Recent comments in /f/askscience

Pertho t1_j828dke wrote

Reply to comment by wonkozsane042 in Can the Radiation from a Sample of Depleted Uranium Sterilize? by Natolx

How long would someone need to be cryogenically frozen for cosmic radiation to be a significant threat? If it’s a couple lifetimes then I could still see people taking that gamble (not something I’m into myself, just enjoy learning about this). Could treatment before freezing with something like iodine or anti-radiant treatment reduce that danger?

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dieEhrevonGrayskull t1_j824pi5 wrote

Reply to what is quantum tunneling out simply? by Piggy468

Quantum tunneling is a consequence of the probabilistic nature of the wave function. In classical mechanics, we can use energy to understand how an object will move. For example, a skateboarder in a half pipe will have kinetic energy, and potential energy from gravity. The skateboarder starts with a fixed amount of energy which is that from gravity, measured at the top of the curve. The curved walls of the half pipe then, are a potential barrier for the skateboarder because momentum will take him to the other edge, and no further (under ideal conditions). This is because the energy level of the system is lower than or equal to the energy of the potential barrier. Therefore, motion is only defined within the potential valley that is the half pipe. Of course, if the energy level were to be increased, say by pushing, the skateboarder can be carried past the energy barrier and motion will then be defined outside of it.

Quantum systems behave differently from this. If you had a scattering photon with energy level E_1, and it was moving towards a potential barrier with energy level E_2 which is higher than E_1, it turns out that the quantum wave function near the barrier will actually extend through it, with exponential falloff. Of course, the quantum wave function is a probability distribution curve of various observable quantities, like position. That is to say that a quantum particle in motion may have its position defined on the other side of a potential barrier, despite the fact that its energy is too low to overcome it. The probabilistic nature of the wave function means sometimes a particle will reflect, and sometimes it will transmit. This is quantum tunneling.

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Natolx OP t1_j822m5l wrote

Reply to comment by [deleted] in Can the Radiation from a Sample of Depleted Uranium Sterilize? by Natolx

> Regardless, even large quantities of purified GFP need to be stored at -20C in the dark to remain fluorescent long-term, and raising that temperature to even 4C will dramatically shorten storage time. The rate of photobleaching and degradation at RT isn't going to be affected by the concentration of the protein, it just might take slightly longer to see a difference by eye. This is still a very temporary piece of jewelry, so sterilizing it at this point isn't going to extend its lifespan by much.

I'm sorry but this is simply incorrect. Photobleaching is by definition caused by light being absorbed. A high concentration of protein on the "shell" of the solution is going to "protect' all of the protein on the inside of that shell from from excitatory light. Again, I don't think you can conceptualize how much protein this is compared to "normal" amounts seen in laboratory experiments.

If I left it out in the sun, sure, it's going to bleach for in a week, but the photobleaching power of incidental lighting is just not enough to photobleach this amount of fluorescent protein any time soon.

I have tubes of nonsterile fluorescent protein that have been kept at room temperature for a year now that are cloudy (with contamination) but still fluorescent. Only my sample kept in the sun lost fluorescence.

Additional Note: this is mNeon, not GFP so it is definitely a "better" generation of fluorescent protein. But even GFP at this concentration is going to resist photobleaching for an absurdly long time.

>The "absorbtion" you see with your laser beam probably has more to do with scattering of the laser rather than pure absorption. Any high-density protein solution will behave similarly.

There is no blue light being "scattered" (I have used a blue filter I scavenged to check) , it is not scattering. You can also clearly see the beam go in, stay a beam but just fade into nothing.

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