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Old 28th January 2020, 09:14 AM   #1
pgimeno
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Brittle liquids

Asphalt is a liquid, see e.g. https://en.wikipedia.org/wiki/Asphalt or https://en.wikipedia.org/wiki/Pitch_drop_experiment

Asphalt is also brittle, see e.g. this image:



My question is, what is required for a liquid to develop cracks when subject to a shock? Are all liquids subject to this?

I realize that defining "crack" in physical terms is a bit complicated. I also realize that even if they are formed, in low viscosity liquids the cracks will immediately "fuse" with the rest of the liquid. I was just puzzled about this. Is there, like a viscosity threshold for a liquid to become brittle?
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Old 28th January 2020, 09:26 AM   #2
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Water is a liquid but it will also crack when less then 32F/0C. I expect asphalt is similar.
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Old 28th January 2020, 09:35 AM   #3
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I made some caramel once and cut it into little pieces and put it in a tin, the next day I had one big piece of caramel.
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Old 28th January 2020, 09:39 AM   #4
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Well, what I've been sold is that asphalt is liquid at ambient room temperature, not solid, while ice is solid, not liquid.

Last edited by pgimeno; 28th January 2020 at 10:50 AM. Reason: ambient temp -> room temp
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Old 28th January 2020, 09:44 AM   #5
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This behavior is described by the concept of “glass transition”.

Quote:
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased.[1] An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification.
https://en.wikipedia.org/wiki/Glass_...on?wprov=sfti1

ETA: So this behavior is characterized as a function of temperature rather than the resulting viscosity change.
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Old 28th January 2020, 10:04 AM   #6
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Originally Posted by ferd burfle View Post
This behavior is described by the concept of “glass transition”.



https://en.wikipedia.org/wiki/Glass_...on?wprov=sfti1

ETA: So this behavior is characterized as a function of temperature rather than the resulting viscosity change.
Ahh, thanks! That makes it clear.

What I'm still puzzled about is why some sites characterize the melting point of bitumen as being around 115°C or 200°C, if it's liquid at room temperature. I was unable to find a value for the melting point of tar, pitch, bitumen or asphalt that was under 20°C (a reasonable value for "room temperature"). The closest one cited "Melting point: 30-180°C" (source) the lowest of which is a reasonable room temperature for a very hot summer day.

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Old 28th January 2020, 10:20 AM   #7
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Originally Posted by pgimeno View Post
Ahh, thanks! That makes it clear.

What I'm still puzzled about is why some sites characterize the melting point of bitumen as being around 115°C or 200°C, if it's liquid at room temperature. I was unable to find a value for the melting point of tar, pitch, bitumen or asphalt that was under 20°C (a reasonable value for "room temperature"). The closest one cited "Melting point: 30-180°C" (source) the lowest of which is a reasonable room temperature for a very hot summer day.

I'm a bit out of my depth here, but I think the behavior you see in old window glass gives some insight. You've seen how the glass in old windows has ripples in the lower part of the pane. This is because the glass flows downward very slowly over many years, behaving like an extremely viscous liquid. I'm not certain but I believe bitumen would behave similarly.
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Old 28th January 2020, 10:30 AM   #8
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Originally Posted by ferd burfle View Post
I'm a bit out of my depth here, but I think the behavior you see in old window glass gives some insight. You've seen how the glass in old windows has ripples in the lower part of the pane. This is because the glass flows downward very slowly over many years, behaving like an extremely viscous liquid.
NO! NO! NO! NO! NO!

Glass does not show appreciable flow rates over time scales comparable with human history, or indeed even over cosmological timescales; this is a long-debunked canard. There are ancient Roman and Egyglass artefacts that show no measurable deformation. Google "glass flow" and you'll find lots of articles explaining all this.

Dave

ETA: Sorry, I used to work in glass science and this is a bit of a trigger for me.
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Old 28th January 2020, 10:51 AM   #9
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Originally Posted by Dave Rogers View Post
NO! NO! NO! NO! NO!

Glass does not show appreciable flow rates over time scales comparable with human history, or indeed even over cosmological timescales; this is a long-debunked canard. There are ancient Roman and Egyglass artefacts that show no measurable deformation. Google "glass flow" and you'll find lots of articles explaining all this.

Dave

ETA: Sorry, I used to work in glass science and this is a bit of a trigger for me.

It's all good, thanks for the correction. Is it correct that the rippled appearance is the result of specific aspects (problems) in the glass manufacturing process?
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Old 28th January 2020, 10:51 AM   #10
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Originally Posted by ahhell View Post
Water is a liquid but it will also crack when less then 32F/0C. I expect asphalt is similar.
Water is liquid, ice is not (ice is a solid). When ice melts the transition is pretty clear - it is water or ice, but does not have any intermediate phase where it gets gooey and soft.

Glass, asphalt, and other similar sorts of "liquids" just get gradually softer as they heat, without the distinct phase change that water goes through. Watch a glass blower, they will sometimes accidentally break glass that is mostly molten if they move too fast - it is gooey, but there are limits to how gooey it is. Whereas with liquid water, you can't break it no matter how fast you move it.

Not sure how metals fit into that concept.
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Old 28th January 2020, 12:03 PM   #11
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Originally Posted by crescent View Post
Water is liquid, ice is not (ice is a solid). When ice melts the transition is pretty clear - it is water or ice, but does not have any intermediate phase where it gets gooey and soft.

Glass, asphalt, and other similar sorts of "liquids" just get gradually softer as they heat, without the distinct phase change that water goes through. Watch a glass blower, they will sometimes accidentally break glass that is mostly molten if they move too fast - it is gooey, but there are limits to how gooey it is. Whereas with liquid water, you can't break it no matter how fast you move it.

Not sure how metals fit into that concept.
Water turning into ice typically produces a crystal structure with the molecules in a defined array. Asphalt does not form crystals or a defined array, which why it is considered a glass-like structure as it cools.

BTW adding glycerol to water allows it to form glass-like structures on cooling; in biology this is a useful way of storing certain enzymes in freezers by avoiding the disruption to the enzyme structure that can occur if crystals were permitted to form.

I think many metals form crystal structures but others here must know a lot more than I do.
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Old 28th January 2020, 12:05 PM   #12
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Old 28th January 2020, 12:47 PM   #13
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somewhat relevant is the world's longest continuously running laboratory experiment
https://livestream.com/accounts/4931571/events/5369913
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Old 28th January 2020, 12:59 PM   #14
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Originally Posted by Planigale View Post
somewhat relevant is the world's longest continuously running laboratory experiment
https://livestream.com/accounts/4931571/events/5369913

That's like watching paint dry without the paint. The Casio analog clock with genuine imitation radium numbers is a nice touch.
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Old 28th January 2020, 04:12 PM   #15
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Originally Posted by ferd burfle View Post
It's all good, thanks for the correction. Is it correct that the rippled appearance is the result of specific aspects (problems) in the glass manufacturing process?
Yes. It was difficult to make uniform thickness glass (plate glass) in large size until the float-glass process (glass on a bed of molten metal).

The artifacts of glass production are found in old windows at the place where the window maker put them. For instance, thicker end to the bottom (as it was thought to be more stable), or ripples where people are less likely to watch through, or for artistic appearance.
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Old 28th January 2020, 06:37 PM   #16
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Originally Posted by elgarak View Post
Yes. It was difficult to make uniform thickness glass (plate glass) in large size until the float-glass process (glass on a bed of molten metal).

The artifacts of glass production are found in old windows at the place where the window maker put them. For instance, thicker end to the bottom (as it was thought to be more stable), or ripples where people are less likely to watch through, or for artistic appearance.

Ah, thanks so much to you, and to Dave.
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Old 28th January 2020, 11:25 PM   #17
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A fluid, although it flows, will resist deformation. This is it's viscosity and it generally increases with a drop in temperature.
Deforming a fluid faster than it can flow to accommodate the deformation and with a force strong enough to overcome its shear strength, breaks it.
Fluid water, not ice, will crack just the same as pitch if deformed fast enough.


How to Fracture a Fluid
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Old 29th January 2020, 01:18 AM   #18
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I suppose the best known example is Potty Putty (UK) Silly Putty (US),
https://en.wikipedia.org/wiki/Silly_Putty
More generally this is a property of non-newtonian fluids, particularly thixotropic fluids.
https://en.wikipedia.org/wiki/Non-Newtonian_fluid
When rapidly stressed they cannot flow so shatter. For some fluids (see video above) flow rate is very slow and they can shatter with a sharp blow as in the case of asphalt.
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Old 29th January 2020, 02:37 AM   #19
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Originally Posted by Planigale View Post
I suppose the best known example is Potty Putty (UK) Silly Putty (US),
https://en.wikipedia.org/wiki/Silly_Putty
More generally this is a property of non-newtonian fluids, particularly thixotropic fluids.
https://en.wikipedia.org/wiki/Non-Newtonian_fluid
When rapidly stressed they cannot flow so shatter. For some fluids (see video above) flow rate is very slow and they can shatter with a sharp blow as in the case of asphalt.
Another classic case being a mixture of cornflour (corn starch in the US, I believe) and water. Under low shear it behaves more or less as a viscous liquid, but if you hit it, thus producing a very high shear rate, it acts more like a solid. This is why it's possible to walk on custard, though it's not a good idea to stand still.

Dave
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Old 29th January 2020, 04:57 AM   #20
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Originally Posted by Cheetah View Post
A fluid, although it flows, will resist deformation. This is it's viscosity and it generally increases with a drop in temperature.
Deforming a fluid faster than it can flow to accommodate the deformation and with a force strong enough to overcome its shear strength, breaks it.
Fluid water, not ice, will crack just the same as pitch if deformed fast enough.


How to Fracture a Fluid
Awesome! That definitively settles the question for me. Thanks!
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Old 29th January 2020, 05:30 AM   #21
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Originally Posted by ferd burfle View Post
This behavior is described by the concept of “glass transition”.



https://en.wikipedia.org/wiki/Glass_...on?wprov=sfti1

ETA: So this behavior is characterized as a function of temperature rather than the resulting viscosity change.
Except that pitch isn't a glass but a liquid, glasses don't run down the over time like is done in the pitch drop experiment, see the glass funnel not changing over time?
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Old 29th January 2020, 05:32 AM   #22
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Originally Posted by ferd burfle View Post
I'm a bit out of my depth here, but I think the behavior you see in old window glass gives some insight. You've seen how the glass in old windows has ripples in the lower part of the pane. This is because the glass flows downward very slowly over many years, behaving like an extremely viscous liquid. I'm not certain but I believe bitumen would behave similarly.
That is a lie. Glass windows do not flow.

https://www.cmog.org/article/does-glass-flow

IN the context of melting pitch were it is still a liquid it is likely that there is a marked rapid change in viscosity at those temperatures not a glass transition though.
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Old 29th January 2020, 12:45 PM   #23
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Originally Posted by ponderingturtle View Post
That is a lie. Glass windows do not flow.

https://www.cmog.org/article/does-glass-flow

IN the context of melting pitch were it is still a liquid it is likely that there is a marked rapid change in viscosity at those temperatures not a glass transition though.

Not a lie; a misunderstanding on my part, thank you. And already corrected by Dave Rogers upthread.
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Old 29th January 2020, 03:35 PM   #24
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It is actually rather complicated. Glass is generally agreed to be an amorphous solid (it does not exhibit a clearly defined crystal structure) at room temperature; however some are willing to also consider it a type of supercooled liquid. Although it is true that the usual formulations of glass will not detectably flow even over geological time, other formulations of glass do detectably flow over days or weeks.


e.g.
https://edu.rsc.org/analysis/do-you-...008331.article

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Old 29th January 2020, 07:27 PM   #25
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Originally Posted by Giordano View Post
It is actually rather complicated. Glass is generally agreed to be an amorphous solid (it does not exhibit a clearly defined crystal structure) at room temperature; however some are willing to also consider it a type of supercooled liquid. Although it is true that the usual formulations of glass will not detectably flow even over geological time, other formulations of glass do detectably flow over days or weeks.


e.g.
https://edu.rsc.org/analysis/do-you-...008331.article
That was a fascinating read, thanks!

This was also enlightening: https://www.quora.com/What-is-the-me...point-of-glass which I guess applies to my question about the melting point of asphalt just the same.

And doing the search that Dave Rogers suggested, I found this: https://www.cmog.org/article/does-glass-flow which helped me complete my understanding of the subject: glass is a liquid, but given its estimated viscosity, it's unrealistic to try to measure any deformation based on that, not even in the age of the universe.
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Old 29th January 2020, 08:12 PM   #26
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Originally Posted by bobdroege7 View Post
I made some caramel once and cut it into little pieces and put it in a tin, the next day I had one big piece of caramel.
I had some Jim Beam Black Label once that cracked my voice when I drank it.
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Old 30th January 2020, 03:57 PM   #27
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Originally Posted by Dave Rogers View Post
NO! NO! NO! NO! NO!

Glass does not show appreciable flow rates over time scales comparable with human history, or indeed even over cosmological timescales; this is a long-debunked canard. There are ancient Roman and Egyglass artefacts that show no measurable deformation. Google "glass flow" and you'll find lots of articles explaining all this.

Dave

ETA: Sorry, I used to work in glass science and this is a bit of a trigger for me.
This was a persistent shibboleth in the Usenet Group alt.folklore.urban (from whence Snopes was born).

Ah. Memories.

The belief that it is true appears to come from the observation that the pieces of glass in old stained glass windows are often thicker at the bottom. The truth is that they were installed that way "because why not?"
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Old 31st January 2020, 05:51 AM   #28
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Gutted that glass is not, in fact, a liquid. I was told it was by my school teacher about 35 years ago and have, unfortunately, been spreading this myth ever since.
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Old 31st January 2020, 10:56 AM   #29
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Longer than that ago for me!
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Old 31st January 2020, 01:01 PM   #30
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Originally Posted by Gord_in_Toronto View Post
This was a persistent shibboleth in the Usenet Group alt.folklore.urban (from whence Snopes was born).

Ah. Memories.

The belief that it is true appears to come from the observation that the pieces of glass in old stained glass windows are often thicker at the bottom. The truth is that they were installed that way "because why not?"
Not "because why not" but because glaziers had realised that glass tended to break more easily if it was installed with the thickest part at the top.

This could be because it meant that the thinest part is where all the impacts are, or because the glass at the bottom is bearing the weight of the material above. Either way, it was a deliberate choice to install glass that way.
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Old 1st February 2020, 02:47 PM   #31
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Originally Posted by novaphile View Post
Not "because why not" but because glaziers had realised that glass tended to break more easily if it was installed with the thickest part at the top.

This could be because it meant that the thinest part is where all the impacts are, or because the glass at the bottom is bearing the weight of the material above. Either way, it was a deliberate choice to install glass that way.
Sorry I was too terse. I know why the pieces of glass are installed thick side up. Because why not?
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Old 1st February 2020, 04:47 PM   #32
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It occurs to me you could do another long-term experiment to test the "liquidity" of glass. Hang a piece over an edge and watch for it to droop.
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Old 1st February 2020, 05:45 PM   #33
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Originally Posted by Trebuchet View Post
It occurs to me you could do another long-term experiment to test the "liquidity" of glass. Hang a piece over an edge and watch for it to droop.
There are already many glass tables which represent this experiment.
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Old 1st February 2020, 06:53 PM   #34
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Originally Posted by Trebuchet View Post
It occurs to me you could do another long-term experiment to test the "liquidity" of glass. Hang a piece over an edge and watch for it to droop.
If I've understood the argument correctly, at room temperature it would take far more than 13.8 billion years (the age of the universe) for the glass to deform visibly due to its viscosity.

According to what I've learned, there's no threshold at which glass stops behaving as a liquid, it just keeps increasing its viscosity until the time scales involved are too big to appreciate any deformation.
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Old 1st February 2020, 09:05 PM   #35
Trebuchet
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Originally Posted by pgimeno View Post
If I've understood the argument correctly, at room temperature it would take far more than 13.8 billion years (the age of the universe) for the glass to deform visibly due to its viscosity.

According to what I've learned, there's no threshold at which glass stops behaving as a liquid, it just keeps increasing its viscosity until the time scales involved are too big to appreciate any deformation.
Like I said, a LOOOOONG term experiment!
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Old 1st February 2020, 09:53 PM   #36
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Then force the damn thing!
If you bend it until it almost breaks and keep it like that, how long before you can let go and it stays?
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Old 2nd February 2020, 02:24 AM   #37
pgimeno
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Originally Posted by Cheetah View Post
Then force the damn thing!
If you bend it until it almost breaks and keep it like that, how long before you can let go and it stays?
I don't know. This source here: https://www.cmog.org/article/does-glass-flow mentions a calculated viscosity for glass at room temperature of about 10^20 poises. The same source says this:
The calculation showed that if a plate of glass a meter tall and a centimeter thick was placed in an upright position at room temperature, the time required for the glass to flow down so as to thicken 10 angstrom units at the bottom (a change the size of only a few atoms) would theoretically be about the same as the age of the universe: close to ten billion years.
Let's put some numbers to it. How long do you estimate it would take for a piece of liquid with that viscosity, that is 1m long and is deformed on its centre by 5 cm, to be permanently deformed by 1mm?

I'm happy to agree that at these rates, you simply consider it a solid for all practical purposes.
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Old 2nd February 2020, 06:34 AM   #38
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Originally Posted by pgimeno View Post
I don't know. This source here: https://www.cmog.org/article/does-glass-flow mentions a calculated viscosity for glass at room temperature of about 10^20 poises...
That is indeed a pocket full of poises ...
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