There are some areas in the world where there are underground caverns full of concentrated helium that could be mined and captured.

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Indemnity4 t1_je8bccp wrote

Oh yeah, it's easy. If you have ever seen a gas BBQ bottle or carbonated drink cartridge, it's basically bigger versions of those.

Laughing gas is a potent greenhouse gas, but you can get a cylinder of it in your whipped cream can. A hospital can get a giant tank of it to disperse into regulators for pain relief.

However, if your question related to climate change the answer is no. The scale of the problem is mind boggling huge. You just have to picture every fuel station you see and replacing their storage tanks, but instead now they are filling a new one every few days and simply leaving it in some empty field to hold the gases, forever, with ongoing maintenance.

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