What is the difference between a cell which is alive and one which is not? | AskScience Blog

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Saturday, February 22, 2020

What is the difference between a cell which is alive and one which is not?

What is the difference between a cell which is alive and one which is not?

What is the difference between a cell which is alive and one which is not?

Posted: 21 Feb 2020 02:40 PM PST

How do supersonic planes operate?

Posted: 21 Feb 2020 07:25 PM PST

Wondering how supersonic planes actually work? I couldn't find anything on the google so I was questioning if you worthy redditers could enlighten me.

submitted by /u/guyoto
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What's the difference between the metrics in differential geometry and general relativity?

Posted: 21 Feb 2020 05:07 PM PST

This past semester I took a general relativity class and a differential geometry class.

In general relativity, we talked very early on about the metric tensor of a system of coordinates, like spherical or cylindrical coordinates, as basically a 3x3 diagonal matrix g=[g1; g2; g3] used to calculate length.

On the other hand, in differential geometry, after talking about parametric surfaces, the metric was defined to be a 2x2 matrix g=(E; F; F; G), with E, F, G being the first fundamental form of the surface.

Now, obviously, the two matrices cannot be equal, one being 2x2 and the other being 3x3. So I thought maybe they just have some of their elements to be equal. Which happens to be true but could be just coincidence. The metric of a sphere and the metric of spherical coordinates seem to be two completely different things, yet they share the same name and seem to have similar functions.

I even emailed my professors, the GR one had no idea what I was talking about, the DG one just told me I should read up on do Carmo's book on Riemannian geometry, which I was able to find, but was a bit over my head and couldn't find what I was looking for. I tried googling the question but I couldn't find anything related, so I don't think I was phrasing the question correctly. So what is the difference between the metric of a parametric surface and that of a system of coordinates? Is there some connection between them?

submitted by /u/harry353
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Is a metric and a metric tensor the same thing?

Posted: 21 Feb 2020 05:09 AM PST

Hi all, I am new to differential geometry, but I am reading about metrics and metric tensors now. My understanding is that metric tensors tell you how to find the length between 2 infinitesimally close points, while a metric provides a distance measure between any 2 points. My question is: are the 2 concepts equivalent or otherwise connected? If you have a metric, i.e. a distance measure, can you always find a metric tensor? What about vice versa? Save me!

submitted by /u/bobbytan85
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How did the Space Shuttle "balance" itself when the SRB's were dropped?

Posted: 21 Feb 2020 12:14 PM PST

I was watching a video of the last Space Shuttle launch and after a while, the two solid rocket boosters were dropped, and the SS was flying with only the big main tank attached. Since the three engines were so off-centre from the centre of mass (I presume), how did the whole thing not spin out of control?

submitted by /u/ruup20
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Questions about High and Low Explosives?

Posted: 20 Feb 2020 11:40 PM PST

First, I am not trying to make an explosive device, I am purely curious as to the chemistry and how they explode.

I understand that gunpowder is a low explosive, so it would need to be pressurized to make an explosion, so thats why it is good as a propellent for bullets.

But I have some questions...

  1. Do high explosives, such as tnt or picric acid have to be contained or pressurized for them to explode or do they explode if they are just on a plate since the pressure and the explosion is so fast?
  2. Could the military add a high explosive to a low explosive (gunpowder), and make the gun powder a high explosive?
  3. How come you need a certain amount of a high explosive to explode a low or another high explosive? (This is super confusing because I would think if you took a high explosive like tnt and tried to set off another high explosive like anfo ig, but videos show it not working.)
  4. Lastly, if the military were making warheads or missiles, would they use a high explosive to start the explosion, would the missile have a high, super sensitive explosive to then explode a low explosive? Or would this not work?
submitted by /u/Nick_9903
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How does a PC obtain an IP address?

Posted: 20 Feb 2020 11:36 PM PST

I am pretty new when it comes to IT, but I am trying.

The question is - According to what data does DHCP assign an IP address to your PC? Is it according to some components inside?

And if so, when I upgrade my PC over time, how does my IPv4 stay the same when there are not the same components inside?

submitted by /u/yolopes_nocz
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How do you differentiate essential fatty acid from non-essential fatty acid?

Posted: 20 Feb 2020 10:26 PM PST

Since both of them can either have a saturated carbon, or unsaturated carbon, I couldn't quite grasp how they differ.

How can one distinguish it from the other?

Edit: i forgot to mention, how do they differ "structurally"?

submitted by /u/Zephynx4476
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Why are there prominent HZE ions in cosmic rays, instead of a high variation?

Posted: 20 Feb 2020 09:18 PM PST

I am doing some reading and came across ultra-high energy cosmic rays, including HZE ions. According to Wikipedia (great source, I know) carbon, oxygen, magnesium, silicon, and iron are prominent HZE ions. But why those specific nuclei, that seem almost random?

submitted by /u/Eluisys
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