What’s physics got to do with it?
We still have a few more days until spring, but March 11 seemed as good a day as any to learn about the physics underlying bird nests, from Professor Corey O’Hern. With real life examples of bird nests from the Yale Peabody Museum, we learnt about some of the features that determine the resilience of a nest. The work that Corey described, supported significantly by the National Science Foundation, included collaborations with Richard Prum and Kristof Zyskowski.
Bird nests are primarily a place for laying and incubating eggs, for raising the hatchlings, and protecting them from predators. Nests come in a variety of shapes and sizes, and can be built from diverse materials such as twigs, leaves, mud, grass, feathers, and sometimes even man-made materials, very often all held together with the bird’s saliva. The location of nests is also diverse and can range from trees and bushes to ledges.
An overview of the diversity in bird nest shape, size and location, courtesy L. Shyamal & Mahesh Iyer
Considering the extreme weather patterns that a bird nest is exposed to, the structural properties that confer the necessary resilience are worth exploring. These properties can be replicated to engineer materials for human-occupied structures like buildings and aircraft. The ability of a nest to withstand pressure is one factor being studied in Corey O’Hern’s laboratory, first by studying features in abandoned bird nests, and then developing computer models to refine our understanding of those features.
One measure of resilience or sturdiness of a material is its yield stress, or the (vertical) force at which it will be crushed. Accordingly, ceramics and metals have a high yield stress. Using footage from a recent PBS special featuring his work on bird nests, Corey showed us how he measures the yield stress of nests. What is remarkable is that the yield stress to break a cup nest, can be almost as high as that required to break ceramics; but the density of a nest is 10 times less than that of ceramics. So, while cup nests may sometimes appear to be breakable and haphazardly put together, they are exceptionally sturdy and the mass of the nest is roughly proportional to the mass of the parent.
Deconstructing the nest of a crissal thrasher by taking x-rays and CT scans; and then physically removing and measuring each piece that went into making the nest, computer models were developed to replicate the nest. The models are continually refined to improve their resilience to pressure. Factors such as the ratio of the length of a twig to its width (aspect ratio) are key to having a cohesive structure, and are included in the computer models, as well as the ability to withstand vibrations. Such studies can provide a quantitative understanding of the nest construction process, and the components that go into nest building. Refinements of these models can help in the development of strong lightweight materials for a variety of uses, as was described in a cafe on materials science led by Professor Sharvan Kumar.
Thank you, Corey, for showing us how strong a bird nest is, even if it appears terribly fragile. The video for the cafe will be available on Friday, March 17 at https://www.youtube.com/user/tildecafe
Here’s a hilarious take by Gary Larson, on the materials birds use to make their nests – this one would likely not be as resilient as the ones studied by Corey O’Hern and his colleagues!
To watch humming birds in their nests, visit http://cams.allaboutbirds.org/channel/52/Green-and-white_Hummingbird/. This video shows a robin reinforcing her nest with mud – https://youtu.be/1s2vpHka3PQ. For a weaver bird making its nest, check https://youtu.be/qbWM1QAVGzs
The history and science of wine distilled into a Tilde Cafe afternoon
We celebrated Chinese New Year with Jonathan McLumski telling us about wine. It was a very different setting for the event, with tables arranged so that attendees could sip the wines comfortably, and get a better appreciation of what Jonathan described.
In 2009, Nayan Chanda spoke at a Tilde Cafe event about the “Globalization of coffee: From Islamic Wine to International Latte“. It was the 8th Tilde Cafe event. Almost sixty cafe events, and eight years later, Jonathan McLumski spoke about non-Islamic wine at Tilde Cafe. We’ve come a long way, and thank you for staying with us and expanding the Tilde Cafe attendee fold! We’ve also significantly improved in our abilities to remember to bring all the things necessary to film the event (if you watch the video for the Globalization of coffee, you might find yourself cringing, if not straining to hear and watch the video!). This of course doesn’t mean we’ve ironed out everything and are now in the TED talk stratosphere, but we like to think that we bring something unique with each event and each newsletter you receive, something that TED talks don’t give you (not to mention, we charge zero dollars to attend).
Jonathan outlined the history of wine – wine has been around for much longer than coffee (you can click this link to see an excerpt from Nayan Chanda’s book that he shared with Tilde Cafe), as far as we can tell. While wine is often associated with the elite and not the hoi polloi, it is really an agricultural product as Jonathan went on to explain. Grow grapes – pick grapes – crush grapes – ferment crushed grapes – drink/bottle/sell.
The oldest evidence of fermentation comes from northern China, and dates some 9,000 years ago. It involved the preparation of a fermented rice based drink.
Archaeological evidence of a winery for grape fermentation in Armenia dates to around 4100 BC, although older evidence of wine production appears in Georgia, Iran and Greece.
Thanks to wars and religion, wine making expanded from its geographic origins, and today wine is produced in more countries than most people are aware of, in bottles of specific shapes and sizes for the type of wine they contain.
Jonathan detailed the process of wine making and how it has changed over time, to make it more efficient and less expensive. Dispensing samples of three different wines, he also demonstrated some of the features that contribute to the complexity of wines and how this varies across regions. From the statistics we heard, it was clear that a wine can either lie unnoticed by the world, or become the drink du jour if marketed relentlessly – case in point is the significant change in sales of Pinot Noir and Merlot after the movie Sideways was released.
Perhaps what he so eloquently told us is to try to ignore the “norms” regarding wines and pairing them with foods – an excellent tip: rather than going with the type of wine, it’s a good idea to choose a wine that is native to the cuisine. Personally, I think that’s going to make it a lot easier than remembering details on pairing. Of course, you can watch the entire event here – although you’ll miss the tasting.
Let’s hope the next time someone offers you wine, it won’t be an Alice’s Adventures in Wonderland moment!
‘Have some wine,’ the March Hare said in an encouraging tone.
Alice looked all round the table, but there was nothing on it but tea. `I don’t see any wine,’ she remarked.
`There isn’t any,’ said the March Hare.
`Then it wasn’t very civil of you to offer it,’ said Alice angrily.
Thank you Jonathan for distilling more than 5,000 years into an excellent afternoon, and for helping us celebrate Chinese New Year, the year of the rooster.