Cicada surface science

Photo of a clanger cicada by Arthur Chapman,
shared on Flickr under a Creative Commons licence.

The east coast of the USA is greeting the latest emergence of the Brood II 17-year cicadas this month, and it reminded me of some interesting science I read about earlier in the year.

The wingcases of the Australian clanger cicada have the special property of killing bacteria that touch them, using just their physical structure—that is, there's no chemical reaction going on. Now an international team of biophysicists have developed and tested a model for how this happens. Their paper was published in the Biophysical Journal this February.

It's been known for a while that the cicada's wingcases are covered in a hexagonal array of nanopillars, up to 200 nm high. You might expect that the pillars pierce the soft walls of the bacteria to kill them. In this model, however, the high surface area that they give the wingcase is more important. The bacterial cell wall adsorbs onto the surfaces of the nanopillars from the top down, stretching the sections of wall in between until they rupture. You can see how this works in the animation below.



Since the model predicts that bacteria with more rigid cell walls will be resistant to death-by-nanopillar, the team could test it by microwaving resilient strains of bacteria, to soften their walls, and observing their survival on the wingcase surface. As expected, softened bacteria were destroyed by the surface, even if the unsoftened strain could survive it.

This work should contribute to developing antibacterial surface treatments that don't need extra cleaning agents to be kept hygienic. I do wonder, though, just which bacteria would be affected by such a surface and which would be resilient against it. Altering the height and spacing of the nanopillars could make them effective against a wider range of germs, as could playing with the chemical makeup of the surface to increase bacterial adsorption.

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Some bonus cicada titbits:

• These insects are gluten-free, high in protein, and taste a bit like asparagus. If that tempts your tastebuds as much as it does mine, the National Geographic has a selection of recipes for you.
• After seventeen years underground, how do the members of Brood II know that the time is now to emerge? New research suggests that they count the spring blooms of the trees whose roots they snuggle up against.
• The Washington Post takes a look at the evolutionary pressures that led to North American periodical cicadas 13- and 17-year lifecycles.
• Scientific American covered the Biophysical Journal paper in March, with an article on nanopillars and a disinfected world.

Science Blog Saturday: Quigley's Cabinet

Science Blog Saturday is a new fortnightly feature. I want to share some of my favourite science blogs and tell you why they're so great. Enjoy!

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Quigley's Cabinet is a one-woman effort that covers an impressive range of subjects.

Chris Quigley blogs mostly about her research interests, death and the anatomical body; she has written six books on these topics, including The Corpse, Modern Mummies and Dissection on Display. The Cabinet is by no means a gorefest, though. It has recently featured posts on the smell of death, the exhumation of a luckless member of the Franklin expedition, and mass grave simulation at the University of Tennessee's 'Body Farm' (note: each of these posts contains a picture of human remains), but Quigley's tone when writing about these topics is matter-of-fact and not exploitative.

There is a new post to the Cabinet every single day (perfect for insatiable readers like me!). Common topics include fossils, animals of all kinds, and archaeology. I would like to point out these posts in particular:

• Yesterday's ingredients: a 150-year-old doctor's store room answers questions about patent medicines
• Stone Age studio: about the discovery of a 100,000-year-old artisan's studio
• Beefy builders: how much livestock was needed to keep the Pyramid builders fed?
• Dragonflies are monsters: I don't think so, but if I were a fly, I'd be terrified of them

Quigley's Cabinet is a recent discovery of mine and I'll be checking it daily for the foreseeable future. I hope you find something interesting there too.

Cool scientific instruments: the nine-lens camera

The curious picture above crossed my Tumblr dashboard this morning, with this caption:

Nine-lens camera fully assembled. This camera was designed by Oliver Scott Reading in the early 1930’s. It was the state-of-the-art aerial camera for many years. (1938)

-NOAA

I wanted to find out more about it, and a quick Google search turned up this description in a 1936 issue of Popular Mechanics. You can see its size much better in their picture, with a man standing next to it. The camera was used for aerial photography and photogrammetry by the US Coast and Geodetic Survey, now part of the National Ocean and Atmospheric Administration. There are thousands of historic photos from the Survey here.

The nine-lens camera was capable of photographing 600 square miles in a single picture. The eight lenses around the edge of the central one were focussed on angled mirrors "of an astronomical type", broadening the area that could be covered. All nine images were projected on a single piece of film, which was held flat by a vacuum pump.

The complex engineering of the nine-lense camera was a great improvement on the five-lens camera that was previously used. It was designed by Captain Oliver Scott Reading of the US Coast and Geodetic Survey, a "mechanical genius" who had joined the Survey straight out of high school and subsequently educated himself in this type of work. Read more about his interesting life here (PDF) and in his obituary (PDF). You can learn more about aerial photogrammetry in this very accessible presentation (PDF).

Incidentally, the nine-lens camera was tough. Even after a fatal plane crash onto Mount Moffat, it was able to be reconstructed, as shown below.

Oliver Scott Reading with components of nine-lens camera. Reassembling camera after Mount Moffat crash.

- NOAA

Scratching the surface of Ancient Greek and Roman painted statues

When you think of an Ancient Greek statue, is the picture above what springs to your mind? If you're like most people, you imagine classical sculptures more like Apollo Sauroktonos, below. (I picked him as my unpainted example because of the cool lizard he's about to catch.)

Archaeological research shows, however, that the Romans and Greeks preferred their statuary to wear all the colours of the real world they mimicked so well. The minimalist look we know springs from thousands of years of weathering, not to mention the cleaning efforts of restorers and curators. Marble sculptures with visible remains of colour were found in the 19th century but neglected during the 20th, according to the Stiftung Archäologie (Google translation here).

Modern scientific techniques have a lot to offer in reconstructing the original appearances of these works of art. For example, energy-dispersive X-ray spectroscopy can reveal the chemical nature of pigments that have been absorbed into the stone. Raking light (light shone across the surface at an oblique angle) shows up changes in surface texture and structure. This is useful because painted patches of stone may have protected by the wax or egg base of the paint, and so have weathered differently from the other parts. Meanwhile, reflected ultraviolet light imaging shows fine surface details that can be hard or impossible to see in visible light.

In the photo above, you can see a UV image of the cape of a statue of Athena from the Temple of Aphaia on Aegina (image from here). To the left is a reconstruction by the Stiftung Archäologie.

The Stiftung's work has been on display since 2003 in the travelling exhibition Gods in Colour (Bunte Götter). Here is the English-language gallery guide (PDF) from its stop at Harvard. It can currently be seen in Vienna, until September 2013. I wonder if I can find the excuse for a trip this summer...

As a fan of historical fiction, I find this work fascinating. It completely changes my vision of Roman and Greek cities. In comparison to the icy and dignified white marble figures we know now, these sculptures make the artists seem much more relatable.

My favourite discovery, though, is that the mysterious figurines made by the Cycladic civilisation were also coloured. Mind you, the mystery is not cleared by the revelation that some of them were covered in apparently randomly-placed eyes.

These two pictures are from Elizabeth Hendrix's article Painted Ladies of the Bronze Age (PDF), which has much more detail on the science of colour reconstruction and the significance of the Early Cycladic figures. It includes this paragraph:

The examination the figures in the collection of the Metropolitan and in other museums makes it clear that most, if not all, of them were covered with strong colors in patterns that are not always comprehensible to viewers today. When recognizable anatomical features were painted in locations that make sense to us (such as the mouth centered below the nose), we are prepared to see the traces of the painting in those areas. It is a greater challenge to accept similar evidence for asymmetrical designs or familiar shapes in the "wrong" locations (such as several eyelike almond shapes on one side of the face). It may well be that symmetrical patterns have been retained more often since they are easier to recognize, thus inspiring more care on the part of the handler, whether curator, dealer, owner, or restorer.

There are more stunning pictures and more information on the coloured gods at Archaeology.org, Harvard Magazine and ColourLovers. (Via.)