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Physics A-Level

"Formidable" Flying Seeds

10/24/2018

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A new mechanism of flight has been discovered… in plants! Plants find all sorts of ingenious ways to disperse their seeds. This work, spearheaded by Naomi Nakayama of the University of Edinburgh, landed them a paper in Nature. The paper describes and explains the fluid dynamics of a mysterious vortex that is generated above a falling Dandelion seed. This vortex is purported to assist in its flight and is the first of its kind to be seen.

You can read the abstract of that paper here. An abstract is the blurb that comes at the beginning of every scientific paper that summarizes the work in a nutshell, or a seed shell (sorry bad joke, I know!). Normally the abstract is open source and available to all. I thought I’d provide commentary on that abstract in a fuller prose. Here’s my expanded version of that abstract:

“There are a huge variety of methods of dispersal of plant seeds, from microscopic to very large. Fungus’ disperse their ‘seeds’ via spores, and pollen in flowering plants are microscopically small. Compare that with large seeds of fruits which are distributed by falling or by animals eating them and releasing the seeds, somewhere far and wide, in their feaces. Somewhere in the middle you have seed dispersal through adaptive flight mechanisms… seeds with wings! The common dandelion uses a bundle of bristles which enhances it’s drag and keep it aloft to be carried by the wind, which is effective “over formidable distances” i.e. ‘far’ (but its catchy to write “formidable distances”!). BUT… nobody knows how on Earth this happens (or anywhere else, for that matter). Here, for the first time, a vortex is visibly detected above a dandelion seed in flight (in it’s ‘wake’). Air passes through the bristles causing the vortex to emerge as a separated entity above the bristles themselves. The vortex left in the wake, being separated, serves to stabilize flight; unlike a solid disc whose wake is normally ‘attached’ to the body-in-flight. Two factors affect this separated vortex formation: 1) size/radius of the disc of bristles, 2) density of bristles (which they call ‘porosity’) i.e. ability of air to flow through it. These two are precisely ‘tuned’ to maximize the amount of seed that can be carried (“aerodynamic loading”) whilst using the least material (i.e. using bristles and not a solid disc). This new discovery is evidence of a new class of fluid dynamic behavior and could help explain the methods that living things utilize to carry seeds and other biologically relevant material across stupendously FORMIDABLE distances.”

This work was (almost certainly) inspired by Inspector Gadget, but I somewhat doubt that he knew how his flying-thingy worked. I think someone should tell him.

(The dandelion photo is from the paper in Nature here, and can be found on a google search! Inspector gadget from here, from DHX media) 

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Unmasking Jupiter: Peaking within...

10/16/2018

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The striking banded zones of Jupiter were observed (and drawn!) 300 years ago by Cassini, shortly after the advent of the telescope and Galileo’s pointing of it skyward. The mystery of the origin of these belts have subsisted ever since. Questions surrounding them, and the eminent ‘red spot’, have given rise to more sophisticated formulations of those earlier questions: What is the dynamics of the storms that rage in these bands? Why are they different colours? How deep do these jet-streams go? What causes them to flow? How does their structure change over time? What is the internal structure of Jupiter and is it related to the structure of these bands? Can some basic principles be used to model the experimental data to forecast how other gas giants may behave?

I recently attended a talk by a scientist working on the (FABULOUS!) Juno project, spearheaded by NASA. In light of new data from Juno, a number of these questions can be tackled for the first time.
Interestingly, Jupiters’ jet-streams run across the gas giant in bands than flow in opposite directions (antiparallel) and are asymmetric in the northern and southern hemispheres. The size, speed of flow and number of bands are related to the radius and mass of the planet. Current modelling of these parameters gives insight to the internal fluid dynamics of the gas planet, but lacking the necessary data regarding Jupiter’s interior, much speculation still remains.

Now though, close fly-bys allowed Juno to collect the necessary data near the surface of Jupiter to detect subtle differences in gravity. These differences in gravity are highly correlated with the inner workings of Jupiter. The deeper the jet-streams, the more mass they contain, the greater the gravitational field signal. They were able to correlate the gravity data with the dynamics of the weather layer and found that the weather layer goes much deeper than expected. On Jupiter (radius ~ 70,000km) the weather layer is about 3000 km deep and contains about 1% of the total mass of Jupiter, compared with Earth’s atmosphere which makes up 1 millionth of the Earth’s mass.

Another finding was that, underneath this weather layer there was a layer that rotated as a rigid body; and work is underway trying to determine the interplay between these two layers. What came first and how do they interact?

Scientists await crucial data that will be able to tackle another long-standing question regarding Jupiter: what is the nature of it’s core, if it even has one?! Current understanding suggests that Jupiter contains a diffuse core, one that does not have a well define boundary, but rather extends from the centre of the planet and is somehow mixed with other layers. However, the way things are going, and with the regular surprises that Juno is delivering, we’ll have to wait and see.

This is groundbreaking stuff! Looking forwards to hearing more from Juno and their team.

Follow Juno on Twitter


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    Theres something interesting in the ether...

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