His oldest, closest friend

I happened upon an interesting phrase in a story, “Signal” by John Lanchester, from the New Yorker (3 Apr 2017):

“Michael wasn’t my oldest friend and he wasn’t my closest friend, but he was older than any of the ones who were closer and closer than any of the ones who were older, ….”

This is an odd way to describe a friendship, but it is precise. However, the more I thought about it, the more dissatisfied I was.

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Thioturbo danicus – The Sulfur Whirl of Denmark

Late last year, my colleague Silke W and I went to Denmark for a short field trip to collect ciliates, where we were hosted by Lasse Riemann of the University of Copenhagen. The site where we collected our material was Nivå Bay, which is famous among environmental microbiologists for the several decades of studies there on sulfur-cycling by microorganisms.


Nivå Bay (above, view from birdwatching tower on a sunny day) is a shallow, sheltered bay where the water is only knee- to waist-height at low tide. Scattered between the tufts of seaweed and seagrass were some off-white, slimy films on the surface of the sediment. These are actually bacterial “veils”, which are sheets of mucus produced by bacteria that embed themselves in them. Like a veil made of lace, each sheet is punctuated by many holes. Unlike a wedding veil, these veils are not meant to hide anything. Instead, you can think of them as a sort of natural-born environmental engineering – the holes allow water to flow through, and the bacteria actively circulate water by beating their flagella. By working together in these colonies, the bacteria can set up a continuous flow of water through the veil. This flow mixes sulfide-rich water coming from below with oxygenated water from above, bringing together the chemicals that they use to generate energy.

There are different species of bacteria that have such behavior. One of them has the wonderful name Thioturbo danicus – the sulfur whirl of Denmark. It has flagella on both poles of its rod-shaped cells. In this video you can see what happens when a single cell is detached from the mucus veil – it ends up tumbling like a propeller, which probably was the inspiration for its name!

Here is a somewhat degraded veil that had been sitting around in a Petri dish for too long. Taken from its natural environment, it soon becomes overgrown with grazing protists and small animals that methodically eat up the bacteria:

You can read more about the veil-forming bacteria from these publications from the microbiologists at Helsingør: Thar & Kühl 2002, Muyzer et al. 2005.

Rising butt hinge

The office bathroom has an unusual hinge on the cubicle door, which I’ve often wondered about while ensconced behind that door.


What’s clever about that design is that the spiral shape of the joint makes the door close itself automatically, as the weight of the door pulling downwards is transformed into a torsional motion.

I finally learned today that such hinges are called rising butt hinges, and that one popular use of them is for doors in rooms with heavy carpeting – the door lifts upwards slightly as it opens, and in the process is able to clear the carpet layer.

What a simple, elegant design!

3D vision with the Pulfrich Effect

The Pulfrich Effect is an optical phenomenon where objects (or images) moving in a single plane can appear to be in 3D when the light reaching one eye is dimmed, e.g. with a filter. It also has a curious history – Carl Pulfrich (biography – pdf), who discovered the phenomenon, was blind in one eye and never observed it for himself, but nonetheless made many contributions to stereoscopy (the study of 3D vision) in both theory and the construction of apparatus.

Unlike other forms of stereoscopy, this only works with moving objects or animations; it does not work with still images! But what’s really cool is that you don’t need any special equipment to view it, beyond a piece of darkened glass or plastic to act as a filter. Videos exhibiting the Pulfrich effect can be viewed on a normal monitor or TV screen.

I’ve made my own Javascript animations as demos for the Pulfrich effect (posted as GitHub Gists and rendered by bl.ocks.org):

Screen Shot 2017-01-10 at 00.57.42.png

Screenshot from my animated explanation of the Pulfrich Effect

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Language evolution in action

Here’s an example of how a word can completely reverse its meaning, from a BBC article about the Mid-Levels escalator in Hong Kong (also a cool subject in itself):

“We did the planning in 1984,” says architect Remo Riva, director of P&T Group, which consulted the government.

The verb “consult”, when used in a sentence like “A consulted B”, usually means that A asked B for their opinion. However in this case, it’s the P&T Group which were offering advice to the Hong Kong government, and not the other way around. So the sense of the word “consult” appears to have evolved like this:

“The government consulted the P&T Group” → “The P&T Group were consultants for the government” → “The P&T Group consulted for the government” → “The P&T Group consulted the government”

Funny to see this in action. And yet it’s still very strange to imagine that the word “nice”, for example, used to be pejorative, meaning a foolish or silly person.

Or in the case of the word “sanction”, made me completely misinterpret this headline: “Thai people urged to ‘socially sanction’ critics of monarchy”.