Recent comments in /f/askscience

cjf2019 t1_j99548b wrote

Reply to comment by [deleted] in When something is bent (a metal ruler for example) and returns to its original shape, what is happening on the molecular level? Where is the information of the original shape stored and what forces do the unbending? by JewNugget2525

I think you might be confusing fatigue failure and strain hardening which are different concepts. Strain hardening occurs when plastically deforming a metal and generating dislocations which are a type of defect in the crystal structure. Dislocations require the atomic bonds joining the atoms around the defect to stretch in different ways, creating areas of compression and tensile strain. The strain fields between different dislocations tend to repel each other, so as more dislocations are introduced to the material as it is deformed, they have a harder and harder time moving around due to the repulsions which in effect strengthens the material.

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auraseer t1_j991ord wrote

Reply to comment by zachtheperson in When something is bent (a metal ruler for example) and returns to its original shape, what is happening on the molecular level? Where is the information of the original shape stored and what forces do the unbending? by JewNugget2525

If you bend it too far, you have passed the elastic limit. It is no longer undergoing elastic deformation, but instead, plastic deformation.

In that mode, you are applying enough force to overcome the atoms' tendency to stay put. Some of the atoms get moved out of place, and rearrange into new places in the crystal structure. They settle into places that are lower energy in the object's bent shape.

Once the crystal structure is deformed, and new atomic bonds form, those new bonds replace the old ones. The object's new shape is the lowest energy configuration, and that is now the shape it wants to stay in.

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deltadeep t1_j991i8s wrote

Reply to comment by Glasnerven in When something is bent (a metal ruler for example) and returns to its original shape, what is happening on the molecular level? Where is the information of the original shape stored and what forces do the unbending? by JewNugget2525

Yes and as the energy of the deformation causes the ruler to return to its original shape, the momentum created in the ruler's motion causes it to overshoot to the other side, and then it's bent too far the other way, and oscillation occurs.

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zachtheperson t1_j9906oo wrote

Reply to comment by Glasnerven in When something is bent (a metal ruler for example) and returns to its original shape, what is happening on the molecular level? Where is the information of the original shape stored and what forces do the unbending? by JewNugget2525

What's the difference then with something like a metal bar, where if you bend it far enough it does actually stay bent, but if you bend it less it goes back?

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Stats_Think t1_j98sdy6 wrote

Reply to Just with a sample of someone's DNA, can a lab tell the approximate age of a person? by Blakut

DNA replicates with a very high amount of fidelity (base pairs rarely get mis-matched), but it's possible to measure these mutations over time, if you had a reference sample from "x" number of years ago. Rates of mutations (and to be clear, by "mutations", I'm simply referring to the DNA polymerase making a "mistake" and the mis-matched repair not catching all of them) could probably be tracked and an age can be estimated. Is there a validated way to do this to account for all variations in someone's DNA (such as due to diet, environment, stress, etc.)? Good question!

Telomeres (ends of chromosomes) are also known to shrink over time, and this is also hard to answer in terms of "measuring" telomere ends to estimate age due to many confounding factors, but I'm sure someone is working on it.

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grumble11 t1_j98sdew wrote

Reply to comment by Welpe in Why does the thyroid use iodine ? by geistererscheinung

Iodine deficiency of some kind isn’t all that rare actually - even in the first world. Severe iodine deficiency used to be very common in the Midwest, with supplementation in salt increasing IQ in the region by double digits. 70% of UK people tested in a 2011 study were iodine deficient. It remains one of the most common micronutrient deficiencies worldwide.

https://en.m.wikipedia.org/wiki/Iodine_deficiency

I kind of worry about it coming back, as restaurant, fast food and processed food is commonly not using iodized salt, and at home ‘sea salt’ that hasn’t been iodized is trendy. Dairy is another important source of iodine but processing facility changes have reduced milk content. This opens the door to more regional or sub population deficiency

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