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  #2121  
Old 28.02.2021, 18:50
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Re: Ask a Scientist

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…did you read all article you quoted?...
…see below I meant something else...

Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of 277 cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning.

Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart. Other consequences include premature aging and problems with the immune system. Another potential problem centres on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink. Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types. As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age. Dolly died when she was six years old, about half the average sheep's 12-year lifespan.
You just posted a short excerpt
Read the whole article.
You even left out the last paragraph in your excerpt
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Two years later, researchers in Japan cloned eight calves from a single cow, but only four survived.

Besides cattle and sheep, other mammals that have been cloned from somatic cells include: cat, deer, dog, horse, mule, ox, rabbit and rat. In addition, a rhesus monkey has been cloned by embryo splitting.
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  #2122  
Old 22.03.2021, 19:01
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Re: Ask a Scientist

Here's one for the geologists.

Caves frequently form in limestone rock caused by water percolating through the rock and dissolving away minute quantities of the rock.

Over millions of years, sufficient material is removed that caves form. Sometimes huge caves. Whole networks of caves.

And then?

Well, stalagtites and stalagmites form inside the cave. These are formed by the same water that has been trickling down through the same layers above and thus that actually formed the caves in the first place. But rather than continue to remove limestone, they actually reverse the process and deposit some and form stalagmites and stalagtites. Every droplet of water adding a minute amount of material.

I guess that if you wait several more millions of years these stalagmites and stalagtites will meet in the middle to form pillars, and the pillars will grow in girth until all available space is filled and effectively the cave is gone and the original condition is restored,

So why does exactly the same process that creates the cave then end up filling it in again?

A shift in temperature maybe? Or in the acidity of the water?

Does this mean there are certain periods in the earth's history that are favourable to the formation of caves, and certain periods that are favourable to them filling back in?
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  #2123  
Old 22.03.2021, 19:40
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Re: Ask a Scientist

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Caves frequently form in limestone rock caused by water percolating through the rock and dissolving away minute quantities of the rock. Over millions of years, sufficient material is removed that caves form. Sometimes huge caves. Whole networks of caves.
Sometimes it's faster than millions of years. Sedimentary rock less a million years old can have human size caves See Florida and Yucatan Peninsulas coastal caves.

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Well, stalagtites and stalagmites form inside the cave. These are formed by the same water that has been trickling down through the same layers above and thus that actually formed the caves in the first place. But rather than continue to remove limestone, they actually reverse the process and deposit some and form stalagmites and stalagtites. Every droplet of water adding a minute amount of material.

I guess that if you wait several more millions of years these stalagmites and stalagtites will meet in the middle to form pillars, and the pillars will grow in girth until all available space is filled and effectively the cave is gone and the original condition is restored.

So why does exactly the same process that creates the cave then end up filling it in again? A shift in temperature maybe? Or in the acidity of the water?Does this mean there are certain periods in the earth's history that are favourable to the formation of caves, and certain periods that are favourable to them filling back in?
Now comes the complicate part. The formation of caves need flow of water and some acidity to dissolve limestone.

Let's tackle the water flow first. The source of water can be rainfall and climate changes a lot along time. So, a decrease in rainfall may be the trigger to switch from growth (dissolution) to fill (stalagmites). An increase in rainfall the opposite.

Back to coastal caves, the sea level has increased 110-120m since the last glacial maximum only 22K years ago. The mix of fresh (rainfall) water and seawater creates some reactivity. So, caves at the mixing zone between fresh and saline water are growing, while caves above water level may be filled with mineral deposits, while caves deep in the saline zone are frozen for the moment. Depending on sea level, growth, fill and nothing is happening at the same time in a coastal cave system.

Back to higher terrains, the terrain surface changes a lot. Erosion is powerful over time. Some caves may be created by a river infiltrating its river bed and growing to the sides, then the river erodes the river bed and those caves are now above water level and start to flll. Now think about continents and islands going up and down due to tectonics. Caves underwater are pushed up above water level and now being filled by deposits.

Not a rule of thumb, but generally caves grow while filled or near partially filled with flowing water. And generally filled with mineral deposits when filled with air. So, more than changes in the Earth, is a change in the conditions of the little limestone block where caves develop (relative to Earth's size).

Now the acidity part. Usually the main source of acidity is CO2. So, bacteria in soil and water can generate acidity. If climate changes and a lush jungle is replaced by a desert, the acidity source is gone and a cave may switch from growth to fill up.

Finally rock mechanics. Caves are cavities that may collapse due to the weight of rock and sediments above. Tectonics may sink a limestone block and sediments start to accumulate above. Eventually the pressure is too high and the cavity collapses.

So, a lot of physical processes competing with each other. Pushing in opposite directions the whole time.

All this read like useless science until people realizes oil/gas are found in paleokarst, and we humans produce a lot of harmful trash that should be stored somewhere safely. That somewhere needs to be safe from erosion and cave development over thousands of years

PS. if you want to read more the keyword is speleogenesis.
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  #2124  
Old 22.03.2021, 20:48
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Re: Ask a Scientist

Thanks Axa for that detailed explanation.

Does a cave having some opening to the outside world have an effect? Caves are obviously discovered by people finding a way in. That way in also leads to an exchange of air and maybe makes it less likely the air in the cave will be saturated. Thus water may evaporate more freely favouring the deposit of carbonates. Do stalagmites grow more slowly in a cave with no opening to the outside?
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  #2125  
Old 22.03.2021, 22:05
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Re: Ask a Scientist

With less evaporation, less mineral deposition. Albeit, don't know the kinetics of the system. Maybe if the stalactites grow slower, the stalagmites grow faster. No idea, never read or worked on that.
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  #2126  
Old 23.03.2021, 01:41
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Re: Ask a Scientist

That was a comprehensive and pretty convincing answer from Axa. All I have to add is that it's stalagmite and stalactite; stalagmites push up from the ground with all their might, while stalactites hold on tight to the ceiling.

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Maybe if the stalactites grow slower, the stalagmites grow faster.
As stalactites feed stalagmites (literally, one drip-feeds the other), wouldn't the rates of growth of stalactites and stalagmites be positively correlated?
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  #2127  
Old 23.03.2021, 09:53
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Re: Ask a Scientist

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That was a comprehensive and pretty convincing answer from Axa. All I have to add is that it's stalagmite and stalactite; stalagmites push up from the ground with all their might, while stalactites hold on tight to the ceiling.


As stalactites feed stalagmites (literally, one drip-feeds the other), wouldn't the rates of growth of stalactites and stalagmites be positively correlated?
We had a shorter version: "When the mites go up, the tights go down." .
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  #2128  
Old 23.03.2021, 10:08
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Re: Ask a Scientist

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That was a comprehensive and pretty convincing answer from Axa. All I have to add is that it's stalagmite and stalactite; stalagmites push up from the ground with all their might, while stalactites hold on tight to the ceiling.


As stalactites feed stalagmites (literally, one drip-feeds the other), wouldn't the rates of growth of stalactites and stalagmites be positively correlated?
I think so. But water flows nicely in a stalactite, while water drops fall and there's some splash in stalagmites. Due to this stalactites are pointy while stalagmites have a rounder top.

Sounds like an interesting numerical simulation to do since the physics are known. Different water flow rates and see what happens
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  #2129  
Old 23.03.2021, 10:21
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Re: Ask a Scientist

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I think so. But water flows nicely in a stalactite, while water drops fall and there's some splash in stalagmites. Due to this stalactites are pointy while stalagmites have a rounder top.

Sounds like an interesting numerical simulation to do since the physics are known. Different water flow rates and see what happens
Possibly the chemical composition of the water varies so has an effect. One could imagine water entering the system with a low limestone content could transfer material from the stalactite to the stalagmite. Unlikely in the real world I assume.
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Old 23.03.2021, 11:37
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Re: Ask a Scientist

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Possibly the chemical composition of the water varies so has an effect. One could imagine water entering the system with a low limestone content could transfer material from the stalactite to the stalagmite. Unlikely in the real world I assume.
Thanks for the Tuesday morning rabbit hole, guys!

Google Scholar shows lots of existing literature. Dreybrodt's theory from the 80's covers the calcite solution side of the story, whereas Rabani (in Nature in 2003) has covered the assembly of calcite nanoparticles into stalagmites and stalagtites.

Lots of other fascinating stuff on offer about the effect of seasonal variation and modelling the variation of isotopes in stalagtites to determine climate, etc.
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Old 23.03.2021, 15:28
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Re: Ask a Scientist

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Possibly the chemical composition of the water varies so has an effect. One could imagine water entering the system with a low limestone content could transfer material from the stalactite to the stalagmite. Unlikely in the real world I assume.
Generally, dissolution reaction kinetics are not that fast to reach equilibrium (saturated with minerals) in the minutes it takes a drop to fall from the ceiling to the floor. But.....there might be a case where it happens, but I assume not that frequent.

@FrankZappa, I have Dreybrodt's book Processes of Speleogenesis, a modelling approach here in my desk. Need it for work
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  #2132  
Old 23.03.2021, 15:37
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Re: Ask a Scientist

From my recollections of the various caves I’ve visited , I would agree that stalagmites tend to be shorter and fatter than stalactites . But I would say there are different types of shape . Whereas stalactites are almost invariably pointy, you get stalacmites with pointy ends , but also rounded ones and crater shaped ends and dribbly looking ones that look like candles . Maybe this depends on the micro conditions , such as size of droplet and speed on impact .
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Old 23.03.2021, 16:22
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Re: Ask a Scientist

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From my recollections of the various caves I’ve visited , I would agree that stalagmites tend to be shorter and fatter than stalactites . But I would say there are different types of shape.
Some of them look like a can of tuna.

Spelunking is great, I think.

The salt mines in Valorbe are cool. Ton of geological wonders.
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Old 23.03.2021, 16:38
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Re: Ask a Scientist

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From my recollections of the various caves I’ve visited , I would agree that stalagmites tend to be shorter and fatter than stalactites . But I would say there are different types of shape . Whereas stalactites are almost invariably pointy, you get stalacmites with pointy ends , but also rounded ones and crater shaped ends and dribbly looking ones that look like candles . Maybe this depends on the micro conditions , such as size of droplet and speed on impact .
People looking into the issue say pointy stalagmites is because they're close to fuse with stalagmite. Round stalagmites is just water drops splashing after falling several meters. So, good intuition
https://www.damtp.cam.ac.uk/user/gol...ctite_long.pdf

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the upper ends of stalagmites are decidedly not pointed like the tips of stalactites, for the fluid drops that impact it do so from such a height as to cause a significant splash, although, when a stalagmite grows close to the stalactite above, it does tend to adopt a mirror-image form, the more so the closer the two are to fusing.
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Old 24.03.2021, 10:11
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Re: Ask a Scientist

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People looking into the issue say pointy stalagmites is because they're close to fuse with stalagmite. Round stalagmites is just water drops splashing after falling several meters. So, good intuition
https://www.damtp.cam.ac.uk/user/gol...ctite_long.pdf
Cracking article! I worried about the dissolution kinetics of slightly soluble molecules in my former job, but for different reasons - the clarity of flavored Vodka, for instance .
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Old 24.03.2021, 10:51
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Re: Ask a Scientist

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Cracking article! I worried about the dissolution kinetics of slightly soluble molecules in my former job, but for different reasons - the clarity of flavored Vodka, for instance .
Woooooo, what's the reaction surface? Or maybe I don't want to know what has been in contact with my vodka. Ignorance is bliss
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Old 24.03.2021, 12:55
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Re: Ask a Scientist

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Woooooo, what's the reaction surface? Or maybe I don't want to know what has been in contact with my vodka. Ignorance is bliss
Good question! But no nasty revelations in this story. The flavour is added as a coarse emulsifier-free emulsion, so you need the initial surface-to-volume average radius. Then as dissolution occurs, the drops get smaller (and even disappear) and the saturation gets higher, so the dissolution rate slows. To quantify the problem, I ended up with a nasty integral that my son's maths teacher solved for me. I gave her a good bottle of red wine in return.
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Old 24.03.2021, 13:07
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Re: Ask a Scientist

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Good question! But no nasty revelations in this story. The flavour is added as a coarse emulsifier-free emulsion, so you need the initial surface-to-volume average radius. Then as dissolution occurs, the drops get smaller (and even disappear) and the saturation gets higher, so the dissolution rate slows. To quantify the problem, I ended up with a nasty integral that my son's maths teacher solved for me. I gave her a good bottle of red wine in return.
So...no solid surface, but the surface of liquid bubbles? The surface area gets smaller along time? It seems you reached to an analytical solution. You're lucky, lots of solutions are only possible to find numerically
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Old 08.04.2021, 21:41
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Re: Coronavirus

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You really don't have to make a point by sharing your family vaccination history, Tony. That beats a bit that argument of vax passport and individual's health data protection. In my view, of course.

I also do not think that shaming people either into vaxing (by comparing again wrongly flu jabs and CV vax - marton, not the same thing) is going to work. Or feeling that you have to overshare your personal health details. Just because some people push here and compare incomparable diseases, vax programs and risks.

I bet my shoes on all of us being vaxed by Christmas. Then we should have EF Christmas drinks.
Happy to be of service.

Trying to take my mind off the pandemic I have been reading a dumbed-down scientific article on the muons — elementary particles similar to electrons - which are now believed by some to travel around surrounded by a cloud of smaller particles that randomly flick into and out of existence.
It is becoming clearer why the brainier folks from my youth who went into particle physics became regular visitors to what used to be known as mental hospitals.

Hope by next Christmas there will masks with integrated drinking straws.
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Old 08.04.2021, 22:05
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Re: Coronavirus

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Happy to be of service.

Trying to take my mind off the pandemic I have been reading a dumbed-down scientific article on the muons — elementary particles similar to electrons - which are now believed by some to travel around surrounded by a cloud of smaller particles that randomly flick into and out of existence.
It is becoming clearer why the brainier folks from my youth who went into particle physics became regular visitors to what used to be known as mental hospitals.
Well. https://www.space.com/7193-death-rays-space-bad.html

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At sea level, the majority of cosmic ray secondaries are highly penetrating muons. About 10,000 muons pass through our bodies every minute. Some of these muons will ionize molecules as they go through our flesh, occasionally leading to genetic mutations that may be harmful.27 Aug 2009
That's twelve years ago. How are you doing? Do your buddies think about this too much?
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Hope by next Christmas there will masks with integrated drinking straws.
Of course.

Thanks for the muons. I will try to sleep now. And not try to think why something that lives for 2.2 microsec makes a difference.
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