Featherstone, J. D. B. (2008). "Dental caries: A dynamic disease process". Australian Dental Journal. 53 (3): 286–291. doi:10.1111/j.1834-7819.2008.00064.x

https://onlinelibrary.wiley.com/doi/10.1111/j.1834-7819.2008.00064.x

I'm also a dentist, and did my training at a dental school where the research behind remineralisation and the dental caries process was heavily promoted and taught

I use those big cubes and like them precisely because they have less surface area than a handful of ice the same size and won't cool it as fast. You want the whiskey cooled, but not ice cold. You can always speed up the cooling if you want by swirling and increasing the convection rate.

[removed]

Almost always yes, but there can be exceptions.

For a bright source the level of detail you can see using an optical instrument is limited by whichever is "worse" of two factors. Firstly, the inherent resolution of the instrument because light is a wave and it diffracts around edges. A perfect point light source produces a blurred image at the focal plane, known as the Airy disc. For a telescope the resolution depends on the diameter of the main mirror/lens (the aperture) and the wavelength. (I don't know for microscopes).

Secondly, the visual acuity of the eye multiplied by the magnification in use.

In general when using "low" magnification for a given instrument the second factor is the limit, while with "high" or "too much" magnification the first factor becomes the limit.

2x is low magnification for almost anything, but if you had a telescope with an exceptionally small objective lens it could be limited by diffraction.

thank you very much i always thought of water as a pot of rice, of fixed, unchangable, determined molecules. so "water" is not just a mix of water, but it's own dynamic system comparable to how in metal electrons just fly around, just that not the electrons but also entire molecules of H and O just swap back and forth.

thank you so much for taking the time to explain it to me!

I guess if you covered the coast in tons of wind turbines, you could capture the energy just fine. The issue with energy sources like wind and solar is storage. These sources are not consistent, so storage devices are needed to contain energy so we can use electricity when the wind isn't blowing. We do not have good enough battery technology to compensate for this, and it would be prohibitively expensive.

Bob Lazar is a nutcase, and gravity generators aren't possible. It's just not how gravity works.

[removed]

I think you get the point but the movment of ions IS a force, meaning you can calculate it or (better example in biochemistry ) translates it in another force. this way, the transfert of H+ ions throught the mitochondria membrane is converted in heat, and mostly in the regeneration of ADP to ATP. another example should be the transfert of seve in tree from roots to leaf : the osmotic pressure is able to elevate a volume of water versus the gravity force of the weight of the water. keep in mind if zero force is involved, any system should be considered at equilibrium. equilibrium in life means death.

While I'm at it, might as well go deeper into the science and mechanism of how fluoride works in other ways.

When enamel dissolves, the calcium and phosphate are released into the solution around it. In a highly acidic environment, the Ca and PO4 do not readily form a solid structure (i.e. crystals). With fluoride, the formation of crystals happens more readily and the required pH to inhibit crystallization is much lower. Hence, fluoride helps encourage remineralisation of teeth after an acid attack.

Calcium and phosphate also exists in other forms such as mono-, di-, tri- and octocalcium phosphates. These are low-energy crystalline forms, less ordered and more prone to dissolution than hydroxyapatite. Calcium and phosphate tend to organise themselves into these low-energy forms, e.g. tartar on teeth. With fluoride, the ions actually tend to want to form fluorapatite instead of the weaker, low-energy forms

[removed]

Any binocular worth spending money on will give you a magnification of a factor 2 even with 20/10 vision, so better vision without binoculars transfers to better vision with one. With the caveat that using binoculars and glasses together can be tricky, but that's not specific to the ideal vision strength. A really cheap binocular might be worse.

'stronger' = more resistant to acid attack.

Teeth are made of a form of hydroxyapatite, mostly composed of calcium and phosphate (with some other traces of magnesium, carbonate etc). Enamel is 99% mineral, with a tiny bit of water and proteins. Acids from bacterial fermentation of sugars are what dissolves tooth enamel and causes tooth decay. The addition of fluoride turns the mineral into fluorapatite, which is much less soluble by acids. It doesn't make the teeth stronger in the physical sense like being able to withstand stronger chewing.

The fluorapatite enamel can still dissolve if there's constant acid attack, just less readily than unfluoridated tooth apatite. It's not invincible

I don't know as far as daylight goes, but in low light conditions a big part of the advantage of optics (even low magnification) is just collecting MORE light. A 5" telescope will gather a lot more photons than a 3" telescope (or a 1/4" eyeball pupil) even if they're the same magnification.

First, the average thickness of the cortex is more like 2.5 mm

Second, we aren't explicitly measuring ig each voxel is cortex or non-cortex with a binary 1-0 mask. The way that cortical thickness is measured is by looking at the signal intensity to each voxel, and an algorithm estimates the barrier between gray matter and white matter, or gray matter and the dura matter on the outside of the brain. It does so by considering the intensity of this voxel relative to deeper voxels that are clearly white matter, or voxels that appear more likely to be gray matter.

So let's pretend a voxel that a cortical voxel would have an intensity value of one. Let's say that a voxel of white matter has an intensity value of 0.5

If you encountered a voxel that was roughly 0.75, you could infer that roughly half of that voxel was in the cortex.

Free surfer runs the algorithm across the entire image and attempts to estimate the inner and outer barrier using this approach. I simplified it of course, it's not really saying 0.75 and half the voxel, the modeling is more complicated than that and frankly I don't understand it more than that.

But, the long story short is that by looking at signal intensity the different voxels we can build an estimate a model of where the ribbon of the cortex is relative to the edges of that voxel.

Interestingly these estimates are very reliable across MRI scans. If I scan you today and scan you next week, most cortical thickness measurements will be very stable

Then once you have the outer ribbon, representing the outside of the cortex, and the inner ribbon representing the inside, you can place a perpendicular vertex in that section and estimate the thickness of the cortex

The process isn't perfect, and errors are not uncommon. Particularly in lower quality MRI scans.

I hope that help explains it

Yes, thank you for you answer, but it seems to me that the problem here is rather to know if the "contribution" of the concentration gradient is caused by a "force", which would be an "osmotic force".

When the pH on the tooth surface becomes acidic, the enamel starts to demineralize so your tooth is more susceptible to bacteria. Fluoride in the mouth enhances remineralization of the enamel using the calcium and phosphate ions in the saliva. There's different sources of oral fluoride. Stannous fluoride in certain toothpaste gels sticks to the enamel surface. It's supposed to be stop bacterial proliferation > biofilm > plaque and kill bacteria. Sodium fluoride works better in a toothpaste because it is more abrasive.

In Europe there's biomimetic hydroxyapatite to create a new layer around teeth to harden the existing enamel so fluoride or lack thereof isn't as big a deal.

[removed]

Teeth enamel is permeable, you can see this by people who smoke having yellowed teeth, people who drink sugary drinks having yellowed teeth etc

Visually it's quite amazing how rough the enamel is upon magnification!

Fluoride, being a mineral suspended in water or, in this case, toothpaste, can go into the small gaps and divets in the enamel. It bonds into the little divets and acts like a shield against bacteria and other gunk.

If an MRI voxel is 1 cubic mm, that just means that the MRI can’t resolve anything smaller than that. If a significant proportion of that 1 cubic mm is made up of white matter, no matter the thickness of the white matter, you’ll see evidence of the white matter in that voxel.

An analogy would be a pixelated image. If you look at a pixelated image of somebody wearing a shirt with some symbol on it that has a lot of thin lines, but is a distinctly different color than the rest of the shirt, you will still see a contribution from that colored symbol in a pixelated image of the shirt.

[removed]

[removed]

[removed]

[removed]

[removed]