Help identifying a length for this paper edge

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Discussion Overview

The discussion revolves around identifying the size of the corrugated "jagged triangles" on a paper towel used by astronauts aboard the ISS, which is critical for analyzing water droplet coalescence experiments. Participants explore various methods to estimate this size and the implications for the experiment's data analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant mentions that the size of the water droplets is approximately 1 cm in radius, but this is debated and leads to uncertainty in the analysis.
  • Another participant suggests a potential measurement of the triangle base at 0.405 cm, but this is not confirmed.
  • Some participants propose that if the paper towel is a standard three-panel type, it may have consistent dimensions due to historical manufacturing practices.
  • One participant expresses skepticism about the ability to obtain precise measurements without direct inquiry to the astronauts involved.
  • Another participant emphasizes the importance of including a measurement scale in future experiments to avoid similar issues.
  • There are conflicting views on whether NASA has detailed knowledge of the materials used on the ISS, with some expressing doubt about this information being readily available.
  • Participants discuss the possibility of using video metadata or additional images to glean more information about the experiment setup.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact size of the triangle bases or the best method to obtain this information. Multiple competing views and uncertainties remain throughout the discussion.

Contextual Notes

There are limitations regarding the assumptions made about the paper towel's dimensions and the lack of direct measurements from the experiment. The discussion also highlights the dependency on the availability of additional visual data and the challenges in obtaining information from NASA.

member 428835
Hi PF!

Two years ago my lab launched experiments aboard the ISS. The experiment was simple: place two water droplets on a substrate, set camera above the drops, and watch them coalesce. However, the exact size of the drops is unknown (approximately 1 cm radii, though this number is debated). So I'm analyzing this data and have done A TON of work to try and back out a length scale, but no two metrics agree within 5% of each other, so I'm not overly confident. Now I may have to scrap the entire project, but before I do, this might be the key: does anyone know the size of the corrugated "jagged triangles" at the end of this wipe being used to dry the surface? An astronaut is holding it, and the drop is total about 20 mL volume (few cm long) to give you a guess.
Screen Shot 2022-02-04 at 3.36.15 PM.png
 
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Edit: I just found something and I THINK each triangle base might be 15/37 = 0.405 cm. But let me know what you think.
 
How could we possibly be able to answer this? Ask the astronaut.

But in the future, put a measurement scale in the experiment and record the specs/dimensions of the camera.
 
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If that is a standard three panel brown paper towel, then (as far as I know) all use the same number of teeth per inch. It's called a serrated cut, and was the standard cutoff on towel folders up to about 15-20 years ago. Check out the local public restrooms for paper towels. You might get lucky.

The industry got away from serrated cutoffs because newer, tougher towel material is difficult to cut using serrated cutoffs. Much of my engineering career was working with cutoff systems.
 
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russ_watters said:
How could we possibly be able to answer this? Ask the astronaut.

But in the future, put a measurement scale in the experiment and record the specs/dimensions of the camera.
I wasn't in the control room. Wasn't even supposed to be my experiment, but my advisor sadly passed away, leaving the project for me to handle.

But regarding how to answer this: I think I found a solution so...
 
jrmichler said:
If that is a standard three panel brown paper towel, then (as far as I know) all use the same number of teeth per inch. It's called a serrated cut, and was the standard cutoff on towel folders up to about 15-20 years ago. Check out the local public restrooms for paper towels. You might get lucky.

The industry got away from serrated cutoffs because newer, tougher towel material is difficult to cut using serrated cutoffs. Much of my engineering career was working with cutoff systems.
This is helpful! What do you think of this?
 
Okay, so I'm pretty sure the triangle bases are 4,5, or 6 mm long. Like, 100% sure, but which...
 
You said no two methods agree within 5% of each other, but if they all agree within 15% of each other, you can figure it out by process of elimination
 
Any reason you can't show us any other pics? You've got enough video to do your experiment, so you can get more pics, but maybe we'll see something in them that you've missed.
 
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I find it hard to believe NASA doesn't know what exact materials were present on/available on/sent to ISS.
 
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Borek said:
I find it hard to believe NASA doesn't know what exact materials were present on/available on/sent to ISS.
These experiments were conducted in late 2020. The wipe they used was not in our payload. I have absolutely no clue how to ask them for this info.
 
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DaveC426913 said:
Any reason you can't show us any other pics? You've got enough video to do your experiment, so you can get more pics, but maybe we'll see something in them that you've missed.
Sadly each video was about 1 minute. This is literally the only shot I have (well, a 3 second clip)
 
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