Lightnews — Scholar-powered news

Cara Giovanetti @idontevencara.bsky.social · 2d

References

link.springer.com/article/10.1...
pubmed.ncbi.nlm.nih.gov/10607378/
www.sciencedirect.com/science/arti...

Cara Giovanetti @idontevencara.bsky.social · 2d

While ants can’t see details and obstacles very well, for them these polarization patterns on the sky are clear as day, and they can use them to find their way around. So human sailors aren’t the only celestial navigators—ants use cues from the sky to get home too!

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Cara Giovanetti @idontevencara.bsky.social · 2d

Here’s a video that shows the effect. These are polarization filters taped together. As the direction of the filters aligns with the direction of polarization in the sky, they block more light, hence the darkening of only some filters as they’re rotated.

www.youtube.com/watch?v=TP5J...

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Show Me Some Science! Polarization of the Sky

YouTube video by CNS Little Shop of Physics

www.youtube.com

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Cara Giovanetti @idontevencara.bsky.social · 2d

When many light waves are emitted at the same time, but they each have a different polarization, the resulting effect is “unpolarized” light. Light from the sun is unpolarized. But when the light scatters with our atmosphere, it becomes polarized and leaves a distinct pattern in the sky.

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Cara Giovanetti @idontevencara.bsky.social · 2d

Here’s a gif that might help visualize. The wave travels along the rope, but the bump is a vertical displacement of the rope—so we’d say this wave is polarized in the vertical direction. But it could just as well have been tilted 90 degrees, so it’s polarized into/out of your screen!

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Cara Giovanetti @idontevencara.bsky.social · 2d

But light has another fundamental property called polarization. The polarization of a wave is the direction of the oscillation relative to the direction the wave travels in. You’re already a little familiar with it—polarized sunglasses take advantage of this quality to filter out sunlight.

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Cara Giovanetti @idontevencara.bsky.social · 2d

Light has a lot of qualities—humans are probably most aware of intensity (amplitude), color (wavelength), and whether the light is monochromatic (one wavelength, like lasers) or polychromatic (many wavelengths, like the sun).

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A bright white lightbulb against a gray background.

Image via PICRYL, PDM 1.0

LED lights in blue, red, and green out of focus in the background.

Image credit Tyler Nienhouse via Wikimedia commons, CC BY-SA 2.0

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Cara Giovanetti @idontevencara.bsky.social · 2d

Imagine you are an ant. You are close to the ground, have pretty poor eyesight, and can’t see all that far ahead of you. How are you going to find your way back home?

Turns out ants and other insects navigate by a property of light humans can’t even see.

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A close-up image of an ant, eyes prominent, mandibles open and ready for action.

Image credit Egor Kamelev via Pexels, public domain

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Cara Giovanetti @idontevencara.bsky.social · 4d

when you stumble upon a GitHub issue describing exactly the problem you're having but the post was made by you from two years ago and you're still waiting for a response

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Cara Giovanetti @idontevencara.bsky.social · 5d

Can't get over how easy it was to vote in @berkeleyca.gov!

I have some last-minute travel that will keep me out of town on election day, and I was worried I was too late to request a mail-in ballot. But Alameda county automatically mails every registered voter a ballot, *and a sticker*

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Cara Giovanetti @idontevencara.bsky.social · 9d

You're right it's definitely too bad that a lot of the references are behind paywalls--but it's extra frustrating when it's stuff that was written for broad audiences. But SciAm gives a few free articles a month, right? At least I was able to access this one without a subscription

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Cara Giovanetti @idontevencara.bsky.social · 9d

References
pubs.geoscienceworld.org/gsa/gsabulle...
www.nature.com/articles/s41...
onlinelibrary.wiley.com/doi/full/10....

Further reading
www.scientificamerican.com/article/tree...
phys.org/news/2019-06...
www.discovermagazine.com/the-first-tr...

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Cara Giovanetti @idontevencara.bsky.social · 9d

The same thing happens with phosphorous fertilizers today; there’s a huge dead zone in the Gulf of Mexico where fertilizer runoff is deposited by the Mississippi river. But when trees did it, it likely helped fuel the Devonian extinction, where at least 70% of all Earth’s species perished.

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Summer satellite observations showing the Gulf of Mexico dead zone. Redder regions have higher concentrations of sediment and phytoplankton, contributing to an environment with less oxygen for marine life.

Image and caption information obtained from https://serc.carleton.edu/microbelife/topics/deadzone/general.html, which includes credits to NASA and the NASA Mississippi Dead Zone web site.

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Cara Giovanetti @idontevencara.bsky.social · 9d

But trees aren’t the only plants who need phosphorous! Algae got a free lunch out of the trees’ hard work—when soil ran off into waterways, the algae population exploded due to this huge nutrient boost. And when the algae died, the decomposition process sucked all of the oxygen out of the water

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An algal bloom in a river at Anderson Lake State Park in Washington, USA.

Image credit wikipedia user ECTran71 via wikimedia commons, CC BY-SA 4.0

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Cara Giovanetti @idontevencara.bsky.social · 9d

Trees dredged up tons of phosphorous out of the ground when their root systems evolved ~370 million years ago. All of that phosphorous, once packed tightly below the surface, scattered easily once these trees started dying and creating soil. Eventually that phosphorous ran off into waterways.

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Soil runoff to a waterway in Costa Rica.

Image credit wikipedia user Kentmanning via wikimedia commons, CC BY-SA 4.0

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Cara Giovanetti @idontevencara.bsky.social · 9d

But to get this to work, trees need to concentrate minerals. The tree gets a boost from minerals dissolved in the water it draws into itself, but it needs to spend a lot of energy on pumps in its cells that draw minerals in—a worthwhile expenditure since the tree needs minerals to survive.

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Cara Giovanetti @idontevencara.bsky.social · 9d

Water absorption in trees can occur pretty passively. Trees concentrate minerals in their roots, which means the ratio of minerals to water is almost always higher in the tree root than it is in the surrounding environment. This means water naturally diffuses into the root via osmosis.

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A diagram of osmosis--the natural, equilibrium state of this system is for the water column to be taller on one side of the barrier than the other, because nature wants to have the same concentration on both sides of the barrier.

Image credit wikipedia user Llywelyn2000 via wikimedia commons, CC BY-SA 4.0. Image has been cropped to remove text.

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Cara Giovanetti @idontevencara.bsky.social · 9d

It turns out humans aren’t the only living creatures to dredge up ancient material and spew it all back over the planet’s surface. When trees evolved deep root systems, they started to access all kinds of minerals in addition to the water they needed to survive.

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Cara Giovanetti @idontevencara.bsky.social · 9d

Trees: a symbol of a healthy ecology, clean air, and a tranquil environment.

And also maybe responsible for a mass extinction.

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A creepy-looking tree standing tall on a farm. It might have murderous intent!

Image credit Eric Johnson via wikimedia commons, CC BY-SA 3.0

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Cara Giovanetti @idontevencara.bsky.social · 17d

arXiv app when

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Cara Giovanetti @idontevencara.bsky.social · 17d

Recently it occurred to me that you can check the arXiv on your phone, and I went from never checking it to checking it on *Saturday*

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Reposted by Cara Giovanetti

Katie Langin @klangin.bsky.social · 18d

Today was a hard day for Ph.D. students who found out that they can no longer apply for NSF's prestigious Graduate Research Fellowship Program. "Devastating“ was how one student described it to me. #GradSchool #NSFGRFP

www.science.org/content/arti...

‘Completely shattered.’ Changes to NSF’s graduate student fellowship spur outcry

The announcement comes months later than usual, leaving many would-be applicants stranded

www.science.org

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Cara Giovanetti @idontevencara.bsky.social · 18d

Really torn up about whether I want to apply for Hubble again this year--of course the funding would be great, but I just can't bring myself to take half the broader impacts items off my CV

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Cara Giovanetti @idontevencara.bsky.social · 19d

LESS PROFICIENCY
MORE JOY

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Cara Giovanetti @idontevencara.bsky.social · 22d

Yes! I had to be really careful about how I discussed the reactivity of titanium oxide--it's not completely inert. In water it continues to react and forms a sort of porous structure that encourages bone growth into its gaps

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